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NUREG/CR-6944, Vol. 3 ORNL/TM-2007/147, Vol. 3
Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) Volume 3: Fission-Product Transport and Dose PIRTs OAK RIDGE NATIONAL LABORATORY
U.S. Nuclear Regulatory Commission Office of Nuclear Regulatory Research Washington, DC 20555-0001
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NUREG/CR-6944, Vol. 3 ORNL/TM-2007/147, Vol. 3
Next Generation Nuclear Plant Phenomena Identification and Ranking Tables (PIRTs) Volume 3: Fission-Product Transport and Dose PIRTs Manuscript Completed: October 2007 Date Published: November 2007 Prepared by: R. N. Morris—Panel Chair Oak Ridge National Laboratory P. O. Box 2008 Oak Ridge, TN 37831 Panel Members: M. Kissane (IRSN) D. Petti (INL)
D. Powers (SNL) R. Wichner (Consultant)
Sudhamay Basu, NRC Project Manager
Prepared for: Division of Risk Assessment and Special Projects Office of Nuclear Regulatory Research U.S. Nuclear Regulatory Commission Washington, DC 20555-0001
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ABSTRACT
This Fission Product Transport (FPT) Phenomena Identification and Ranking Technique (PIRT) report briefly reviews the high-temperature gas-cooled reactor (HTGR) FPT mechanisms and then documents the step-by-step PIRT process for FPT. The panel examined three FPT modes of operation:
1. Normal operation which, for the purposes of the FPT PIRT, established the fission product circuit loading and distribution for the accident phase.
2. Anticipated transients which were of less importance to the panel because a break in the pressure circuit boundary is generally necessary for the release of fission products. The transients can change the fission product distribution within the circuit, however, because temperature changes, flow perturbations, and mechanical vibrations or shocks can result in fission product movement.
3. Postulated accidents drew the majority of the panel’s time because a breach in the pressure boundary is necessary to release fission products to the confinement. The accidents of interest involved a vessel or pipe break, a safety valve opening with or without sticking, or leak of some kind.
Two generic scenarios were selected as postulated accidents:
1. the pressurized loss-of-forced circulation (P-LOFC) accident, and 2. the depressurized loss-of-forced circulation (D-LOFC) accidents.
FPT is not an accident driver; it is the result of an accident, and the PIRT was broken down into a two-part task. First, normal operation was seen as the initial starting point for the analysis. Fission products will be released by the fuel and distributed throughout the reactor circuit in some fashion. Second, a primary circuit breach can then lead to their release. It is the magnitude of the release into and out of the confinement that is of interest.
Depending on the design of a confinement or containment, the impact of a pressure boundary breach can be minimized if a modest, but not excessively large, fission product attenuation factor can be introduced into the release path. This exercise has identified a host of material properties, thermofluid states, and physics models that must be collected, defined, and understood to evaluate this attenuation factor.
The assembled PIRT table underwent two iterations with extensive reorganization between meetings. Generally, convergence was obtained on most issues, but different approaches to the specific physics and transport paths shade the answers accordingly.
The reader should be cautioned that merely selecting phenomena based on high importance and low knowledge may not capture the true uncertainty of the situation. This is because a transport path is composed of several serial linkages, each with its own uncertainty. The propagation of a chain of modest uncertainties can lead to a very large uncertainty at the end of a long path, resulting in a situation that is of little regulatory guidance.
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FOREWORD
The Energy Policy Act of 2005 (EPAct), Public Law 109-58, mandates the U.S. Nuclear Regulatory Commission (NRC) and the U.S. Department of Energy (DOE) to develop jointly a licensing strategy for the Next Generation Nuclear plant (NGNP), a very high temperature gas-cooled reactor (VHTR) for generating electricity and co-generating hydrogen using the process heat from the reactor. The elements of the NGNP licensing strategy include a description of analytical tools that the NRC will need to develop to verify the NGNP design and its safety performance, and a description of other research and development (R&D) activities that the NRC will need to conduct to review an NGNP license application.
To address the analytical tools and data that will be needed, NRC conducted a Phenomena Identification and Ranking Table (PIRT) exercise in major topical areas of NGNP. The topical areas are: (1) accident analysis and thermal-fluids including neutronics, (2) fission product transport, (3) high temperature materials, (4) graphite, and (5) process heat and hydrogen production. Five panels of national and international experts were convened, one in each of the five areas, to identify and rank safety-relevant phenomena and assess the current knowledge base. The products of the panel deliberations are Phenomena Identification and Ranking Tables (PIRTs) in each of the five areas and the associated documentation (Volumes 2 through 6 of NUREG/CR-6944). The main report (Volume 1 of NUREG/CR-6944) summarizes the important findings in each of the five areas. Previously, a separate PIRT was conducted on TRISO-coated particle fuel for VHTR and high temperature gas-cooled reactor (HTGR) technology and documented in a NUREG report (NUREG/CR-6844, Vols. 1 to 3).
The most significant phenomena (those assigned an importance rank of “high” with the corresponding knowledge level of “low” or “medium”) in the thermal-fluids area include primary system heat transport phenomena which impact fuel and component temperatures, reactor physics phenomena which impact peak fuel temperatures in many events, and postulated air ingress accidents that, however unlikely, could lead to major core and core support damage.
The most significant phenomena in the fission products transport area include source term during normal operation which provides initial and boundary conditions for accident source term calculations, transport phenomena during an unmitigated air or water ingress accident, and transport of fission products into the confinement building and the environment.
The most significant phenomena in the graphite area include irradiation effect on material properties, consistency of graphite quality and performance over the service life, and the graphite dust issue which has an impact on the source term.
The most significant phenomena in the high temperature materials area include those relating to high-temperature stability and a component’s ability to withstand service conditions, long term thermal aging and environmental degradation, and issues associated with fabrication and heavy-section properties of the reactor pressure vessel.
The most significant phenomenon in the process heat area was identified as the external threat to the nuclear plant due to a release of ground-hugging gases from the hydrogen plant. Additional phenomena of significance are accidental hydrogen releases and impact on the primary system from a blowdown caused by heat exchanger failure.
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The PIRT process for the NGNP completes a major step towards assessing NRC’s research and development needs necessary to support its licensing activities, and the reports satisfy a major EPAct milestone. The results will be used by the agency to: (1) prioritize NRC’s confirmatory research activities to address the safety-significant NGNP issues, (2) inform decisions regarding the development of independent and confirmatory analytical tools for safety analysis, (3) assist in defining test data needs for the validation and verification of analytical tools and codes, and (4) provide insights for the review of vendors’ safety analysis and supporting data bases.
_____________________________________________
Farouk Eltawila, Director Division of Systems Analysis Office of Nuclear Regulatory Research
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CONTENTS
Page
ABSTRACT.................................................................................................................................................iii
FOREWORD ................................................................................................................................................ v
LIST OF FIGURES ..................................................................................................................................... ix
LIST OF TABLES....................................................................................................................................... ix
ACRONYMS...............................................................................................................................................xi
1. INTRODUCTION.................................................................................................................................. 1
2. BRIEF HTGR FISSION PRODUCT TRANSPORT BACKGROUND................................................ 3
3. FISSION PRODUCT TRANSPORT PIRT PROCESS ......................................................................... 7
3.1 Step 1—Issues ............................................................................................................................. 7
3.2 Step 2—PIRT Objectives ............................................................................................................ 9
3.3 Step 3—Hardware and Scenarios ................................................................................................ 9
3.3.1 Hardware........................................................................................................................ 9 3.3.2 Accident scenarios ....................................................................................................... 11 3.3.3 Significant radionuclides ............................................................................................. 14
3.4 Step 4—Evaluation Criteria....................................................................................................... 14
3.5 Step 5—Knowledge Base.......................................................................................................... 15
3.6 Steps 6 through 8—Identify Phenomena and Rank................................................................... 16
3.7 Step 9—Document PIRT—Summary ....................................................................................... 31
REFERENCES ........................................................................................................................................... 39
APPENDIX A. COMMENTS ON TRANSPORTATION MODELING................................................A-1
A.1 Brief Discussion of Transport Modeling Through Porous Media ...........................................A-1
A.2 Speciation ................................................................................................................................A-2
A.3 Aerosols...................................................................................................................................A-2
APPENDIX B. INDIVIDUAL PANELISTS’ RANKING TABLES...................................................... B-1
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LIST OF FIGURES
Figure Page
1 Transport of fission products from fuel to reactor materials............................................................... 4 2 Fission-product transport through the reactor circuit .......................................................................... 4
LIST OF TABLES
Table Page
1 Historically dominant radionuclides in a VHTR................................................................................. 5 2 Rough comparison between the GT-MHR (DOE version as developed by GA) and
the NGNP for normal operating conditions ........................................................................................ 9 3 Rough comparison between the GT-MHR (DOE version as developed by GA) and the NGNP
for design basis accident conditions.................................................................................................. 10 4 Public dose radionuclides.................................................................................................................. 14 5 Operation and maintenance dose radionuclides ................................................................................ 14 6 Fission product transport pathways from the fuel particle surface ................................................... 17 7 Phenomena importance ranking scale ............................................................................................... 20 8 State-of-knowledge (SOK) ranking scale ......................................................................................... 20 9 Status of fission-product modeling ranking scale ............................................................................. 20 10 Overall PIRT ranking........................................................................................................................ 21 11 Selected PIRT items from Tables 10 that have at least one high importance and low
knowledge ranking ............................................................................................................................ 32 B-1 Individual FPT PIRT Ranking Table .............................................................................................. B-3 B-2 Individual FPT PIRT Ranking Table ............................................................................................ B-13 B-3 Individual FPT PIRT Ranking Table ............................................................................................ B-21 B-4 Individual FPT PIRT Ranking Table ............................................................................................ B-29 B-5 Individual PIRT Ranking Table .................................................................................................... B-37
Part A: General issues affecting FP transport ............................................................................. B-39 Part B: Transport holdup in carbon matrix and graphite ............................................................ B-41 Part C: Emission from fuel element surface ............................................................................... B-44 Part D: FP transport in the coolant, normal operation ................................................................ B-45 Part E: Deposition sorption on primary system surfaces—normal operation ............................ B-47 Part F: Releases from the primary system—normal operation................................................... B-49 Part G: Factors affecting releases from the primary system—accident conditions .................... B-50 Part H: Releases from the confinement....................................................................................... B-54
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ACRONYMS
D-LOFC depressurized loss-of-forced circulation FPT fission-product transport GA General Atomics GT-MHR gas-turbine–modular helium reactor HTGR high-temperature gas-cooled reactor IC initial condition IHX intermediate heat exchanger INL Idaho National Laboratory IRSN L’Institut de Radioprotection et de Sûreté Nucléaire LWR light-water reactor NGNP next generation nuclear plant NRC Nuclear Regulatory Commission O&M operations and maintenance P-LOFC pressurized loss-of-forced circulation PBMR pebble-bed modular reactor PIRT phenomena identification and ranking tables RCCS reactor cavity cooling system SNL Sandia National Laboratory SOK state of knowledge VHTR very high temperature gas-cooled reactor
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1. INTRODUCTION
This section of the next generation nuclear plant phenomena identification and ranking tables (NGNP PIRT) applies the Nuclear Regulatory Commission (NRC) PIRT process to the issue of fission-product transport (FPT) under routine and accident conditions in both the process heat and the electric-power-producing versions of the very high temperature gas-cooled reactor (VHTR) (either prismatic core or pebble-bed fuel). Currently, the direct-cycle VHTR is the main concept for power generation; the process heat version of the VHTR differs from earlier applications in that its purpose is to provide high-temperature process heat to some chemical process. As such, there is a linkage to the chemical process [through the intermediate heat exchanger (IHX)], the safety implications of which are relatively new. In addition, the chemical process itself can become a factor in fission-product transport evaluations. NGNP is based on aspects of VHTR, and for the purposes of the PIRT, they are considered equivalent.
The VHTR is expected to use one of the standard high-temperature gas-cooled reactor (HTGR) core configurations. HTGRs have been analyzed for fission-product transport many times; however, there still appear to be several incompletely resolved issues. In particular, use of a gas turbine in a direct cycle is relatively new with respect to safety and fission product-transport analysis.
Each version of the VHTR may use either a pebble-type fuel element or a fuel element of prismatic geometry. To date, the U.S. General Atomics and AREVA designs favor the prismatic fuel element, while the pebble-bed modular reactor (PBMR) of South Africa has adopted the pebble-type fuel element. The materials are somewhat different in these two fuel element types. While the PBMR uses fuel particles with UO2 kernels, prismatic fuel-element designers prefer a UCO fuel form for future use, because this fuel offers improved burnup capability (due to less CO formation) and lessens the effect of “amoeba”-type fuel problems.
The main driver for the FPT PIRT exercise is the NGNP. This nuclear plant is based on a VHTR, as mentioned above, that is constructed of materials that are quite different from those used in a light water reactor (LWR), and the accident characteristics identified to date develop along different lines. Thus, there is reason to believe that the approaches used for LWR analysis may not be appropriate or successful when applied to VHTRs. A technology-neutral safety approach is needed and should be applied to the VHTR. Finally, the regulatory experience for this reactor type, especially in its high-temperature process heat configuration, is very limited [1–5, 50]. Material presented at the February 2007 PIRT meeting was used as guidance for the process.
Implicit in the panel’s discussions was the role played by high-temperature materials, the large amounts of graphite, the high-pressure noncondensable coolant, and the dual role that the VHTR reactor could play.
One particular issue was noted, and this issue revolves around the fact that the FPT task depends on a high level of coordination with other groups. FPT is not an accident driver; it is the result of an accident, and in general, these accident scenarios will be identified and their evolution calculated by others. The role of this PIRT is seen as a two-part task. First, normal operation is seen as the initial starting point for the analysis. Fission products will be released by the fuel and distributed throughout the reactor circuit in some fashion. The major concern at this point is the dose and contamination associated with maintenance and operational issues. In the event of an accident, a transient occurs along with the possible redistribution of fission products within the reactor circuit; a primary circuit breach could then lead to their release. It is the magnitude of the release into and out of the confinement that then becomes the matter of interest.
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This report segment first briefly reviews the HTGR fission-product transport mechanisms and then proceeds with the step-by-step PIRT process for fission-product transport. A previous fuel PIRT was conducted, and the starting point for this analysis is the outer surface of the fuel particle [49].
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2. BRIEF HTGR FISSION PRODUCT TRANSPORT BACKGROUND
Even though the VHTR fuels are designed to preclude large scale fuel failure during accidents, dose significant fission product transport from the reactor cannot be discounted [1–8, 50], especially for the higher temperature VHTR. Even in the ideal case of no fuel failures during the accident, fission products are available for release because of three main factors:
1. The fuel is not perfect and some fraction (~10-5) of the particles is defective or damaged during fabrication. In addition, a small fraction of the fuel may fail during normal operation. These fuel populations partially release their fission products to the reactor system during normal operation and during the accident.
2. The reactor graphite components have uranium contamination due to natural causes or due to fuel particles that have been crushed during fuel element fabrication. This uranium fissions and releases some part of its fission products to the reactor circuit.
3. The high pressure coolant provides a means to transport fission products from the reactor circuit to the confinement building following primary system breaks.
Past VHTR (prior HTGR) work sets the desired maximum level of 10-4 as the fuel fraction release at the time of the accident, and the acceptable core release fraction at roughly 10-7; thus, a fission-product attenuation factor (order of magnitude) of about 1000 is needed between the core and the site boundary [5, 9, 10]. Clearly, even with the best fuel and no additional fuel failures during the accident, fission-product transport will be an important issue.
Fission products released from the fuel can travel to and through the matrix material that holds the fuel particles, the graphite fuel blocks (prismatic), the graphite reflector and structural components, and into the coolant [11–17] (see Fig. 1). They can then travel onto and into metallic components and dust generated within the reactor circuit.
During normal operation, the fission products distribute themselves throughout the reactor circuit, depending on material diffusive and sorptive properties, chemical affinities, temperatures, material and coolant chemical impurities, flows, and mechanical vibrations (see Fig. 2).
Computing the distribution of fission products is a complex problem, and considerable effort has been expended in this area, both in the areas of single-effects data collection and integral testing [18–26]. The resulting distribution and its stability determines the starting point for the accident analysis. There may also be some interest in 14C production and the transport of uranium and plutonium [27–29], although these are not expected to be important accident contributors. The transport area is much less developed in VHTRs than the analogous situation in LWRs; however, the LWR releases are much larger and can be more energetic. Some LWR analytical techniques may be applicable, especially for the transport in the containment [30–31], and some technical modeling problems are comparable (e.g., aerosol/dust retention in complex structures such as the IHX or gas turbine as compared to the secondary side of a steam generator for LWRs).
Three forms of radioactivity are usually categorized in the VHTR (note: past HTGR work will be assumed to be applicable to the VHTR and the qualifier HTGR will be dropped) reactor:
1. Circulating activity that is composed of gases/vapors (iodine, krypton, xenon), any aerosols that may be formed, and dust (mostly carbon with sorbed radionuclides).
2. Surface activity that is composed of radionuclides chemisorbed on steel and graphite, plated-out dust, and chemically combined with oxide films (impurities in the coolant establish the oxygen potential).
3. Activity embedded in solids such as fission products alloyed with metal components and retained on or within the graphite.
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Fig. 1. Transport of fission products from fuel to reactor materials.
Fig. 2. Fission-product transport through the reactor circuit.
The first two items are of most concern as circulating activity is the most likely to be expelled during
a pressure boundary break and surface activity may be spalled or lifted off by fluid or mechanical action [32–40]. Material embedded in solids is the least likely to be rapidly released but acts as a dose driver for maintenance because it is difficult to remove (decontaminate).
Historically, a handful of radionuclides have been the dominant drivers in VHTR dose and effluent calculations [41–42, 51]. Table 1 lists these elements and their primary impacts; this is for information only as the situation with the NGNP may or may not be the same.
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Table 1. Historically dominant radionuclides in a VHTR
Nuclide Half-life Primary impact 131I 8 days Offsite dose, operations and
maintenance (O&M) dose 137Cs 30 years Offsite dose, O&M dose 110mAg 250 days O&M dose 90Sr 28 years Offsite dose Kr and Xe Hours to years Gaseous effluent 3H 12 years Gaseous effluent
During normal operation, the five sources of circulating radionuclides originating from the core are
[6–8]:
1. uranium contamination of graphite, 2. exposed fuel kernels (fuel particles broken during manufacture), 3. fuel with damaged SiC (metal release), 4. fuel that fails during normal operation (variety of reasons), and 5. activation of core structural materials (fixed but may spall off).
Over many years of operation, these five sources provide fission products and other radionuclides to the various transport mechanisms that spread radionuclides through the reactor circuit. About 10-4 of the core inventory of cesium and 10-6 of the iodine inventory are outside of the fuel particles and deposited either on the fuel, graphite, metal components, or dust [5, 9, 10].
In summary, a number of phenomena drive FPT on both the large and small scale; the fundamental driver is the release from the fuel and uranium contamination during normal operation and its deposition throughout the reactor circuit in a manner that allows some portion of it to be removed from the circuit as the result of a depressurization.
It should be noted at this point that the accident scenarios for the fission-product transport PIRT are actually generated by other PIRT groups as fission-product transport is a consequence of an event rather than an event driver [1–5] (only a massive redistribution of fission products would change the heat-generation profile of the core). The event of primary interest for the gas-turbine designs is a pressure boundary break that allows the high-pressure helium to expel fission products and provides a conduit from the reactor circuit to the confinement. This path has been the subject of the above introduction. For the historical steam cycle, HTGR steam generator failures which allow water into the core have been of major interest as they will open a primary-circuit pressure-relief valve and provide a transport path. The gas turbine or process heat designs are believed to be much less susceptible to this failure mode, and thus it is of much less concern.
For the NGNP, three other paths might be of interest. The first is diffusion from the primary side of an IHX to the secondary side. Currently, this appears to be more of a tritium diffusion issue for normal operation than an accident issue [42–44]. Another path is from the secondary side to the primary side and/or into the confinement. If the IHX were to suffer a major failure that exposed a high-pressure secondary side to the confinement, the confinement atmosphere and heat transfer properties might be drastically changed. This could affect the operation of the reactor cavity cooling system (RCCS) and the (possible) confinement filters. The simultaneous failure of both the primary side and the secondary side of the IHX would add the reactor coolant inventory as well as fission products to the confinement. A third IHX failure mode would be between the primary and secondary sides. In this case the working fluids could mix as well as transfer fission products. Chemical reactions as well as pressure boundary issues could then arise. These three IHX accidents are very application and design specific. While the
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basic HTGR design relies on passive safety to handle issues such as coolant flow transients, station blackouts, and seismic events, it is very design specific as to how these issues will affect the IHX circuit and feedback into the reactor system.
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3. FISSION PRODUCT TRANSPORT PIRT PROCESS
The PIRT process was outlined in our introductory meeting by the NRC coordinator, Sudhamay Basu. It consists of nine steps, which are discussed below [45–47].
3.1 Step 1—Issues
The VHTR presents some new issues to FPT considerations. Generally, these new aspects are in addition to the more well-known issues relating to the past HTGR designs.
1. Higher-temperature fuel and primary coolant during normal operation leading to higher levels of circulating activity and a higher fraction of the core experiencing elevated temperature.
2. An IHX in place of a gas turbine or steam generator that may malfunction during normal operation, or fail during some accident.
3. The possibility of product contamination with radiation from the primary circuit either during normal operation or an accident.
4. Possibly higher occupational exposures. 5. Possibly new variations of accident scenarios involving the IHX or the process heat sink.
In addition, the VHTR has some well-known fission-product issues, some of which remain only partially resolved:
1. Fission-product contamination of the moderator graphite (for prismatic fuel element versions) and primary coolant during normal operation. This issue contributes to occupational dose and also presents an immediate source (coolant) for release during depressurization events.
2. Fission-product contamination of primary circuit surfaces incurred during normal operation, including the power conversion unit components. Such contamination may be of four types: a. chemisorption on metal surfaces, b. chemical combination with the oxide film of the metal surfaces, c. alloyed in the metal, and d. plated-out dust contaminated with fission products.
3. Transport of fission products into the containment building as a result of various types of accidents involving depressurization. There are a number of separate sub-issues related to fission-product transfer into the containment building: a. Liftoff of plated-out dust particles either by hydrodynamic forces or by vibrational
forces resulting from the break or rapid gas flow. b. Desorption of chemically adsorbed fission products due to the generation of higher
temperatures during the accident (for the particular component) or by change of oxygen potential in the case of water or air ingress.
c. Transport of fission products during the natural convection phase of the depressurization event. This is basically a fluid dynamics issue but is affected by oxidation (air or steam ingress) of the graphite by modifying helium properties (gas mixture).
4. Transport of fission products from the containment or confinement building to the atmosphere. This is also primarily a building leakage problem but depends on the gaseous and suspended aerosol inventory of fission products in the building. In addition, chemical
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reactions of fission products in the building may affect their transport. Other chemical reactions could also affect building pressure (e.g., cable fire) and transport. Dust combustion could lead to higher pressures and fission-product liberation.
5. Behavior of the fission-product inventory in the chemical cleanup or fuel handling system during an accident. An overheat event or loss of power may cause release from this system and transport by some pathway into the confinement building or environment.
During an unmitigated air or water ingress accident, four more radionuclide transport issues arise [8, 49, 52]:
1. Chemical reactions (and overall oxygen potential change in the reactor system) with fuel and graphite due to water and/or air.
2. Generation of particulates from matrix and graphite component oxidation and failure. 3. Change of the fission products’ chemical state and the component surface properties which
can affect the ability of components to retain fissions products. 4. Additional fuel failures due to high temperatures and chemical attack.
One issue of immediate transport concern is the amount of dust in the reactor circuit as dust is easily released during a primary boundary breach. Carbon-based dust is generally quite absorptive of fission products and, when combined with its high mobility, leads to an important path from the reactor core to the environment. Sources of dust in the reactor circuit include the following [6]:
1. Abrasion due to the relative movement of fuel pebbles (high) and prismatic blocks (low). 2. Metal corrosion products. 3. Carbon filaments that grow from the gas-phase reaction 2CO6CO2 + C due to coolant
impurities and temperature gradients. 4. Soot from fast neutron damage (reflector graphite). 5. Construction and other debris.
The highest dust quantities are expected in the pebble-bed core (~10–50 kg for a test reactor and perhaps much more for a power reactor) and the lowest in the prismatic core (at least an order of magnitude less) [9, 10]. Dust is significant in at least three areas:
1. Circulating dust is readily available for depressurization release. 2. Plated-out dust can be re-entrained by shearing fluid forces due to flow velocity changes
driven by the pressure boundary break or by the mechanical and acoustical forces generated by the shock of the break or generated by flow-driven vibrations.
3. Dust can have an erosive effect on turbine blades. 4. There has been some speculation on the possibility of dust ignition and explosions [9, 10].
Dust could be a major source of fission-product release for pebble-bed reactors; it is expected to be much less of an issue for the prismatic core reactors [6].
Dust size is a key parameter that may be highly dependent on the system design materials and manufacturing techniques used, so extrapolation of past knowledge to new reactors has to be done with caution. In particular, graphite-component manufacture may be different with different grain structure and different levels of impurities. In addition, the pebble design uses a mixture of binder and graphite for pebble-fabrication, so the pebble generated dust may be more sorptive of fission products.
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3.2 Step 2—PIRT Objectives
The major objectives are to identify the safety-relevant phenomena and knowledge base and rank them in an approximately quantitative way. Since the NGNP exists as only a rough concept, it is not possible to take a concrete approach to this process; however, it must be surmised that the NGNP would share much in common with past HTGR designs, and these were used as a reference.
3.3 Step 3—Hardware and Scenarios
3.3.1 Hardware
At the present time, the NGNP is only in the concept stage, and historical analogues as well as PIRT presentations were used to model the hardware and possible scenarios. Tables 2 and 3 are a rough comparison between the direct-cycle prismatic block gas turbine HTGR (GT-MHR) investigated by the DOE and the Fissile Materials Deposition Program over the last decade and the conceptual NGNP. These tables are meant to be only a conceptual starting point and should not be taken as a point-by-point analysis.
Several confinement and containment options have been investigated in the past, with the vented confinement option generally selected as a baseline (with or without filters, depending on designer); see Ref. 54 for the results of a trade study (steam cycle) which assumes high-quality fuel and limited release of plated-out activity. The releases are time separated into a small early release and a larger later release. The early release is assumed to be very small and requires no holdup while the later release is assumed to be modest with little or no driving force. Reference 55 discusses the vented confinement with both ideal and less-than-ideal fuel for the steam-cycle version. It was presumed that this type of analysis would be the starting point for the NGNP design, to be modified later by analysis and test results.
Table 2. Rough comparison between the GT-MHR (DOE version as developed by GA)
and the NGNP for normal operating conditions
Item GT-MHR NGNP
Coolant and primary-loop containment
Lower Same or higher, depending on temperature; higher if pebbles are used (dust).
Maintenance dose Depends on turbine issues; cesium and silver dose
Same if turbine; perhaps less if IHX system.
Contamination of secondary coolant
N/A Issue will probably be tritium.
Confinement vs containment Confinement Probably confinement.
Primary coolant cleanup system Fission gas collection; long-term issue is 85Kr and some contaminated dust (?)
Fission gas collection; long-term issue is 85Kr and perhaps contaminated dust; advanced designs may capture dust.
Fuel handling Special equipment for handling blocks; reactor down during handling
Could be blocks (offline batch refueling) or pebbles (continuous online refueling).
10
Table 3. Rough comparison between the GT-MHR (DOE version as developed by GA) and the NGNP for design basis accident conditions
Item GT-MHR NGNP
Release to the atmosphere. Designed to avoid public evacuation and sheltering requirements.
About equal unless the IHX or process heat side introduces unusual behavior; higher potential for fuel failure because of higher fuel and reactor outlet temperatures.
Release to the secondary coolant N/A Design specific; IHX breaks could transfer heat-transfer fluid either way and into confinement.
Releases from the cleanup system and/or fuel handling system
Designed to avoid public evacuation and sheltering requirements.
Not clearly established but likely similar except for dust and pebble handling faults; higher fuel failures could increase releases.
At the present time, an important issue is the type of fuel to be used by the reactor. Both prismatic
and pebbles have been used in the past, and both have advantages and disadvantages. The following differences need to be understood however:
1. The pebble-fuel element consists of a 6-cm-diam sphere containing a central region of fuel particles and matrix material (graphite and binder) covered by a fuel-free region (a few mm thick) of matrix material only. The pebble has high mechanical integrity to withstand the drops and movement that are part of the function of the fuel form. The pebbles move continuously through the reactor during operation; as they exit the reactor, they are assessed for burnup and are then either returned to the reactor or sent to spent fuel. The reactor is continuously refueled and does not required downtime for refueling operations. The fuel burnup is modest (~10%) and the fuel-particle packing fraction is low (~10%).
