ERMSAR 2012, Cologne March 21 – 23, 2012 RANKING OF SEVERE ACCIDENT RESEARCH PRIORITIES W. Klein-Heßling (GRS) M. Sonnenkalb, J.-P. Van Dorsselaere, P

ERMSAR 2012, Cologne March 21 – 23, 2012

RANKING OF SEVERE ACCIDENT RESEARCH PRIORITIES

W. Klein-Heßling (GRS)

M. Sonnenkalb, J.-P. Van Dorsselaere, P. Chatelard, E. Raimond,B. Clément, H. Dimmelmeier, M.-A. Movahed, G. Urzua, G. Azarian, G. Ducros,

C. Journeau, T. Dagusé, A. Schumm, T. Jordan, A. Miassoedov, I. Kljenak, B. R. Sehgal, W. Ma, J. Birchley, S. Güntay, M. K. Koch, I. Ivanov, I. Lindholm, A. Auvinen


Content

Background

Methodology

Re-evaluation of ERI issues and new proposals

Conclusions

2


Background

Severe Accident Research Priority (SARP) work already started in SARNET FP6 SARP Report D96

SARP work is an ongoing process

Members of SARP in SARNET FP7– IRSN, AREVA, CEA, EDF, KIT, GRS, JSI, KTH, PSI, RUB, TUS,

VTT

Objectives:– Reassess issues ranking and eventually reorient priorities– Analyze R&D progress and results from Level 2 PSA studies– Make recommendations for R&D programme revision

3


Background – Information

EURSAFE FP5 PIRT

4

1016239

106

Description of phenomena and processes

Risk relevance based on consequences and

probability

Safety oriented votes

Level of knowledge

Phenomenaoriented votes

Combined to21 ERI - issues

Number of entries In-vessel Ex-vessel Dynamic loading

Long term loading

Fission products Sum

Phenomenon identification 162 149 461 116 128 1016

Selected due to high importance for safety 43 48 82 36 30 239 Selected due to significant lack of knowledge + safety importance

24 28 26 10 18 106

Integrated items for needed research 6 4 5 1 5 21

..


Background – Information

Other sources– On-going SARNET2 FP7 work packages– ASAMPSA2 project – OECD Projects (BIP, THAI, MCCI)

Phenomena related to Fukushima Accidents

New issues

5


Methodology and decision procedure

Process similar to that of EURSAFE and SARP FP6,but

– More focusing on phenomena vote (first)– Extent the meaning of safety-oriented vote

Consequences are more than radiological consequences(e. g. consequences on accident management procedures)

Consider changes of regulator‘s point of view

Long term radiologic consequences

Set up of template for new issues (see SARNET2 ACT)

Decision process is based on discussion process during meetings

6


ERI issues: In-vessel hydrogen generation

Knowledge of 1,1a and 1,1b is quite different Strong dependence on accident sequence

7

ERI Topic Explanation Previous Status

RevisedStatus

1,1a Hydrogen generation during re-flooding

Rapid generation of hydrogen which may not be accommodated by recombiners and the risk of early containment failure. Improve knowledge about the magnitude of hydrogen generation.

M L

1,1b Hydrogen generation during melt relocation into water

Rapid generation of hydrogen which may not be accommodated by recombiners and the risk of early containment failure. Improve knowledge about the magnitude of hydrogen generation.

M M


ERI issues: In-vessel cooling / RPV cooling

Still a point of discussion in L2 PSA studies Models are still quite poor in simulating multidimensional effects Knowledge is precondition for possible in-vessel melt retention

considerations (SAM measures)

8


RevisedStatus

1,2 Core coolability during re-flooding and thermal-hydraulics within particulate debris

Termination of the accident by re-flooding of the core while maintaining RCS integrity. Increase predictability of core cooling during re-flooding.

H H

1,3a Corium coolability in lower head

Improve predictability of the thermal loading on RPV lower head to maintain their integrity.

M H

1,4 Integrity of RPV due to external vessel cooling

Improve data base for critical heat flux and external cooling conditions to evaluate and design AM strategies of external vessel cooling for in-vessel melt retention.

M H


ERI issues: In-vessel cooling / RPV cooling (cont.)

Special point for BWRs because of the control rod guide tubes Main Topics of interest:

– Heat flux to metal layer in layered melt & 3-layer configuration– Thickness of metallic layer– Use of additives, “dirty” water, pressure dependence, hot spots

9


RevisedStatus

1,2 Core coolability during re-flooding and thermal-hydraulics within particulate debris

Termination of the accident by re-flooding of the core while maintaining RCS integrity. Increase predictability of core cooling during re-flooding.

