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Hindawi Publishing CorporationScience and Technology of Nuclear InstallationsVolume 2012, Article ID 812130, 15 pagesdoi:10.1155/2012/812130

Research Article

Advanced Presentation of BETHSY 6.2TC Test ResultsCalculated by RELAP5 and TRACE

Andrej Prosek and Ovidiu-Adrian Berar

Reactor Engineering Division, Jozef Stefan Institute, Jamova Cesta 39, SI-1000 Ljubljana, Slovenia

Correspondence should be addressed to Andrej Prosek, [email protected]

Received 16 December 2011; Revised 23 March 2012; Accepted 10 April 2012

Academic Editor: Stephen M. Bajorek

Copyright © 2012 A. Prosek and O.-A. Berar. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

Today most software applications come with a graphical user interface, including U.S. Nuclear Regulatory CommissionTRAC/RELAP Advanced Computational Engine (TRACE) best-estimate reactor system code. The graphical user interface is calledSymbolic Nuclear Analysis Package (SNAP). The purpose of the present study was to assess the TRACE computer code and toassess the SNAP capabilities for input deck preparation and advanced presentation of the results. BETHSY 6.2 TC test was selected,which is 15.24 cm equivalent diameter horizontal cold leg break. For calculations the TRACE V5.0 Patch 1 and RELAP5/MOD3.3Patch 4 were used. The RELAP5 legacy input deck was converted to TRACE input deck using SNAP. The RELAP5 and TRACEcomparison to experimental data showed that TRACE results are as good as or better than the RELAP5 calculated results. Thedeveloped animation masks were of great help in comparison of results and investigating the calculated physical phenomena andprocesses.

1. Introduction

The TRAC/RELAP Advanced Computational Engine(TRACE) is the latest in a series of advanced best-estimatereactor systems codes developed by the US NuclearRegulatory Commission (US NRC) [1]. The advancedTRACE computer code comes with a graphical user interface(GUI) called SNAP (Symbolic Nuclear Analysis Package)[2], which is intended for pre- and postprocessing, runningthe codes, RELAP5 to TRACE input deck conversion, inputdeck database generation, and so forth. Also other advancedthermal-hydraulic codes, for example RELAP5-3D [3] andMARS come with GUI [4]. According to [4] MARS has asimple GUI, which is provided for program execution andto display the calculation results online. On the other hand,RELAP5-3D can also use SNAP as GUI.

The advanced TRACE computer code is still underdevelopment and it will have all capabilities of RELAP5 [5].Although the TRACE computer code is the future of USNRC, its use in countries members of Code Applicationsand Maintenance Program (CAMP) it is still not dominantagainst the RELAP5 computer code. Nevertheless, TRACE

is now more and more used [6–8], also by RELAP5 users,because of better RELAP5 to TRACE conversion capabil-ity using SNAP as reported on CAMP meetings [9–11].However, not much information is available in the openliterature on RELAP5 to TRACE conversion. In general,the typical RELAP5 users start with RELAP5 legacy inputdeck, which is first automatically converted to TRACEinput decks using SNAP and then manual corrections aredone. Namely, much of efforts were done in the pastto develop the RELAP5 input decks. The purpose of thepresent study was therefore to show advances in safetyanalysis using SNAP regarding input deck preparation andgraphical presentation of the results (including animations)comparing to traditional ASCII editing the input modeland extracting the calculated data from restart-plot files forgraphical comparison. Such tools finally contribute to betterassessment of the advanced TRACE code. In the paper theTRACE assessment against BETHSY 6.2TC test is presented.TRACE input model is converted and adapted RELAP5 inputmodel, which was developed in the past for internationalstandard problem no. 27 (ISP-27) at Institut “Jozef Stefan”(IJS) [12]. The RELAP5 legacy input deck developed at IJS is

2 Science and Technology of Nuclear Installations

different than the one which has been used for conversionto TRACE in the original TRACE code assessment study[13]. In the TRACE code assessment study [13] it wasconcluded that the timing of core heatup is of a concernfor the BETHSY 6.2TC test. This motivated the authors tomake their own TRACE calculation of the BETHSY 6.2TCtest, besides the fact that RELAP5 and TRACE results canbe directly compared too. When comparing results of twodifferent codes with the experimental data it can be moreeasily judged, if the differences between the calculation andmeasured data are due to the code, or other reasons (e.g.,nodalization). When comparing our TRACE calculation tothe RELAP5 calculation and to TRACE calculation describedin the code assessment manual [13], one can more easilysee the peculiarities of the TRACE code. Finally, RELAP5and TRACE calculations were compared between each otherusing animation masks, which presents advanced analysistechnique. Finally, the procedure for conversion input deckfrom RELAP5 to TRACE is presented, which is practically notavailable in the open literature.

2. Methodology Description

The selected BETHSY 6.2TC test was 15.24 cm (6 inch)equivalent diameter horizontal cold leg break in the referencepressurized water reactor without high pressure and lowpressure safety injection. The transient ended at 2179 s whenprimary pressure dropped below 0.7 MPa. BETHSY facilitywas a 3-loop replica of a 900 MWe Framatome pressurizedwater reactor. For calculations the RELAP5/MOD3.3 Patch 4[14] and TRACE V5.0 Patch 1 computer codes were used [1].The TRACE input model was obtained by conversion fromRELAP5 input model using SNAP and manual correctionsand additions. For better presentation of the calculatedphysical phenomena and processes, animation models usingSNAP were developed for displaying results obtained byRELAP5 and TRACE.

In the following subsections the BETHSY facility and testscenario are described first. Then the RELAP5 and TRACEinput models are described. At the end, the RELAP5 andTRACE computer codes and SNAP tool are described briefly.