2. The prismatic fuel element consists of many fuel compacts, which are right cylinders composed of fuel particles and matrix material roughly 12 mm in diameter by 50 mm long, inserted into deep holes drilled into graphite hexagonal prisms roughly 300 mm across the flats and 800 mm long and cemented into place. The compacts have relatively high packing fractions (~30–50%) and the fuel has a higher burnup( ~15–25%).
3. The actual fuel kernel to be used is not defined at present but is likely to be either UO2 or a two-phase mixture of UC/UC2 and UO2 known as UCO. The UO2 material has much better characterization but suffers from burnup limitations and a problem known as the amoeba affect, which causes the kernel to migrate within the particle in the presence of temperature gradients; this migration ultimately damages the particle coatings. The prismatic core is believed to require the use of UCO because of this effect and the higher burnup; the pebble core will probably use UO2.
11
4. The fission-product transport rate from the fuel particle to the coolant may be different for the pebble than for the prismatic block because of differences in temperature and transport path. For the purposes of this PIRT, it will be assumed that the time in operation prior to the accident is long enough that both systems have come to equilibrium with respect to the fission products deposited within the reactor circuit.
5. Air and water ingress accidents will require a separate evaluation of the pebbles and blocks because of the large differences in chemical reactions rates between graphite block and the pebble matrix material.
3.3.2 Accident scenarios
Possible accidents were presented at the February 2007 PIRT meeting which outlined the expected behavior of the concept. The following three areas were discussed by the panel:
1. Normal operation, which, for the purposes of the FPT PIRT, established the fission-product circuit loading and distribution for the accident phase. In addition, it will be input for evaluating the occupational dose.
2. Anticipated transients, which were of less importance to the panel because a break in the pressure circuit boundary is generally necessary for the release of fission products. The transients can change the fission-product distribution within the circuit, however, because temperature changes, flow perturbations, and mechanical vibrations or shocks can result in fission-product movement. They could also cause releases from pressure relief valves. The other issue associated with these transients is the possible redistribution of fission products that increases maintenance dose rates. Finally, minor leaks are a pathway for the release of fission products.
3. Postulated accidents drew the majority of the panel’s attention because a breach in the pressure boundary is necessary to release fission products to the confinement. The accidents of interest involved a vessel or pipe break, a safety valve opening with or without sticking, or leak of some kind.
The following two generic scenarios were selected as the drivers for the accident [48]:
1. the pressurized loss-of-forced circulation (P-LOFC) accident; and 2. the depressurized loss-of-forced circulation (D-LOFC) accidents.
3.3.2.1 The P-LOFC accident
The reference case for P-LOFC is modeled on that for the GT-MHR and assumes a flow coast-down and scram with the passive reactor cavity cooling system (RCCS) operational for the duration of the event. The natural circulation of the pressurized helium coolant within the core tends to make core temperatures more uniform, lowering the peak temperatures, than would otherwise be the case for a depressurized core where the buoyancy forces would not establish significant recirculation flows. The chimney effect in P-LOFC events also tends to make the core (and vessel) temperatures higher near the top. Maximum vessel-head temperatures are typically limited by judiciously placed insulation, and the use of Alloy 800H for the core barrel allows for extra margin in that area. For the reference case, the peak fuel temperature of 1290ºC occurs at 24 h, and the maximum vessel temperature is 509ºC at 72 h (note: the reader should consider these and the following temperatures as representative values to estimate margins and not actual design values). In P-LOFCs, the peak fuel temperature is not a concern (well within the typical nominal limit for TRISO fuel ~1600ºC ); the major concern is more likely to be the maximum vessel temperature and the shift in peak heat load to near the top of the reactor cavity, resulting in the reactor axial distribution of maximum fuel temperature peaking toward the inlet (top of the core).
12
Depending on the high-temperature capabilities of the vessel steel, some variations in vessel insulation strategies may be needed.
The parameter most likely to affect the P-LOFC outcome, assuming that the RCCS is functioning properly, is the emissivity controlling the radiation heat transfer between the vessel and RCCS (assumed to be 0.8 over the full range of normal-to-accident temperatures). For an assumed (unlikely) 25% decrease in both vessel and RCCS surface effective emissivities, the peak vessel temperature is 37ºC higher. The difference in peak fuel temperature is small (7ºC ), which is typical of the decoupling between the peak fuel and vessel temperature in LOFC events [48].
These temperature changes can cause some fission product redistribution, but the convective flows (weaker than the forced flow) are not expected to drive major fission-product redistribution. The major concern with the P-LOFC is how it may change the distribution of fission products prior to a pressure boundary breach as the event itself does not release fission products. If the P-LOFC results in a pressure-relief-valve opening with or without sticking, a fission-product transport path will be generated. This path is design specific as a filter may be incorporated into the exhaust circuit.
3.3.2.2 The D-LOFC accident
The D-LOFC reference case assumes a rapid depressurization along with a flow coast-down and scram with the passive RCCS operational. It also assumes that the depressurized coolant is helium (no air ingress). This event is also known as a “conduction-heat-up” (or “-cool-down”) accident, since the core effective conductivity is the dominant mechanism for the transfer of afterheat from the fuel to the reactor vessel. In the reference case, the maximum fuel temperature peaks at 1494ºC 53 h into the transient and the maximum vessel temperature (555ºC ) occurs at 81 h. For this case, the peak fuel (and vessel) temperatures occur near the core center rather than near the top as in the P-LOFC case, since the convection effects for atmospheric pressure helium are minimal [48].
There are several parameter variations of interest for this accident, which is generally considered to be the defining accident for determining the reference-case-accident peak fuel temperature. These variations are effective core graphite conductivity (which is a function of irradiation history, temperature, orientation, and whether or not annealing is accounted for), afterheat power versus time after shutdown, and the power-peaking factor distribution in the core after shutdown. If maximum vessel temperatures are of concern, emissivity effects should again be considered.
For variations from the reference case event, the sensitivity of peak fuel temperature for the various assumed parameter changes is as follows:
1. 20% decrease in core conductivity (including annealing effects): a 124°C increase in fuel maximum temperature.
2. 15% increase in afterheat: a 120°C increase in fuel maximum temperature. 3. 20% increase in maximum radial peaking factor: a 30°C increase in fuel maximum
temperature. For the maximum vessel temperatures, again the emissivities figure in most prominently. An
assumed 25% decrease in vessel and RCCS opposing surface emissivities results in an increase in maximum vessel temperature of 54ºC , while the increase in fuel maximum temperature is only 14ºC [48].
This event has a two-part impact on FPT. The first is the initial depressurization which releases fission products from the core by the physical shock of the event, any system vibrations, and the entrainment by the existing flow. This event can be the most important because some conceptual reactor building designs do not include a provision for filtering this rapid high-volume flow. Combustion of dust may add heat and more completely distribute the fission products in the confinement volume. The second
13
part of interest is after the depressurization and the heat-up of the core and reactor system. The higher temperatures can cause the redistribution of fission products (and perhaps, some limited fuel failure depending on design and design margins); however, the driving force for the release of fission products is only the very weak thermal expansion of the gas. In addition, at this point in the accident, the building filters are expected to be operational in all designs.
The more extreme case of this accident is the significant and continued flow of air into the core, which is only possible with a major reactor building and reactor system fault that establishes a convective air path between the reactor vessel and the environment. In this case, high fuel temperatures are possible, high-fission product release is possible, and a convective path is available for the transport of material out of the building. Three mechanisms are available for the enhancement of fission product releases:
1. The locally increased temperatures due to graphite combustion can drive the movement of the volatile fission products such as cesium and if high enough and increase the amount of failed fuel and subsequent fuel releases.
2. The destruction of the graphite and matrix material releases the trapped fission products, which can then be carried along with the flow as particles, vapors, or aerosols.
3. The increased oxygen potential of the reactor environment may change the chemical forms of the fission products and surfaces they interact with.
Graphite oxidation with core consumption and possible collapse is a complex process which is highly dependent on the particular design, materials, and accident configuration. The key feature is the flow path and the amount of oxidizer available; the free flow of oxidizer must be stopped early in the accident to prevent serious fission-product releases from the core.
A more remote accident scenario is an intact sealed containment with the failure of the RCCS and the subsequent heat-driven decomposition of the nearby concrete, liberating H2O and CO2. These gases could react with the exposed core graphite (due to the pressure boundary failure), generating combustible gases that could pose a burning and thus overpressure hazard to the containment if air was part of the normal containment atmosphere [53].
As was noted above, historical designs and accident scenarios were used as the basis for this exercise; rather than focusing on the actual details of the scenario, the panel focused on the results of the scenarios that would significantly impact the release the fission products:
1. Large and small pressure boundary breaches. These breaks and leaks were assumed to have the potential to release not only the material entrained in the gas during normal operation but also material such as dust and fission products on metal surfaces. The main emphasis was on using normal operating conditions as the starting point and assuming that major fuel failure did not take place during the accident. However, if major fuel failure did take place during the accident, only the fission-product inventory available for release would change in the ranking; this would be supplied by the fuels material group as part of an accident scenario. Thus, this scenario is quite general as long as one has the steady-state fission-product inventory and distribution prior to the accident and is supplied information about additional fuel failures and their timing that may occur. A pressure-relief valve opening also falls into this category, but design-specific issues are more relevant because a specialized filter can be placed after the valve. Chemical attack, air or steam ingress, is also included in this scenario; however, the exact details are important for this situation because the core and fuel will be destroyed if the reactions are allows to run to completion.
2. Releases from the cleanup and hold-up systems. Breaks and leaks in these systems can release fission products to the confinement. These systems are only vaguely defined at the present time, but in addition to the historical inventory of inert gases and perhaps iodine, newer designs may include a facility for handling dust.
14
It should be noted that spent fuel storage is also a potential area for fission-product release and at the present time is treated like a hold-up system. As the design matures, this area should be broken out as an issue by itself, especially if it has unique subsystems for controlling contamination and releases.
3.3.3 Significant radionuclides
Based on historical information, the important radionuclides were categorized into two groups, public dose drivers and operational and maintenance drivers. Tables 4 and 5 list the significant radionuclides and the characteristics of interest for the two cases. These tables should be understood in the light of the incomplete design.
At the present time, the most significant radionuclide for the contamination of the secondary side is tritium. This should be considered to be quite tentative as very little is known about any secondary circuit; however, tritium is known to permeate metals at high temperatures.
Table 4. Public dose radionuclides
Nuclide Characteristics 131I High inventory; high dose factor; high vapor pressure within HTGR circuit; effectively
diffuses in graphite; adsorbs strongly on metals—weakly on graphite and oxide layers; can react with paint in confinement to form organic iodide.
137Cs High inventory; high dose factor; high mobility in graphite; likely to be in metallic form in reactor circuit, likely to be oxide in confinement; fairly high volatility at reactor circuit temperatures; can adsorb or condense on particles (dust and aerosols).
90Sr Inventory in graphite; high dose factor; low mobility in graphite; likely to be present in dust; probably SrO in confinement.
3H Effluent releases (and potential contamination of hydrogen produced by the NGNP).
Table 5. Operation and maintenance dose radionuclides
Nuclide Characteristics 110mAg Believed to plate-out on turbine and heat exchangers; activation product; high diffusion
through fuel, matrix, and graphite; high energy gamma; may alloy with nickel based alloys; principal form is the metal which may transport as vapor, aerosol, or on dust.
137Cs and 134Cs Believed to plate out on turbine and heat exchangers, but much less so than silver. 90Sr Could be important in a dust collection system. 131I, 132I, and 132Te
Might be important for short-term maintenance issues in heat exchangers.
60Co Activation product of nickel, high-energy gamma, largely fixed, but may circulate in dust.
3.4 Step 4—Evaluation Criteria
Step 4 of the PIRT process involved the selection of figures of merit and determination of the component and phenomenological hierarchies. The following four figures of merit were selected:
1. Level 1 (Regulatory): Dose to control room and offsite location 2. Level 2 (System): Release to confinement/containment
15
3. Level 3 (Component): Release into primary system 4. Level 4 (Sub-component): Release from graphite in fuel form
These figures of merit were then used as the basis to determine the release from the fuel outward. Four areas of concern implied by the figures of merit are as follows:
1. The inventory of the fission products outside of the fuel (due to defects, contamination, and in-service failures) and fission products that are released due to accident-driven fuel failures (designers assume this to be very small for design base accidents).
2. Total curies released into the confinement, which is composed of the fission products of radiological (dose) interest. These are not clearly identified at present but are expected to be the ones that have been historically identified such as I, Te, Cs, and Sr.
3. Total curies beyond confinement, which is composed of the relevant fission products that penetrate all the boundaries and travel into the environment.
4. Time evolution of the cumulative release(s), which is the history of the release(s) into the confinement and beyond the confinement into the environment.
3.5 Step 5—Knowledge Base
The analysis of FPT must involve all three phenomenological levels; the system level to define the specific scenario, the component level to determine the overall fluid flow and temperatures, and, finally, the local level to determine relevant material properties, chemical interactions, and fission-product mass (and dust) fluxes. The system and component levels may be thought of as setting the fluid flow and thermodynamic environment, while the local level determines the fluxes into and out of the components and surfaces. The knowledge base is detailed in the next section as it is an intrinsic part of evaluating the transport path.
Implicit in the needs of the VHTR FPT are the models to be used for the determination of the fission-product distribution in the core and reactor circuit during normal operating conditions as this is the starting point for the accident. During the accident, similar models will be necessary with the addition of more aggressive dust entrainment models and the chemical reaction models. Models for the FPT might include the following [6, 8, 11–15, 23–44]:
1. Transport models, both simple effective diffusion and more mechanistic, first-principle models, which are needed to model the redistribution from the fuel through the matrix and into the graphite.
2. Sorption models, both Langmuir and empirical, to model the transfer of radionuclidies from the surface of the graphite block or pebble into the coolant.
3. Chemical species, surface state of materials, and coolant chemistry as the sorption on surfaces is very sensitive to the chemical state of both the surface and fission product.
4. Graphite oxidation models for air- or moisture-ingress accidents. 5. Dust abrasion models to determine the dust generation during normal operation. 6. Dust deposition and re-entrainment models that can model the dust distribution in the reactor
circuit both prior to and during the accident. Vibration can result in continuous deposition and re-entrainment in circulating systems; also the shock, vibration, and acoustical noise of a high-pressure pipe break needs to be considered as a transport driver.
Appendix A contains some additional comments on transport modeling and issues that separate the VHTR from the more familiar LWR.
16
3.6 Steps 6 through 8—Identify Phenomena and Rank
Table 6 details the fission-product pathway from the fuel surface and serves as a foundation for the phenomena identification process. Note that most transport mechanisms are in place during both normal operation and accident conditions; only confinement transport is exclusively accident related.
Tables 7 through 10 are the individual phenomenological breakdown and ranking of the more general items identified in Table 6. Table 7 defines the ranking scale, Table 8 defines the knowledge scale, and Table 9 details the model and code knowledge level (ability to conduct useful and practical computations). All are approximate in nature but serve to provide insight into the general status of the evaluation.
Table 10 is the collective panel ranking of the table with the number of panelists ranking the particular item High, Medium, or Low. Individual ranking are contained in Appendix B, and the overall panel result is discussed in the next section.
After the individual phenomena have been identified and ranked, an assessment of the state of knowledge (SOK) was formulated. In particular, areas requiring additional experiments and models are identified. This includes an overall panel consensus assessment for the scenarios considered. As is the case for ranking the importance of phenomena, a High (H), Medium (M) and Low (L) scale is used to rank the SOK relative to the phenomena in the context shown in Table 9. Again, individual rationales for the assigned SOK rankings are provided in the PIRT entries.
The ranking table applies to all three situations—normal operations, anticipated transients, and postulated accidents—because all three conditions require detailed knowledge of the local parameters of the reactor circuit to compute the physical and chemical balances required. The major differences that could exist among the three conditions are the local flows which could be radically different from normal, the core temperature distribution, and the entrainment of dust, generation of aerosols, and sorption of fission products on graphite and metals. However, for the most part, the same information is needed for each case; there appears to be no computational shortcuts or approximations that allow one to drastically reduce the required data or effort. The only two exceptions are the effort required for the confinement and the failures associated with the IHX. Under normal conditions, the confinement and the secondary side are free of fission products. These two cases are noted in the table.
17
Tab
le 6
. Fi
ssio
n pr
oduc
t tra
nspo
rt p
athw
ays f
rom
the
fuel
par
ticle
surf
ace
ID
No.
T
rans
port
step
A
ccid
ent/n
orm
al
cond
ition
M
ajor
phe
nom
ena
Aff
ectin
g fa
ctor
s
1 Th
roug
h th
e ca
rbon
mat
rix
surr
ound
ing
the
parti
cle
Bot
h 1.
C
hem
isor
ptio
n on
the
carb
on
mat
rix
2.
Diff
usio
n th
roug
h m
atrix
1.
Fiss
ion-
prod
uct c
hem
ical
stat
e 2.
R
adia
tion
dam
age
3.
Mat
rix d
ensi
ty/q
ualit
y 4.
C
hem
ical
reac
tions
(im
purit
ies a
nd a
ttack
) 5.
Te
mpe
ratu
re
2 A
cros
s the
com
pact
/blo
ck g
ap
(pris
mat
ic) o
r the
car
bon
mat
rix o
f the
peb
ble
fuel
.
Bot
h 1.
V
apor
izat
ion
1.
Isot
herm
s for
mat
rix a
nd g
raph
ite
2.
Che
mic
al fo
rm
3.
Tem
pera
ture
3
Thro
ugh
the
grap
hite
blo
ck
(pris
mat
ic) o
r thr
ough
the
pebb
le o
uter
, unf
uele
d la
yer
Bot
h 1.
D
iffus
ion
thro
ugh
grap
hite
or
mat
rix o
uter
laye
r 2.
C
hem
isor
ptio
n on
gra
phite
1.
Fiss
ion
prod
uct c
hem
ical
stat
e 2.
R
adia
tion
dam
age
3.
Gra
phite
pro
perti
es
4.
Tem
pera
ture
5.
C
hem
ical
reac
tions
(im
purit
ies)
4
From
the
fuel
form
out
er
surf
ace
to th
e co
olan
t B
oth
1.
Vap
oriz
atio
n 2.
A
bras
ion
1.
Isot
herm
s for
gra
phite
and
mat
rix
2.
Rad
iatio
n da
mag
e 3.
C
hem
ical
form
4.
Te
mpe
ratu
re
5.
Gas
-pha
se c
once
ntra
tions
6.
M
ass t
rans
fer c
oeff
icie
nts
7.
Abr
asio
n fa
ctor
s
5 Tr
ansp
ort i
n th
e co
olan
t, ga
s sp
ecie
s, ae
roso
l, or
dus
t B
oth
1.
Che
mis
orpt
ion
of F
Ps o
n du
sts,
and
aero
sols
2.
D
ust d
epos
ition
and
re-s
uspe
nsio
n 3.
A
eros
ol p
hysi
cs
1.
Isot
herm
s for
mat
rix, g
raph
ite, m
etal
s 2.
Su
rfac
e qu
ality
3.
C
hem
ical
form
4.
Te
mpe
ratu
re
5.
Gas
-pha
se c
once
ntra
tions
6.
Fo
rmat
ion
of a
eros
ols
7.
Aer
osol
con
cent
ratio
ns a
nd e
ffec
ts su
ch a
s ag
glom
erat
ion
and
grow
th
8.
Dus
t for
mat
ion
mec
hani
sms a
nd ra
te
9.
Flow
forc
es o
n du
st a
nd a
eros
ols a
nd
vibr
atio
n
T
able
6 (c
ontin
ued)
18
ID
No.
T
rans
port
step
A
ccid
ent/n
orm
al
cond
ition
M
ajor
phe
nom
ena
Aff
ectin
g fa
ctor
s
6 Fr
om c
oola
nt to
reac
tor c
ircui
t co
mpo
nent
s and
pow
er
conv
ersi
on e
quip
men
t
Bot
h 1.
Fi
ssio
n pr
oduc
t che
mis
orpt
ion,
es
peci
ally
on
met
als
2.
Dus
t pla
te-o
ut
1.
Isot
herm
s for
mat
rix, g
raph
ite, m
etal
s, es
peci
ally
for c
esiu
m a
nd si
lver
2.
Su
rfac
e qu
ality
of p
ower
con
vers
ion
equi
pmen
t 3.
C
hem
ical
form
4.
R
eact
ions
with
oxi
de fi
lm a
nd a
lloyi
ng
with
bas
e m
etal
. 5.
Te
mpe
ratu
re
6.
Gas
-pha
se c
once
ntra
tions
7.
Fo
rmat
ion
of a
eros
ols
8.
Aer
osol
con
cent
ratio
ns a
nd e
ffec
ts su
ch a
s ag
glom
erat
ion
and
grow
th
9.
Dus
t for
mat
ion
mec
hani
sms
7 Tr
ansp
ort o
ut o
f the
reac
tor
circ
uit d
urin
g no
rmal
op
erat
ion
(triti
um p
erm
eatio
n,
refu
elin
g)
Nor
mal
1.
Tr
itium
per
mea
tion,
leak
s 1.
Te
mpe
ratu
re
2.
Perm
eatio
n fa
ctor
3.
Pr
imar
y an
d se
cond
ary
cool
ant
conc
entra
tions
4.
Si
ze a
nd n
umbe
r of l
eaks
8
Tran
spor
t out
of t
he re
acto
r ci
rcui
t due
to p
ress
ure
boun
dary
bre
ech,
lift-
off,
vent
ing,
des
orpt
ion,
dus
t, ae
roso
ls
Acc
iden
t (s
ome
varia
tion
of a
de
pres
suriz
atio
n)
1.
Lift-
off o
f dus
ts, a
eros
ols,
mec
hani
cal e
ffec
ts, s
palla
tion
of
surf
ace
laye
rs
2.
Des
orpt
ion
3.
Iner
tial i
mpa
ctio
n 4.
R
e-su
spen
sion
1.
Dus
t re-
entra
inm
ent
2.
Surf
ace
laye
r cra
ckin
g an
d sp
alla
tion
3.
Effe
cts o
f mec
hani
cal v
ibra
tion
and
acou
stic
al n
oise
4.
C
hem
ical
form
5.
Te
mpe
ratu
re
6.
Form
atio
n an
d gr
owth
of a
eros
ols
7.
Aer
osol
s con
cent
ratio
ns
8.
Isot
herm
s on
met
al su
rfac
es
9.
Dus
t com
bust
ion
9 Tr
ansp
ort f
rom
the
conf
inem
ent t
o th
e en
viro
nmen
t
Acc
iden
t 1.
A
eros
ols,
dust
s,
2.
Gas
eous
iodi
ne
3.
Che
mic
al re
actio
n of
iodi
ne w
ith
surf
ace
4.
Leak
age
from
the
conf
inem
ent
build
ing
1.
Dus
t re-
entra
inm
ent
2.
Aer
osol
con
cent
ratio
ns
3.
Che
mic
al fo
rm
4.
Tem
pera
ture
5.
Fi
lter e
ffic
ienc
ies
6.
Rad
iatio
n en
viro
nmen
t 10
R
elea
se fr
om th
e cl
ean-
up
syst
em (a
nd sp
ent f
uel s
tora
ge)
Acc
iden
t 1.
D
esor
ptio
n fr
om c
lean
up sy
stem
co
mpo
nent
s 2.
Li
ft-of
f of d
usts
, aer
osol
s,
1.
Dus
t re-
entra
inm
ent
2.
Surf
ace
laye
r cra
ckin
g an
d sp
alla
tion
3.
Effe
cts o
f mec
hani
cal v
ibra
tion
and
T
able
6 (c
ontin
ued)
19
ID
No.
T
rans
port
step
A
ccid
ent/n
orm
al
cond
ition
M
ajor
phe
nom
ena
Aff
ectin
g fa
ctor
s
mec
hani
cal e
ffec
ts, s
palla
tion
of
surf
ace
laye
rs
acou
stic
al n
oise
4.
C
hem
ical
form
5.
Te
mpe
ratu
re
6.
Form
atio
n of
aer
osol
s 7.
A
eros
ols c
once
ntra
tions
8.
Pr
oper
ties o
f cle
anup
syst
em c
ompo
nent
s. 9.
C
lean
up sy
stem
failu
re m
odes
and
loca
tion
of c
lean
up sy
stem
s 11
Tr
ansp
ort i
ssue
s ass
ocia
ted
with
the
IHX
N
orm
al
Acc
iden
t 1.
Tr
itium
per
mea
tion
2.
IHX
leak
s 3.
IH
X fa
ilure
s
1.
Tem
pera
ture
s 2.
M
ater
ials
3.
Su
rfac
e la
yers
4.
D
esig
n-sp
ecifi
c fa
ilure
mod
es
20
Table 7. Phenomena importance ranking scale
Rank Definition Application outcomes High (H) Phenomenon has a controlling
impact on the Figure of Merit Experimental simulation and analytical modeling with a high degree of accuracy is critical
Medium (M) Phenomenon has a moderate impact on the Figure of Merit
Experimental simulation and/or analytical modeling with a moderate degree of accuracy
Low (L) Phenomenon has a minimal impact on the Figure of Merit
Modeling must be present to preserve functional dependencies
Table 8. State-of-knowledge (SOK) ranking scale
Rank Definition High (H) Experimental simulation and analytical modeling with a high degree of accuracy is
currently possible Medium (M) Experimental simulation and/or analytical modeling with a moderate degree of
accuracy is currently possible
Low (L) Experimental simulation and/or analytical modeling is currently marginal or not available
Table 9. Status of fission-product modeling ranking scale
Rank Definition
Adequate Existing codes and/or analytic models can be adapted to the problem with minimal effort
Minor mod Deficiencies exist within existing codes and/or analytic models, or modest, measurable effort is required to adapt them to the problem
Major need Useful codes and/or analytic models do not exist for this problem. Requires major development
21
Tab
le 1
0. O
vera
ll PI
RT
ran
king
Thi
s tab
le g
ener
ally
app
lies t
o al
l cas
es—
norm
al, a
ntic
ipat
ed tr
ansi
ents
, and
acc
iden
ts.
Spec
ific
case
s are
not
ed.
Thi
s tab
le c
onta
ins a
sum
mar
y of
the
indi
vidu
al r
anki
ngs a
nd th
e A
pril
18, 2
007,
con
sens
us R
atio
nale
s.
See
App
endi
x B
for
deta
ils o
n in
divi
dual
ran
king
and
thei
r ad
ditio
n co
mm
ents
on
the
liste
d ra
tiona
les (
“Med
ium
–Hig
h” w
as ta
llied
as “
Med
ium
,” a
nd
“Med
ium
–Low
” w
as ta
llied
as “
Low
.” S
ome
min
or in
terp
olat
ion
was
req
uire
d w
hen
usin
g th
e re
orga
nize
d ta
ble)
. O
vera
ll, th
ere
was
gen
eral
ag
reem
ent w
ith o
nly
one
extr
eme
split
(Hig
hs a
nd L
ows)
—en
try
#49.
N
otes
: *d
enot
es n
eed
for i
nter
face
with
oth
er g
roup
s (m
ater
ials
, tra
nsie
nt sc
enar
ios)
IC
—in
itial
con
ditio
n, th
e re
sult
of lo
ng-te
rm n
orm
al o
pera
tion
Tran
s.—tr
ansi
ent a
nd a
ccid
ent c
ondi
tion
TF—
ther
mal
flui
ds
FP—
fissi
on p
rodu
cts
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
)
Cri
tical
initi
al a
nd/o
r bou
ndar
y co
nditi
on
1 D
ecay
hea
t and
tran
sien
t po
wer
leve
l 5–
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) 5–
*Hig
h B
ound
ary
cond
ition
s ex
pect
ed fr
om T
F PI
RT
Ade
quat
e
2 M
ater
ial/s
truct
ure
prop
ertie
s 5–
Hig
h D
ensi
ty, v
isco
sity
, co
nduc
tivity
, etc
., im
porta
nt p
aram
eter
s in
calc
ulat
ions
(IC
and
Tr
ans.)
5–*M
ed (g
raph
ite):
Hig
h (s
teel
, con
cret
e)
Gra
phite
type
not
se
lect
ed, e
xpec
ted
from
mat
eria
l PI
RT
Min
or m
od (g
raph
ite)
Ade
quat
e (s
teel
, co
ncre
te)
3 G
raph
ite im
purit
y le
vels
4–
Med
ium
1–
Hig
h Im
purit
y re
actio
n w
ith
FP, n
ucle
ar g
raph
ite
expe
cted
to h
ave
low
im
purit
y le
vels
5–*H
igh
Will
be
mea
sure
d,
expe
cted
from
m
ater
ial P
IRT
Ade
quat
e
4 G
raph
ite g
eom
etry
5–
Hig
h C
ore
stru
ctur
e (d
esig
n in
form
atio
n)
1–M
ediu
m
4–H
igh
Wel
l kno
wn
for
IC
Ade
quat
e fo
r IC
M
ajor
Nee
d fo
r air
ingr
ess
T
able
10
(con
tinue
d)
22
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 5
Ther
mal
-flu
id p
rope
rties
5–
Hig
h Te
mpe
ratu
re, p
ress
ure,
ve
loci
ty c
ompu
tatio
ns
(IC
and
Tra
ns.)