H H

1,3a Corium coolability in lower head

Improve predictability of the thermal loading on RPV lower head to maintain their integrity.

M H

1,4 Integrity of RPV due to external vessel cooling

Improve data base for critical heat flux and external cooling conditions to evaluate and design AM strategies of external vessel cooling for in-vessel melt retention.

M H


ERI issues: Integrity of RCS

Scenario: SBO & high pressure Effect of high thermo mechanical loads on SG tubes is still a point of

investigations Natural circulation characterized by a counter-current flow pattern in

the hot leg RCS failure has consequences for possible DCH process On-going experiments (WENKA at KIT) & projects

change to medium10


RevisedStatus

1,5 Integrity of RCS Improve predictability of heat distribution in the RCS to quantify the risk of RCS failure and possible containment bypass.

CL M


ERI issues: Melt release and FCI

Prediction of break size (hole ablation) is not possible– Consequences for DCH and possible steam explosion

Special situation for BWR Evaluation of different experiments in SARNET FP6, OECD SERENA

but difficult to investigate11


RevisedStatus

1,6 Corium release following vessel failure

Improve predictability of mode and location of RPV failure to characterise the corium release into the containment.

L L

3,1 Melt relocation into water and particulate formation

Determine characteristics of jet fragmentation, debris bed formation and debris coolability towards maintenance of vessel and containment integrity respectively.

H H

3,2 FCI incl. steam explosion: melt into water, in-vessel and ex-vessel

Increase the knowledge of parameters affecting steam explosion energetic during corium relocation into water and determine the risk of vessel or containment failure.

H H

3,3 FCI incl. steam explosion in stratified situation

Investigate the risk of weakened vessel failure during re-flooding of a molten pool in the lower head.

CL CL


ERI issues: Melt release and FCI (cont.)

Fragmentation and dynamic loading by FCI, energy conversion, propagation and jet break up in deep pools are regarded as first priority

In-vessel: FCI Issue stays at priority level “closed”

12


RevisedStatus

1,6 Corium release following vessel failure

Improve predictability of mode and location of RPV failure to characterise the corium release into the containment.

L L

3,1 Melt relocation into water and particulate formation

Determine characteristics of jet fragmentation, debris bed formation and debris coolability towards maintenance of vessel and containment integrity respectively.

H H

3,2 FCI incl. steam explosion: melt into water, in-vessel and ex-vessel

Increase the knowledge of parameters affecting steam explosion energetic during corium relocation into water and determine the risk of vessel or containment failure.

H H

3,3 FCI incl. steam explosion in stratified situation

Investigate the risk of weakened vessel failure during re-flooding of a molten pool in the lower head.

CL CL


ERI issues: MCCI and Corium Catcher

13


RevisedStatus

1,3b External corium catcher device

Improve predictability of corium catcher devices to maintain their integrity

L L *) bilateral projects

2,1 MCCI: molten pool configuration and concrete ablation

Improve predictability of axial versus radial ablation up to late phase MCCI to determine basement material failure time and loss of containment integrity.

H H

2,2 Ex-Vessel corium coolability, top flooding

Increase the knowledge of cooling mechanisms by top flooding the corium pool to demonstrate termination of accident progression and maintenance of containment integrity

H H

2,3 Ex-Vessel corium catcher: corium ceramics interaction and properties

Demonstrate the efficiency of specific corium catcher designs by improving the predictability of the corium interaction with corium catcher materials.

CL L*) bilateral projects

2,4 Ex-Vessel corium catcher: coolability and water bottom injection

Demonstrate the efficiency of water bottom injection to cool corium pool and its impact on containment pressurisation.

CL L*) bilateral projects


ERI issues: MCCI and Corium Catcher (cont.)

“Corium Catcher” Issues treated in SARNET FP6 and experimentally closed (related to EPR extension to other types, bilateral projects)

MCCI– Relation between axial and radial ablation for different type of

concretes– Main uncertainties: Oxide-metal corium interactions– Simultaneous interaction of corium with ceramic and concrete

must be reassessed in view of the recent results of corium-concrete interaction

14


ERI issues: MCCI and Corium Catcher (cont.)