2.1. Description of BETHSY Integral Test Facility. BETHSYwas an integral test facility, which was designed to sim-ulate most pressurized water reactor accidents of interest,study accident management procedures and validate thecomputer codes. It was a scaled down model of three-loopFramatome (now AREVA NC) nuclear power plant withthe thermal power 2775 MW (see Figure 1). Volume, massflow and power were scaled to 1 : 96.9, while the elevationsand the pressures of the primary and secondary systemwere preserved [15]. The core power has been limited toapproximately 10% of nominal value, that is, 3 MW. Thismeans that the power was limited to the decay heat level andthe transients without reactor trip could not be simulated.The design pressure on the primary side was 17.2 MPa andon the secondary side 8 MPa. There were 428 electricallyheated rods, which could reach 1273 K. Like in the reference

reactor, the BETHSY facility had three identical loops, eachequipped with a main coolant pump and an active steamgenerator (see Figure 1). Every primary- and secondary-side-engineered safety system was simulated. This includedhigh and low pressure safety injection systems, accumulators(one per loop), pressurizer spray and relief circuits, auxiliaryfeedwater system, and steam dumps to the atmosphere andto the condenser.

The break system enabled simulation of the break indifferent locations, that is, in cold leg, lower plenum,pressurizer, steam generator U tubes and feedwater pipe. Theinstrumentation data system measured all data needed forthe transient analysis. The control system could simulate theplant control systems and operator actions.

2.2. BETHSY 6.2TC Test Description. BETHSY 6.2TC testwas a 15.24 cm (6 inch) cold leg break in the loop no.1 without available high pressure and low pressure safetyinjection system [6]. This test is a counterpart test of LSTFSB-CL-21 [16]. To duplicate test as closely as possible, theBETHSY upper head/downcomer bypass was modified totake account of LSTF (0.28% of the total flow in the threeloops at LSTF nominal conditions). The pressurizer wasconnected to the broken loop. The sprays and heaters werenot used. The core power was maintained at a constantlevel in the period from break opening time till the timeof scram plus 8 s. Then the core power followed the LSTFcurve. Primary circuit charging and letdown system were notused. Accumulators were available in the intact loops. Untilthe scram the secondary pressure was maintained constantat approximately 6.8 MPa. After scram signal, the condenserwas isolated and the atmospheric relief valves were used tocontrol pressure at 7.2 MPa. The main feedwater supply wasalso stopped at scram signal, while the auxiliary feedwatersystem was assumed not operable.

The main aims of BETHSY 6.2TC test were to comparethe counterpart test data from BETHSY and LSTF facilitiesand qualification of CATHARE 2 computer code. Theexperiment started with the opening of the valve simulatingthe break in the cold leg no. 1 at the time 0 s. Sudden primarypressure drop caused scram signal when pressure was below13.0 MPa and safety injection (SI) signal was generated, whenprimary pressure was below 11.7 MPa. At scram signal allthree primary pumps were stopped and natural circulationregime took over the primary system. The hot parts of theprimary circuit (upper head, upper plenum, SG U-tubes)started to boil. The formation of loop seal caused the corelevel depression. The drop in the core-collapsed liquid levelwas stopped at 134 s by loop seal clearance on the threeloops. The loop seal clearance occurred at the same timeon all three loops. After loop seal clearance the core liquidlevel rose again due to pressure balances and then started todrop again due to inventory loss through the break. Whenprimary pressure dropped below 4.2 MPa, the accumulatorinjection started, which recovered the core. The accumulatorinjection was stopped on the basis of low level criterion.After it stopped, in the absence of high pressure injection,the primary circuit emptied through the break and third

Science and Technology of Nuclear Installations 3

Main steam line with reliefand safety valves

SG3 SG2 Auxiliaryspray

Spray SG1

Condenser

Main feedwater

Auxiliaryfeedwater

Break system

P1

Pressure vessel

P2P3

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Safety injection

Accumulators

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ssu

rize

r

Figure 1: BETHSY schematic diagram.

core uncovery occurred. The low pressure injection wasnot activated by assumption. The test was ended when theprimary pressure dropped below 0.7 MPa.

2.3. RELAP5 Input Model Description. The base RELAP5/MOD3.3 Patch 4 input model of BETHSY has been devel-oped first, which is described in detail in [17]. In thefollowing brief description is given. The RELAP5/MOD2input model was developed, when participating to ISP-27.This base RELAP5/MOD2 input model was later upgradedto RELAP5/MOD3.1 and RELAP5/MOD3.1.2 and RELAP5/MOD3.2 models [12]. The RELAP5/MOD3.2 input modelwas developed for all available BETHSY tests consistingfrom 398 volumes, 408 junctions, and 402 heat structures[18, 19]. This model was in 2010 adapted for the use with theRELAP5/MOD3.3 computer code. No changes were made tothe geometry and the number of hydrodynamic componentsand heat structures. From the RELAP5/MOD3.3 ASCII inputmodel the hydrodynamic view was generated by SNAP,requiring also manual editing in SNAP Model Editor. TheSNAP hydrodynamic components view of RELAP5/MOD3.3input model for BETHSY 6.2TC transient is shown inFigure 2. The artificial pressurizer pressure and level controlneeded for steady-state calculation are switched off duringtransient calculation. There are 151 hydraulic componentsand 72 heat structures.

2.4. TRACE Input Model Description. The TRACE inputmodel was converted from RELAP5/MOD3.3 input model.For conversion the SNAP was used. The SNAP conversion

to TRACE mostly preserved the RELAP5 numbering ofcomponents (see [1] and compare Figures 2 and 3). Theconverted TRACE input model consisted of 172 hydrauliccomponents and 72 heat structures and was not running.Several manual corrections and adaptations of componentswere needed. The final view of adapted TRACE input modelfor transient calculation is shown in Figure 3. It consistsof 160 hydraulic components, while the number of heatstructures was preserved.