4–*M
ediu
m
1–*H
igh
Wel
l kno
wn
for
heliu
m,
unce
rtain
ty in
co
mpo
sitio
n of
ga
s mix
ture
s m
akes
gas
pr
oper
ty
calc
ulat
ion
mor
e di
ffic
ult,
expe
cted
fr
om T
F PI
RT
Ade
quat
e
6 G
as c
ompo
sitio
n 5–
Hig
h O
xyge
n po
tent
ial a
nd
chem
ical
act
ivity
4–
Med
ium
1–
Low
C
entra
l iss
ue fo
r ch
emic
al re
actio
n m
odel
ing,
FP
spec
iatio
n,
scen
ario
de
pend
ent
Ade
quat
e (d
epre
ssur
izat
ion)
M
ajor
nee
d (a
ir in
gres
s)
7 G
as fl
ow p
ath
prio
r, du
ring
and
post
acc
iden
t 5–
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s.)
5–*S
ame
as T
F gr
oup
Nee
d to
co
ordi
nate
with
ot
her g
roup
s;
expe
cted
from
TF
PIR
T
Sam
e as
TF
grou
p
8 Te
mpe
ratu
re (s
truct
ure
and
gas)
and
pre
ssur
e di
strib
utio
n
5–H
igh
Info
rmat
ion
need
ed to
m
odel
acc
iden
t (IC
and
Tr
ans.)
5–H
igh
Nee
d to
co
ordi
nate
with
ot
her g
roup
s;
expe
cted
from
TF
PIR
T
Sam
e as
TF
grou
p
9 FP
pla
te-o
ut a
nd d
ust
dist
ribut
ion
unde
r nor
mal
op
erat
ion
5–H
igh
Star
ting
cond
ition
s 1–
Low
4–
Med
ium
Th
eory
and
m
odel
s lac
k sp
ecifi
cs
Maj
or n
eed
T
able
10
(con
tinue
d)
23
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) G
raph
ite a
nd c
ore
mat
eria
ls
10
Mat
rix p
erm
eabi
lity,
to
rtuos
ity
1–M
ediu
m
4–H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s.)
4–*L
ow
1–*M
ediu
m
FP h
oldu
p as
ba
rrie
r, re
leas
e as
du
st; e
xpec
ted
from
mat
eria
l PI
RT.
Maj
or n
eed
11
FP tr
ansp
ort t
hrou
gh
mat
rix
5–H
igh
Effe
ctiv
e re
leas
e ra
te
coef
ficie
nt (e
mpi
rical
co
nsta
nt) a
s an
alte
rnat
ive
to fi
rst
prin
cipl
es (I
C a
nd
Tran
s.)
5–Lo
w
FP h
oldu
p as
ba
rrie
r, re
leas
e as
du
st; e
xpec
ted
from
mat
eria
l PI
RT
Maj
or n
eed
12
Fuel
blo
ck p
erm
eabi
lity,
to
rtuos
ity
1–M
ediu
m
4–H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s.)
5–*M
ediu
m
Dep
ends
on
spec
ific
grap
hite
; ex
pect
ed fr
om
mat
eria
l PIR
T
Maj
or n
eed
13
FP tr
ansp
ort t
hrou
gh fu
el
bloc
k 5–
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tr
ans.)
1–*L
ow
4– M
ediu
m
Dep
ends
on
spec
ific
grap
hite
; ex
pect
ed fr
om
mat
eria
l PIR
T
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
5–Lo
w
Ther
mal
gra
dien
ts a
re
not l
arge
out
side
of f
uel
5–Lo
w
Littl
e da
ta
Not
req’
d
15
Bas
al p
lane
diff
usio
n 5–
Low
Po
rosi
ty is
pre
ferr
ed
trans
port
path
way
th
roug
h gr
aphi
te
5–M
ediu
m
Past
wor
k an
d lit
erat
ure
avai
labl
e N
ot re
q’d
T
able
10
(con
tinue
d)
24
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 16
R
efle
ctor
(in
cont
act
w/fl
ow) p
erm
eabi
lity,
to
rtuos
ity
5–Lo
w
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s.)
5–*M
ediu
m
Dep
ends
on
spec
ific
grap
hite
; ex
pect
ed fr
om
mat
eria
l PIR
T
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
5–Lo
w
Effe
ctiv
e re
leas
e ra
te
coef
ficie
nt (e
mpi
rical
co
nsta
nt) a
s an
alte
rnat
ive
to fi
rst
prin
cipl
es (I
C a
nd
Tran
s.)
1–*L
ow
4–*M
ediu
m
Dep
ends
on
spec
ific
grap
hite
; ex
pect
ed fr
om
mat
eria
l PIR
T
Min
or m
od
18
Sorb
tivity
gra
phite
5–
Hig
h C
an d
eter
min
e ho
ldup
an
d re
leas
e of
FP
(IC
and
Tr
ans.)
5–M
ediu
m
His
toric
al d
ata,
ne
ed sp
ecifi
c in
form
atio
n on
gr
aphi
te a
nd
radi
atio
n ef
fect
s
Min
or m
od
19
Flue
nce
effe
ct o
n tra
nspo
rt in
gra
phite
5–
Hig
h In
fluen
ces t
rans
port,
ch
emic
al re
activ
ity
5–M
ediu
m
His
toric
al d
ata,
ne
ed sp
ecifi
c in
form
atio
n on
gr
aphi
te a
nd
radi
atio
n ef
fect
s
Maj
or n
eed
20
C-1
4, C
l-36,
Co-
60
gene
ratio
n an
d in
vent
ory
4–Lo
w
1–M
ediu
m
Rad
iois
otop
e ge
nera
ted
from
impu
ritie
s, m
ight
be
com
e op
erat
iona
l iss
ue
(IC
)
5–M
ediu
m
His
toric
al d
ata,
Pe
ach
Bot
tom
H
TGR
Min
or m
od, s
ensi
tive
to g
raph
ite h
andl
ing
21
Air
atta
ck o
n gr
aphi
te
5–H
igh
Gra
phite
er
osio
n/ox
idat
ion,
Fe/
Cs
cata
lysi
s lib
erat
ing
FPs
(Tra
ns.)
1–Lo
w
4–M
ediu
m
His
toric
al d
ata
Maj
or n
eed
for s
ever
e ac
cide
nts
22
Stea
m a
ttack
on
grap
hite
5–
Hig
h If
cre
dibl
e so
urce
of
wat
er p
rese
nt; d
esig
n de
pend
ent (
Tran
s.)
1–Lo
w
4–M
ediu
m
His
toric
al d
ata
Maj
or n
eed
for s
ever
e ac
cide
nts
T
able
10
(con
tinue
d)
25
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) F
issi
on p
rodu
ct tr
ansp
ort i
n re
acto
r coo
lant
syst
em a
nd c
onfin
emen
t
23
FP sp
ecia
tion
in
carb
onat
ious
mat
eria
l 5–
Hgh
C
hem
ical
form
in
grap
hite
aff
ects
tran
spor
t (I
C a
nd T
rans
.)
5–Lo
w
Unc
erta
in a
nd/o
r in
com
plet
e M
ajor
nee
d
24
FP sp
ecia
tion
durin
g m
ass t
rans
fer
5–H
igh
Che
mic
al c
hang
e ca
n al
ter v
olat
ility
1–
Low
4–
Med
ium
H
isto
rical
dat
a;
need
spec
ific
info
rmat
ion.
Goo
d fo
r met
als,
oxid
es.
Unc
erta
in fo
r ca
rbid
es a
nd
carb
onyl
s.
Maj
or n
eed
25
“Kno
ck-a
long
” 5–
Low
A
lpha
reco
il tra
nspo
rt of
de
posi
ted
parti
cles
on
surf
aces
slow
com
pare
d to
flui
d flo
w tr
ansp
ort
5–M
ediu
m
Stud
ied
in
actin
ide-
bear
ing
parti
cles
Ade
quat
e
26
Dus
t gen
erat
ion
5–H
igh
Vec
tor f
or F
P tra
nspo
rt;
poss
ibili
ty o
f hig
h m
obili
ty
5–M
ediu
m
Lim
ited
expe
rienc
e; la
ck
spec
ific
syst
em
info
rmat
ion
Maj
or n
eed,
impo
rt fr
om o
ther
gro
ups
27
(De)
Abs
orpt
ion
on d
ust
5–H
igh
Prov
ides
cop
ious
surf
ace
area
for F
P ab
sorp
tion
2–
Low
3–
Med
ium
Li
mite
d ex
perie
nce,
lack
sp
ecifi
c de
tails
Maj
or n
eed
28
H-3
gen
erat
ion
and
circ
ulat
ing
cool
ant
inve
ntor
y
4–M
ediu
m
1–H
igh
Rad
iois
otop
e, a
n is
sue
with
ope
ratio
nal r
elea
se.
H-3
pro
duct
ion
from
He-
3 in
coo
lant
, ter
nary
fis
sion
, and
Li-6
in
grap
hite
5–M
ediu
m
His
toric
al d
ata;
Pe
ach
Bot
tom
H
TGR
Min
or m
od
T
able
10
(con
tinue
d)
26
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 29
A
g-11
0m g
ener
atio
n,
trans
port
5–H
igh
(O&
M)
5–Lo
w (r
elea
se)
Rad
iois
otop
e, si
gnifi
cant
O
&M
dos
e on
coo
l, m
etal
lic c
ompo
nent
s
5–Lo
w
Lim
ited
data
, un
know
n tra
nspo
rt m
echa
nism
Maj
or n
eed
30
Oth
er a
ctiv
atio
n pr
oduc
ts
(e.g
., C
s-13
4, M
n-55
, Fe
-56)
5–Lo
w
Rad
iois
otop
es, p
oten
tial
O&
M d
ose
5–M
ediu
m
Expe
rienc
e,
limite
d in
form
atio
n
Min
or m
od
31
Nuc
leat
ion
5–
Med
ium
U
ncle
ar d
ue to
ext
rem
ely
low
FP
vapo
r co
ncen
tratio
n an
ticip
ated
5–M
ediu
m
His
toric
al d
ata
Maj
or n
eed
32
Aer
osol
gro
wth
1–
Med
ium
4–
Hig
h Lo
w c
once
ntra
tion
grow
th c
an le
ad to
hig
h-sh
ape
fact
ors a
nd
unus
ual s
ize
dist
ribut
ion
5–Lo
w
Reg
ime
has n
ot
been
stud
ied
prev
ious
ly
Maj
or n
eed
33
Surf
ace
roug
hnes
s 5–
Med
ium
A
ffec
ts a
eros
ol
depo
sitio
n 1–
5 m
icro
n pa
rticl
es (I
C a
nd T
rans
.)
5–M
ediu
m
Initi
al in
form
atio
n fr
om
man
ufac
ture
r; ev
olut
ion
of
surf
ace
roug
hnes
s du
ring
oper
atio
n no
t wel
l kno
wn
Min
or m
od
34
Coo
lant
che
mic
al
inte
ract
ion
with
surf
aces
5–
Hig
h C
hang
es o
xyge
n an
d ca
rbon
pot
entia
l whi
ch
can
affe
ct n
atur
e an
d qu
antit
y of
sorb
ed
spec
ies (
IC a
nd T
rans
.)
5–M
ediu
m
Surf
ace
prop
ertie
s ar
e cr
itica
l; ne
ed
allo
y da
ta
Maj
or n
eed
35
FP d
iffus
ivity
, sor
btiv
ity
in n
ongr
aphi
te su
rfac
es
5–H
igh
Det
erm
ines
FP
loca
tion
durin
g op
erat
ion;
act
s as
a tra
p du
ring
trans
ient
(I
C a
nd T
rans
.)
5–Lo
w
Littl
e in
form
atio
n on
mat
eria
ls o
f in
tere
st
Maj
or n
eed
T
able
10
(con
tinue
d)
27
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 36
A
eros
ol/d
ust d
epos
ition
5–
Hig
h G
ravi
tatio
nal,
iner
tial,
ther
mop
hore
sis,
elec
trost
atic
, diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
5–M
ediu
m
Rea
sona
bly
wel
l-de
velo
ped
theo
ry
of a
eros
ol
depo
sitio
n by
m
ost m
echa
nism
s ex
cept
iner
tial
impa
ct in
com
plex
ge
omet
ries;
ap
plic
abili
ty to
N
GN
P un
clea
r
Min
or m
od
37
Aer
osol
/dus
t bou
nce,
br
eaku
p du
ring
depo
sitio
n
4–M
ediu
m
1–H
igh
Can
mod
ify d
epos
ition
pr
ofile
and
susp
ende
d ae
roso
l dis
tribu
tion
4–Lo
w
1–M
ediu
m
Theo
ry, d
ata,
and
m
odel
s lac
king
M
ajor
nee
d
38
Res
uspe
nsio
n 5–
Hig
h Fl
ow/v
ibra
tion
indu
ced,
sa
ltatio
n; m
echa
nica
l fo
rces
can
rele
ase
FPs
from
pip
e su
rfac
e la
yers
/film
s (Tr
ans.)
4–Lo
w
1–M
ediu
m
Lack
of d
ata
and
mod
els f
or
antic
ipat
ed
cond
ition
s
Maj
or n
eed
39
Con
finem
ent a
eros
ol
phys
ics
5–H
igh
Ana
logo
us to
LW
R
aero
sol b
ehav
ior/p
hysi
cs,
delta
-T, c
hem
istry
; im
porta
nt h
oldu
p m
echa
nism
(Tra
ns.)
5–M
ediu
m
Rea
sona
bly
wel
l-de
velo
ped
theo
ry
of a
eros
ol
beha
vior
; ap
plic
abili
ty to
N
GN
P un
clea
r
Min
or m
od
40
Dus
t dep
ositi
on o
n ve
ssel
and
RC
CS
hard
war
e
5–Lo
w
Not
impo
rtant
for F
P tra
nspo
rt bu
t may
aff
ect
radi
ativ
e he
at tr
ansf
er in
re
acto
r cav
ity
5–Lo
w
Ver
y lim
ited
data
M
ajor
nee
d
T
able
10
(con
tinue
d)
28
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 41
C
orro
sion
pro
duct
s 5–
Low
Sp
alle
d su
rfac
e fil
ms;
lo
w c
orro
sion
en
viro
nmen
t (I
C a
nd T
rans
.)
5–H
igh
Past
exp
erie
nce
Ade
quat
e
42
Eros
ion
prod
ucts
, no
ncar
bon
5–Lo
w
Low
con
cent
ratio
n of
co
arse
mat
eria
ls (I
C a
nd
Tran
s.)
5–Lo
w
Lack
of d
esig
n in
form
atio
n;
conf
igur
atio
n an
d m
ater
ials
spec
ific
Ade
quat
e
43
Was
h-of
f 5–
Hig
h If
cre
dibl
e so
urce
of
wat
er p
rese
nt; d
esig
n de
pend
ent (
Tran
s.)
5–M
ediu
m
Som
e ex
perim
enta
l dat
a av
aila
ble
Min
or m
od
44
Failu
re m
odes
of
auxi
liary
syst
ems (
e.g.
, ga
s cle
anup
, hol
dup,
re
fuel
ing)
5–M
ediu
m
Pote
ntia
l rel
ease
due
to
failu
re (T
rans
.) 5–
Med
ium
D
esig
n sp
ecifi
c;
have
exp
erie
nce
from
oth
er d
esig
ns
Min
or m
od
45
Rad
ioly
sis e
ffec
ts in
co
nfin
emen
t 5–
Hig
h FP
(e.g
., I,
Ru,
Te)
ch
emis
try, p
aint
ch
emis
try (d
epen
dent
on
conf
inem
ent r
adia
tion
leve
l) (T
rans
.)
5–M
ediu
m
LWR
exp
erie
nce
and
data
M
inor
mod
46
Filtr
atio
n 5–
Hig
h Tr
aditi
onal
pas
sive
ch
arco
al/H
EPA
(Tra
ns.)
5–H
igh
His
toric
al
expe
rienc
e A
dequ
ate
47
Prod
uctio
n/co
mbu
stio
n of
flam
mab
le g
as
5–M
ediu
m
CO
, H2 p
rodu
ctio
n is
sues
, IH
X se
cond
ary-
prim
ary
leak
, pot
entia
l re
susp
ensi
on a
nd
chem
ical
tran
sfor
mat
ion
of F
Ps (T
rans
.)
1–M
ediu
m
4–H
igh
His
toric
al
expe
rienc
e A
dequ
ate
T
able
10
(con
tinue
d)
29
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 48
C
ombu
stio
n of
dus
t in
conf
inem
ent
5–H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
with
in
con
finem
ent
1–Lo
w
4–M
ediu
m
ITER
dat
a M
ajor
nee
d
49
NG
NP-
uniq
ue le
akag
e pa
th b
eyon
d co
nfin
emen
t 5–
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n; c
ould
be
risk
dom
inan
t (Tr
ans.)
1–Lo
w
4–H
igh
Con
tinge
nt o
n sp
ecifi
c de
sign
kn
owle
dge
Min
or m
od
50
Con
finem
ent l
eaka
ge
path
, rel
ease
rate
thro
ugh
pene
tratio
ns
5–H
igh
Cab
le/p
ipe
pene
tratio
ns,
crac
ks, h
oles
, HV
AC
(T
rans
.)
5–M
ediu
m
Bui
ldin
g le
akag
e ex
perie
nce,
des
ign
spec
ific
Ade
quat
e
51
Cab
le p
yrol
ysis
, fire
5–
Hig
h So
ot g
ener
atio
n an
d ch
ange
s to
iodi
ne
chem
istry
5–M
ediu
m
LWR
exp
erie
nce
Maj
or n
eed
52
Pres
sure
-rel
ief-
valv
e fil
ter
5–Lo
w
Ope
ning
of t
he re
lief
valv
e ge
nera
tes a
tra
nspo
rt pa
th th
at m
ay
be fi
ltere
d; d
epen
ds o
n de
sign
5–H
igh
Air
clea
ning
te
chno
logy
A
dequ
ate
53
Rec
ritic
ality
(slo
w)
5–H
igh
Add
ition
al th
erm
al lo
ad
to fu
el. I
ncre
ases
sour
ce
but n
ot e
xpec
ted
to a
ffec
t tra
nspo
rt pa
th.
5–M
ediu
m
Hea
t loa
d ea
sily
co
mpu
ted
with
ex
istin
g to
ols;
ef
fect
on
fissi
on
prod
ucts
not
co
mpl
etel
y kn
own
Min
or m
od
54
Fuel
-dam
agin
g R
IA
5–H
igh
An
inte
nse
puls
e co
uld
dam
age
fuel
. In
crea
ses
sour
ce b
ut n
ot e
xpec
ted
to a
ffec
t tra
nspo
rt pa
th
5–M
ediu
m
Som
e da
ta e
xist
s, bu
t out
side
of
expe
cted
acc
iden
t en
velo
pe
Min
or m
od
T
able
10
(con
tinue
d)
30
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P (H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
m
inor
mod
, maj
or
need
) 55
A
rgon
act
ivat
ion
in
reac
tor c
avity
5–
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
5–H
igh
Easi
ly c
ompu
ted
with
exi
stin
g to
ols
Ade
quat
e
56
Red
istri
butio
n of
fiss
ion
prod
ucts
due
to c
ontro
l ro
d m
ovem
ent
5–Lo
w
Arti
cula
ted
cont
rol r
od
join
ts c
an c
olle
ct a
nd
redi
strib
ute
fissi
on
prod
ucts
5–Lo
w
Spec
ifics
on
CR
D
hous
ing
and
artic
ulat
ed S
iC
com
posi
te
hous
ing
TBD
Min
or m
od
31
The crucial information that is required to begin an accident analysis is the initial condition (IC), the situation prior to the accident. It is this situation that will set the basic source term for a depressurization release. Unlike the LWR case, massive fuel failure is not anticipated during the course of the accident (unless unlimited air ingress occurs); any incremental fuel failure is anticipated to occur after the depressurization is complete; thus, the late accident release driver is then reduced because the major driving term, helium pressure, is gone due to the leak or break. The driving terms later in the accident are the weak flows driven by temperature and atmospheric variations. In addition, some designs may filter the later releases, but not all designs may filter the main source of dust and fission-product aerosols during the initial (large volume and short duration) depressurization.
If an air or moisture ingress accident occurs with an unimpeded flow path and is allowed to run to completion, high levels of fuel failure due to high temperatures are possible. In this case, large fission-product releases can occur later in the accident and the convective flows will carry the fission products outside the core.
3.7 Step 9—Document PIRT—Summary
The panel discussions allowed the assembly of the desired ranking table; however, it must be noted that the FPT issue is a consequence of an accident scenario and not the accident driver. Depending on the design of a confinement or containment, the impact of a pressure boundary breach can be minimized if a modest, but not excessively large, fission-product attenuation factor can be introduced into the release path. This exercise has identified a host of material properties, thermofluid states, and physics models that must be collected, defined, and understood to evaluate this attenuation factor.
Table 11 is a condensed version of Table 10, containing only those items with at least one ranking of high importance and one ranking of low knowledge. An expanded rationale column has been added to more completely explain the issues and why they were ranked in this manner. Because of the small allowable releases during a depressurization from this reactor type (due to a vented confinement), dust and aerosol issues are important even though the amounts of fission products involved may be modest (compared to an LWR accident). Also, the mechanical impact of the failure needs to be assessed because it can re-entrain dust as well as generate particles by spalling off internal surface layers. The mechanical shock issue has seen less emphasis in the gas reactor transport literature, and NUREG-0800 specifically calls for the evaluation of “pipe whip” issues.
The reader should be cautioned that merely selecting phenomena based on high importance and low knowledge may not capture the true uncertainty of the situation. This is because a transport path is composed of several serial linkages, each with its own uncertainty. The propagation of a chain of modest uncertainties can lead to a very large uncertainty at the end of a long path, resulting in a situation that is of little regulatory value.
32
Tab
le 1
1. S
elec
ted
PIR
T it
ems f
rom
Tab
les 1
0 th
at h
ave
at le
ast o
ne h
igh
impo
rtan
ce a
nd lo
w k
now
ledg
e ra
nkin
g
Not
es:
*den
otes
nee
d fo
r int
erfa
ce w
ith o
ther
gro
ups (
mat
eria
ls, t
rans
ient
scen
ario
s)
IC—
initi
al c
ondi
tion,
the
resu
lt of
long
term
nor
mal
ope
ratio
n Tr
ans.—
tran
sien
t and
acc
iden
t con
ditio
n TF
—th
erm
al fl
uids
FP
—fis
sion
pro
duct
s
ID
No.
Is
sue
(phe
nom
ena,
pro
cess
, ge
omet
ry c
ondi
tion)
Im
port
ance
for
NG
NP
(Hig
h, M
ediu
m, L
ow)
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
6 G
as c
ompo
sitio
n 5–
Hig
h 4–
Med
ium
1–
Low
O
xyge
n po
tent
ial a
nd c
hem
ical
act
ivity
are
cen
tral i
ssue
s for
ch
emic
al re
actio
n m
odel
ing
and
FP sp
ecia
tion.
Vol
atili
ty o
f FPs
ca
n de
pend
on
chem
ical
form
and
oxi
dizi
ng c
ondi
tions
will
cau
se
mat
rix a
nd g
raph
ite d
amag
e le
adin
g to
the
rele
ase
of c
onta
ined
FP
s. H
oldu
p of
FPs
on
met
al su
rfac
es c
an d
epen
d on
surf
ace
oxid
atio
n st
ate.
Thi
s is s
cena
rio d
epen
dent
. C
an in
fluen
ce th
e IC
du
e to
gas
impu
ritie
s. M
ost n
eede
d fo
r the
air
ingr
ess a
ccid
ent.
9 FP
Pla
te-o
ut a
nd d
ust
dist
ribut
ion
unde
r nor
mal
op
erat
ion
5–H
igh
1–Lo
w
4–M
ediu
m
The
plat
e-ou
t and
dus
t dis
tribu
tion
form
the
IC fo
r an
acci
dent
. Th
eory
and
mod
els l
ack
spec
ifics
; mus
t be
coup
led
with
flow
and
m
echa
nica
l mod
els a
s hig
h de
posi
tion
area
s sub
ject
ed to
larg
e ch
ange
s in
flow
, tem
pera
ture
, and
mec
hani
cal s
hock
/vib
ratio
n ar
e ca
ndid
ates
for r
e-en
train
men
t dur
ing
an a
ccid
ent.
10
Mat
rix p
erm
eabi
lity,
to
rtuos
ity
1–M
ediu
m
4–H
igh
4–*L
ow
1–*M
ediu
m
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C a
nd T
rans
) and
fu
nctio
ns a
s FP
hold
up b
arrie
r for
less
vol
atile
FPs
(bot
h in
fuel
fo
rm a
nd a
s dus
t). S
ome
form
of f
airly
com
preh
ensi
ve m
odel
ov
er th
e co
nditi
ons o
f int
eres
t is n
eede
d. N
ote
that
this
aff
ects
FP
dust
(peb
ble
bed)
mod
elin
g as
wel
l. Se
e ite
m 1
1 be
low
.
T
able
11
(con
tinue
d)
33
ID
No.
Is
sue
(phe
nom
ena,
pro
cess
, ge
omet
ry c
ondi
tion)
Im
port
ance
for
NG
NP
(Hig
h, M
ediu
m, L
ow)
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
11
FP tr
ansp
ort t
hrou
gh m
atrix
5–
Hig
h 5–
Low
O
nce
thro
ugh
the
parti
cle,
the
mat
rix is
the
first
bar
rier (
note
that
pe
bble
s are
larg
ely
mat
rix);
it al
so c
olle
cts F
Ps a
s dus
t. E
ffec
tive
rele
ase
rate
coe
ffic
ient
(em
piric
al c
onst
ant)
as a
n al
tern
ativ
e to
fir
st p
rinci
ples
(IC
and
Tra
ns) m
ay b
e m
ore
tract
able
. M
atrix
ho
ldup
can
be
impo
rtant
for t
he le
ss v
olat
ile F
Ps.
Dus
t in
the
PBM
R m
ay b
e la
rgel
y co
mpo
sed
of m
atrix
, so
this
issu
e w
ill
affe
ct d
ust F
P m
odel
ing
as w
ell.
13
FP tr
ansp
ort t
hrou
gh fu
el
bloc
k 5–
Hig
h 1–
*Low
4–
*Med
ium
G
raph
ite c
an o
ffer
subs
tant
ial a
ttenu
atio
n to
the
trans
port
of F
Ps
and
hold
up
the
less
vol
atile
one
s. E
ffec
tive
rele
ase
rate
co
effic
ient
(em
piric
al c
onst
ant)
as a
n al
tern
ativ
e to
firs
t prin
cipl
es
(IC
and
Tra
ns) m
ay b
e m
ore
tract
able
but
cou
ld b
e hi
ghly
de
pend
ent o
n th
e ty
pe o
f gra
phite
. Im
porta
nt fo
r pris
mat
ic c
ore
beca
use
of th
e se
ries p
ath.
Abs
orpt
ion
in g
raph
ite b
lock
s is
desi
rabl
e to
that
in d
ust b
ecau
se o
f les
s mob
ility
.
21
Air
atta
ck o
n gr
aphi
te
5–H
igh
1–Lo
w
4–M
ediu
m
Gra
phite
ero
sion
/oxi
datio
n ca
n re
leas
e th
e co
ntai
ned
FPs a
nd
chan
ge th
e ch
emic
al fo
rm o
f the
FPs
as w
ell a
s wea
ken
the
core
an
d da
mag
e th
e fu
el.
Issu
es su
ch a
s Fe/
Cs c
atal
ysis
can
cha
nge
pore
stru
ctur
e, le
adin
g to
gre
ater
FP
rele
ase.
Som
e hi
stor
ical
dat
a is
ava
ilabl
e, b
ut th
e ve
ry sm
all a
ccep
tabl
e re
leas
e fr
actio
n m
ay
requ
ire m
ore
deta
il. M
ajor
nee
d fo
r sev
ere
acci
dent
s.
22
Stea
m a
ttack
on
grap
hite
5–
Hig
h 1–
Low
4–
Med
ium
If
cre
dibl
e so
urce
of w
ater
are
pre
sent
, con
tain
ed F
Ps c
an b
e re
leas
ed w
ith p
robl
ems s
imila
r to
abov
e; th
is is
des
ign
depe
nden
t an
d m
uch
less
of a
pro
blem
for a
hel
ium
-onl
y sy
stem
. M
ajor
ne
ed fo
r sev
ere
acci
dent
s.