Top flooding

– Knowledge of the cooling mechanisms by top flooding of the ex-vessel corium pool needs to be increased (melt eruption phenomena)

Bottom flooding

– Water bottom injection were demonstrated for Gen.III applications

– Gen.II plant back-fitting process may lead to new investigations Consideration of new designs and materials

High relevance for AM measures

15


ERI issues: Hydrogen & DCH inside containment

Hydrogen Issue remains open with high priority due to risk significance– Modelling of hydrogen combustion with CFD codes

– Simulation of hydrogen combustion during DCH still not possible

– Influence of CO on combustion limits usually not considered

16


RevisedStatus

3,4 Containment atmosphere mixing and hydrogen combustion / detonation

Identify the risk of early containment failure due to hydrogen accumulation leading to deflagration / detonation and to identify counter-measures

H H

4,1 Direct containment heating

Increase the knowledge of parameters affecting the pressure build-up due to DCH and determine the risk of containment failure.

M M


ERI issues: Hydrogen & DCH inside containment (cont.)

DCH

– Large number of DISCO experiments performed

– Main open issues are the influence of water inside the cavity on the DCH process

– Link to H2 combustion (ERI 3,4) and melt injection (ERI 1,6)

17


RevisedStatus

3,4 Containment atmosphere mixing and hydrogen combustion / detonation

Identify the risk of early containment failure due to hydrogen accumulation leading to deflagration / detonation and to identify counter-measures

H H

4,1 Direct containment heating

Increase the knowledge of parameters affecting the pressure build-up due to DCH and determine the risk of containment failure.

M M


ERI issues: Leakage at penetrations

SANDIA experiments available Candidate for closing

18


RevisedStatus

3,5 Dynamic and static behaviour of containment, crack formation and leakage at penetrations

Estimate the leakage of fission products to the environment L CL


ERI issues: Source Term (in-vessel)

Numerous projects are on-going: VERDON (CEA), ISTP programme FP release of a highly degraded core is uncertain and has high risk

potential

19


RevisedStatus

5,1 Oxidizing environment impact on source term

Quantify the source term, in particular for Ru, under oxidation conditions / air ingress for HBU and MOX.

H H

5,5a Core re-flooding impact on source term (early phase)

Characterise and quantify the FP release during core re-flooding.

L*) former

5,5

L

5,5b Core re-flooding impact on source term (late phase, degraded core)

Characterise and quantify the FP release during core re-flooding.

L*) former

5,5

M*) link to 1,1b


ERI issues: Source Term (Chemistry & Aerosols)

Large number of experiments related to iodine in RCS and containment (e.g. PHEBUS.FP) & start of new OECD projects (STEM, BIP2)

Iodine experimental data are considered in accident codes (e. g. ASTEC, COCOSYS)

High relevance on source term20


RevisedStatus

5,2 RCS high temperature chemistry impact on source term

Improve predictability of iodine species exiting RCS to provide the best estimate of the source into the containment

H H

5,4 Containment chemistry impact on source term

Improve the predictability of iodine chemistry in the containment to reduce the uncertainty in iodine source term.

H H

5,3 Aerosol behaviour impact on source term

Quantify the source term for aerosol retention in the secondary side of steam generator and leakage through cracks in the containment wall as well as the source into the containment due to re-volatilization in RCS.

L L


ERI issues: Source Term (Chemistry & Aerosols) (cont.)

Certain link to Fukushima accident– Pool scrubbing– Influence on impurities on iodine behaviour and pool scrubbing

21


RevisedStatus

5,2 RCS high temperature chemistry impact on source term

Improve predictability of iodine species exiting RCS to provide the best estimate of the source into the containment

H H

5,4 Containment chemistry impact on source term

Improve the predictability of iodine chemistry in the containment to reduce the uncertainty in iodine source term.

H H

5,3 Aerosol behaviour impact on source term

Quantify the source term for aerosol retention in the secondary side of steam generator and leakage through cracks in the containment wall as well as the source into the containment due to re-volatilization in RCS.

L L


New issues

Improvement of the thermo-dynamic and thermo-physical databases for corium and fission products

– Thermal properties / phase diagrams are required for modelling of MCCI

– NUCLEA database is used as look-up table in ASTEC, but still uncertainties exist

MCCI aerosol effect on iodine chemistry in sump (link to impurities in water)

22


New issues related to Fukushima accident

Pool scrubbing under boiling conditions

Effect of impurities in water– Core degradation, chemistry and FCI

Spent fuel pool scenarios

23


Conclusions

The evaluation of research priorities is an ongoing process; it will be continued

Just a “few” changes– But change of content in the ERI issues– Extended requirements and “boundary” conditions

Caused by Fukushima accident, several “Severe accident topics” get higher relevance

24

Documents

ERMSAR 2012, Cologne March 21 – 23, 2012 RANKING OF SEVERE ACCIDENT RESEARCH PRIORITIES W. Klein-Heßling (GRS) M. Sonnenkalb, J.-P. Van Dorsselaere, P