All converted hydraulic diameters were replaced manu-ally with the hydraulic diameters obtained from the RELAP5/MOD3.3 output file. The nitrogen vessel represented by anAccumulator component in the RELAP5 input model wasautomatically converted to Liquid separator type insteadof Accumulator type of Pipe component. It was thenmanually changed to Accumulator type of pipe. SNAP 1.2.6conversion tool failed short in the respect of convertingthe wall-roughness for some hydraulic components fromRELAP5 to TRACE. The data for the wall-roughness for thesecomponents were therefore manually added to the TRACEinput model. Problems were also found with Separatorcomponent—RELAP5 liquid carryover and carryunder valuewere converted to minimum and maximum barrel voidfraction, while to liquid carryover and carryunder othervalues were assigned.

For TRACE input model the calculated area of adjacentvolumes are also compared in SNAP. If the volumes differby more than a user-modifiable ratio, the volumes aredetermined to involve an area change. An error is reportedif the intervening edge between the two volumes does not


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Figure 3: SNAP hydrodynamic components view for TRACE transient input model of BETHSY 6.2TC test.


Table 1: Comparison of initial conditions for BETHSY 6.2TC test.

Parameter Measured RELAP5 TRACE

Core thermal power (kW) 2863± 30 2864 2860

Pressurizer pressure (MPa) 15.38± 0.15 15.38 15.38

Pressurizer level (m) 7.45± 0.2 7.45 7.45

Total flow (kg/s) 16.81 (calculated from core power) 16.84 16.61

Core inlet temperature (K) 557.2± 0.4 557.2 557.2

Core outlet temperature (K) 588.2± 0.4 588.1 588.8

Reactor coolant system mass (kg) 1984± 50 1948 1948

Secondary side pressure per SG (MPa) 6.84± 0.07 6.83 6.69

Steam generator level per SG (m) 11.1± 0.05 11.1 11.1

Feedwater temperature (K) 523.2± 4 523.2 523.2

Heat loss (kW) 54.82 N.A. N.A.

Downcomer to upper head flow (kg/s) 0.047 0.047 0.047

have either friction defined, or the abrupt area changemodel enabled. Solution was to input very small values ofloss coefficients. This was needed for areas of componentsconverted from the RELAP5 servo valves and accumulators.

Several important side junctions resulting from RELAP5Branch components converted to TRACE Pipe componentswere renodalized using Tee components (e.g., break, accu-mulator injection point, steam generator dome). Thesespecific adaptations were important for the calculationresults. The break modeled by originally converted sidejunction produced different results in the steady state ofBETHSY 9.1b test [20]. Similar was true for the accumulatorinjection. In the case of RELAP5 time-dependent junctionsconverted to TRACE Pump (type mass flow controlled singlejunctions) such adaptations were not needed. Nevertheless,such pump components were replaced by Fill components.Each Fill component replaces one volume and one junc-tion component, what reduced the number of hydrauliccomponents. Also, much of adaptation was needed forheat structures. In the RELAP5 input model the source ofheating was realized by control variables. Therefore, in theconverted TRACE input model several power componentswere generated. Unfortunately, by power components onlythe positive power can be modeled, while to model heatlosses the heat structures should be powered by negativepower. Therefore heat fluxes were assigned to the outersurfaces (the desired power divided by heat structure outersurface area), while power components were deleted allexcept the one representing the core heating.

Finally, it should be noted that TRACE has the capabilityto model and analyze three-dimensional components suchas a reactor vessel. However, for this assessment the TRACEinput model which was converted by SNAP from theRELAP5 input model using one-dimensional components.Namely, SNAP does not have the capability to convert one-dimensional reactor vessel model into three-dimensionalreactor vessel model. This has to be done manually.

2.5. Description of Computer Codes. The basic RELAP5thermal-hydraulic model uses six equations: two mass

conservation equations, two momentum conservation equa-tions, and two energy conservation equations. Closure of thefield equations is provided through the use of constitutiverelations and correlations. Since the release of RELAP5/MOD2 in 1985 the code was continuously improved andextended. New models were included like zirconium-waterreaction model, level tracking model, thermal stratificationmodel, countercurrent flow limiting correlation, and soforth. Several improvements to existing models were alsodone, for example Henry-Fauske and Moody choking flowmodels, new correlations for interfacial friction, modifiedreflood model, and new critical heat flux correlation forrod bundles. Finally, user conveniences have been added forcode execution on a variety of systems. The latest versionis RELAP5/MOD3.3 Patch 04, released in 2010. For moredetails on RELAP5 the reader can refer to [14].

TRACE was combined from four main system codes(TRAC-P, TRAC-B, RELAP5, and RAMONA), which weredeveloped under US NRC to perform safety analyses ofloss-of-coolant accidents and operational transients, andother accident scenarios in pressurized light-water reactorsand boiling light-water reactors. TRACE can also modelphenomena occurring in experimental facilities designedto simulate transients in reactor systems. TRACE includesmodels for multidimensional two-phase flow, nonequilib-rium thermodynamics, generalized heat transfer, reflood,level tracking, reactor kinetics, and passive systems. Thepartial differential equations that describe two-phase flowand heat transfer are solved using finite volume numericalmethods. The heat-transfer equations are evaluated usinga semi-implicit time-differencing technique. A component-based approach is used to modeling a reactor system. Eachphysical piece of equipment in a flow loop can be representedas some type of component, and each component can befurther nodalized into some number of physical volumes(also called cells) over which the fluid, conduction, andkinetics equations are averaged. There is no built-in limit forthe number of components or volumes that can be modeled;the size of a problem is theoretically only limited by theavailable computer memory. With hydraulic components



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Figure 4: RELAP5 initial and boundary conditions for BETHSY 6.2TC test—animated view.