23
FP sp
ecia
tion
in c
arbo
natio
us
mat
eria
l 5–
Hig
h 5–
Low
Th
e ch
emic
al fo
rm o
f the
FPs
in g
raph
ite a
nd m
atrix
mat
eria
l af
fect
s tra
nspo
rt an
d ho
ld u
p un
der b
oth
IC a
nd a
ccid
ents
. U
ncer
tain
and
/or i
ncom
plet
e in
form
atio
n in
this
are
a. T
he h
ighe
r te
mpe
ratu
res i
n th
e V
HTR
may
influ
ence
this
. M
ajor
nee
d as
ch
emic
al fo
rms s
trong
ly in
fluen
ce tr
ansp
ort.
T
able
11
(con
tinue
d)
34
ID
No.
Is
sue
(phe
nom
ena,
pro
cess
, ge
omet
ry c
ondi
tion)
Im
port
ance
for
NG
NP
(Hig
h, M
ediu
m, L
ow)
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
24
FP sp
ecia
tion
durin
g m
ass
trans
fer
5–H
igh
1–Lo
w
4–M
ediu
m
Che
mic
al c
hang
e ca
n al
ter F
P vo
latil
ity. T
here
is so
me
hist
oric
al
data
, but
spec
ific
data
may
be
need
ed fo
r the
VH
TR.
Ther
e ap
pear
s to
be g
ood
info
rmat
ion
for m
etal
s and
oxi
des.
Unc
erta
in
for c
arbi
des a
nd c
arbo
nyls
. N
eed
to d
eter
min
e th
e im
porta
nce
of
the
issu
e.
27
(De)
Abs
orpt
ion
on d
ust
5–H
igh
2–Lo
w
3–M
ediu
m
Dus
t pro
vide
s cop
ious
surf
ace
area
for F
P ab
sorp
tion,
and
the
high
mob
ility
of d
ust a
llow
s the
tran
spor
t of F
Ps th
roug
hout
the
reac
tor s
yste
m.
Can
be
a m
echa
nism
that
wor
ks in
par
alle
l with
FP
vol
atili
ty fo
r the
dis
tribu
tion
of F
Ps.
Lim
ited
expe
rienc
e; la
ck
spec
ific
deta
ils.
Som
e da
ta fr
om A
VR
.
29
Ag-
110m
gen
erat
ion,
tra
nspo
rt 5–
Hig
h (O
&M
) 5–
Low
(rel
ease
) 5–
Low
B
oth
Ag
(and
Cs)
can
driv
e a
sign
ifica
nt O
&M
dos
e on
pow
er
conv
ersi
on a
nd h
eat e
xcha
nger
equ
ipm
ent.
Lim
ited
data
; un
know
n tra
nspo
rt m
echa
nism
. M
ay a
lloy
with
met
al
com
pone
nts a
nd m
ake
deco
ntam
inat
ion
diff
icul
t. P
ossi
ble
larg
e im
pact
on
mai
nten
ance
shie
ldin
g.
32
Aer
osol
gro
wth
1–
Med
ium
4–
Hig
h 5–
Low
Lo
w a
eros
ol c
once
ntra
tion
and
dry
envi
ronm
ent c
an re
sult
in th
e gr
owth
of p
artic
les w
ith h
igh
shap
es fa
ctor
s and
unu
sual
size
di
strib
utio
n. R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
, and
resu
lts
need
to b
e de
term
ined
to a
sses
s im
pact
. V
ente
d co
nfin
emen
t m
akes
eve
n m
odes
t aer
osol
con
cent
ratio
ns im
porta
nt.
35
FP d
iffus
ivity
, sor
btiv
ity in
no
ngra
phite
surf
aces
5–
Hig
h 5–
Low
Th
ese
fact
ors d
eter
min
e FP
loca
tion
durin
g no
rmal
ope
ratio
n an
d ac
t as t
raps
dur
ing
trans
ient
con
ditio
ns.
Can
impa
ct O
&M
as w
ell
as a
ccid
ent d
oses
. Pa
st w
ork
has e
xam
ined
som
e m
etal
s, bu
t litt
le
info
rmat
ion
may
be
avai
labl
e fo
r the
mat
eria
ls a
nd te
mpe
ratu
res
of in
tere
st.
Cou
ld b
e se
nsiti
ve to
the
surf
ace
oxid
atio
n st
ate.
M
ajor
nee
d fo
r mod
elin
g th
e re
acto
r circ
uit.
37
Aer
osol
/dus
t bou
nce,
bre
akup
du
ring
depo
sitio
n 4–
Med
ium
1–
Hig
h 4–
Low
1–
Med
ium
A
eros
ol b
ehav
ior c
an m
odify
dep
ositi
on p
rofil
e an
d th
e su
spen
ded
aero
sol d
istri
butio
n—th
eory
, dat
a, a
nd m
odel
s lac
king
. B
ecau
se o
f the
smal
l acc
epta
ble
rele
ases
due
to th
e ve
nted
co
nfin
emen
t opt
ion,
aer
osol
s and
dus
ts ta
ke o
n an
exa
gger
ated
tra
nspo
rt im
porta
nce.
Mec
hani
cal i
ssue
s suc
h as
vib
ratio
n an
d m
echa
nica
l sho
cks n
eed
to b
e ta
ken
into
con
side
ratio
n as
wel
l.
T
able
11
(con
tinue
d)
35
ID
No.
Is
sue
(phe
nom
ena,
pro
cess
, ge
omet
ry c
ondi
tion)
Im
port
ance
for
NG
NP
(Hig
h, M
ediu
m, L
ow)
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
38
Res
uspe
nsio
n 5–
Hig
h 4–
Low
1–
Med
ium
Si
nce
the
actu
al F
P co
nten
t of t
he g
as is
exp
ecte
d to
be
low
, the
FP
s tha
t can
be
rele
ased
from
the
surf
aces
of c
ompo
nent
s be
com
es im
porta
nt.
Past
ana
lysi
s has
ofte
n fo
cuse
d on
flow
-in
duce
d lif
t-off
of o
xide
laye
rs a
nd d
ust,
but m
echa
nica
l- sh
ock-
an
d vi
brat
ion-
indu
ced
lift-o
ff c
an b
e m
ajor
driv
ers a
s wel
l.
NU
REG
-080
0 re
quire
s tha
t pip
e w
hip
issu
es b
e ex
amin
ed.
Mec
hani
cal s
hock
s/fo
rces
/vib
ratio
ns c
an re
leas
e FP
s fro
m p
ipe
surf
ace
laye
rs/fi
lms d
urin
g ac
cide
nts.
Lac
k of
dat
a an
d m
odel
s fo
r ant
icip
ated
con
ditio
ns, e
spec
ially
mec
hani
cally
indu
ced
ones
.
48
Com
bust
ion
of d
ust i
n co
nfin
emen
t 5–
Hig
h 1–
Low
4–
Med
ium
So
urce
of h
eat a
nd d
istri
butio
n of
FPs
with
in c
onfin
emen
t if
cond
ition
s allo
w th
e ox
idat
ion
of th
e du
st.
Res
ults
may
dep
end
on c
ompo
sitio
n—gr
aphi
te o
r mat
rix—
and
the
amou
nt o
f air
in th
e co
nfin
emen
t. S
ome
ITER
dat
a. N
eed
to a
sses
s. B
igge
st im
pact
on
ven
ted
conf
inem
ent.
A m
ore
rem
ote
issu
e is
dam
age
to th
e ve
nts t
hat p
reve
nt la
ter c
losu
re.
49
NG
NP-
uniq
ue le
akag
e pa
th
beyo
nd c
onfin
emen
t 5–
Hig
h 1–
Low
4–
Hig
h IH
X to
seco
ndar
y si
te c
onta
min
atio
n co
uld
be ri
sk d
omin
ant i
n so
me
acci
dent
s. T
his i
s onl
y va
guel
y de
fined
and
hig
hly
cont
inge
nt o
n sp
ecifi
c de
sign
kno
wle
dge.
Wid
e va
riatio
n in
pa
nel r
espo
nse
is d
ue to
the
lack
of d
esig
n de
tails
. Onc
e de
sign
in
form
atio
n is
ava
ilabl
e, ra
nkin
g sh
ould
be
muc
h ea
sier
as i
t is
susp
ecte
d th
at k
now
ledg
e ab
out h
isto
rical
failu
re m
odes
will
ap
ply
to th
e de
sign
. Th
ere
is a
wea
lth o
f exp
erie
nce
with
LW
R
cont
ainm
ent l
eaka
ges i
ssue
s and
gen
eral
hea
t exc
hang
er
oper
atio
n.
36
The initial fission product contamination of the reactor circuit is of great importance because the most powerful driving term, helium pressure, will provide the driving force for transport of the source term out of the primary circuit during the earliest stages of the accident. If an air ingress accident occurs with an unimpeded flow path, large fission product releases can occur later in the accident.
In addition to the consensus and compiled entries in Table 10, the individual ranking tables (Appendix B) may be of particular interest to the reader.
The PIRT table underwent two iterations with extensive reorganization between meetings; the results shown in the Appendix are the panelists’ changes and additions to the final PIRT table, which was assembled after extensive discussions. The panelists’ thoughts (after several days of additional individual review, noted in red italics) are contrasted with the group consensus of the last meeting.
Generally, convergence is seen on most issues, but different approaches to the specific physics and transport paths shade the answers accordingly. One item of particular interest is the final approach to the ranking process. Two methods are apparent; the identification of the phenomena in either a general or path-dependent way. The general identification method allows one to collect all the items of interest without specifically outlining a transport path within the ranking table, although Table 6 was used as a general guide. This method avoids forcing a specific transport path model on the analyses but may not clearly identify the relative importance of particular phenomena along a specific path.
The path-dependent approach allows the reader to see the importance of the particular phenomena along a path (at the expense of some redundancy in the PIRT entries), but requires the identification of the transport subpaths. These paths were based on historical work because of the lack of a specific NGNP design, but should be relevant unless some truly unique design is proposed. The reader is encouraged to explore each approach to help develop insight that can be applied to a VHTR once a particular design has been developed along with its approach to FP transport needs. Even with these two approaches to the PIRT table layout, the results are very similar.
One item of interest that may not have been clearly identified in the starting PIRT table but was listed in the path-dependent reorganized table is the release of fission products due to normal helium leakage from the reactor system (implied in table item #7 but not individually listed). This table also contains many other (redundant) entries that are related to the original PIRT table entries; this was necessary because of the path structure.
A second issue of importance is the approach to modeling graphite properties. Technically, this issue is beyond the scope of the PIRT as the panel was to focus only on phenomena, but it does impact how one approaches the collection of data for the models. Briefly, one approach is basic physics in nature, and the other is more empirical in nature. The basic physics approach would have the advantage that measured graphite and fission product properties can be related to transport over a wide range of situations, but the physics may be very challenging. The empirical approach offers less theoretical complexity but may be limited by the cost of experiments and the range of accidents that can be covered. In any event, this issue will have to be resolved by a review of the state of the art in graphite and transport theory and will be influenced by the specific safety approaches taken by the designers.
Other table entry comments included variations in nomenclature and the physics of particular phenomena, but these clarifications and comments did not appear to change the ranking in any substantial way.
Finally, one item that was rated as important and may not have been explored in the past was the effect of mechanical shock and vibration on the transport and re-entrainment of dust and spalled-off oxide flakes. A failure of a large pipe would generate large mechanical forces (vibration, shocks, and pipe whip), and the resulting flow can generate a large amount of acoustic energy, both of which can launch dust and small particles into the existing gas flow as well as cause additional failures. Much of the literature is concerned with changes in temperature and flow velocity during an accident, but these
37
impulsive and vibratory mechanical effects should also be considered, especially if the reactor internal surfaces are formally required to retain fission products during an accident to meet safety requirements.
38
Page intentionally blank
39
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40
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26. N. Iniotakis, et al., “Plate-Out of Fission Products and Its Effect on Maintenance and Repair,” Nuclear Engineering and Design, 78, 273–284 (1984).
27. R. Wichner and F. Dyer, Carbon-14 Production in the Peach Bottom HTGR Core, ORNL-5597, 1980.
28. O. Tallent, et al., Diffusion of Uranium in H-451 Graphite at 900 to 14001C, ORNL/TM-8205, 1983.
29. O. Tallent, et al., Vapor Pressure of Plutonium Carbide Adsorbed on Graphite, ORNL/TM-9161, 1984.
30. M. Sage, “A Conceptual Study of the Retention of Fission Products from a Delayed Release in the PBMR Building,” Proceedings HTR2006: 3rd International Topical Meeting on High Temperature Reactor Technology, October 1–4, 2006, Johannesburg, South Africa.
31. M.P. Kissane, State-of-the-Art Fission-Product Transport Modelling: How This Is Done for LWRs and a Preliminary View of Potential Difficulties for HTRs, NRC PIRT Meeting, Washington, D.C., February 27–28, 2007.
32. G. Ziskind, et al., “Resuspension of Particulates from Surfaces to Turbulent Flows—Review and Analysis,” Journal of Aerosol Science, 26, 613–644 (1995).
33. E. Hontanon, et al., “The CAESAR Code for Aerosol Resuspension in Turbulent Pipe Flows. Assessment Against the Storm Experiments,” Journal of Aerosol Science, 31, 1061–1076 (2000).
34. G. Ziskind, et al., “Adhesion Moment Model for Estimating Particle Detachment from a Surface,” Journal of Aerosol Science, 28, 623–634 (1997).
35. M. Reeks and D. Hall, “Kinetic Models for Particle Resuspension in Turbulent Flows: Theory and Measurement,” Journal of Aerosol Science, 32, 1–31 (2001).
36. L. Biasi, et al., “Use of a Simple Model for the Interpretation of Experimental Data on Particle Resuspension in Turbulent Flows,” Journal of Aerosol Science, 32, 1175–1200 (2001).
37. G. Ziskind, et al., “Particle Behavior on Surfaces Subjected to External Excitations,” Journal of Aerosol Science, 31, 703–719 (2000).
38. W. Theerachaisupakij, et al., “Effects of Wall Vibration on Particle Deposition and Reentrainment in Aerosol Flow,” Advanced Powder Technology. 13, 287–300 (2002).
39. R. Sandstroem and M. Olsson, “High Intensity Low Frequency Sound Used for Cleaning Purposes,” Journal of Low Frequency Noise and Vibration, 5, 9–13 (1986).
40. H. Masuda and S. Matsusaka, “Particle Deposition and Reentrainment,” in Powder Technology Handbook, edited by Keishi Gotoh, pp. 143–154, Narcek Dekker, Inc., New York, 1997.
41
41. D. McEachern, “GT-MHR Fuel Performance and Fission Product Transport Technology,” presented at ANS Gas Reactor Technology Course, ANS Winter Meeting, Washington, D.C., November 22, 2002.
42. R. Strehlow and H. Savage, “The Permeation of Hydrogen Isotopes Through Structural Metals at Low Pressures and Through Metals with Oxide File Barriers,” Nuclear Technology, 22, 127–137 (1974).
43. R. Wichner and F. Dyer, Distribution and Transport of Tritium in the Peach Bottom HTGR, ORNL-5497, 1979.
44. B. Gainey, A Review of Tritium Behavior in HTGR Systems, GA-A13461, April 1976 45. S. Basu, NGNP PIRT An Introduction, NRC PIRT Meeting, Washington, D.C., February 27–28,
2007. 46. S. Rubin, NRC Advanced Reactor Research Program, NRC PIRT Meeting, Washington, D,C,,
February 27–28, 2007. 47. P. Robinson, FP Transport PIRT, NRC PIRT Meeting, Washington, D,C,, February 27–28, 2007. 48. S. Ball, Modular HTGR Safety and Accident Characteristics, NRC PIRT Meeting, Washington,
D.C., February 27–28, 2007. 49. TRISO-Coated Particle Fuel Phenomenon Identification and Ranking Tables (PIRTs) for Fission
Product Transport Due to Manufacturing, Operations, and Accidents, NUREG/CR-6844, July 2004. 50. K. C. Rogers, “Key Questions Facing the NRC on the MHTGR,” Energy, 16(1/2), 345–351 (1991). 51. S. B. Inamati, et al., “MHTGR Radio-Nuclide Source Terms for Use in Siting,” Energy, 16(1/2),
425–431 (1991). 52. K. Kugeler, et al., “Aerosol Formation by Graphite Corrosion in Case of Water and Air Ingress to
the Core of a High-Temperature Reactor,” Energy, 16(1/2), 491–499 (1991). 53. P. G. Kroeger, Containment Building Atmosphere Response Due to Reactor Gas Burning Under
Remote Severe Accident Conditions, NUREG/CR-3868 (BNL-NUREG-51793), June 1984. 54. D. A. Dilling, et al., “The Modular High Temperature Gas-Cooled Reactor (MHTGR) Containment
Trade Study,” ASME/IEEE Joint Power Generation Conference, Boston, MA (USA), October 21–25 1990.
55. D. A. Dilling, et al., A Vented Low Pressure Containment Strategy for The Modular High Temperature Gas-Cooled Reactor (MHTGR), GA-A21622, April 1994.
42
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A-1
APPENDIX A
COMMENTS ON TRANSPORT MODELING
A.1 Brief Discussion of Transport Modeling Through Porous Media
Once fission product vapors have migrated from a fuel particle, or are created from fissioning of “tramp uranium,” transport of these vapors through the porous medium of matrix graphite and other graphite structures becomes a key process leading to release of radionuclides to the more open regions of the reactor coolant system and eventually to the confinement in accident situations. Porous materials that the vapors must transit may be cracked, and such cracks provide parallel and often more efficient routes for transport than the inherent, interconnected porosity of the graphite material. Transport through cracks and the pore structure can be driven by concentration differences, temperature differences, and pressure differences. The resistance to transport is created by the collision of the vapor molecules with each other and with surfaces lining the transport pathway. When molecule-molecule collisions dominate, the diffusion process is classical gas-phase diffusion. When molecular collisions with surfaces dominate, the transport is Knudsen diffusion. Most situations of interest for safety analyses lie within the transition between the molecular diffusion and Knudsen diffusion extremes. For these situations, small changes in the permeability, slip, and tortuosity features of the transport pathway can have significant impacts on the total vapor flux through a porous material.
In the past, it was common to treat vapor transport through a porous material in terms of either an effective diffusivity or an effective permeability measured under particular conditions of temperature, pressure, and gas composition. Such empirical practices work satisfactorily when the range of conditions is narrow and well known. Unfortunately, for accident conditions, a much wider range of conditions, depending on the particular features of the accident initiation and progression, can be anticipated. It is not feasible to develop empirical effective diffusivities for all the conditions and all of the radionuclides of interest. Thus, it may be necessary to take a more fundamental approach to the transport processes if detailed path-dependent calculations are required to analyze a particular event. Fortunately, there have been rather significant advances in the understanding of porous medium transport processes since the last gas-cooled reactors were built. This more advanced understanding of multicomponent mass transport in porous media makes it possible to approach radionuclide transport under accident conditions from a more fundamental point of view.
Essential characterization of the porous medium for the analysis of radionuclide transport includes the following:
1. Porosity, especially interconnected porosity 2. Tortuosity—essentially the actual path length through a porous body relative to the
geometrical distance across the body 3. Poiseulle permeability parameter 4. Knudsen permeability parameter
The initial porosity of a specific graphite will be well known. Indeed, this porosity may well be specified in the course of acquisition of the graphite. Permeability parameters for nuclear graphites have been measured with acceptable accuracy since the late 1950s. Tortuosity is not routinely measured for graphites, though it is routinely measured for catalyst support materials.
Porosity and permeability properties of the graphite can be expected to change during power plant operation and under accident conditions. Certainly, irradiation is expected to cause some initial
A-2
densification of graphite followed by expansion as atomic and unit cell displacements accumulate in the material. Locations along transport paths where displacements have occurred are high-energy sites, and radionuclide vapors may well absorb preferentially onto these sites. Under conditions where the graphite is exposed to an oxidant and temperatures are sufficiently low that chemical kinetics controls the rate of graphite reaction with the oxidant (typically ~<1200°C), locations of irradiation-induced displacements along transport pathways will be preferred sites for reaction and gasification of the graphite. This removal of material will open the transport pathways. Such changes in the graphite and the ease with which vapors can transport through porous graphite will need to be predicted mechanistically by accident analysis computer codes. Such predictions cannot be made when effective diffusivities and effective permeabilities are used to calculate the vapor transport of radionuclides. Again, a more fundamental approach to vapor mass transport through a porous medium is needed.
A.2 Speciation
Speciation of radionuclides and the diversity of speciation will affect the volatility and the transport of radionuclides. It can be anticipated that the speciation will be determined especially for the gas phase by thermochemical calculations. Thermochemical databases available for the prediction are reasonably well developed for elements and oxides. The database is less well developed but still useful for vapor-phase carbides. Predictions of vapor pressures for solid carbides are always complicated by the tendency for these phases to be nonstoichiometric, which demands modeling of the nonstoichiometry. The intrusion of water raises the possibility of the formation of vapor-phase hydrides and hydroxides. Most of the available thermodynamic data on vapor-phase hydroxides and hydrides for elements of interest have been estimated by analogy to other systems. A class of possible vapor-phase compounds for which there are few data are vapor-phase carbonyls. Stable carbonyls of elements like ruthenium, palladium, and rhodium are fairly well known, but these carbonyls are unlikely to contribute significantly to vaporization or transport of these elements since the polycarbonyls are not especially stable. Of more interest are mono- and di-carbonyls that can accentuate vaporization of otherwise fairly nonvolatile radionuclides. Such species have received some theoretical consideration, but the necessary high CO pressure experiments to demonstrate the contributions of these elements to either release or transport have not been usually done.
A.3 Aerosols
Certainly in the containment and to some extent in the reactor coolant system, radionuclide transport will be predominantly by aerosol transport. Modeling of conventional aerosol has been well developed and validated by the NRC, and routine calculations can be done. By and large these computational tools have been optimized for rather “wet” or highly humid environments. The dry environment typical of many classes of gas reactors will pose a challenge. In such dry environments, water condensation within the interstices of particle agglomerates will not be possible. There will, then, not be a strong surface-tension driving force to convert linear-chain agglomerates into more spherical aerosol particles assumed for the analyses with existing computer codes. Shape factors will have to be introduced into the calculations, and these shape factors will not necessarily be small. Kops and coworkers have reported shape factors as high as 35 for dry aerosols formed from the condensation of high-temperature vapors. Furthermore, the shape factors will vary with particle size—something codes such as MAEROS, used widely for nuclear application, cannot handle.
A more bothersome issue is that of electrostatic charging of aerosols in the dry environment. Aerosol particles can be charged in the dry environment because of gas-phase ions formed in the intense radiation field. Negatively charged ions typically have higher mobilities than do positively charged ions. Consequently aerosol particles are bombarded more often by negatively charged ions and can assume a
A-3
negative charge. The magnitude of the charge depends on the particle size. Coulombic forces among aerosol particles due to like charges on particles are not addressed in currently available models of aerosol behavior. The electrostatic forces among charged particles are much stronger than the forces that ordinarily drive the agglomeration of aerosol particles to sizes such that they readily deposit by gravitational settling or inertial impaction on structures. What deposition of particles does occur will develop either a surface charge or a mirror image charge that could also produce forces capable of interfering with the deposition of additional particles. Again, current models do not account for such effects that are important only where the radiation field is large.
A-4
Page intentionally blank
APPENDIX B
INDIVIDUAL PANELISTS’ RANKING TABLES
Each panelist individually reviewed the last PIRT table and included rankings and comments if they differed from the group consensus. Both the original text and the change are shown so that the reader can understand the rationale for the change.
Page intentionally blank
B-3
Tab
le B
-1.
Indi
vidu
al F
PT P
IRT
Ran
king
Tab
le
Fina
l Ver
sion
Apr
il 18
, 200
7 Pa
nelis
t: D
ana
A. P
ower
s
Cha
nges
in IT
ALI
CS
are
diff
eren
ces f
rom
the
final
gro
up d
iscu
ssio
ns o
n A
pril
18, 2
007
T
his t
able
gen
eral
ly a
pplie
s to
all c
ases
, nor
mal
, ant
icip
ated
tran
sien
ts, a
nd a
ccid
ents
. Sp
ecifi
c ca
ses a
re n
oted
. N
otes
: *
deno
tes n
eed
for i
nter
face
with
oth
er g
roup
s (m
ater
ials
, tra
nsie
nt sc
enar
ios)
IC
—in
itial
con
ditio
n, th
e re
sult
of lo
ng te
rm n
orm
al o
pera
tion
Tran
s.—tr
ansi
ent a
nd a
ccid
ent c
ondi
tion
TF—
ther
mal
flui
ds
FP—
fissi
on p
rodu
cts
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
C
ritic
al in
itial
and
/or b
ound
ary
cond
ition
1
Dec
ay h
eat a
nd
trans
ient
pow
er le
vel
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) *H
igh
Bou
ndar
y co
nditi
ons
expe
cted
from
TF
PIR
T
Ade
quat
e
2 M
ater
ial/s
truct
ure
pr
oper
ties
Hig
h D
ensi
ty, v
isco
sity
, co
nduc
tivity
, etc
., im
porta
nt p
aram
eter
s in
calc
ulat
ions
(IC
and
Tr
ans.)
*Med
(gra
phite
) H
igh
(ste
el, c
oncr
ete)
G
raph
ite ty
pe n
ot
sele
cted
; exp
ecte
d fr
om m
ater
ial P
IRT
Min
or m
od
(gra
phite
) A
dequ
ate
(ste
el,
conc
rete
)
3 G
raph
ite im
purit
y le
vels
M
ediu
m
Impu
rity
reac
tion
with
FP
, nuc
lear
gra
phite
ex
pect
ed to
hav
e lo
w
impu
rity
leve
ls
*Hig
h W
ill b
e m
easu
red;
ex
pect
ed fr
om m
ater
ial
PIR
T
Ade
quat
e be
caus
e im
puri
ty le
vels
are
ex
pect
ed to
be
quite
lo
w
4 G
raph
ite g
eom
etry
H
igh
Cor
e st
ruct
ure
(des
ign
info
rmat
ion)
H
igh
Wel
l kno
wn
for I
C
Ade
quat
e fo
r IC
M
ajor
nee
d fo
r air
ingr
ess
T
able
B-1
(con
tinue
d)
B-4
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
5
Ther
mal
-flu
id
prop
ertie
s H
igh
Tem
pera
ture
, pre
ssur
e,
velo
city
com
puta
tions
(I
C a
nd T
rans
.)
*Med
ium
W
ell k
now
n fo
r He,
un
certa
inty
in
com
posi
tion
of g
as
mix
ture
s mak
es g
as
prop
erty
cal
cula
tion
mor
e di
ffic
ult,
expe
cted
from
TF
PIR
T
Ade
quat
e
6 G
as c
ompo
sitio
n H
igh
Oxy
gen
pote
ntia
l and
ch
emic
al a
ctiv
ity; a
lso
carb
on p
oten
tial a
nd
hydr
ogen
pot
entia
l
Med
ium
C
entra
l iss
ue fo
r ch
emic
al re
actio
n m
odel
ing,
FP
spec
iatio
n, sc
enar
io
depe
nden
t
Ade
quat
e (d
epre
ssur
izat
ion)
M
ajor
mee
d (a
ir in
gres
s or w
ater
in
gres
s)
7 G
as fl
ow p
ath
prio
r, du
ring
and
post
ac
cide
nt
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s). T
he fl
ow p
ath
will
be
affe
cted
dur
ing
air i
ngre
ssio
n an
d w
ater
in
gres
sion
acc
iden
ts a
s a
resu
lt of
gra
phite
ox
idat
ion
alon
g th
e flo
w
path
.
*Sam
e as
TF
grou
p N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; rx
pect
ed
from
TF
PIR
T. O
nly
the
initi
al c
ondi
tions
of
the
path
way
s will
co
me
from
ther
mal
flu
ids.
Tran
sfor
mat
ion
of th
e pa
thw
ays a
s a
resu
lt of
long
-term
ch
emic
al e
rosi
on
duri
ng a
n ai
r or w
ater
in
gres
s acc
iden
t will
ha
ve to
be
calc
ulat
ed.
Ther
mal
stre
ss a
nd
crac
king
to fo
rm n
ew
path
way
s nee
ds to
be
cons
ider
ed p
erha
ps b
y th
e m
ater
ials
gro
up.
Sam
e as
TF
grou
p C
alcu
latio
n of
the
open
ing
of p
athw
ays
as a
resu
lt of
ch
emic
al re
actio
ns
can
be c
halle
ngin
g es
peci
ally
if
tem
pera
ture
s are
su
ch th
at g
raph
ite
oxid
atio
n is
affe
cted
by
cat
alys
is.