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Figure 5: TRACE initial and boundary conditions for BETHSY 6.2TC test—animated view.


Table 2: Main sequence of events.

EventsTime (s)

Experiment RELAP5 TRACE

Break opening 0 0 0

Scram signal (13.1 MPa) 8 2 3

Safety injection signal (11.7 MPa) 12 8 9

First core uncover 92 90 136

Loop seal clearing 134 155 173

Primary/secondary pressure reversal 172 175 203

Second core uncovery 334 280 253

Accumulator no. 2 and 3 injection start (4.2 MPa) 345 365 329

Accumulator isolation no. 2 (no. 3) (1.5 MPa) 948 (976) 925 801

Pressurizer pressure <0.7 MPa 2065 2230 2167

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Figure 6: Mass flow rate at the break.

the pipes, pressurizer, upper and lower plenum of the reactorvessel, pumps, separators, tees, valves, reactor vessel withassociated internals, and containment. There are also heatstructures and components for boundary condition andbreak. For more details on TRACE the reader can refer to[1].

SNAP [2] consists of a suite of integrated applicationsdesigned to simplify the process of performing engineeringanalysis. SNAP is intended for creating and editing input forengineering analysis codes and it has functionality for sub-mitting, monitoring, and interacting with the codes. SNAPcurrently support the CONTAIN, COBRA, FRAPCON-3, MELCOR, PARCS, RADTRAD, RELAP5, and TRACEanalysis codes. Each code is supported by a separate plug-in. SNAP’s interactive and postprocessing capabilities arepredominately realized within its animation displays. Withinsuch a display, the results of a calculation may be animated ina variety of ways. An animation display retrieves data fromthe server and represents it visually in some fashion. Thedata can be from an actively running calculation, a completedcalculation, external data, and so forth.

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Figure 7: Integrated mass flow rate at the break.

3. Results

The results of steady-state and transient calculations ofBETHSY 6.2TC test using TRACE V5.0 Patch 1 and RELAP5/MOD3.3 Patch 4 computer codes are presented in thefollowing subsections. The results are presented in classicalway with graphs and in advanced way as animated represen-tations of calculation results.

3.1. Steady-State Calculation. The comparison between cal-culated and measured initial conditions for BETHSY 6.2TCtest is shown in Table 1. The RELAP5 and TRACE inputmodels were initialized to the cold leg temperature ratherto secondary pressure. The secondary pressure is thendependent on the heat transfer across the steam generators.In the case of TRACE the secondary pressure is not perfectlymatched. The difference comes from the geometry and thecode models. For example, in the TRACE assessment report[13] the cold leg temperature was not matched for the sakeof matching the secondary pressure. The steam generatorlevels and masses were matched to measured values both


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Tem

pera

ture

(K

)

Time (s)

RELAP5

TRACE

Exp

Figure 10: Heater rod surface temperature at the middle of the core.

RELAP5TRACE

Exp

400

450

500

550

600

650

700

750

800

850

0 500 1000 1500 2000 2500

Tem

pera

ture

(K

)

Time (s)

Figure 11: Heater rod surface temperature at the top of the core.

RELAP5

TRACE

Exp

0

1

2

3

4

0 500 1000 1500 2000 2500

Leve

l (m

)

Time (s)

Figure 12: Core-collapsed liquid level.

RELAP5TRACE

Exp

0

500

1000

1500

2000

0 500 1000 1500 2000 2500

Mas

s (k

g)

Time (s)

Figure 13: Primary circuit total mass.


0

10

20

30

40

0 500 1000 1500 2000 2500

Pre

ssu

re d

rop

(KPa

)

Time (s)

RELAP5TRACE

Exp

Figure 14: Intermediate leg 1 DP (SG side).

0

5

10

15

20

0 500 1000 1500 2000 2500

Pre

ssu

re d

rop

(kPa

)

Time (s)

RELAP5

TRACE

Exp

Figure 15: Intermediate leg 1 DP (pump side).

RELAP5TRACE

Exp

0

1

2

3

4

5

0 500 1000 1500 2000 2500

Pre

ssu

re (

MPa

)

Time (s)

Figure 16: Accumulator number 2 pressure.

RELAP5TRACE

Exp

0

100

200

300

400

500

600

0 500 1000 1500 2000 2500

Mas

s (k

g)

Time (s)

Figure 17: Integrated accumulators injected mass.

for RELAP5 and TRACE. The pressurizer pressure and levelwere also matched to measured values. The core powerwas boundary condition. In the experiment the electricaltrace heating system was installed of the power of 54.82 kWand was operating till the transient start. Therefore in thecalculations the heat losses were modeled after the electricaltrace heating system was turned off.

The TRACE input model was initialized using built inartificial controls, which were obtained by conversion fromRELAP5 and then simplified by introducing Fill components.The primary pressure was set by boundary condition, whilethe pressurizer level was set by an artificial Fill component.The controller to set the desired cold leg temperature was alsoused. For steam generator level the Fill component was used(using the Fill component simulating auxiliary feedwaterduring transient). The primary mass flow was adjusted bythe pump speed. Figures 4 and 5 show the animation masksof BETHSY facility for RELAP5 and TRACE, respectively.On the masks the fluid condition color map is used anddata values are shown at time 0 s, that is, presenting thecalculated initial and boundary conditions. It can be seenthat primary side is filled with subcooled liquid except thepressurizer, which is filled with saturated liquid and saturatedsteam at the top. On the secondary side the bottom parts ofsteam generators are saturated liquid, while at the top there issaturated steam. Please also note, that in Figure 5 for TRACEFills and Breaks the status is shown instead of fluid condition.Green color means the Fill or Break component is activeand red color means it is off. The initial conditions shownin Figures 4 and 5 are complement to the values given inTable 1.