8 Te
mpe
ratu
re (s
truct
ure
and
gas)
and
Pre
ssur
e di
strib
utio
n
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
*Hig
h N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
T
able
B-1
(con
tinue
d)
B-5
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
9
FP P
late
-out
and
dus
t di
strib
utio
n un
der
norm
al o
pera
tion
Hig
h St
artin
g co
nditi
ons
Med
ium
Th
eory
and
mod
els
lack
spec
ifics
M
ajor
nee
d
Gra
phite
and
cor
e m
ater
ials
10
M
atrix
per
mea
bilit
y,
tortu
osity
H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s). M
odel
ing
fissi
on p
rodu
ct tr
ansp
ort
on a
mor
e fu
ndam
enta
l ba
sis i
s req
uire
d si
nce
it w
ill n
ot b
e po
ssib
le to
te
st fo
r all
acci
dent
co
nditi
ons a
nd a
ll pa
thw
ays t
hat m
ay a
rise
.
*Low
FP
hol
dup
as b
arrie
r, re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed.
Suc
h in
form
atio
n ha
s be
en p
rovi
ded
for
othe
r nuc
lear
gr
aphi
tes.
Mas
s tr
ansp
ort t
hrou
gh
poro
us m
edia
has
de
velo
ped
subs
tant
ially
sinc
e ea
rly
gas r
eact
ors
wer
e de
sign
ed, s
o m
odel
ing
on a
mor
e fu
ndam
enta
l bas
is is
en
tirel
y fe
asib
le.
11
FP tr
ansp
ort t
hrou
gh
mat
rix
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
Low
FP
hol
dup
as b
arrie
r, re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed
12
Fuel
blo
ck
perm
eabi
lity,
to
rtuos
ity
Hig
h N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
. Mod
elin
g fis
sion
pro
duct
tran
spor
t on
a m
ore
fund
amen
tal
basi
s is r
equi
red
sinc
e it
will
not
be
poss
ible
to
test
for a
ll ac
cide
nt
cond
ition
s and
all
path
way
s tha
t may
ari
se.
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed.
Suc
h in
form
atio
n ha
s be
en p
rovi
ded
for
othe
r nuc
lear
gr
aphi
tes.
Mas
s tr
ansp
ort t
hrou
gh
poro
us m
edia
has
de
velo
ped
subs
tant
ially
sinc
e ea
rly
gas r
eact
ors
wer
e de
sign
ed, s
o m
odel
ing
on a
mor
e
T
able
B-1
(con
tinue
d)
B-6
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
fu
ndam
enta
l bas
is is
en
tirel
y fe
asib
le
13
FP tr
ansp
ort t
hrou
gh
fuel
blo
ck
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
Low
Th
erm
al g
radi
ents
are
no
t lar
ge o
utsi
de o
f fue
l Lo
w
Littl
e da
ta
Not
req’
d
15
Bas
al p
lane
diff
usio
n Lo
w
Poro
sity
is p
refe
rred
tra
nspo
rt pa
thw
ay
thro
ugh
grap
hite
Med
ium
Pa
st w
ork
and
liter
atur
e av
aila
ble
Not
req’
d
16
Ref
lect
or (i
n co
ntac
t w
/flow
) per
mea
bilit
y,
tortu
osity
Low
N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
Low
Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
18
Sorb
tivity
gra
phite
Hig
h C
an d
eter
min
e ho
ldup
an
d re
leas
e of
FP
(IC
and
Tr
ans.)
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion
on g
raph
ite a
nd
radi
atio
n ef
fect
s
Min
or m
od;
deve
lopm
ent o
f ad
sorp
tion/
deso
rptio
n m
odifi
catio
ns to
a
poro
us m
ediu
m m
ass
tran
spor
t mod
el m
ay
requ
ire
mor
e th
an
min
or e
ffort
. 19
Fl
uenc
e ef
fect
on
trans
port
in g
raph
ite
Hig
h In
fluen
ces t
rans
port,
ch
emic
al re
activ
ity
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion
on g
raph
ite a
nd
radi
atio
n ef
fect
s
Maj
or n
eed
T
able
B-1
(con
tinue
d)
B-7
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
20
C
-14,
Cl-3
6, C
o-60
ge
nera
tion
and
inve
ntor
y
Low
R
adio
isot
ope
gene
rate
d fr
om im
purit
ies,
mig
ht
beco
me
oper
atio
nal i
ssue
(I
C)
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
M
inor
mod
, se
nsiti
ve to
gra
phite
ha
ndlin
g
21
Air
atta
ck o
n gr
aphi
te
Hig
h G
raph
ite
eros
ion/
oxid
atio
n, F
e/C
s ca
taly
sis l
iber
atin
g FP
s (T
rans
.)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
22
Stea
m a
ttack
on
grap
hite
H
igh
If c
redi
ble
sour
ce o
f w
ater
pre
sent
; des
ign
depe
nden
t (Tr
ans.)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
Fis
sion
pro
duct
tran
spor
t in
reac
tor c
oola
nt sy
stem
and
con
finem
ent
23
FP S
peci
atio
n in
ca
rbon
aceo
us m
ater
ial
Hig
h C
hem
ical
form
in
grap
hite
aff
ects
tran
spor
t (I
C a
nd T
rans
.)
Low
U
ncer
tain
and
/or
inco
mpl
ete
Maj
or n
eed
24
FP S
peci
atio
n du
ring
mas
s tra
nsfe
r H
igh
Che
mic
al fo
rm c
hang
e ca
n al
ter v
olat
ility
M
ediu
m
His
toric
al d
ata,
nee
d sp
ecifi
c in
form
atio
n.
Goo
d fo
r met
als,
oxid
es.
Unc
erta
in fo
r ca
rbid
es a
nd c
arbo
nyls
Maj
or n
eed
25
“Kno
ck-a
long
” Lo
w
Alp
ha re
coil
trans
port
of
depo
site
d pa
rticl
es o
n su
rfac
es sl
ow c
ompa
red
to fl
uid
flow
tran
spor
t; m
ay b
e m
uch
mor
e im
port
ant i
n th
e ev
alua
tion
of th
e ef
fect
iven
ess o
f filt
ers
Med
ium
St
udie
d in
act
inid
e-be
arin
g pa
rticl
es
Ade
quat
e
26
Dus
t gen
erat
ion
Hig
h V
ecto
r for
FP
trans
port,
po
ssib
ility
of h
igh
mob
ility
Med
ium
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c sy
stem
in
form
atio
n
Maj
or n
eed;
impo
rt fr
om o
ther
gro
ups
27
(De)
Abs
orpt
ion
on
dust
H
igh
Prov
ides
cop
ious
surf
ace
area
for F
P ab
sorp
tion
M
ediu
m
Lim
ited
expe
rienc
e;
lack
spec
ific
deta
ils
Maj
or n
eed;
dus
t su
spen
sion
and
ex
puls
ion
from
the
T
able
B-1
(con
tinue
d)
B-8
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
re
acto
r coo
lant
sy
stem
dur
ing
a de
pres
suri
zatio
n ev
ent m
ay p
rovi
de
the
equi
vale
nt o
f gap
re
leas
e to
the
cont
ainm
ent i
n ac
cide
nts
28
H-3
gen
erat
ion
and
circ
ulat
ing
cool
ant
inve
ntor
y
Med
ium
R
adio
isot
ope,
an
issu
e w
ith o
pera
tiona
l rel
ease
. H
-3 p
rodu
ctio
n fr
om
He-
3 in
coo
lant
, ter
nary
fis
sion
, and
Li-6
in
grap
hite
Med
ium
H
isto
rical
dat
a, P
each
B
otto
m H
TGR
M
inor
mod
29
Ag-
110m
gen
erat
ion,
tra
nspo
rt H
igh
(O&
M)
Low
(rel
ease
) R
adio
isot
ope,
sign
ifica
nt
O&
M d
ose
on c
ool,
met
allic
com
pone
nts
Low
Li
mite
d da
ta, u
nkno
wn
trans
port
mec
hani
sm
Maj
or n
eed
30
Oth
er a
ctiv
atio
n pr
oduc
ts (e
.g.,
Cs-
134,
M
n-55
, Fe-
56)
Low
R
adio
isot
opes
, pot
entia
l O
&M
dos
e M
ediu
m
Expe
rienc
e, li
mite
d in
form
atio
n M
inor
mod
31
Nuc
leat
ion
M
ediu
m
Unc
lear
due
to e
xtre
mel
y lo
w F
P va
por
conc
entra
tion
antic
ipat
ed
Med
ium
H
isto
rical
dat
a M
ajor
nee
d
32
Aer
osol
gro
wth
H
igh
Low
con
cent
ratio
n
grow
th c
an le
ad to
hig
h sh
ape
fact
ors a
nd
unus
ual s
ize
dist
ribut
ion
Low
R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
M
ajor
nee
d
33
Surf
ace
roug
hnes
s M
ediu
m
Aff
ects
aer
osol
de
posi
tion
1 to
5 m
icro
n pa
rticl
es (I
C a
nd T
rans
.)
Med
ium
In
itial
info
rmat
ion
from
man
ufac
ture
r; ev
olut
ion
of su
rfac
e ro
ughn
ess d
urin
g op
erat
ion
not w
ell
know
n
Min
or m
od
T
able
B-1
(con
tinue
d)
B-9
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
34
C
oola
nt c
hem
ical
in
tera
ctio
n w
/ sur
face
s H
igh
Cha
nges
oxy
gen
and
carb
on p
oten
tial w
hich
ca
n af
fect
nat
ure
and
quan
tity
of so
rbed
sp
ecie
s (IC
and
Tra
ns.)
Med
ium
Su
rfac
e pr
oper
ties a
re
criti
cal;
need
allo
y da
ta o
n th
e fo
rmat
ion
of o
xide
and
car
bide
su
rfac
e fil
ms
Maj
or n
eed
35
FP d
iffus
ivity
, so
rbtiv
ity in
no
ngra
phite
surf
aces
Hig
h D
eter
min
es F
P lo
catio
n du
ring
oper
atio
n; a
cts a
s a
trap
durin
g tra
nsie
nt
(IC
and
Tra
ns.)
Low
Li
ttle
info
rmat
ion
on
mat
eria
ls o
f int
eres
t M
ajor
nee
d
36
Aer
osol
/dus
t de
posi
tion
Hig
h G
ravi
tatio
nal,
iner
tial,
ther
mop
hore
sis,
elec
trost
atic
, diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol d
epos
ition
by
mos
t mec
hani
sms
exce
pt in
ertia
l im
pact
in
com
plex
ge
omet
ries;
ap
plic
abili
ty to
NG
NP
uncl
ear;
mod
elin
g th
e ef
fect
s of e
lect
rost
atic
ch
argi
ng o
f par
ticle
s is
not
dev
elop
ed. S
ize-
depe
nden
t par
ticle
sh
ape
fact
ors n
eed
to
be m
odel
ed in
so
lutio
ns to
the
aero
sol d
ynam
ic
equa
tion
Min
or m
od
37
Aer
osol
/dus
t bou
nce,
br
eaku
p du
ring
depo
sitio
n
Med
ium
C
an m
odify
dep
ositi
on
prof
ile a
nd su
spen
ded
aero
sol d
istri
butio
n
Low
Th
eory
, dat
a, a
nd
mod
els l
acki
ng
Maj
or n
eed
for
part
icle
s lar
ger t
han
abou
t 1 µ
m.
T
able
B-1
(con
tinue
d)
B-10
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
38
R
esus
pens
ion
Hig
h Fl
ow/v
ibra
tion
indu
ced,
sa
ltatio
n; m
echa
nica
l fo
rces
can
rele
ase
FPs
from
pip
e su
rfac
e la
yers
/film
s (Tr
ans.)
Low
La
ck o
f dat
a an
d m
odel
s for
ant
icip
ated
co
nditi
ons
Maj
or n
eed
to m
odel
th
e re
susp
ensi
on a
nd
to p
redi
ct th
e sh
ocks
an
d vi
brat
ions
to
equi
pmen
t dur
ing
an
acci
dent
39
C
onfin
emen
t aer
osol
ph
ysic
s H
igh
Ana
logo
us to
LW
R
aero
sol b
ehav
ior/p
hysi
cs,
delta
-T, c
hem
istry
; im
porta
nt h
oldu
p m
echa
nism
(Tra
ns.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol b
ehav
ior;
appl
icab
ility
to N
GN
P un
clea
r
Min
or m
od
40
Dus
t dep
ositi
on o
n ve
ssel
and
RC
CS
hard
war
e
Low
N
ot im
porta
nt fo
r FP
trans
port
but m
ay a
ffec
t ra
diat
ive
heat
tran
sfer
in
reac
tor c
avity
Low
V
ery
limite
d da
ta
Maj
or n
eed
41
Cor
rosi
on p
rodu
cts
Low
Sp
alle
d su
rfac
e fil
ms;
lo
w c
orro
sion
en
viro
nmen
t (IC
and
Tr
ans.)
Hig
h Pa
st e
xper
ienc
e A
dequ
ate
42
Eros
ion
prod
ucts
, no
ncar
bon
Low
Lo
w c
once
ntra
tion
of
coar
se m
ater
ials
(IC
and
Tr
ans.)
Low
La
ck o
f des
ign
info
rmat
ion;
co
nfig
urat
ion
and
mat
eria
ls sp
ecifi
c
Ade
quat
e
43
Was
h-of
f H
igh
If c
redi
ble
sour
ce o
f w
ater
pre
sent
; des
ign
depe
nden
t (Tr
ans.)
Med
ium
So
me
expe
rimen
tal
data
ava
ilabl
e M
inor
mod
44
Failu
re m
odes
of
auxi
liary
syst
ems (
e.g.
, ga
s cle
anup
, hol
dup,
re
fuel
ing)
Med
ium
Po
tent
ial r
elea
se d
ue to
fa
ilure
(Tra
ns.)
Med
ium
D
esig
n sp
ecifi
c; h
ave
expe
rienc
e fr
om o
ther
de
sign
s
Min
or m
od
T
able
B-1
(con
tinue
d)
B-11
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
45
R
adio
lysi
s eff
ects
in
conf
inem
ent
Hig
h FP
(e.g
., I,
Ru,
Te)
ch
emis
try, p
aint
ch
emis
try (d
epen
dent
on
conf
inem
ent r
adia
tion
leve
l) (T
rans
.)
Med
ium
LW
R e
xper
ienc
e an
d da
ta
Min
or m
od
46
Filtr
atio
n H
igh
Trad
ition
al p
assi
ve
char
coal
/HEP
A (T
rans
.) H
igh
His
toric
al e
xper
ienc
e A
dequ
ate;
kno
ck
alon
g ef
fect
may
lim
it ef
fect
iven
ess o
f fil
ters
for a
ctin
ides
if
they
are
rele
ased
fr
om th
e fu
el
47
Prod
uctio
n/co
mbu
stio
n of
flam
mab
le g
as
Med
ium
C
O, H
2 pro
duct
ion
issu
es, I
HX
seco
ndar
y-pr
imar
y le
ak, p
oten
tial
resu
spen
sion
and
ch
emic
al tr
ansf
orm
atio
n of
FPs
. (Tr
ans.)
Hig
h H
isto
rical
exp
erie
nce
Ade
quat
e
48
Com
bust
ion
of d
ust i
n co
nfin
emen
t H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
w/in
co
nfin
emen
t
Med
ium
; Low
IT
ER d
ata
Maj
or n
eed
49
NG
NP-
uniq
ue le
akag
e pa
th b
eyon
d co
nfin
emen
t
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n, c
ould
be
risk-
dom
inan
t (Tr
ans.)
Hig
h C
ontin
gent
on
spec
ific
desi
gn k
now
ledg
e M
inor
mod
50
Con
finem
ent l
eaka
ge
path
, rel
ease
rate
th
roug
h pe
netra
tions
Hig
h C
able
/pip
e pe
netra
tions
, cr
acks
, hol
es, H
VA
C
(Tra
ns.)
Med
ium
B
uild
ing
leak
age
expe
rienc
e, d
esig
n sp
ecifi
c
Ade
quat
e
51
Cab
le p
yrol
ysis
, fire
H
igh
Soot
gen
erat
ion
and
chan
ges t
o io
dine
ch
emis
try
Med
ium
LW
R e
xper
ienc
e M
ajor
nee
d
52
Pres
sure
-rel
ief-
valv
e fil
ter
Low
O
peni
ng o
f the
relie
f va
lve
gene
rate
s a
trans
port
path
that
may
be
filte
red;
dep
ends
on
desi
gn
Hig
h A
ir cl
eani
ng
tech
nolo
gy
Ade
quat
e
T
able
B-1
(con
tinue
d)
B-12
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
53
R
ecrit
ical
ity (s
low
) H
igh
Add
ition
al th
erm
al lo
ad
to fu
el. I
ncre
ases
sour
ce
but n
ot e
xpec
ted
to a
ffec
t tra
nspo
rt pa
th
Med
ium
H
eat l
oad
easi
ly
com
pute
d w
ith
exis
ting
tool
s; e
ffec
t on
fiss
ion
prod
ucts
not
co
mpl
etel
y kn
own
Min
or m
od
54
Fuel
-dam
agin
g R
IA
Hig
h A
n in
tens
e pu
lse
coul
d da
mag
e fu
el.
Incr
ease
s so
urce
but
not
exp
ecte
d to
aff
ect t
rans
port
path
Med
ium
So
me
data
exi
sts,
but
outs
ide
of e
xpec
ted
acci
dent
env
elop
e
Min
or m
od
55
Arg
on a
ctiv
atio
n in
re
acto
r cav
ity
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
Hig
h Ea
sily
com
pute
d w
ith
exis
ting
tool
s A
dequ
ate
56
Red
istri
butio
n of
fis
sion
pro
duct
s due
to
cont
rol r
od m
ovem
ent
Low
A
rticu
late
d co
ntro
l rod
jo
ints
can
col
lect
and
re
dist
ribut
e fis
sion
pr
oduc
ts
Low
Sp
ecifi
cs o
n C
RD
ho
usin
g an
d ar
ticul
ated
SiC
co
mpo
site
hou
sing
TB
D
Min
or m
od
B-13
Tab
le B
-2.
Indi
vidu
al F
PT P
IRT
Ran
king
Tab
le
Fina
l Ver
sion
Apr
il 18
, 200
7 Pa
nelis
t: D
avid
Pet
ti
Cha
nges
in IT
ALI
CS
are
diff
eren
ces f
rom
the
final
gro
up d
iscu
ssio
ns o
n A
pril
18, 2
007
T
his t
able
gen
eral
ly a
pplie
s to
all c
ases
, nor
mal
, ant
icip
ated
tran
sien
ts, a
nd a
ccid
ents
. Sp
ecifi
c ca
ses a
re n
oted
. N
otes
: *
deno
tes n
eed
for i
nter
face
with
oth
er g
roup
s (m
ater
ials
, tra
nsie
nt sc
enar
ios)
IC
—in
itial
con
ditio
n, th
e re
sult
of lo
ng te
rm n
orm
al o
pera
tion
Tran
s.—tr
ansi
ent a
nd a
ccid
ent c
ondi
tion
TF—
ther
mal
flui
ds
FP—
fissi
on p
rodu
cts
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
C
ritic
al in
itial
and
/or b
ound
ary
cond
ition
1
Dec
ay h
eat a
nd
trans
ient
pow
er le
vel
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) *H
igh
Bou
ndar
y co
nditi
ons
expe
cted
from
TF
PIR
T
Ade
quat
e
2 M
ater
ial/s
truct
ure
pr
oper
ties
Hig
h D
ensi
ty, v
isco
sity
, co
nduc
tivity
, etc
., im
porta
nt p
aram
eter
s in
calc
ulat
ions
(IC
and
Tr
ans.)
*Med
(gra
phite
) H
igh
(ste
el, c
oncr
ete)
G
raph
ite ty
pe n
ot
sele
cted
; exp
ecte
d fr
om m
ater
ial P
IRT
Min
or m
od
(gra
phite
) A
dequ
ate
(ste
el,
conc
rete
)
3 G
raph
ite im
purit
y le
vels
M
ediu
m
Impu
rity
reac
tion
with
FP;
nu
clea
r gra
phite
exp
ecte
d to
hav
e lo
w im
purit
y le
vels
*Hig
h W
ill b
e m
easu
red;
ex
pect
ed fr
om
mat
eria
l PIR
T
Ade
quat
e
4 G
raph
ite g
eom
etry
H
igh
Cor
e st
ruct
ure
(des
ign
info
rmat
ion)
H
igh
Wel
l kno
wn
for I
C
Ade
quat
e fo
r IC
M
ajor
nee
d fo
r air
ingr
ess
T
able
B-2
(con
tinue
d)
B-14
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
5
Ther
mal
-flu
id
prop
ertie
s H
igh
Tem
pera
ture
, pre
ssur
e,
velo
city
com
puta
tions
(IC
an
d Tr
ans.)
Hig
h W
ell k
now
n fo
r He;
un
certa
inty
in
com
posi
tion
of g
as
mix
ture
s mak
es g
as
prop
erty
cal
cula
tion
mor
e di
ffic
ult;
expe
cted
from
TF
PIR
T
Ade
quat
e
6 G
as c
ompo
sitio
n H
igh
Oxy
gen
pote
ntia
l and
ch
emic
al a
ctiv
ity
Med
ium
C
entra
l iss
ue fo
r ch
emic
al re
actio
n m
odel
ing,
FP
spec
iatio
n, sc
enar
io
depe
nden
t
Ade
quat
e (d
epre
ssur
izat
ion)
M
ajor
nee
d (a
ir in
gres
s)
7 G
as fl
ow p
ath
prio
r, du
ring
and
post
ac
cide
nt
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
*Sam
e as
TF
grou
p N
eed
to c
oord
inat
e w
/oth
er g
roup
s;
expe
cted
from
TF
PIR
T
Sam
e as
TF
grou
p
8 Te
mpe
ratu
re (s
truct
ure
and
gas)
and
pre
ssur
e di
strib
utio
n
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
Hig
h N
eed
to c
oord
inat
e w
/ oth
er g
roup
s, Ex
pect
ed fr
om T
F PI
RT
Sam
e as
TF
grou
p
9 FP
pla
te-o
ut a
nd d
ust
dist
ribut
ion
unde
r no
rmal
ope
ratio
n
Hig
h St
artin
g co
nditi
ons
Med
ium
Th
eory
and
mod
els
lack
spec
ifics
; m
odes
t un
ders
tand
ing
in
Fort
St.
Vrai
n an
d AV
R
Maj
or n
eed
Gra
phite
and
cor
e m
ater
ials
10
M
atrix
per
mea
bilit
y,
tortu
osity
H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s)
*Low
FP
hol
dup
as
barr
ier;
rele
ase
as
dust
; exp
ecte
d fr
om
mat
eria
l PIR
T
Maj
or n
eed
11
FP tr
ansp
ort t
hrou
gh
mat
rix
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
Low
FP
hol
dup
as b
arrie
r, re
leas
e as
dus
t; ne
w
Maj
or n
eed
T
able
B-2
(con
tinue
d)
B-15
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
co
nsta
nt) a
s an
alte
rnat
ive
to fi
rst p
rinci
ples
(IC
and
Tr
ans)
mat
rix
mat
eria
l re
quir
es
char
acte
riza
tion
Expe
cted
from
m
ater
ial P
IRT
12
Fu
el b
lock
pe
rmea
bilit
y, to
rtuos
ity
Hig
h N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed
13
FP tr
ansp
ort t
hrou
gh
fuel
blo
ck
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
Low
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
Low
Th
erm
al g
radi
ents
are
not
la
rge
outs
ide
of fu
el
Low
Li
ttle
data
N
ot re
q’d
15
Bas
al p
lane
diff
usio
n Lo
w
Poro
sity
is p
refe
rred
tra
nspo
rt pa
thw
ay th
roug
h gr
aphi
te
Med
ium
Pa
st w
ork
and
liter
atur
e av
aila
ble
Not
req’
d
16
Ref
lect
or (i
n co
ntac
t w
/flow
) per
mea
bilit
y,
tortu
osity
Low
N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
Low
Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
Low
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
18
Sorb
tivity
gra
phite
H
igh
Can
det
erm
ine
hold
up a
nd
rele
ase
of F
P (I
C a
nd
Tran
s.)
Med
ium
H
isto
rical
dat
a, n
eed
spec
ific
info
rmat
ion
on g
raph
ite a
nd
radi
atio
n ef
fect
s
Min
or m
od
19
Flue
nce
effe
ct o
n tra
nspo
rt in
gra
phite
H
igh
Influ
ence
s tra
nspo
rt,
chem
ical
reac
tivity
M
ediu
m
His
toric
al d
ata,
nee
d sp
ecifi
c in
form
atio
n on
gra
phite
and
ra
diat
ion
effe
cts
Maj
or n
eed
T
able
B-2
(con
tinue
d)
B-16
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
20
C
-14,
Cl-3
6, C
o-60
ge
nera
tion
and
inve
ntor
y
Low
R
adio
isot
ope
gene
rate
d fr
om im
purit
ies;
mig
ht
beco
me
oper
atio
nal i
ssue
(I
C)
Med
ium
H
isto
rical
dat
a;
Peac
h B
otto
m
HTG
R
Min
or m
od,
sens
itive
to
grap
hite
han
dlin
g
21
Air
atta
ck o
n gr
aphi
te
Hig
h G
raph
ite
eros
ion/
oxid
atio
n; F
e/C
s ca
taly
sis l
iber
atin
g FP
s (T
rans
)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
22
Stea
m a
ttack
on
grap
hite
H
igh
If c
redi
ble
sour
ce o
f wat
er
pres
ent;
desi
gn d
epen
dent
(T
rans
)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
Fis
sion
pro
duct
tran
spor
t in
reac
tor c
oola
nt sy
stem
and
con
finem
ent
23
FP sp
ecia
tion
in
carb
onat
ious
mat
eria
l H
igh
Che
mic
al fo
rm in
gra
phite
af
fect
s tra
nspo
rt (I
C a
nd
Tran
s.)
Low
U
ncer
tain
and
/or
inco
mpl
ete
Maj
or n
eed
24
FP sp
ecia
tion
durin
g m
ass t
rans
fer
Hig
h C
hem
ical
cha
nge
can
alte
r vo
latil
ity
Low
H
isto
rical
dat
a, n
eed
spec
ific
info
rmat
ion.
G
ood
for m
etal
s, ox
ides
. U
ncer
tain
fo
r car
bide
s and
ca
rbon
yls;
low
co
ncen
trat
ions
ex
pect
ed m
ay re
sult
in k
inet
ic is
sues
that
m
ake
spec
iatio
n m
ore
com
plex
Maj
or n
eed
25
“Kno
ck-a
long
” Lo
w
Alp
ha re
coil
trans
port
of
depo
site
d pa
rticl
es o
n su
rfac
es sl
ow c
ompa
red
to
fluid
flow
tran
spor
t. M
ajor
FPs
are
not
alp
ha
emitt
ers
Med
ium
St
udie
d in
act
inid
e-be
arin
g pa
rticl
es
Ade
quat
e
T
able
B-2
(con
tinue
d)
B-17
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
26
D
ust g
ener
atio
n H
igh
Vec
tor f
or F
P tra
nspo
rt,
poss
ibili
ty o
f hig
h m
obili
ty
Med
ium
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c sy
stem
in
form
atio
n
Maj
or n
eed,
impo
rt fr
om o
ther
gro
ups
27
(De)
Abs
orpt
ion
on d
ust
Hig
h Pr
ovid
es c
opio
us su
rfac
e ar
ea fo
r FP
abso
rptio
n
Med
ium
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c de
tails
M
ajor
nee
d
28
H-3
gen
erat
ion
and
circ
ulat
ing
cool
ant
inve
ntor
y
Med
ium
R
adio
isot
ope,
an
issu
e w
ith o
pera
tiona
l rel
ease
. H
-3 p
rodu
ctio
n fr
om H
e-3
in c
oola
nt, t
erna
ry fi
ssio
n,
and
Li-6
in g
raph
ite
Med
ium
H
isto
rical
dat
a;
Peac
h B
otto
m
HTG
R
Min
or m
od
29
Ag-
110m
gen
erat
ion,
tra
nspo
rt H
igh
(O&
M)
Low
(rel
ease
) R
adio
isot
ope,
sign
ifica
nt
O&
M d
ose
on c
ool,
met
allic
com
pone
nts
Low
Li
mite
d da
ta;
unkn
own
trans
port
mec
hani
sm
Maj
or n
eed
30
Oth
er a
ctiv
atio
n pr
oduc
ts (e
.g.,
Cs-
134,
M
n-55
, Fe-
56)
Low
R
adio
isot
opes
, pot
entia
l O
&M
dos
e M
ediu
m
Expe
rienc
e; li
mite
d in
form
atio
n M
inor
mod
31
Nuc
leat
ion
M
ediu
m
Unc
lear
due
to e
xtre
mel
y lo
w F
P va
por
conc
entra
tion
antic
ipat
ed
Med
ium
H
isto
rical
dat
a M
ajor
nee
d
32
Aer
osol
gro
wth
H
igh
Low
con
cent
ratio
n
grow
th c
an le
ad to
hig
h sh
ape
fact
ors a
nd u
nusu
al
size
dis
tribu
tion
Low
R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
M
ajor
nee
d
33
Surf
ace
roug
hnes
s M
ediu
m
Aff
ects
aer
osol
dep
ositi
on
1 to
5 m
icro
n pa
rticl
es (I
C
and
Tran
s.)