3.2. Transient Calculation. The main sequence of events isshown in Table 2. The comparison between the experimentand RELAP5 and TRACE calculated results is shown inFigure 6 through Figure 17. The calculation results showedthat occurrences and trends of key transient phenomena arereasonably predicted by both computer codes.


92 sTime:

0.24 kg/s

1.23 kg/s

0 rad/s

7.03 kg/s

7.7 MPa

ACC1 ACC2

P1

SG1

PRZ

DC

PV

2

2

1

3

Relap5Mod3.3

+30(K)

Sat. steam

Sat. liquid

−30(K)4005006007008009001000

0

0.5

1

Cor

e te

mp.

(K

)

Voi

d fr

acti

on

Flu

id c

ondi

tion

(K

)

Color maps

1 2 3

Loop1 facility view

0 kg/s 0 kg/s

0 kg/s

Fluid conditionvoid fractionTemperature (k)

−0.02 kg/s

(a)

0.34 kg/s

0 kg/s

5.59 kg/s

8 MPa

ACC2 ACC2

P1

SG1

PRZ

DC

PV

2

2

1

3

2.36 kg/s

92 s

TRACE V5.0 p1

Color maps

1 2 3

−0.03kg/s

Loop1 facility view

0 kg/s0 kg/s

Cor

e te

mp.

(K

)

4005006007008009001000

Voi

d fr

acti

on

0

0.5

1

Flu

id c

ondi

tion

(K

)

+30(K)

Sat. steam

Sat. liquid

−30(K)

Temperature (k) Fluid conditionvoid fraction

Time:

(b)

Figure 18: Animation mask for RELAP5 (a) and TRACE (b) at time t = 92 s (first core uncovery).

As shown in Table 2 most of event times were reasonablycaptured. The reactor trip time and safety injection signalactuation time are similar for both RELAP5 and TRACEcalculation. Because the pressure drop in TRACE calculationis slower than in the experiment, the primary to secondarypressure reversal is delayed in the case of TRACE. The mainreason is probably the secondary side behavior. Namely,the mass released through atmospheric relief valves in theinitial period greatly influenced the primary pressure drop.Higher measured secondary pressure indicated that in thefirst 100 s the atmospheric relief valves were open few tensof seconds only, while in the calculation the pressure wascontrolled to 7.2 MPa according to test procedure. Theoverall accumulator time performance is better for RELAP5than for TRACE calculation.

The timing of the transient very much depends on themass flow rate at the break. For RELAP5 original Ransom-Trapp break flow model the values of 0.85, 1.25 and 0.75 were

used for subcooled, two-phase, and superheated dischargecoefficient, respectively. For TRACE break model the valuesof 0.8 and 0.9 were used for subcooled and two phasedischarge coefficients, respectively. The values for TRACEwere selected after some sensitivity studies. In Figures 6 and 7are shown the mass flow rate at the break and integrated massflow rate at the break. It can be seen that the calculated breakflows are quite well matched, in the range of 10% uncertainty.The integrated mass flow rate at the break better agree for theTRACE calculation. Primary pressure is shown in Figure 8.In spite of larger RELAP5 mass flow rate at the break thanTRACE mass flow rate at the break the pressure drop isfaster in case of TRACE calculation. Secondary pressure isshown in Figure 9. Already it was noted, that experimentalvalues indicated that atmospheric relief valves were open afew tens of seconds. The agreement between experiment andcalculation is slightly better for RELAP5 than for TRACE.Nevertheless, in general after initial period the secondary


400

500

600

700

800

900

1000

0

0.5

1 +30(K)

Sat. steam

Sat. liquid

−30(K)C

ore

tem

p. (

K)

Voi

d fr

acti

on

Flu

id c

ondi

tion

(K

)

160 s

1247.7 kWReactor power:

Time:

Core inlet temp: 562.3 K

Core outlet temp: 563.2 K

Upper head temp:

Core level: 1.792 m

Break flow: 6.585 kg/s

LPSI1 flow: 0 kg/s

LPSI2 flow: 0 kg/s

1500000

2000000

2500000

3000000

3500000

4000000

1 2 3 4

Legend

P: pump

PRZ: pressurizerSG: steam generatorPV: pressure vessel

Color maps

0 kg/s

0.118 kg/s

0.402 kg/s

−4.725kg/s

0 rad/s

7.861 kg/s

0.005 kg/s

0.119 kg/s

0.836 kg/s

0.354 kg/s

ACC1 ACC2

SG1

PV

DC

PRZ

LPSI1

LPSI2

Loop 2

Loop 3

Loop1 nodalization view4

4

4

2

2

2

2

2

2

3

0 kg/s

0 kg/s

0 kg/s 0 kg/s

ACC: accumulator

DC: downcomer

LPSI: low pressure

safety injection

Pre

ssu

re (

Pa)

−0.013 kg/s

−4.725 kg/s

563 K

Figure 19: Animation mask for RELAP5 at time t = 160 s (after loop seal clearance).

side has small influence on the primary side and by this onthe overall calculation. Figures 10 and 11 show the heaterrod surface temperatures in the middle and at the top ofthe core, respectively. The core heatup time corresponds bythe minimum core collapsed liquid level shown in Figure 12.Both calculations predicted with delay the first peak of heaterrod surface temperature at the middle of the core. The secondrod heatup was better calculated by TRACE. In the caseof heater rod surface temperature at the top of the corethe timing of heatup prediction was better in the case ofTRACE, while heatup rate was better in the case of RELAP5.The primary circuit total mass is shown in Figure 13. Inspite of correct TRACE calculated mass discharged throughthe break the TRACE calculated primary mass is smallerthan the experimental. It should be noted that uncertaintyin mass was reported to be 50 kg. In the case of RELAP5calculation the core level was lower, while RELAP5 calculateddischarged mass was slightly lower than TRACE. The reasonis that slightly larger mass discharged through the break wascalculated by RELAP5 than by TRACE. It can be concludedthat TRACE is more consistent when comparing both thecore level and mass in the primary system. The informationon the loop seal clearing can be obtained from Figures 14 and15, showing the differential pressures on the steam generator

and pump side, respectively. It may be seen that some furtheradjustment is needed for TRACE initial pressure drop on thepump side. Finally, the accumulator behavior is shown inFigure 16 showing the accumulator pressure and Figure 17showing the integrated accumulator injected mass. The trendfor RELAP5 is very good but the discharge is not smooth,while in the case of TRACE the accumulator discharged fasterthan in the experiment but smoothly like in the experiment.

3.3. Results Discussion. Comparison of TRACE and RELAP5calculations show that in general there are very similar. Itwas confirmed that TRACE using the converted input modelfrom RELAP5 produced results comparable to RELAP5. Suchfinding was confirmed in the study of BETHSY 9.1b test[20], being TRACE is even slightly better than RELAP5.When looking the timing of accumulator injection and coreheatup in the presented BETHSY 6.2TC test, the presentedTRACE calculation was better than the calculation reportedin TRACE assessment manual [13].

3.4. Code Comparison through Animation Masks. Timetrends are very good to show the time progression ofthe variables, while animation masks can give snapshotsat certain times for the whole facility condition. This


400

500

600

700

800

900

1000

Cor

e te

mp.

(K

)

0

0.5

1

Voi

d fr

acti

on

Flu

id c

ondi

tion

(K

) +30(K)

Sat. steam

Sat. liquid

−30(K)

Pre

ssu

re (

Pa)

1500000

2000000

2500000

3000000

3500000

4000000

P: pump


ACC: accumulator

DC: downcomer

LPSI: low pressure

safety injection

1247 kWReactor power:

Core inlet temp: 562.1 K

Core outlet temp: 565.2 K

Upper head temp: 565 K

Core level: 2.06 m

Break flow: 3.95 kg/s

LPSI1 flow:

LPSI2 flow:

Legend

Color maps

ACC2 ACC3

SG1

PV

DC

PRZ

LPSI1

LPSI2

Loop 2

Loop 3

Loop1 nodalization view4

4

2

2

2

2

2

2

3

CHARGINGFLOW

0.18 kg/s

0.01 kg/s

0.15 kg/s

0.12 kg/s

−0.92kg/s

−4.82kg/s

−2.57kg/s

−0.01kg/s

5.46 kg/s

SG1 pressure control

Steam dump 1


160 sTime:

1 2 3 4

0 kg/s

0 kg/s

0 kg/s0 kg/s

0 kg/s

Main feedwater 1

0 kg/s

0 kg/s

−0.013 kg/s

Figure 20: Animation mask for TRACE at time t = 160 s (before loop seal clearance).

is especially important when there is a need to followdistribution of liquid, temperature, pressure, and any othervariable around the loop. To follow the time progression, amovie can be generated too. For the purpose of this paper thesnapshots at important events are shown. The componentsare labeled with number in circles, designating which colormap is used by component. The color map no. 1 representsthe core temperature (i.e., heat structure temperature). Itis used just for core heat structures. Namely, other heatstructures are not shown in the mask. The color map no. 2 isvoid fraction color map, blue color presenting the fluid andwhite color presenting the gas. The color map no. 3 is fluidcondition color map. The subcooled liquid is in blue color,the saturated liquid is in green, and the saturated gas is inorange color. When the temperature is 30 K above saturationtemperature, the red color is used. The color map no. 4 ispressure color map. The color goes from orange to red, wherered color represents higher pressure.

In Figure 18 it is shown the loop 1 BETHSY facility maskat 92 s, at which the core in the experiment first uncovered.From Figure 18 it can be seen that much of primary circuit isfilled with liquid, except pressurizer and upper head, both

for RELAP5 (a) and TRACE calculation (b). By this thestatement in the experiment description is confirmed [21]:“The hot parts of the primary circuit (upper head, upperplenum, SG U-tubes) started to boil. The formation of loopseal causes the core level depression.” It can be also seenthat accumulators are partially filled. The color map no.3 is used to show the condition on the secondary side ofsteam generator. For RELAP5 the steam generator is in thesaturation condition, in the lower part of downcomer andriser is saturated liquid and in the upper part of steamgenerator is saturated steam. In the case of TRACE inthe separator component there is saturated liquid. Pleaserefer to Section 2.4 for problems we had with modeling.Namely, the separator components could not be replacedwith Pipe components, since the input model fail to run,therefore the separator was retained in the model. The fluidcondition in other TRACE components is very similar tothe corresponding RELAP5 components. Also it can be seenthat accumulators are not injecting at this time. Finally, fromTable 2 and Figure 12 it can be seen that the timing of coreuncovery is good for RELAP5, while in the case of TRACEthis uncovery is later. This finding is supported by Figure 18,


0.94 kg/s

SG1

SG2

SG3

P1

P2

P3

ACC3

ACC2

PRZ

PV

DC

1

2

3

4

Side view345 sTime:Relap5mod3.3

Color maps

0 kg/s

0 kg/s

Tem

pera

ture

(K

)

1 2 3 4

4005006007008009001000

0

0.5

1

Voi

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on

+30(K)

Sat. steam

Sat. liquid

−30(K)

Flu

id c

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tion

(K

)

150000020000002500000300000035000004000000

Pre

ssu

re (

Pa)

(a)

1.01 kg/s

SG1

SG2

SG3

P1

P2

P3

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ACC2

PRZ

PV

DC

1

2

3

4

TRACE V5 p1

0.94 kg/s

0.85 kg/s

Side view345 sTime:

Cor

e te

mp.