Med
ium
In
itial
info
rmat
ion
from
man
ufac
ture
r; ev
olut
ion
of su
rfac
e ro
ughn
ess d
urin
g op
erat
ion
not w
ell
know
n
Min
or m
od
34
Coo
lant
che
mic
al
inte
ract
ion
w/s
urfa
ces
Hig
h C
hang
es lo
cal o
xyge
n an
d ca
rbon
pot
entia
l whi
ch
can
affe
ct n
atur
e an
d qu
antit
y of
sorb
ed sp
ecie
s (I
C a
nd T
rans
.)
Med
ium
Su
rfac
e pr
oper
ties
are
criti
cal,
need
al
loy
data
Maj
or n
eed
T
able
B-2
(con
tinue
d)
B-18
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
35
FP
diff
usiv
ity,
sorb
tivity
in
nong
raph
ite su
rfac
es
Hig
h D
eter
min
es F
P lo
catio
n du
ring
oper
atio
n; a
cts a
s a
trap
durin
g tra
nsie
nt (I
C
and
Tran
s.)
Low
Li
ttle
info
rmat
ion
on
mat
eria
ls o
f int
eres
t M
ajor
nee
d
36
Aer
osol
/dus
t dep
ositi
on
Hig
h G
ravi
tatio
nal,
iner
tial,
ther
mop
hore
sis,
elec
trost
atic
, diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol d
epos
ition
by
mos
t mec
hani
sms
exce
pt in
ertia
l im
pact
in c
ompl
ex
geom
etrie
s;
appl
icab
ility
to
NG
NP
uncl
ear
Min
or m
od
37
Aer
osol
/dus
t bou
nce,
br
eaku
p du
ring
depo
sitio
n
Med
ium
C
an m
odify
dep
ositi
on
prof
ile a
nd su
spen
ded
aero
sol d
istri
butio
n
Low
Th
eory
, dat
a, a
nd
mod
els l
acki
ng
Maj
or n
eed
38
Res
uspe
nsio
n H
igh
Flow
/vib
ratio
n in
duce
d,
salta
tion;
mec
hani
cal
forc
es c
an re
leas
e FP
s fr
om p
ipe
surf
ace
laye
rs/fi
lms (
Tran
s.)
Low
La
ck o
f dat
a an
d m
odel
s for
an
ticip
ated
co
nditi
ons
Maj
or n
eed
39
Con
finem
ent a
eros
ol
phys
ics
Hig
h A
nalo
gous
to L
WR
ae
roso
l beh
avio
r/phy
sics
, de
lta-T
, che
mis
try;
impo
rtant
hol
dup
mec
hani
sm (T
rans
.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol b
ehav
ior;
appl
icab
ility
to
NG
NP
uncl
ear
Min
or m
od
40
Dus
t dep
ositi
on o
n ve
ssel
and
RC
CS
hard
war
e
Low
N
ot im
porta
nt fo
r FP
trans
port
but m
ay a
ffec
t ra
diat
ive
heat
tran
sfer
in
reac
tor c
avity
Low
V
ery
limite
d da
ta
Maj
or n
eed
41
Cor
rosi
on p
rodu
cts
Low
Sp
alle
d su
rfac
e fil
ms;
low
co
rros
ion
envi
ronm
ent (
IC
and
Tran
s.)
Hig
h Pa
st e
xper
ienc
e A
dequ
ate
T
able
B-2
(con
tinue
d)
B-19
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
42
Er
osio
n pr
oduc
ts,
nonc
arbo
n Lo
w
Low
con
cent
ratio
n of
co
arse
mat
eria
ls (I
C a
nd
Tran
s.)
Low
La
ck o
f des
ign
info
rmat
ion;
co
nfig
urat
ion
and
mat
eria
ls sp
ecifi
c
Ade
quat
e
43
Was
h-of
f H
igh
If c
redi
ble
sour
ce o
f wat
er
pres
ent;
desi
gn d
epen
dent
(T
rans
.)
Med
ium
So
me
expe
rimen
tal
data
ava
ilabl
e M
inor
mod
44
Failu
re m
odes
of
auxi
liary
syst
ems (
e.g.
, ga
s cle
anup
, hol
dup,
re
fuel
ing)
Med
ium
Po
tent
ial r
elea
se d
ue to
fa
ilure
(Tra
ns.)
Med
ium
D
esig
n sp
ecifi
c;
have
exp
erie
nce
from
oth
er d
esig
ns
Min
or m
od
45
Rad
ioly
sis e
ffec
ts in
co
nfin
emen
t H
igh
FP (e
.g.,
I, R
u, T
e)
chem
istry
, pai
nt c
hem
istry
(d
epen
dent
on
conf
inem
ent r
adia
tion
leve
l) (T
rans
.)
Med
ium
LW
R e
xper
ienc
e an
d da
ta
Min
or m
od
46
Filtr
atio
n H
igh
Trad
ition
al p
assi
ve
char
coal
/HEP
A (T
rans
.) H
igh
His
toric
al
expe
rienc
e A
dequ
ate
47
Prod
uctio
n/co
mbu
stio
n of
flam
mab
le g
as
Med
ium
C
O, H
2 pro
duct
ion
issu
es,
IHX
seco
ndar
y-pr
imar
y le
ak, p
oten
tial
resu
spen
sion
and
ch
emic
al tr
ansf
orm
atio
n of
FPs
(Tra
ns.)
Hig
h H
isto
rical
ex
perie
nce
Ade
quat
e
48
Com
bust
ion
of d
ust i
n co
nfin
emen
t H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
w/in
co
nfin
emen
t
Med
ium
IT
ER d
ata
Maj
or n
eed
49
NG
NP-
uniq
ue le
akag
e pa
th b
eyon
d co
nfin
emen
t
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n; c
ould
be
risk
dom
inan
t (Tr
ans.)
Hig
h C
ontin
gent
on
spec
ific
desi
gn
know
ledg
e
Min
or m
od
50
Con
finem
ent l
eaka
ge
path
, rel
ease
rate
th
roug
h pe
netra
tions
Hig
h C
able
/pip
e pe
netra
tions
, cr
acks
, hol
es, H
VA
C
(Tra
ns.)
Med
ium
B
uild
ing
leak
age
expe
rienc
e, d
esig
n sp
ecifi
c
Ade
quat
e
T
able
B-2
(con
tinue
d)
B-20
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
51
C
able
pyr
olys
is, f
ire
Hig
h So
ot g
ener
atio
n an
d ch
ange
s to
iodi
ne
chem
istry
Med
ium
LW
R e
xper
ienc
e M
ajor
nee
d
52
Pres
sure
relie
f val
ve
filte
r Lo
w
Ope
ning
of t
he re
lief
valv
e ge
nera
tes a
tra
nspo
rt pa
th th
at m
ay b
e fil
tere
d; d
epen
ds o
n de
sign
Hig
h A
ir cl
eani
ng
tech
nolo
gy
Ade
quat
e
53
Rec
ritic
ality
(slo
w)
Hig
h A
dditi
onal
ther
mal
load
to
fuel
. Inc
reas
es so
urce
but
no
t exp
ecte
d to
aff
ect
trans
port
path
Med
ium
H
eat l
oad
easi
ly
com
pute
d w
ith
exis
ting
tool
s; e
ffec
t on
fiss
ion
prod
ucts
no
t com
plet
ely
know
n
Min
or m
od
54
Fuel
-dam
agin
g R
IA
Hig
h A
n in
tens
e pu
lse
coul
d da
mag
e fu
el.
Incr
ease
s so
urce
but
not
exp
ecte
d to
af
fect
tran
spor
t pat
h
Med
ium
So
me
data
exi
sts,
but o
utsi
de o
f ex
pect
ed a
ccid
ent
enve
lope
Min
or m
od
55
Arg
on a
ctiv
atio
n in
re
acto
r cav
ity
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
Hig
h Ea
sily
com
pute
d w
ith e
xist
ing
tool
s A
dequ
ate
56
Red
istri
butio
n of
fiss
ion
prod
ucts
due
to c
ontro
l ro
d m
ovem
ent
Low
A
rticu
late
d co
ntro
l rod
jo
ints
can
col
lect
and
re
dist
ribut
e fis
sion
pr
oduc
ts
Low
Sp
ecifi
cs o
n C
RD
ho
usin
g an
d ar
ticul
ated
SiC
co
mpo
site
hou
sing
TB
D
Min
or m
od
B-21
Tab
le B
-3.
Indi
vidu
al F
PT P
IRT
Ran
king
Tab
le
Fina
l Ver
sion
Apr
il 18
, 200
7 Pa
nelis
t: R
ober
t Mor
ris
C
hang
es in
ITA
LIC
S ar
e di
ffer
ence
s fro
m th
e fin
al g
roup
dis
cuss
ions
on
Apr
il 18
, 200
7
Thi
s tab
le g
ener
ally
app
lies t
o al
l cas
es, n
orm
al, a
ntic
ipat
ed tr
ansi
ents
, and
acc
iden
ts.
Spec
ific
case
s are
not
ed.
Not
es:
* de
note
s nee
d fo
r int
erfa
ce w
ith o
ther
gro
ups (
mat
eria
ls, t
rans
ient
scen
ario
s)
IC—
initi
al c
ondi
tion,
the
resu
lt of
long
term
nor
mal
ope
ratio
n Tr
ans.—
tran
sien
t and
acc
iden
t con
ditio
n TF
—th
erm
al fl
uids
FP
—fis
sion
pro
duct
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
C
ritic
al in
itial
and
/or b
ound
ary
cond
ition
1
Dec
ay h
eat a
nd
trans
ient
pow
er le
vel
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) *H
igh
Bou
ndar
y co
nditi
ons
expe
cted
from
TF
PIR
T
Ade
quat
e
2 M
ater
ial/s
truct
ure
pr
oper
ties
Hig
h D
ensi
ty, v
isco
sity
, co
nduc
tivity
, etc
., im
porta
nt p
aram
eter
s in
calc
ulat
ions
(IC
and
Tr
ans.)
*Med
(gra
phite
) H
igh
(ste
el, c
oncr
ete)
G
raph
ite ty
pe n
ot
sele
cted
, exp
ecte
d fr
om m
ater
ial P
IRT
Min
or m
od
(gra
phite
) A
dequ
ate
(ste
el,
conc
rete
)
3 G
raph
ite im
purit
y le
vels
M
ediu
m
Impu
rity
reac
tion
with
FP
; nuc
lear
gra
phite
ex
pect
ed to
hav
e lo
w
impu
rity
leve
ls
*Hig
h W
ill b
e m
easu
red;
ex
pect
ed fr
om m
ater
ial
PIR
T
Ade
quat
e
4 G
raph
ite g
eom
etry
H
igh
Cor
e st
ruct
ure
(des
ign
info
rmat
ion)
H
igh
Wel
l kno
wn
for I
C
Ade
quat
e fo
r IC
M
ajor
nee
d fo
r air
ingr
ess
T
able
B-3
(con
tinue
d)
B-22
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
5
Ther
mal
-flu
id
prop
ertie
s H
igh
Tem
pera
ture
, pre
ssur
e,
velo
city
com
puta
tions
(I
C a
nd T
rans
.)
*Med
ium
W
ell k
now
n fo
r He,
un
certa
inty
in
com
posi
tion
of g
as
mix
ture
s mak
es g
as
prop
erty
cal
cula
tion
mor
e di
ffic
ult,
expe
cted
from
TF
PIR
T
Ade
quat
e
6 G
as c
ompo
sitio
n H
igh
Oxy
gen
pote
ntia
l and
ch
emic
al a
ctiv
ity
Med
ium
C
entra
l iss
ue fo
r ch
emic
al re
actio
n m
odel
ing,
FP
spec
iatio
n, sc
enar
io
depe
nden
t
Ade
quat
e (d
epre
ssur
izat
ion)
M
ajor
nee
d (a
ir in
gres
s)
7 G
as fl
ow p
ath
prio
r, du
ring,
and
pos
t ac
cide
nt
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
*Sam
e as
TF
grou
p N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
8 Te
mpe
ratu
re (s
truct
ure
and
gas)
and
pre
ssur
e di
strib
utio
n
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
Hig
h N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
9 FP
pla
te-o
ut a
nd d
ust
dist
ribut
ion
unde
r no
rmal
ope
ratio
n
Hig
h St
artin
g co
nditi
ons
Med
ium
Th
eory
and
mod
els
lack
spec
ifics
M
ajor
nee
d
Gra
phite
and
cor
e m
ater
ials
10
M
atrix
per
mea
bilit
y,
tortu
osity
H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s)
*Low
FP
hol
dup
as b
arrie
r; re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed
11
FP tr
ansp
ort t
hrou
gh
mat
rix
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
Low
FP
hol
dup
as b
arrie
r; re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed
T
able
B-3
(con
tinue
d)
B-23
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
12
Fu
el b
lock
pe
rmea
bilit
y, to
rtuos
ity
Hig
h N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed
13
FP tr
ansp
ort t
hrou
gh
fuel
blo
ck
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
Low
Th
erm
al g
radi
ents
are
not
la
rge
outs
ide
of fu
el
Low
Li
ttle
dat
a N
ot re
q’d
15
Bas
al p
lane
diff
usio
n Lo
w
Poro
sity
is p
refe
rred
tra
nspo
rt pa
thw
ay
thro
ugh
grap
hite
Med
ium
Pa
st w
ork
and
liter
atur
e av
aila
ble
Not
req’
d
16
Ref
lect
or (i
n co
ntac
t w
/flow
) per
mea
bilit
y,
tortu
osity
Low
N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
Low
Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t pr
inci
ples
(IC
and
Tra
ns)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
mat
eria
l PIR
T
Min
or m
od
18
Sorb
tivity
gra
phite
H
igh
Can
det
erm
ine
hold
up
and
rele
ase
of F
P (I
C a
nd
Tran
s.)
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion
on g
raph
ite a
nd
radi
atio
n ef
fect
s
Min
or m
od
19
Flue
nce
effe
ct o
n tra
nspo
rt in
gra
phite
H
igh
Influ
ence
s tra
nspo
rt,
chem
ical
reac
tivity
M
ediu
m
His
toric
al d
ata;
nee
d sp
ecifi
c in
form
atio
n on
gra
phite
and
ra
diat
ion
effe
cts
Maj
or n
eed
20
C-1
4, C
l-36,
Co-
60
gene
ratio
n an
d in
vent
ory
Low
R
adio
isot
ope
gene
rate
d fr
om im
purit
ies;
mig
ht
beco
me
oper
atio
nal i
ssue
(I
C)
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
M
inor
mod
, se
nsiti
ve to
gr
aphi
te h
andl
ing
T
able
B-3
(con
tinue
d)
B-24
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
21
A
ir at
tack
on
grap
hite
H
igh
Gra
phite
er
osio
n/ox
idat
ion;
Fe/
Cs
cata
lysi
s lib
erat
ing
FPs
(Tra
ns)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
22
Stea
m a
ttack
on
grap
hite
H
igh
If c
redi
ble
sour
ce o
f w
ater
pre
sent
; des
ign
depe
nden
t (Tr
ans)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
Fis
sion
pro
duct
tran
spor
t in
reac
tor c
oola
nt sy
stem
and
con
finem
ent
23
FP sp
ecia
tion
in
carb
onat
ious
mat
eria
l H
igh
Che
mic
al fo
rm in
gr
aphi
te a
ffec
ts tr
ansp
ort
(IC
and
Tra
ns.)
Low
U
ncer
tain
and
/or
inco
mpl
ete
Maj
or n
eed
24
FP sp
ecia
tion
durin
g m
ass t
rans
fer
Hig
h C
hem
ical
cha
nge
can
alte
r vol
atili
ty
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion;
go
od fo
r met
als,
oxid
es; u
ncer
tain
for
carb
ides
and
car
bony
ls
Maj
or n
eed
25
“Kno
ck-a
long
” Lo
w
Alp
ha re
coil
trans
port
of
depo
site
d pa
rticl
es o
n su
rfac
es sl
ow c
ompa
red
to fl
uid
flow
tran
spor
t
Med
ium
St
udie
d in
act
inid
e-be
arin
g pa
rticl
es
Ade
quat
e
26
Dus
t gen
erat
ion
Hig
h V
ecto
r for
FP
trans
port,
po
ssib
ility
of h
igh
mob
ility
.
Med
ium
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c sy
stem
in
form
atio
n
Maj
or n
eed,
impo
rt fr
om o
ther
gro
ups
27
(De)
Abs
orpt
ion
on d
ust
Hig
h Pr
ovid
es c
opio
us su
rfac
e ar
ea fo
r FP
abso
rptio
n
Med
ium
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c de
tails
M
ajor
nee
d
28
H-3
gen
erat
ion
and
circ
ulat
ing
cool
ant
inve
ntor
y
Med
ium
R
adio
isot
ope,
an
issu
e w
ith o
pera
tiona
l rel
ease
. H
-3 p
rodu
ctio
n fr
om H
e-3
in c
oola
nt, t
erna
ry
fissi
on, a
nd L
i-6 in
gr
aphi
te
Med
ium
H
isto
rical
dat
a, P
each
B
otto
m H
TGR
M
inor
mod
29
Ag-
110m
gen
erat
ion,
tra
nspo
rt H
igh
(O&
M)
Low
(rel
ease
) R
adio
isot
ope,
sign
ifica
nt
O&
M d
ose
on c
ool,
met
allic
com
pone
nts
Low
Li
mite
d da
ta, u
nkno
wn
trans
port
mec
hani
sm
Maj
or n
eed
T
able
B-3
(con
tinue
d)
B-25
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
30
O
ther
act
ivat
ion
prod
ucts
(e.g
., C
s-13
4,
Mn-
55, F
e-56
)
Low
R
adio
isot
opes
, pot
entia
l O
&M
dos
e M
ediu
m
Expe
rienc
e, li
mite
d in
form
atio
n M
inor
mod
31
Nuc
leat
ion
M
ediu
m
Unc
lear
due
to e
xtre
mel
y lo
w F
P va
por
conc
entra
tion
antic
ipat
ed
Med
ium
H
isto
rical
dat
a M
ajor
nee
d
32
Aer
osol
gro
wth
H
igh
Low
con
cent
ratio
n
grow
th c
an le
ad to
hig
h sh
ape
fact
ors a
nd
unus
ual s
ize
dist
ribut
ion
Low
R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
M
ajor
nee
d
33
Surf
ace
roug
hnes
s M
ediu
m
Aff
ects
aer
osol
de
posi
tion
1 to
5 m
icro
n pa
rticl
es (I
C a
nd T
rans
.)
Med
ium
In
itial
info
rmat
ion
from
man
ufac
ture
r; ev
olut
ion
of su
rfac
e ro
ughn
ess d
urin
g op
erat
ion
not w
ell
know
n
Min
or m
od
34
Coo
lant
che
mic
al
inte
ract
ion
w/s
urfa
ces
Hig
h C
hang
es o
xyge
n an
d ca
rbon
pot
entia
l, w
hich
ca
n af
fect
nat
ure
and
quan
tity
of so
rbed
sp
ecie
s (IC
and
Tra
ns.)
Med
ium
Su
rfac
e pr
oper
ties a
re
criti
cal;
need
allo
y da
ta
Maj
or n
eed
35
FP d
iffus
ivity
, so
rbtiv
ity in
no
ngra
phite
surf
aces
Hig
h D
eter
min
es F
P lo
catio
n du
ring
oper
atio
n; a
cts a
s a
trap
durin
g tra
nsie
nt
(IC
and
Tra
ns.)
Low
Li
ttle
info
rmat
ion
on
mat
eria
ls o
f int
eres
t M
ajor
nee
d
36
Aer
osol
/dus
t dep
ositi
on
Hig
h G
ravi
tatio
nal,
iner
tial,
ther
mop
hore
sis,
elec
trost
atic
, diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol d
epos
ition
by
mos
t mec
hani
sms
exce
pt in
ertia
l im
pact
in
com
plex
ge
omet
ries;
ap
plic
abili
ty to
NG
NP
uncl
ear
Min
or m
od
T
able
B-3
(con
tinue
d)
B-26
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
37
A
eros
ol/d
ust b
ounc
e,
brea
kup
durin
g de
posi
tion
Med
ium
C
an m
odify
dep
ositi
on
prof
ile a
nd su
spen
ded
aero
sol d
istri
butio
n
Low
Th
eory
, dat
a, a
nd
mod
els l
acki
ng
Maj
or n
eed
38
Res
uspe
nsio
n H
igh
Flow
/vib
ratio
n in
duce
d,
salta
tion;
mec
hani
cal
forc
es c
an re
leas
e FP
s fr
om p
ipe
surf
ace
laye
rs/fi
lms (
Tran
s.)
Low
La
ck o
f dat
a an
d m
odel
s for
ant
icip
ated
co
nditi
ons
Maj
or n
eed
39
Con
finem
ent a
eros
ol
phys
ics
Hig
h A
nalo
gous
to L
WR
ae
roso
l beh
avio
r/phy
sics
, de
lta-T
, che
mis
try;
impo
rtant
hol
dup
mec
hani
sm (T
rans
.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol b
ehav
ior;
appl
icab
ility
to N
GN
P un
clea
r
Min
or m
od
40
Dus
t dep
ositi
on o
n ve
ssel
and
RC
CS
hard
war
e
Low
N
ot im
porta
nt fo
r FP
trans
port
but m
ay a
ffec
t ra
diat
ive
heat
tran
sfer
in
reac
tor c
avity
Low
V
ery
limite
d da
ta
Maj
or n
eed
41
Cor
rosi
on p
rodu
cts
Low
Sp
alle
d su
rfac
e fil
ms;
lo
w c
orro
sion
en
viro
nmen
t (IC
and
Tr
ans.)
Hig
h Pa
st e
xper
ienc
e A
dequ
ate
42
Eros
ion
prod
ucts
, no
ncar
bon
Low
Lo
w c
once
ntra
tion
of
coar
se m
ater
ials
(IC
and
Tr
ans.)
Low
La
ck o
f des
ign
info
rmat
ion;
co
nfig
urat
ion
and
mat
eria
ls sp
ecifi
c
Ade
quat
e
43
Was
h-of
f H
igh
If c
redi
ble
sour
ce o
f w
ater
pre
sent
; des
ign
depe
nden
t (Tr
ans.)
Med
ium
So
me
expe
rimen
tal
data
ava
ilabl
e M
inor
mod
44
Failu
re m
odes
of
auxi
liary
syst
ems (
e.g.
, ga
s cle
anup
, hol
dup,
re
fuel
ing)
Med
ium
Po
tent
ial r
elea
se d
ue to
fa
ilure
(Tra
ns.)
Med
ium
D
esig
n sp
ecifi
c; h
ave
expe
rienc
e fr
om o
ther
de
sign
s
Min
or m
od
T
able
B-3
(con
tinue
d)
B-27
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
45
R
adio
lysi
s eff
ects
in
conf
inem
ent
Hig
h FP
(e.g
., I,
Ru,
Te)
ch
emis
try, p
aint
ch
emis
try (d
epen
dent
on
conf
inem
ent r
adia
tion
leve
l) (T
rans
.)
Med
ium
LW
R e
xper
ienc
e an
d da
ta
Min
or m
od
46
Filtr
atio
n H
igh
Trad
ition
al p
assi
ve
char
coal
/HEP
A (T
rans
.) H
igh
His
toric
al e
xper
ienc
e A
dequ
ate
47
Prod
uctio
n/co
mbu
stio
n of
flam
mab
le g
as
Med
ium
C
O, H
2 pro
duct
ion
issu
es, I
HX
seco
ndar
y-pr
imar
y le
ak, p
oten
tial
resu
spen
sion
and
ch
emic
al tr
ansf
orm
atio
n of
FPs
. (Tr
ans.)
Hig
h H
isto
rical
exp
erie
nce
Ade
quat
e
48
Com
bust
ion
of d
ust i
n co
nfin
emen
t H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
w/in
co
nfin
emen
t
Med
ium
IT
ER d
ata
Maj
or n
eed
49
NG
NP-
uniq
ue le
akag
e pa
th b
eyon
d co
nfin
emen
t
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n, c
ould
be
risk-
dom
inan
t (Tr
ans.)
Hig
h C
ontin
gent
on
spec
ific
desi
gn k
now
ledg
e M
inor
mod
50
Con
finem
ent l
eaka
ge
path
, rel
ease
rate
th
roug
h pe
netra
tions
Hig
h C
able
/pip
e pe
netra
tions
, cr
acks
, hol
es, H
VA
C
(Tra
ns.)
Med
ium
B
uild
ing
leak
age
expe
rienc
e, d
esig
n sp
ecifi
c
Ade
quat
e
51
Cab
le p
yrol
ysis
, fire
H
igh
Soot
gen
erat
ion
and
chan
ges t
o io
dine
ch
emis
try
Med
ium
LW
R e
xper
ienc
e M
ajor
nee
d
52
Pres
sure
-rel
ief-
valv
e fil
ter
Low
O
peni
ng o
f the
relie
f va
lve
gene
rate
s a
trans
port
path
that
may
be
filte
red;
dep
ends
on
desi
gn
Hig
h A
ir cl
eani
ng
tech
nolo
gy
Ade
quat
e
T
able
B-3
(con
tinue
d)
B-28
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
53
R
ecrit
ical
ity (s
low
) H
igh
Add
ition
al th
erm
al lo
ad
to fu
el; i
ncre
ases
sour
ce
but n
ot e
xpec
ted
to a
ffec
t tra
nspo
rt pa
th
Med
ium
H
eat l
oad
easi
ly
com
pute
d w
ith
exis
ting
tool
s; e
ffec
t on
fiss
ion
prod
ucts
not
co
mpl
etel
y kn
own
Min
or m
od
54
Fuel
-dam
agin
g R
IA
Hig
h A
n in
tens
e pu
lse
coul
d da
mag
e fu
el; i
ncre
ases
so
urce
but
not
exp
ecte
d to
aff
ect t
rans
port
path
Med
ium
So
me
data
exi
sts,
but
outs
ide
of e
xpec
ted
acci
dent
env
elop
e
Min
or m
od
55
Arg
on a
ctiv
atio
n in
re
acto
r cav
ity
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
Hig
h Ea
sily
com
pute
d w
ith
exis
ting
tool
s A
dequ
ate
56
Red
istri
butio
n of
fiss
ion
prod
ucts
due
to c
ontro
l ro
d m
ovem
ent
Low
A
rticu
late
d co
ntro
l rod
jo
ints
can
col
lect
and
re
dist
ribut
e fis
sion
pr
oduc
ts
Low
Sp
ecifi
cs o
n C
RD
ho
usin
g an
d ar
ticul
ated
SiC
co
mpo
site
hou
sing
TB
D
Min
or m
od
B-29
T
able
B-4
. In
divi
dual
FPT
PIR
T R
anki
ng T
able
Fi
nal V
ersi
on A
pril
18, 2
007
Pane
list:
Mar
tin K
issa
ne
C
hang
es in
ITA
LIC
S ar
e di
ffer
ence
s fro
m th
e fin
al g
roup
dis
cuss
ions
on
Apr
il 18
, 200
7
Thi
s tab
le g
ener
ally
app
lies t
o al
l cas
es, n
orm
al, a
ntic
ipat
ed tr
ansi
ents
, and
acc
iden
ts.
Spec
ific
case
s are
not
ed.
Not
es:
* de
note
s nee
d fo
r int
erfa
ce w
ith o
ther
gro
ups (
mat
eria
ls, t
rans
ient
scen
ario
s)
IC—
initi
al c
ondi
tion,
the
resu
lt of
long
term
nor
mal
ope
ratio
n Tr
ans.—
tran
sien
t and
acc
iden
t con
ditio
n TF
—th
erm
al fl
uids
FP
—fis
sion
pro
duct
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
C
ritic
al in
itial
and
/or b
ound
ary
cond
ition
1
Dec
ay h
eat a
nd
trans
ient
pow
er le
vel
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) *H
igh
Bou
ndar
y co
nditi
ons
expe
cted
from
TF
PIR
T A
dequ
ate
2 M
ater
ial/s
truct
ure
prop
ertie
s H
igh
Den
sity
, vis
cosi
ty,
cond
uctiv
ity, e
tc.,
impo
rtant
par
amet
ers i
n ca
lcul
atio
ns (I
C a
nd
Tran
s.)