(K

)

4005006007008009001000

Voi

d fr

acti

on

0

0.5

1

Flu

id c

ondi

tion

(K

)

+30(K)

Sat. steam

Sat. liquid

−30(K) 150000020000002500000300000035000004000000

Pre

ssu

re (

Pa)

1 2 3 4

Color maps

(b)

Figure 21: Animation mask for RELAP5 (a) and TRACE (b) at time t = 345 s (loop seal clearance).

2000 s

0.190 kg/s P1

P2

P3

SG1

SG2

SG3

0.091 kg/s

0.013 kg/s

0.044 kg/s

278.1 kW

SG1

SG2

SG3

P1

P2

P3

ACC3

ACC2

PRZ

PV

DC

ACC1

ACC2

PRZ

PV

DC

1

2

3

4

4

2

3

449.082 K

449.601 K

545.065 K

688.575 K

654.564 K

Top view

Reactor power:Time:

Core inlet temp.: 448.2 K

Core outlet temp.: 447.1 KUpper head temp.:

Core level: 0.936 m

Core temperature

LPSI1

LPSI2

Legend

Side view

3.66

0

2.93

2.19

1.46

0.73Cor

e le

vel (

m)

Break flow: 0.190 kg/sLPSI1 flow: 0 kg/sLPSI2 flow: 0 kg/s

447.1 K

150000020000002500000300000035000004000000

Pre

ssu

re (

Pa)

4

+30(K)

Sat. steam

Sat. liquid

−30(K)

Flu

id c

ondi

tion

(K

)

0

0.5

1

Voi

d fr

acti

on

4005006007008009001000

Cor

e te

mp.

(K

)

1 2 3

Color mapsP: pump


ACC: accumulatorDC: downcomerLPSI: low pressure

safety injection

Figure 22: Animation mask for RELAP5 at time t = 2000 s (core heatup).


2000 s

0.2 kg/s P1

P2

P3

SG1

SG2

SG3

0.057 kg/s

0.002 kg/s

0.001 kg/s

313.1 kW

SG1

SG2

SG3

P1

P2

P3

ACC2

ACC1

PRZ

PV

DC

ACC1ACC2

PRZ

PV

DC

1

2

3

4

4

2

3

449.504 K

449.967 K

450.102 K

591.721 K

695.727 K

Top view

445.7 K

445.7 K445.7 K1.278 m

Core temperature

LPSI1

LPSI2

Legend

Side view0.011 kg/s0.011 kg/s0 kg/s

150000020000002500000300000035000004000000

Pre

ssu

re (

Pa)

4

+30(K)

Sat. steam

Sat. liquid

−30(K)

Flu

id c

ondi

tion

(K

)

0

0.5

1

Voi

d fr

acti

on

4005006007008009001000

Cor

e te

mp.

(K

)

1 2 3

Color maps

3.66

0

2.93

2.19

1.46

0.73Cor

e le

vel (

m)

Reactor power:Time:

Core inlet temp.:

Core outlet temp.:Upper head temp.:

Core level:

Break flow:LPSI1 flow:LPSI2 flow:

P: pump


ACC: accumulatorDC: downcomerLPSI: low pressure

safety injection

Figure 23: Animation mask for TRACE at time t = 2000 s (core heatup).

where uncovery can be seen for RELAP5 calculation, whilethis is not the case for TRACE calculation.

Next important event shown is loop seal clearing attime 134 s. Both RELAP5 and TRACE calculation predictedloops seal clearing with delay, therefore the time 160 s wasselected. At that time the loop seal cleared in the caseof RELAP5 calculation (Figure 19), while in the case ofTRACE the loop seal can still be seen (Figure 20). In thecase of RELAP5 low level was also reached in the core (asin experiment), while TRACE calculation did not predictsignificant first core uncovery at the time 160 s. It can alsobe seen that pressure in the steam generator and pressurizeris above 4.5 MPa what prevents injection by accumulatorsin both calculations, which is also in agreement with theexperimental data.

In the experiment the accumulator injection started in345 s. From Table 2 we can see that at this time in theTRACE calculation the accumulator is injecting, while in theRELAP5 calculation the accumulator started to inject laterat 363 s. Figure 21 shows the BETHSY facility animated withfour color maps. For the primary circuit void fraction colormap is used. The numerical values of break flow rate andaccumulator flow rate are given. In the case of TRACE bothaccumulators are injected, and the total injection mass flowrate is larger than the break mass flow rate.

At time 976 s the accumulator injection was terminatedin the test. There is no other injection available and theprimary circuit mass started to decrease. At 2000 s the corestarted to uncover again resulting in the core heatup. Figures22 and 23 are rather complex animation masks displayingside view and top view of the BETHSY facility and core heatstructure at 2000 s. Four color maps are used for animations.The side view of the facility shows that most liquid is presentin the lower part of the reactor vessel. Some amount of

liquid remained in the accumulators due to their closure.The situation is similar for both calculations. The top viewof both calculations shows that all three loops are in thesaturated condition. Finally, from the core temperatures itcan be seen that the rods start to heat from top to the bottombecause of uncovering the core from top to the bottom.

4. Conclusions

The overall results obtained with TRACE V5.0 Patch 1 usingconverted one-dimensional reactor vessel model were com-parable to the results obtained by RELAP5/MOD3.3 Patch4. The results show that the main discrepancies in the caseof TRACE calculation are connected with the predictions ofprimary pressure and break flow in the first 200 s, influencingthe accumulator emptying and primary mass inventory. Boththe TRACE and RELAP5 code predicted first core uncoveryuntil accumulators started to inject and after emptyingaccumulators the second core heatup was predicted due tosecond core boil off. It was shown that TRACE calculationsobtained by converted input model from RELAP5 to TRACEare as good as the RELAP5 calculations obtained by theoriginal RELAP5 input model. In addition the results werecompared by animation masks, presenting several physicalphenomena and processes as well as data values of variablesand status of equipment. The results suggested that suchadvanced comparison analysis technique between two codesis beneficial because several in-depth insights into analysisresults can be obtained.