*Med
(gra
phite
) H
igh
(ste
el, c
oncr
ete)
G
raph
ite ty
pe n
ot
sele
cted
, exp
ecte
d fr
om
mat
eria
l PIR
T
Min
or m
od
(gra
phite
) A
dequ
ate
(ste
el,
conc
rete
)
3 G
raph
ite im
purit
y le
vels
H
igh
Impu
rity
reac
tion
with
FP;
nu
clea
r gra
phite
exp
ecte
d to
hav
e lo
w im
purit
y le
vels
*Hig
h W
ill b
e m
easu
red,
ex
pect
ed fr
om m
ater
ial
PIR
T
Ade
quat
e
4 G
raph
ite g
eom
etry
H
igh
Cor
e st
ruct
ure
(des
ign
info
rmat
ion)
H
igh
Wel
l kno
wn
for I
C
Ade
quat
e fo
r IC
. M
ajor
nee
d fo
r air
ingr
ess
T
able
B-4
(con
tinue
d)
B-30
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
5
Ther
mal
-flu
id
prop
ertie
s H
igh
Tem
pera
ture
, pre
ssur
e,
velo
city
com
puta
tions
(IC
an
d Tr
ans.)
*Med
ium
W
ell k
now
n fo
r hel
ium
; un
certa
inty
in
com
posi
tion
of g
as
mix
ture
s mak
es g
as
prop
erty
cal
cula
tion
mor
e di
ffic
ult,
expe
cted
fr
om T
F PI
RT
Ade
quat
e
6 G
as c
ompo
sitio
n H
igh
Oxy
gen
pote
ntia
l and
ch
emic
al a
ctiv
ity
Med
ium
C
entra
l iss
ue fo
r ch
emic
al re
actio
n m
odel
ing,
FP
spec
iatio
n, sc
enar
io
depe
nden
t
Ade
quat
e (d
epre
ssur
izat
ion)
M
ajor
nee
d (a
ir in
gres
s)
7 G
as fl
ow p
ath
prio
r, du
ring,
and
pos
t ac
cide
nt
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
*Sam
e as
TF
grou
p N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
8 Te
mpe
ratu
re
(stru
ctur
e an
d ga
s)
and
pres
sure
di
strib
utio
n
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
Hig
h N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
9 FP
Pla
te-o
ut a
nd
dust
dis
tribu
tion
unde
r nor
mal
op
erat
ion
Hig
h St
artin
g co
nditi
ons
Med
ium
Th
eory
and
mod
els l
ack
spec
ifics
M
ajor
nee
d
Gra
phite
and
cor
e m
ater
ials
10
M
atrix
per
mea
bilit
y,
tortu
osity
H
igh
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C a
nd
Tran
s)
*Low
FP
hol
dup
as b
arrie
r, re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed
11
FP tr
ansp
ort t
hrou
gh
mat
rix
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
Low
FP
hol
dup
as b
arrie
r, re
leas
e as
dus
t; ex
pect
ed fr
om m
ater
ial
PIR
T
Maj
or n
eed
T
able
B-4
(con
tinue
d)
B-31
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
12
Fu
el b
lock
pe
rmea
bilit
y,
tortu
osity
Hig
h N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
and
Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
m
ater
ial P
IRT
Maj
or n
eed
13
FP tr
ansp
ort t
hrou
gh
fuel
blo
ck
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
m
ater
ial P
IRT
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
Low
Th
erm
al g
radi
ents
are
not
la
rge
outs
ide
of fu
el
Low
Li
ttle
dat
a N
ot re
q’d
15
Bas
al p
lane
di
ffus
ion
Low
Po
rosi
ty is
pre
ferr
ed
trans
port
path
way
thro
ugh
grap
hite
Med
ium
Pa
st w
ork
and
liter
atur
e av
aila
ble
Not
req’
d
16
Ref
lect
or (i
n co
ntac
t w
/flow
) pe
rmea
bilit
y,
tortu
osity
Low
N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
and
Tr
ans)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
m
ater
ial P
IRT
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
Low
Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te; e
xpec
ted
from
m
ater
ial P
IRT
Min
or m
od
18
Sorb
tivity
gra
phite
H
igh
Can
det
erm
ine
hold
up a
nd
rele
ase
of F
P (I
C a
nd
Tran
s.)
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion
on
grap
hite
and
radi
atio
n ef
fect
s
Min
or M
od
19
Flue
nce
effe
ct o
n tra
nspo
rt in
gra
phite
H
igh
Influ
ence
s tra
nspo
rt,
chem
ical
reac
tivity
M
ediu
m
His
toric
al d
ata;
nee
d sp
ecifi
c in
form
atio
n on
gr
aphi
te a
nd ra
diat
ion
effe
cts
Maj
or n
eed
20
C-1
4, C
l-36,
Co-
60
gene
ratio
n an
d in
vent
ory
Low
R
adio
isot
ope
gene
rate
d fr
om im
purit
ies,
mig
ht
beco
me
oper
atio
nal i
ssue
(I
C)
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
M
inor
mod
, se
nsiti
ve to
gr
aphi
te h
andl
ing
T
able
B-4
(con
tinue
d)
B-32
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
21
A
ir at
tack
on
grap
hite
H
igh
Gra
phite
ero
sion
/oxi
datio
n;
Fe/C
s cat
alys
is li
bera
ting
FPs (
Tran
s)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
22
Stea
m a
ttack
on
grap
hite
H
igh
If c
redi
ble
sour
ce o
f wat
er
pres
ent;
desi
gn d
epen
dent
(T
rans
)
Med
ium
H
isto
rical
dat
a M
ajor
nee
d fo
r se
vere
acc
iden
ts
Fis
sion
pro
duct
tran
spor
t in
reac
tor c
oola
nt sy
stem
and
con
finem
ent
23
FP sp
ecia
tion
in
carb
onac
eous
m
ater
ial
Hig
h C
hem
ical
form
in g
raph
ite
affe
cts t
rans
port
(IC
and
Tr
ans.)
Low
U
ncer
tain
and
/or
inco
mpl
ete;
spec
ific
impu
rity
effe
cts n
eed
to
be d
eter
min
ed
Maj
or n
eed
24
FP sp
ecia
tion
durin
g m
ass t
rans
fer
Hig
h C
hem
ical
cha
nge
can
alte
r vo
latil
ity
Med
ium
H
isto
rical
dat
a, n
eed
spec
ific
info
rmat
ion.
G
ood
for m
etal
s, ox
ides
. U
ncer
tain
for
carb
ides
and
car
bony
ls
Maj
or n
eed
25
“Kno
ck-a
long
” Lo
w
Alp
ha re
coil
trans
port
of
depo
site
d pa
rticl
es o
n su
rfac
es; s
low
com
pare
d to
flu
id fl
ow tr
ansp
ort
Med
ium
St
udie
d in
act
inid
e-be
arin
g pa
rticl
es
Ade
quat
e
26
Dus
t gen
erat
ion
Hig
h V
ecto
r for
FP
trans
port;
po
ssib
ility
of h
igh
mob
ility
M
ediu
m
Lim
ited
expe
rienc
e;
lack
spec
ific
syst
em
info
rmat
ion
Maj
or n
eed;
impo
rt fr
om o
ther
gro
ups
27
(De)
Abs
orpt
ion
on
dust
H
igh
Prov
ides
cop
ious
surf
ace
area
for F
P ab
sorp
tion
Low
Li
mite
d ex
perie
nce;
la
ck sp
ecifi
c de
tails
M
ajor
nee
d
28
H-3
gen
erat
ion
and
circ
ulat
ing
cool
ant
inve
ntor
y
Med
ium
R
adio
isot
ope,
an
issu
e w
ith
oper
atio
nal r
elea
se. H
-3
prod
uctio
n fr
om H
e-3
in
cool
ant,
tern
ary
fissi
on,
and
Li-6
in g
raph
ite
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
M
inor
mod
29
Ag-
110m
ge
nera
tion,
tran
spor
t H
igh
(O&
M)
Low
(rel
ease
) R
adio
isot
ope;
sign
ifica
nt
O&
M d
ose
on c
ool;
met
allic
com
pone
nts
Low
Li
mite
d da
ta; u
nkno
wn
trans
port
mec
hani
sm
Maj
or n
eed
T
able
B-4
(con
tinue
d)
B-33
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
30
O
ther
act
ivat
ion
prod
ucts
(e.g
., C
s-13
4, M
n-55
, Fe-
56)
Low
R
adio
isot
opes
; pot
entia
l O
&M
dos
e M
ediu
m
Expe
rienc
e; li
mite
d in
form
atio
n M
inor
mod
31
Nuc
leat
ion
M
ediu
m
Unc
lear
due
to e
xtre
mel
y lo
w F
P va
por c
once
ntra
tion
antic
ipat
ed
Med
ium
H
isto
rical
dat
a M
ajor
nee
d
32
Aer
osol
gro
wth
M
ediu
m
Low
con
cent
ratio
n g
row
th
can
lead
to h
igh
shap
e fa
ctor
s and
unu
sual
size
di
strib
utio
n; b
asic
dus
t ch
arac
teri
stic
s (kn
own)
w
ill h
ave
a m
ajor
influ
ence
Low
R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
M
ajor
nee
d
33
Surf
ace
roug
hnes
s M
ediu
m
Aff
ects
aer
osol
dep
ositi
on
1-5
mic
ron
parti
cles
(IC
an
d Tr
ans.)
Med
ium
In
itial
info
rmat
ion
from
m
anuf
actu
rer;
evol
utio
n of
surf
ace
roug
hnes
s du
ring
oper
atio
n no
t w
ell k
now
n
Min
or m
od
34
Coo
lant
che
mic
al
inte
ract
ion
w/
surf
aces
Hig
h C
hang
es o
xyge
n an
d ca
rbon
pot
entia
l whi
ch c
an
affe
ct n
atur
e an
d qu
antit
y of
sorb
ed sp
ecie
s (IC
and
Tr
ans.)
Med
ium
Su
rfac
e pr
oper
ties a
re
criti
cal,
need
allo
y da
ta
Maj
or n
eed
35
FP d
iffus
ivity
; so
rbtiv
ity in
no
ngra
phite
surf
aces
Hig
h D
eter
min
es F
P lo
catio
n du
ring
oper
atio
n; a
cts a
s a
trap
durin
g tra
nsie
nt (I
C
and
Tran
s.)
Low
Li
ttle
info
rmat
ion
on
mat
eria
ls o
f int
eres
t M
ajor
nee
d
36
Aer
osol
/dus
t de
posi
tion
Hig
h G
ravi
tatio
nal,
iner
tial,
ther
mop
hore
sis,
elec
trost
atic
, diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol d
epos
ition
by
mos
t mec
hani
sms
exce
pt in
ertia
l im
pact
in
com
plex
geo
met
ries;
ap
plic
abili
ty to
NG
NP
uncl
ear
Min
or m
od; m
ajor
ne
ed w
ith re
spec
t to
com
pone
nts s
uch
as tu
rbin
e an
d IH
X
T
able
B-4
(con
tinue
d)
B-34
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
37
A
eros
ol/d
ust
boun
ce, b
reak
up
durin
g de
posi
tion
Med
ium
C
an m
odify
dep
ositi
on
prof
ile a
nd su
spen
ded
aero
sol d
istri
butio
n
Low
Th
eory
, dat
a, a
nd
mod
els l
acki
ng
Maj
or n
eed
38
Res
uspe
nsio
n H
igh
Flow
/vib
ratio
n in
duce
d,
salta
tion;
mec
hani
cal
forc
es c
an re
leas
e FP
s fro
m
pipe
surf
ace
laye
rs/fi
lms
(Tra
ns.)
Low
La
ck o
f dat
a an
d m
odel
s for
ant
icip
ated
co
nditi
ons
Maj
or n
eed
39
Con
finem
ent a
eros
ol
phys
ics
Hig
h A
nalo
gous
to L
WR
aer
osol
be
havi
or/p
hysi
cs, d
elta
-T,
chem
istry
; im
porta
nt
hold
up m
echa
nism
(Tra
ns.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol b
ehav
ior;
appl
icab
ility
to N
GN
P un
clea
r
Min
or m
od
40
Dus
t dep
ositi
on o
n ve
ssel
and
RC
CS
hard
war
e
Low
N
ot im
porta
nt fo
r FP
trans
port;
but
may
aff
ect
radi
ativ
e he
at tr
ansf
er in
re
acto
r cav
ity
Low
V
ery
limite
d da
ta
Maj
or n
eed
41
Cor
rosi
on p
rodu
cts
Low
Sp
alle
d su
rfac
e fil
ms;
low
co
rros
ion
envi
ronm
ent (
IC
and
Tran
s.)
Hig
h Pa
st e
xper
ienc
e A
dequ
ate
42
Eros
ion
prod
ucts
, no
ncar
bon
Low
Lo
w c
once
ntra
tion
of
coar
se m
ater
ials
(IC
and
Tr
ans.)
Low
La
ck o
f des
ign
info
rmat
ion;
co
nfig
urat
ion
and
mat
eria
ls sp
ecifi
c
Ade
quat
e
43
Was
h-of
f H
igh
If c
redi
ble
sour
ce o
f wat
er
pres
ent;
desi
gn d
epen
dent
(T
rans
.)
Med
ium
So
me
expe
rimen
tal d
ata
avai
labl
e M
inor
mod
44
Failu
re m
odes
of
auxi
liary
syst
ems
(e.g
., ga
s cle
anup
, ho
ldup
, ref
uelin
g)
Med
ium
Po
tent
ial r
elea
se d
ue to
fa
ilure
(Tra
ns.)
Med
ium
D
esig
n sp
ecifi
c; h
ave
expe
rienc
e fr
om o
ther
de
sign
s
Min
or m
od
T
able
B-4
(con
tinue
d)
B-35
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
45
R
adio
lysi
s eff
ects
in
conf
inem
ent
Hig
h FP
(e.g
., I,
Ru,
Te)
ch
emis
try, p
aint
che
mis
try
(dep
ende
nt o
n co
nfin
emen
t ra
diat
ion
leve
l) (T
rans
.)
Med
ium
LW
R e
xper
ienc
e an
d da
ta
Min
or m
od
46
Filtr
atio
n H
igh
Trad
ition
al p
assi
ve
char
coal
/HEP
A (T
rans
.) H
igh
His
toric
al e
xper
ienc
e A
dequ
ate
47
Prod
uctio
n/co
mbu
sti
on o
f fla
mm
able
gas
M
ediu
m
CO
, H2 p
rodu
ctio
n is
sues
, IH
X se
cond
ary-
prim
ary
leak
, pot
entia
l res
uspe
nsio
n an
d ch
emic
al
trans
form
atio
n of
FPs
(T
rans
.)
Hig
h H
isto
rical
exp
erie
nce
Ade
quat
e
48
Com
bust
ion
of d
ust
in c
onfin
emen
t H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
w/in
co
nfin
emen
t
Med
ium
IT
ER d
ata
Maj
or n
eed
49
NG
NP-
uniq
ue
leak
age
path
bey
ond
conf
inem
ent
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n; c
ould
be
risk
dom
inan
t (Tr
ans.)
Hig
h C
ontin
gent
on
spec
ific
desi
gn k
now
ledg
e M
inor
mod
50
Con
finem
ent
leak
age
path
; rel
ease
ra
te th
roug
h pe
netra
tions
Hig
h C
able
/pip
e pe
netra
tions
, cr
acks
, hol
es, H
VA
C
(Tra
ns.)
Med
ium
B
uild
ing
leak
age
expe
rienc
e, d
esig
n sp
ecifi
c
Ade
quat
e
51
Cab
le p
yrol
ysis
, fire
H
igh
Soot
gen
erat
ion
and
chan
ges t
o io
dine
ch
emis
try
Med
ium
LW
R e
xper
ienc
e M
ajor
nee
d
52
Pres
sure
relie
f-va
lve-
filte
r Lo
w
Ope
ning
of t
he re
lief v
alve
ge
nera
tes a
tran
spor
t pat
h th
at m
ay b
e fil
tere
d;
depe
nds o
n de
sign
.
Hig
h A
ir cl
eani
ng te
chno
logy
A
dequ
ate
53
Rec
ritic
ality
(slo
w)
Hig
h A
dditi
onal
ther
mal
load
to
fuel
; inc
reas
es so
urce
but
no
t exp
ecte
d to
aff
ect
trans
port
path
Med
ium
H
eat l
oad
easi
ly
com
pute
d w
ith e
xist
ing
tool
s; e
ffec
t on
fissi
on
prod
ucts
not
com
plet
ely
know
n
Min
or m
od
T
able
B-4
(con
tinue
d)
B-36
ID
No.
Issu
e (p
heno
men
a,
proc
ess,
geom
etry
co
nditi
on)
Impo
rtan
ce fo
r N
GN
P(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
54
Fu
el-d
amag
ing
RIA
H
igh
An
inte
nse
puls
e co
uld
dam
age
fuel
; inc
reas
es
sour
ce b
ut n
ot e
xpec
ted
to
affe
ct tr
ansp
ort p
ath
Med
ium
So
me
data
exi
sts b
ut
outs
ide
of e
xpec
ted
acci
dent
env
elop
e
Min
or m
od
55
Arg
on a
ctiv
atio
n in
re
acto
r cav
ity
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
Hig
h Ea
sily
com
pute
d w
ith
exis
ting
tool
s A
dequ
ate
56
Red
istri
butio
n of
fis
sion
pro
duct
s due
to
con
trol r
od
mov
emen
t
Low
A
rticu
late
d co
ntro
l rod
jo
ints
can
col
lect
and
re
dist
ribut
e fis
sion
pr
oduc
ts
Low
Sp
ecifi
cs o
n C
RD
ho
usin
g an
d ar
ticul
ated
Si
C c
ompo
site
hou
sing
TB
D
Min
or m
od
B-37
Table B-5. Individual PIRT Ranking Table Panelist: Robert Wichner
April 23, 2007 OUTLINE PART A: GENERAL ISSUES PART B: FP TRANSPORT/HOLDUP IN CARBON MATRIX AND GRAPHITE PART C: FP EMISSION FROM GRAPHITE/MATRIX SURFACE PART D: FP TRANSPORT/BEHAVIOR IN COOLANT PART E: FP DEPOSITION/SORPTION ON PRIMARY SYSTEM SURFACES PART F: RELEASES FROM THE PRIMARY SYSTEM—NORMAL OPERATION PART G: RELEASES FROM THE PRIMARY SYSTEM—ACCIDENT CONDITIONS
G.1 POWER VERSION AND GENERAL ISSUES G.2 PROCESS HEAT VERSION
PART H: RELEASES FROM THE CONFINEMENT
B-38
Page intentionally blank
B-39
Part
A:
Gen
eral
issu
es a
ffec
ting
FP tr
ansp
ort
Issu
es:
●
Inpu
t fro
m o
ther
PIR
T ar
eas
● Pr
oduc
tion
of a
ctiv
atio
n pr
oduc
ts
● M
ater
ial p
rope
rties
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
1
Dec
ay h
eat &
tran
sien
t po
wer
leve
l
Not
dir
ect i
nput
to F
P tr
ansp
ort;
subs
umed
in
item
-8
Hig
h En
ergy
sour
ce d
rivin
g pr
oble
m (I
C a
nd T
rans
.) *H
igh
Bou
ndar
y co
nditi
ons
expe
cted
from
TF
PIR
T A
dequ
ate
2 M
ater
ial/s
truct
ure
pr
oper
ties
Too
gene
ral.
Spec
ific
prop
ertie
s cite
d in
Pa
rts B
, D a
nd G
.
Hig
h D
ensi
ty, v
isco
sity
, co
nduc
tivity
, etc
., im
porta
nt p
aram
eter
s in
calc
ulat
ions
(IC
and
Tr
ans.)
*Med
(gra
phite
) H
igh
(ste
el, c
oncr
ete)
G
raph
ite ty
pe n
ot
sele
cted
, exp
ecte
d fr
om
mat
eria
l PIR
T
Min
or M
od
(gra
phite
) A
dequ
ate
(ste
el,
conc
rete
)
4 G
raph
ite g
eom
etry
To
o ge
nera
l, an
d ba
sic
Hig
h C
ore
stru
ctur
e (d
esig
n in
form
atio
n)
Hig
h W
ell k
now
n fo
r IC
A
dequ
ate
for I
C
Maj
or N
eed
for a
ir in
gres
s 5
Ther
mal
-flu
id
prop
ertie
s, Tr
ansf
erre
d to
item
6,
Part
D, a
nd it
em 1
25,
Part
H.1
Hig
h Te
mpe
ratu
re, p
ress
ure,
ve
loci
ty c
ompu
tatio
ns
(IC
and
Tra
ns.)
*Med
ium
W
ell k
now
n fo
r He.
U
ncer
tain
ty in
co
mpo
sitio
n of
gas
m
ixtu
res m
akes
gas
pr
oper
ty c
alcu
latio
n m
ore
diff
icul
t, ex
pect
ed
from
TF
PIR
T
Ade
quat
e
8 Te
mpe
ratu
re (s
truct
ure
and
gas)
and
pre
ssur
e di
strib
utio
n
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
Hig
h N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
20
C-1
4, C
l-36,
Co-
60
Low
M
ediu
m
Rad
iois
otop
e ge
nera
ted
from
impu
ritie
s, m
ight
be
com
e op
erat
iona
l is
sue.
C-1
4 m
ay b
ecom
e a
publ
ic is
sue
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
M
inor
mod
, se
nsiti
ve to
gr
aphi
te h
andl
ing
Pa
rt A
(con
tinue
d)
B-40
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
29
A
g-11
0m g
ener
atio
n,
trans
port,
and
in
vent
ory
dist
ribu
tion
Hig
h (O
&M
) Lo
w (r
elea
se)
Rad
iois
otop
e; si
gnifi
cant
O
&M
dos
e on
coo
l; m
etal
lic c
ompo
nent
s
Low
Li
mite
d da
ta, u
nkno
wn
trans
port
mec
hani
sm
Maj
or n
eed
30
Oth
er a
ctiv
atio
n pr
oduc
ts (e
.g. C
s-13
4,
Mn-
55, F
e-56
)
Low
R
adio
isot
opes
; pot
entia
l O
&M
dos
e M
ediu
m
Expe
rienc
e, li
mite
d in
form
atio
n M
inor
mod
33
Surf
ace
roug
hnes
s M
ediu
m
Aff
ects
aer
osol
de
posi
tion
1 to
5 m
icro
n pa
rticl
es (I
C a
nd T
rans
.)
Med
ium
In
itial
info
rmat
ion
from
m
anuf
actu
rer;
evol
utio
n of
surf
ace
roug
hnes
s du
ring
oper
atio
n no
t w
ell k
now
n
Min
or m
od
53
Rec
ritic
ality
(slo
w)
Hig
h A
dditi
onal
ther
mal
load
to
fuel
. Inc
reas
es so
urce
bu
t not
exp
ecte
d to
aff
ect
trans
port
path
.
Med
ium
H
eat l
oad
easi
ly
com
pute
d w
ith e
xist
ing
tool
s; e
ffec
t on
fissi
on
prod
ucts
not
com
plet
ely
know
n
Min
or m
od
54
Fuel
-dam
agin
g R
IA
Hig
h A
n in
tens
e pu
lse
coul
d da
mag
e fu
el.
Incr
ease
s so
urce
but
not
exp
ecte
d to
aff
ect t
rans
port
path
.
Med
ium
So
me
data
exi
sts,
but
outs
ide
of e
xpec
ted
acci
dent
env
elop
e
Min
or m
od
100
Cs-
134,
Cs-
136
prod
uctio
n M
ediu
m
Affe
cts m
aint
enan
ce d
ose
Hig
h Pr
oduc
tion
met
hod
know
n M
inor
Mod
101
H-3
, pro
duct
ion
from
al
l sou
rces
, inv
ento
ry
dist
ribu
tion
Hig
h C
an d
iffus
e ac
ross
IHX
boun
dary
. M
ediu
m
Dat
a on
ear
lier
mat
eria
ls a
vaila
ble
Min
or m
od
B-41
Part
B:
Tra
nspo
rt h
oldu
p in
car
bon
mat
rix
and
grap
hite
[Ter
min
olog
y: P
BM
R c
arbo
n is
term
ed “
mat
rix”
in b
oth
the
fuel
led
and
unfu
eled
zon
es.
Pris
mat
ic fu
el “
mat
rix”
refe
rs to
the
com
pact
; gra
phite
to th
e bl
ock.
] Is
sues
: ●
FP tr
ansp
ort r
ates
● FP
Inve
ntor
y in
mat
rix/g
raph
ite
●
FP B
ehav
ior d
urin
g ac
cide
nts
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
3
Gra
phite
impu
rity
leve
ls
Med
ium
Im
purit
y re
actio
n w
ith F
P,
nucl
ear g
raph
ite e
xpec
ted
to h
ave
low
impu
rity
leve
ls
*Hig
h W
ill b
e m
easu
red;
ex
pect
ed fr
om
mat
eria
l PIR
T
Ade
quat
e
10
Mat
rix p
erm
eabi
lity,
to
rtuos
ity
Tort
uosi
ty is
a d
eriv
ed
quan
tity,
not
dir
ectly
us
able
Hig
h M
ediu
m
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s)
Nee
ded
to d
eter
min
e pe
rmea
tion
flow
due
to _
P ac
ross
mat
rix;
som
e FP
s m
ay b
e so
tran
spor
ted
Low
M
ediu
m
FP h
oldu
p as
ba
rrie
r; re
leas
e as
du
st; e
xpec
ted
from
m
ater
ial P
IRT
Maj
or n
eed
11
FP tr
ansp
ort t
hrou
gh
mat
rix
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
Requ
ired
to a
sses
s FP
hold
up a
nd tr
ansp
ort i
n m
atri
x
Low
FP
hol
dup
as
barr
ier,
rele
ase
as
dust
, Exp
ecte
d fr
om m
ater
ial
PIR
T. O
ne o
r tw
o co
nsta
nt e
mpi
rica
l m
odel
nee
ds to
be
deve
lope
d.
Radi
atio
n ef
fect
m
ay b
e si
gnifi
cant
.
Maj
or n
eed
Pa
rt B
(con
tinue
d)
B-42
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
12
Fu
el b
lock
pe
rmea
bilit
y, to
rtuos
ity
Tort
uosi
ty is
a d
eriv
ed
quan
tity,
not
dir
ectly
us
able
Hig
h M
ediu
m
Nee
ded
for f
irst p
rinci
ple
trans
port
mod
elin
g (I
C
and
Tran
s)
Nee
ded
for d
eter
min
ing
perm
eatio
n flo
w d
ue to
a
ΔP a
cros
s gra
phite
web
; so
me
FPs m
ay b
e so
tr
ansp
orte
d
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te;
expe
cted
from
m
ater
ial P
IRT
Maj
or n
eed
Min
or m
od;
perm
eatio
n fo
r a
give
n ΔP
is
pred
icta
ble
from
a
wel
l-kno
wn
corr
elat
ion.
13
FP tr
ansp
ort t
hrou
gh
fuel
blo
ck
Hig
h Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
Requ
ired
to a
sses
s FP
hold
up a
nd tr
ansp
ort i
n gr
aphi
te; s
igni
fican
t tr
ansp
ort f
acto
r
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te;
Expe
cted
from
m
ater
ial P
IRT
affe
cted
by
radi
atio
n le
vel a
nd
fluen
ce; d
epen
ds
on F
P sp
ecie
s in
grap
hite
; req
uire
s te
st d
ata,
som
e of
w
hich
is a
vaila
ble
Maj
or n
eed
14
Ther
mal
(Sor
et)
diff
usio
n
Low
Th
erm
al g
radi
ents
are
not
la
rge
outs
ide
of fu
el
Low
Li
ttle
dat
a N
ot re
q’d
15
Bas
al p
lane
diff
usio
n Lo
w
Poro
sity
is p
refe
rred
tra
nspo
rt pa
thw
ay th
roug
h gr
aphi
te
Med
ium
Pa
st w
ork
and
liter
atur
e av
aila
ble
Not
req’
d
16
Ref
lect
or (i
n co
ntac
t w
/flow
) per
mea
bilit
y;
tortu
osity
to
rtuo
sity
is n
ot d
irec
tly
usab
le
Low
N
eede
d fo
r firs
t prin
cipl
e tra
nspo
rt m
odel
ing
(IC
an
d Tr
ans)
. Req
uire
d to
de
term
ine
perm
eatio
n flo
w d
ue to
an
appl
ied ΔP
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te;
expe
cted
from
m
ater
ial P
IRT
Min
or m
od
17
FP tr
ansp
ort t
hrou
gh
refle
ctor
(in
cont
act
w/fl
ow)
Low
Ef
fect
ive
rele
ase
rate
co
effic
ient
(em
piric
al
cons
tant
) as a
n al
tern
ativ
e to
firs
t prin
cipl
es (I
C a
nd
Tran
s)
*Med
ium
D
epen
ds o
n sp
ecifi
c gr
aphi
te;
expe
cted
from
m
ater
ial P
IRT
Min
or m
od
Pa
rt B
(con
tinue
d)
B-43
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
18
So
rbtiv
ity o
f gr
aphi
te
(i.e.