Acknowledgments

The authors acknowledge the financial support from thestate budget by the Slovenian Research Agency Program no.


P2-0026 and financial support from Slovenian Nuclear SafetyAdministration and Krsko Nuclear Power Plant by Projectno. POG-3473.

References

[1] U. S. Nuclear Regulatory Commission, TRACE V5.0 UserManual, Division of Risk Assessment and Special Projects,Office of Nuclear Regulatory Research, Washington, DC, USA.

[2] APT, Symbolic Nuclear Analysis Package (SNAP), User’sManual. Report, Applied Programming Technology (APT),Inc., 2011.

[3] G. L. Mesina, “Visualization of RELAP5-3D best estimatecode,” in Proceedings of the International Meeting on Updatesin Best Estimate Methods in Nuclear Installation Safety Analysis(BE ’04), pp. 314–323, Washington, DC, USA, November2004.

[4] W. P. Baek, J. E. Yang, and J. J. Ha, “Safety assessment ofKOREAN nuclear facilities: current status and future,” NuclearEngineering and Technology, vol. 41, no. 4, pp. 391–402, 2009.

[5] J. D. Talley, S. Kim, J. Mahaffy, S. M. Bajorek, and K. Tien,“Implementation and evaluation of one-group interfacialarea transport equation in TRACE,” Nuclear Engineering andDesign, vol. 241, no. 3, pp. 865–873, 2011.

[6] F. Mascari, G. Vella, B. G. Woods et al., “Sensitivity analysisof the MASLWR helical coil steam generator using TRACE,”Nuclear Engineering and Design, vol. 241, no. 4, pp. 1137–1144,2011.

[7] J. Freixa and A. Manera, “Analysis of an RPV upper headSBLOCA at the ROSA facility using TRACE,” Nuclear Engi-neering and Design, vol. 240, no. 7, pp. 1779–1788, 2010.

[8] E. Coscarelli, A. Del Nevo, and F. D’Auria, “Qualificationof TRACE v5 code against fast cooldown transient in thePKL-III integral test facility,” in Proceedings of the 14thInternational Topical Meeting on Nuclear Reactor ThermalHydraulics (NURETH-14), Toronto, Canada, September 2011,paper no. 419.

[9] U.S. NRC, “Status of CAMP activities in Slovenia,” in Pro-ceedings of the Fall CAMP Meeting, Williamsburg, VA, USA,November 2009.

[10] U.S. NRC, “SNAP Status Report,” in Proceedings of the FallCAMP Meeting, State College, Pa, USA, October 2010.

[11] U.S. NRC, “SNAP overview and plans,” in Proceedings of theFall CAMP Meeting, Philadelphia, Pa, USA, November 2011.

[12] S. Petelin, B. Mavko, O. Gortnar, I. Ravnikar, and G. Cerne,“Result of BETHSY test 9.1.b using RELAP5/MOD3,” Inter-national Agreement Report NUREG/IA-0141, U.S. NuclearRegulatory Commission, Washington, DC, USA, 1998.

[13] U.S. Nuclear Regulatory Commission, TRACE V5.0 Assess-ment Manual, Division of Risk Assessment and SpecialProjects, Office of Nuclear Regulatory Research, Washington,DC, USA.

[14] U.S. NRC, “RELAP5/MOD3.3 code manual,” Patch 04, Vols.1 to 8, Information Systems Laboratories, Inc., Rockville, Md,USA, Idaho Falls, Idaho, prepared for USNRC, 2010.

[15] CEA, “BETHSY, General Description,” Note SETh/LES/90-97, CEA (Commissariat a l’energie atomique et aux energiesalternatives), Grenoble, France, 1990.

[16] S. Belsito, F. D’Auria, M. Ingegneri, E. Chonjacki, and R. Gon-zalez, “Post test analysis of counterpart tests in LOBI, SPES,BETHSY; LSTF facilities performed with the CATHARE2code,” in Proceedings of the Nuclear Energy in Central Europe(NECE ’96), Portoroz, Slovenia, September 1996.

[17] A. Prosek, “RELAP5 calculations of bethsy 9.1b test,” Scienceand Technology of Nuclear Installations, vol. 2012, Article ID238090, 11 pages, 2012.

[18] S. Hrvatin, A. Prosek, and I. Kljenak, “Quantitative assessmentof the BETHSY 6.2 TC test simulation,” in Proceedings ofthe 8th International Conference on Nuclear Engineering, TheAmerican Society of Mechanical Engineers, The AmericanSociety of Mechanical Engineers, 2000.

[19] S. Hrvatin and A. Prosek, “Quantitative assessment of theBETHSY 6.9c test simulation,” in Proceedings of the Inter-national Conference Nuclear Energy in Central Europe, Bled,Slovenia, September 2000.

[20] A. Prosek and O. A. Berar, “Analysis of small-break loss-of-coolant accident test 9.1b at BETHSY facility with TRACEand RELAP5,” in Proceedings of the International Congress onAdvances in Nuclear Power Plants (ICAPP ’11), Nice, France,May 2011.

[21] G. Briday and D. Juhel, “BETHSY—test 6.2 TC, 6 inch cold legbreak counterpart test,” Tech. Rep. STR/LES/91-034, 1991.

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Documents

AdvancedPresentationofBETHSY6.2TCTestResults ...downloads.hindawi.com/journals/stni/2012/812130.pdf · BETHSY facility was a 3-loop replica of a 900MWe Framatome pressurized waterreactor.For