, che
mis
orpt
ion
of
FPs i
n m
atri
x an
d gr
aphi
te)
Hig
h C
an d
eter
min
e af
fect
ho
ldup
and
rele
ase
of F
P (I
C a
nd T
rans
.)
Med
ium
H
isto
rical
dat
a;
need
spec
ific
info
rmat
ion
on
grap
hite
and
ra
diat
ion
effe
cts
Min
or m
od
19
Flue
nce
effe
ct o
n tra
nspo
rt in
gra
phite
H
igh
Influ
ence
s tra
nspo
rt;
chem
ical
reac
tivity
M
ediu
m
His
toric
al d
ata;
ne
ed sp
ecifi
c in
form
atio
n on
gr
aphi
te a
nd
radi
atio
n ef
fect
s
Maj
or n
eed
23
FP sp
ecia
tion
in
carb
onac
eous
mat
eria
l in
mat
rix
and
grap
hite
Hig
h C
hem
ical
form
in g
raph
ite
affe
cts t
rans
port
Low
U
ncer
tain
and
/or
inco
mpl
ete
Maj
or n
eed
26
Dus
t gen
erat
ion
in
mat
rix a
nd g
raph
ite b
y ab
rasi
on a
nd o
ther
m
echa
nism
s
Hig
h D
estin
atio
n fo
r FP
via
sorp
tion
Med
ium
So
me
data
for
pebb
le fu
els;
less
fo
r pris
mat
ic
Min
or m
od
102
Inte
rnal
surf
ace
area
of
mat
rix
and
grap
hite
M
ediu
m
Para
met
er a
ffect
s in
terp
reta
tion
of tr
ansp
ort
rate
Med
ium
W
ill b
e sp
ecifi
ed
and/
or m
easu
red
Min
or m
od
103
Inve
ntor
y of
FPs
in
mat
rix
and
grap
hite
H
igh
Initi
al c
ondi
tion
for
acci
dent
ass
essm
ent.
Med
ium
M
ay b
e es
timat
ed
from
pro
duct
ion,
tr
ansp
ort a
nd
sorp
tion
data
Min
or m
od
104
Impu
rity
leve
ls in
m
atri
x an
d gr
aphi
te
Low
Af
fect
s sor
ptio
n an
d ox
idat
ion
rate
s M
ediu
m
To b
e gi
ven
by te
ch
spec
s Ad
equa
te
105
Che
mic
al a
nd p
hysi
cal
inte
ract
ion
of F
Ps w
ith
grap
hite
Med
ium
Ai
ds u
nder
stan
ding
of
tran
spor
t Lo
w
Kno
wn
for s
ome
FPs;
not
kno
wn
for
man
y
Min
or m
od
B-44
Part
C:
Em
issi
on fr
om fu
el e
lem
ent s
urfa
ce
Issu
es:
● V
olat
ility
of F
P sp
ecie
s on
grap
hite
/mat
rix su
rfac
e
● M
ass t
rans
fer r
ate
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
24
FP sp
ecia
tion
durin
g m
ass
trans
fer
Hig
h C
hem
ical
cha
nge
can
alte
r vol
atili
ty
Med
ium
H
isto
rical
dat
a; n
eed
spec
ific
info
rmat
ion;
go
od fo
r met
als,
oxid
es;
unce
rtain
for c
arbi
des
and
carb
onyl
s
Maj
or n
eed
25
“Kno
ck-a
long
” Lo
w
Alp
ha re
coil
trans
port
of d
epos
ited
parti
cles
on
surf
aces
; slo
w
com
pare
d to
flui
d flo
w
trans
port
Med
ium
St
udie
d in
act
inid
e-be
arin
g pa
rticl
es
Ade
quat
e
106
Vola
tility
of F
Ps o
n gr
aphi
te a
nd m
atri
x su
rfac
es
Hig
h K
ey fa
ctor
in m
ass
tran
spor
t Lo
w
FP sp
ecie
s usu
ally
not
w
ell-k
now
n M
inor
mod
107
FP re
mov
al w
ith d
ust
Med
ium
U
neva
luat
ed tr
ansp
ort
step
Lo
w
No
know
n da
ta
Min
or m
od
108
Mas
s tra
nsfe
r rat
e fr
om
mat
rix
and
grap
hite
to
cool
ant
Hig
h D
efin
es g
raph
ite to
co
olan
t tra
nsfe
r rat
e M
ediu
m
May
be
estim
ated
, if F
P sp
ecie
s are
kno
wn
Min
or m
od
B-45
Part
D:
FP tr
ansp
ort i
n th
e co
olan
t, no
rmal
ope
ratio
n
Issu
es:
● FP
spec
iatio
n in
coo
lant
● O
xyge
n po
tent
ial
●
FP a
ssoc
iatio
n w
ith d
ust
●
Nuc
leat
ion
of lo
w v
olat
ile F
Ps
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kn
owle
dge
(Hig
h, M
ed, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
6
Gas
com
posi
tion
durin
g no
rmal
ope
ratio
n H
igh
Oxy
gen
pote
ntia
l and
ch
emic
al a
ctiv
ity. T
here
is
also
a n
eed
to k
now
the
He-
3 le
vel f
or a
sses
sing
H-3
pr
oduc
tion
in th
e co
olan
t.
Med
ium
Lo
w
Cen
tral i
ssue
for
chem
ical
reac
tion
mod
elin
g; F
P sp
ecia
tion;
scen
ario
de
pend
ent,
no
t kno
wn
for n
orm
al
oper
atio
n
Ade
quat
e (d
epre
ssur
izat
ion)
Maj
or n
eed
(air
ingr
ess)
27
(De)
Abs
orpt
ion
on d
ust
Adso
rptio
n H
igh
Prov
ides
cop
ious
surf
ace
area
fo
r FP
abso
rptio
n ad
sorp
tion
Med
ium
Lo
w
Lim
ited
expe
rienc
e;
lack
spec
ific
deta
ils;
little
or n
o da
ta
Maj
or n
eed
28
H-3
gen
erat
ion
in th
e co
olan
t and
circ
ulat
ing
cool
ant i
nven
tory
Med
ium
H
igh
Cri
tical
issu
e fo
r pro
cess
he
at v
ersi
ons;
radi
oiso
tope
, an
issu
e w
ith o
pera
tiona
l re
leas
e; H
-3 p
rodu
ctio
n fr
om
He-
3 in
coo
lant
; (al
so te
rnar
y fis
sion
, and
Li-6
in g
raph
ite)
Med
ium
H
isto
rical
dat
a; P
each
B
otto
m H
TGR
; may
be
det
erm
ined
from
ne
utro
n flu
x an
d H
e-3
leve
l
Min
or m
od
31
Nuc
leat
ion
M
ediu
m
Unc
lear
due
to e
xtre
mel
y lo
w
FP v
apor
con
cent
ratio
n an
ticip
ated
. An
impo
rtan
t fa
ctor
in d
epos
ition
and
lifto
ff
Med
ium
H
isto
rical
dat
a U
ncle
ar d
ue to
ex
trem
ely
low
FP
vapo
r con
cent
ratio
n
Maj
or n
eed
32
Aer
osol
gro
wth
H
igh
Low
con
cent
ratio
n gr
owth
ca
n le
ad to
hig
h sh
ape
fact
ors
and
unus
ual s
ize
dist
ribut
ion
Low
R
egim
e ha
s not
bee
n st
udie
d pr
evio
usly
M
ajor
nee
d
55
Arg
on a
ctiv
atio
n in
re
acto
r cav
ity
Hig
h (n
orm
al
oper
atio
n)
Air
in c
avity
act
ivat
ed b
y ne
utro
n le
akag
e an
d ca
n es
cape
to e
nviro
nmen
t
Hig
h Ea
sily
com
pute
d w
ith
exis
ting
tool
s A
dequ
ate
Pa
rt D
(con
tinue
d)
B-46
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kn
owle
dge
(Hig
h, M
ed, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
11
0 FP
spec
iatio
n in
the
cool
ant
Hig
h Af
fect
s dep
ositi
on a
nd
sorp
tion
Med
ium
C
an b
e ap
prox
imat
ed
if co
nditi
ons a
re
spec
ified
Min
or m
od
111
Ag-1
10m
and
Cs-
137
tran
spor
t in
the
cool
ant
Hig
h Im
port
ant s
peci
al c
ases
of
item
110
Lo
w
Dep
ends
on
cool
ant
envi
ronm
ent
Maj
or n
eed
120
FP in
vent
ory
in th
e co
olan
t cle
anup
syst
em
Med
ium
Sh
ould
be
eval
uate
d fo
r po
ssib
le in
volv
emen
t in
acci
dent
rele
ases
Low
N
ot y
et a
naly
zed
Min
or m
od
B-47
Part
E:
Dep
ositi
on so
rptio
n on
pri
mar
y sy
stem
surf
aces
—no
rmal
ope
ratio
n
Issu
es:
● A
eros
ol a
nd d
ust d
epos
ition
● C
hem
isor
ptio
n on
met
allic
surf
aces
● C
hem
ical
reac
tion
with
surf
aces
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
9
FP p
late
-out
and
dus
t di
strib
utio
n un
der n
orm
al
oper
atio
n.
FP p
late
-out
is a
n am
bigu
ous
term
that
can
app
ly to
eith
er
chem
ical
ads
orpt
ion
or d
ust
depo
sitio
n; it
shou
ld b
e av
oide
d
Hig
h In
itial
con
ditio
n fo
r ac
cide
nt
Med
ium
Lo
w
Theo
ry a
nd m
odel
s la
ck sp
ecifi
cs;
enor
mou
s err
or b
ands
in
dus
t dep
ositi
on d
ata;
di
sagr
eem
ents
in
pred
ictiv
e m
odel
s
Maj
or n
eed
34
Coo
lant
che
mic
al in
tera
ctio
n w
/ sur
face
s H
igh
Cha
nges
oxy
gen
and
carb
on p
oten
tial w
hich
ca
n af
fect
nat
ure
and
quan
tity
of so
rbed
sp
ecie
s (IC
and
Tra
ns.)
Affe
cts d
epos
ition
and
lif
toff
pred
ictio
ns;
affe
cts
deco
ntam
inat
ion
met
hods
Med
ium
Su
rfac
e pr
oper
ties a
re
criti
cal;
need
allo
y da
ta; i
nter
actio
ns
depe
nd o
n co
olan
t ox
ygen
pot
entia
l, an
d co
olan
t im
puri
ties
Maj
or N
eed
35
FP d
iffus
ivity
, sor
btiv
ity in
no
ngra
phite
surf
aces
; ch
emic
al so
rptiv
ity sh
ould
be
emph
asiz
ed
Hig
h D
eter
min
es A
ffect
s FP
loca
tion
durin
g op
erat
ion;
act
s as a
tra
p du
ring
trans
ient
(I
C a
nd T
rans
.)
Low
Li
ttle
info
rmat
ion
on
mat
eria
ls o
f int
eres
t; af
fect
s of r
adia
tion
on
sorp
tivity
are
si
gnifi
cant
and
in
suffi
cien
tly k
now
n
Maj
or N
eed
36
Aer
osol
/dus
t dep
ositi
on
(Clo
sely
rela
ted
to it
em 9
) H
igh
Gra
vita
tiona
l, in
ertia
l, th
erm
opho
resi
s, el
ectro
stat
ic,
diff
usio
nal,
turb
opho
resi
s (Tr
ans.)
Med
ium
R
easo
nabl
y w
ell-
deve
lope
d th
eory
of
aero
sol d
epos
ition
by
mos
t mec
hani
sms
exce
pt in
ertia
l im
pact
Min
or m
od
Pa
rt E
(con
tinue
d)
B-48
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
N
o gr
avita
tiona
l se
ttlin
g in
the
prim
ary
syst
em; t
urbo
phor
esis
is
a n
ew o
ne o
n m
e
in c
ompl
ex g
eom
etrie
s;
Enor
mou
s err
or b
ands
fo
r pri
mar
y lo
op
cond
ition
s;
“rea
sona
bly
wel
l-de
velo
ped”
may
refe
r to
con
finem
ent
App
licab
ility
to N
GN
P un
clea
r 37
A
eros
ol/d
ust b
ounc
e, b
reak
up
durin
g de
posi
tion
Det
ails
subs
umed
in
depo
sitio
n co
rrel
atio
n.
Med
ium
C
an m
odify
dep
ositi
on
prof
ile a
nd su
spen
ded
aero
sol d
istri
butio
n
Low
Th
eory
, dat
a, a
nd
mod
els l
acki
ng
Maj
or N
eed
40
Dus
t dep
ositi
on o
n ve
ssel
and
R
CC
S ha
rdw
are
Low
N
ot im
porta
nt fo
r FP
trans
port
but m
ay
affe
ct ra
diat
ive
heat
tra
nsfe
r in
reac
tor
cavi
ty
Low
V
ery
limite
d da
ta
Maj
or n
eed
41
Cor
rosi
on p
rodu
cts
Low
Sp
alle
d su
rfac
e fil
ms;
lo
w c
orro
sion
en
viro
nmen
t (IC
and
Tr
ans.)
Hig
h Pa
st e
xper
ienc
e A
dequ
ate
42
Eros
ion
prod
ucts
, non
carb
on
Low
Lo
w c
once
ntra
tion
of
coar
se m
ater
ials
(IC
an
d Tr
ans.)
Low
La
ck o
f des
ign
info
rmat
ion;
co
nfig
urat
ion
and
mat
eria
ls sp
ecifi
c
Ade
quat
e
113
Sorp
tion
and
dust
dep
ositi
on
on tu
rbin
e su
rfac
es
Hig
h Im
port
ant s
peci
al
case
; affe
cts t
urbi
ne
life
and
mai
nten
ance
pr
oced
ures
; spe
cial
ca
se o
f dep
ositi
on a
nd
sorp
tion
Low
Ex
trem
e co
nditi
ons;
be
yond
usu
al
corr
elat
ions
Maj
or n
eed
B-49
Part
F:
Rel
ease
s fro
m th
e pr
imar
y sy
stem
—no
rmal
ope
ratio
n
Issu
es:
● R
elea
se m
odes
(lea
kage
, ref
uelin
g)
●
Diff
usio
n in
to th
e IH
X
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
11
5 D
iffus
ion
of H
-3 th
roug
h th
e IH
X
Hig
h Im
port
ant f
or p
roce
ss
heat
con
cept
s M
ediu
m
Som
e da
ta o
n ot
her
met
als;
nee
d to
im
prov
e er
ror b
and
Min
or m
od
116
Prod
uct c
onta
min
atio
n, o
ther
th
an H
-3
Hig
h Im
port
ant f
or p
roce
ss
heat
con
cept
s M
ediu
m
Une
xplo
red
area
; ef
fect
of s
mal
l lea
ks
in th
e IH
X
Min
or m
od
117
Con
tam
inat
ion
of th
e H
e co
olan
t by
the
seco
ndar
y flu
id
Hig
h Po
ssib
le e
ffect
on
the
reac
tor;
inve
stm
ent
ques
tion
Med
ium
U
nexp
lore
d ar
ea;
effe
ct o
f sm
all l
eaks
in
the
IHX
Min
or m
od
118
He
(con
tain
ing
FPs)
leak
age
into
the
seco
ndar
y sy
stem
M
ediu
m
Doe
s not
app
ear t
o be
a
seri
ous i
ssue
M
ediu
m
Une
xplo
red
area
M
inor
mod
119
He
(con
tain
ing
FPs)
leak
age
into
the
conf
inem
ent
Med
ium
Le
akag
e m
odes
und
er
norm
al o
pera
tion
shou
ld b
e id
entif
ied
Med
ium
U
nexp
lore
d ar
ea (?
) M
inor
mod
B-50
Part
G:
Fact
ors a
ffec
ting
rele
ases
from
the
prim
ary
syst
em—
acci
dent
con
ditio
ns
G.1
Gen
eral
issu
es a
nd p
ower
ver
sion
G
.2 P
roce
ss h
eat v
ersi
on
Is
sues
: ●
Rel
ease
s due
to D
-LO
FC
●
Rel
ease
s due
to P
-LO
FC w
ith v
entin
g
Part
G.1
—G
ener
al is
sues
and
pow
er c
onve
rsio
n
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
7
Gas
flow
pat
h pr
ior,
durin
g an
d po
st a
ccid
ent (
also
ap
plie
s to
Part
F)
Hig
h In
form
atio
n ne
eded
to
mod
el a
ccid
ent (
IC a
nd
Tran
s)
*Sam
e as
TF
grou
p N
eed
to c
oord
inat
e w
/ ot
her g
roup
s; e
xpec
ted
from
TF
PIR
T
Sam
e as
TF
grou
p
21
Air
atta
ck o
n gr
aphi
te a
nd it
s af
fect
on
FP re
leas
e H
igh
Gra
phite
ero
sion
/ ox
idat
ion;
Fe/
Cs
cata
lysi
s lib
erat
ing
FPs
(Tra
ns)
Med
ium
Lo
w
His
toric
al d
ata
Ther
e ar
e no
dat
a on
th
e ef
fect
of a
ir
oxid
atio
n on
rete
ntio
n of
FPs
in g
raph
ite
Maj
or n
eed
for
seve
re a
ccid
ents
22
Stea
m a
ttack
on
grap
hite
and
its
affe
ct o
n FP
rele
ase
Hig
h G
raph
ite e
rosi
on a
nd
oxid
atio
n; F
e/C
s ca
taly
sis l
iber
atin
g FP
s (tr
ans)
Med
ium
Lo
w
His
toric
al d
ata
Ther
e ar
e no
dat
a on
th
e ef
fect
of a
ir
oxid
atio
n on
rete
ntio
n of
FPs
in g
raph
ite
Maj
or n
eed
for
seve
re a
ccid
ents
43
Was
hoff
H
igh
If c
redi
ble
sour
ce o
f w
ater
is p
rese
nt; d
esig
n de
pend
ent
Med
ium
So
me
expe
rimen
tal
data
ava
ilabl
e M
inor
mod
44
Failu
re m
odes
of a
uxili
ary
syst
ems (
e.g.
, gas
cle
anup
, ho
ldup
, ref
uelin
g) a
nd F
P re
leas
e fr
om th
e ga
s cle
anup
sy
stem
Med
ium
H
igh
Pote
ntia
l rel
ease
due
to
failu
re; p
ossi
ble
dire
ct
path
to th
e at
mos
pher
e fr
om g
as c
lean
up
syst
em fa
ilure
(Tra
ns.)
Med
ium
D
esig
n sp
ecifi
c; h
ave
expe
rienc
e fr
om o
ther
de
sign
s but
no
expe
rienc
e fo
r gas
cl
eanu
p sy
stem
failu
re
Min
or m
od
Pa
rt G
(con
tinue
d)
B-51
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
52
Pr
essu
re re
lief v
alve
filte
r Lo
w
Ope
ning
of t
he re
lief
valv
e ge
nera
tes a
tra
nspo
rt pa
th th
at m
ay
be fi
ltere
d; d
epen
ds o
n de
sign
Hig
h A
ir cl
eani
ng
tech
nolo
gy
Ade
quat
e
47
Prod
uctio
n/co
mbu
stio
n of
fla
mm
able
gas
M
ediu
m
Hig
h C
O, H
2 pro
duct
ion
issu
es; I
HX
seco
ndar
y-pr
imar
y le
ak; p
oten
tial
resu
spen
sion
and
ch
emic
al tr
ansf
orm
atio
n of
FPs
. (Tr
ans.)
dur
ing
air i
ngre
ss e
vent
Hig
h M
ediu
m
His
toric
al e
xper
ienc
e;
inad
equa
te d
ata
on
CO
, H2,
CO
2 pr
oduc
tion
durin
g ai
r in
gres
s
Ade
quat
e
56
Red
istri
butio
n of
fiss
ion
prod
ucts
due
to c
ontro
l rod
m
ovem
ent
Low
A
rticu
late
d co
ntro
l rod
jo
ints
can
col
lect
and
re
dist
ribut
e fis
sion
pr
oduc
ts
Low
Sp
ecifi
cs o
n C
RD
ho
usin
g an
d ar
ticul
ated
SiC
co
mpo
site
hou
sing
TB
D
Min
or m
od
112
Che
mic
al d
esor
ptio
n fr
om
met
al su
rfac
es u
nder
ac
cide
nt c
ondi
tions
, due
to
depr
essu
riza
tion
and/
or
heat
up
Hig
h Im
port
ant r
elea
se
sour
ce
Low
Re
quir
e hi
gh
tem
pera
ture
dat
a an
d da
ta u
nder
acc
iden
t en
viro
nmen
ts
Maj
or n
eed
114
Che
mic
al d
esor
ptio
n of
FPs
un
der a
ccid
ent c
ondi
tions
fr
om g
raph
ite a
nd m
atri
x (P
BMR)
, due
to v
entin
g an
d he
atup
Hig
h D
esor
ptio
n fr
om
grap
hite
or m
atri
x (P
BMR)
may
be
sign
ifica
nt in
put t
o so
urce
term
Low
Af
fect
s of i
mpo
sitio
n of
acc
iden
t con
ditio
ns
on g
raph
ite u
nkno
wn
Min
or m
od.
109
Gas
com
posi
tion
duri
ng
acci
dent
s H
igh
Intr
usio
n of
O2 a
nd N
2 du
ring
D-L
OFC
and
C
O a
nd C
O2 g
ener
atio
n af
fect
s spe
ciat
ion,
gas
pr
oper
ties,
and
prod
uctio
n of
flam
mab
le
gase
s
Low
Re
quir
es in
put f
rom
ac
cide
nt fl
ow a
naly
sis
Maj
or n
eed
Pa
rt G
(con
tinue
d)
B-52
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
12
1 D
ust a
nd a
eros
ol li
ftoff
from
m
etal
surf
aces
due
to
depr
essu
riza
tion
flow
s and
vi
brat
ion
Hig
h Im
port
ant s
ourc
e of
re
leas
e Lo
w
1. A
ffect
of v
ibra
tion
unkn
own
2. L
iftof
f cor
rela
tions
fo
r de
pres
suri
zatio
n flo
ws u
ncer
tain
3.
Affe
ct o
f rel
ief
valv
e ve
ntin
g sh
ould
be
exam
ined
Maj
or n
eed
122
Affe
ct o
f air
ingr
ess o
n de
sorp
tion
from
met
al
surf
aces
Hig
h Im
port
ant f
or a
ir
ingr
ess c
ase
Low
Fe
w d
ata
Min
or m
od
125
Affe
ct o
f air
ingr
ess o
n co
olan
t pro
pert
ies
Hig
h La
rge
chan
ge p
ossi
ble
in v
isco
sity
and
ther
mal
di
ffusi
vity
; affe
cts R
e an
d Pr
mod
uli a
nd
ther
efor
e he
at a
nd m
ass
tran
sfer
coe
ffici
ent.
Med
ium
Th
eory
on
affe
ct o
f C
O, C
O2,
O2,
N2 o
n vi
scos
ity a
nd th
erm
al
diffu
sivi
ty o
f He
is n
ot
wel
l est
ablis
hed
Maj
or m
od
126
Spal
latio
n fr
om m
etal
su
rfac
es d
urin
g ac
cide
nts
Med
ium
Po
ssib
le so
urce
of d
ust
on w
hich
FPs
may
ad
sorb
Low
N
o da
ta fo
r acc
iden
t co
nditi
ons a
nd
rele
vant
mat
eria
ls
Min
or m
od
Pa
rt G
(con
tinue
d)
B-53
Part
G.2
—Pr
oces
s hea
t ver
sion
ID N
o.
Phen
omen
a Im
port
ance
(H
igh,
Med
ium
, Low
) R
atio
nale
L
evel
of k
now
ledg
e (H
igh,
Med
ium
, Low
) R
atio
nale
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
12
7 IH
X fa
ilure
mod
es u
nder
D
-LO
FC o
r exc
essi
ve
acci
dent
tem
pera
ture
s
Hig
h [R
equi
res i
nput
from
the
Proc
ess H
eat o
r Hig
h Te
mpe
ratu
re M
ater
ials
Pa
nel]
[Low
] N
ot y
et st
udie
d
128
Affe
cts o
f sec
onda
ry fl
uid
on th
e re
leas
e of
FPs
from
m
etal
and
gra
phite
su
rfac
es
Hig
h Af
fect
s FP
rele
ase
Low
N
ot y
et st
udie
d M
ajor
mod
129
FP c
onta
min
atio
n of
the
seco
ndar
y sy
stem
due
to
IHX
failu
re
Hig
h Im
port
ant c
onsi
dera
tion
for p
roce
ss h
eat
conc
epts
Low
N
ot y
et st
udie
d M
ajor
mod
130
Af
fect
of I
HX
failu
re o
n th
e re
acto
r sys
tem
, che
mic
al
effe
cts
Hig
h In
vest
men
t ris
k co
nsid
erat
ion
Low
N
ot y
et st
udie
d M
ajor
mod
B-54
Part
H:
Rel
ease
s fro
m th
e co
nfin
emen
t
Issu
es:
● Ph
ysic
al/c
hem
ical
aff
ects
of a
ccid
ents
on
conf
inem
ent
●
Leak
age
rate
● Po
ssib
le fi
ltrat
ion
or c
lean
up sy
stem
ID
No.
Ph
enom
ena
Impo
rtan
ce
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Lev
el o
f kno
wle
dge
(Hig
h, M
ediu
m, L
ow)
Rat
iona
le
Stat
us o
f FP
mod
elin
g (a
dequ
ate,
min
or
mod
, maj
or n
eed)
39
C
onfin
emen
t aer
osol
ph
ysic
s dy
nam
ics (
i.e.,
aggl
omer
atio
n an
d de
posi
tion)
Hig
h A
nalo
gous
to L
WR
aer
osol
be
havi
or/p
hysi
cs, d
elta
-T,
chem
istry
; im
porta
nt h
oldu
p m
echa
nism
Med
ium
R
easo
nabl
e w
ell-
deve
lope
d th
eory
of
aero
sol b
ehav
ior;
appl
icab
ility
to N
GN
P un
clea
r
Min
or m
od
45
Rad
ioly
sis e
ffec
ts in
co
nfin
emen
t H
igh
FP (e
.g.,
I, R
u, T
e) c
hem
istry
, pa
int c
hem
istry
(dep
ende
nt
on c
onfin
emen
t rad
iatio
n le
vel)
(Tra
ns.)
Med
ium
LW
R e
xper
ienc
e an
d da
ta
Min
or m
od
46
Filtr
atio
n H
igh
Trad
ition
al p
assi
ve
char
coal
/HEP
A (T
rans
.) H
igh
His
toric
al e
xper
ienc
e A
dequ
ate
48
Com
bust
ion
of g
raph
ite
dust
in c
onfin
emen
t H
igh
Sour
ce o
f hea
t and
di
strib
utio
n of
FPs
w/in
co
nfin
emen
t
Med
ium
IT
ER d
ata
Maj
or n
eed
49
NG
NP-
uniq
ue le
akag
e pa
th b
eyon
d co
nfin
emen
t
Hig
h IH
X to
seco
ndar
y si
te
cont
amin
atio
n; c
ould
be
risk
dom
inan
t (Tr
ans.)
Hig
h Lo
w
Con
tinge
nt o
n sp
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sign
kno
wle
dge
Min
or m
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50
Con
finem
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path
, rel
ease
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th
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tions
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able
/pip
e pe
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, cr
acks
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VA
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.) M
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perie
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des
ign
spec
ific
Ade
quat
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51
Cab
le p
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, fire
H
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Soot
gen
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and
chan
ges
to io
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mis
try
Med
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LW
R e
xper
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e M
ajor
nee
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132
FP sp
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in th
e co
nfin
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t H
igh
Affe
cts d
epos
ition
rate
M
ediu
m
Unc
erta
in k
inet
ics a
t lo
w te
mpe
ratu
re
Min
or m
od
133
Che
mic
al in
tera
ctio
n of
FP
s with
con
finem
ent
surf
aces
Hig
h Af
fect
s FP
atte
nuat
ion
by
conf
inem
ent
Med
ium
U
ncer
tain
kin
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s at
low
tem
pera
ture
M
inor
mod
Pa
rt H
(con
tinue
d)
B-55
ID
No.
Ph
enom
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Impo
rtan
ce
(Hig
h, M
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m, L
ow)
Rat
iona
le
Lev
el o
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(Hig
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ediu
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ow)
Rat
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Stat
us o
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elin
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dequ
ate,
min
or
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, maj
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13
4 Fl
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gas
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into
the
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and
poss
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sequ
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M
ajor
nee
d
B-56
Page intentionally blank
NUREG/CR-6944, Vol. 3 ORNL/TM-2007/147, Vol. 3
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