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

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

1 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

2 ERMSAR 2012, Cologne March 21 – 23, 2012 Content Background Methodology Re-evaluation of ERI issues and new proposals Conclusions 2

3 ERMSAR 2012, Cologne March 21 – 23, 2012 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

4 ERMSAR 2012, Cologne March 21 – 23, 2012 Background – Information EURSAFE FP5 PIRT 4 1016 239 106 Description of phenomena and processes Risk relevance based on consequences and probability Safety oriented votes Level of knowledge Phenomena oriented votes Combined to 21 ERI - issues

5 ERMSAR 2012, Cologne March 21 – 23, 2012 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

6 ERMSAR 2012, Cologne March 21 – 23, 2012 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

7 ERMSAR 2012, Cologne March 21 – 23, 2012 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 Revised Status 1,1aHydrogen 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. ML 1,1bHydrogen 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. MM

8 ERMSAR 2012, Cologne March 21 – 23, 2012 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 ERI Topic Explanation Previous Status Revised Status 1,2Core 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. HH 1,3a Corium coolability in lower head Improve predictability of the thermal loading on RPV lower head to maintain their integrity. MH 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. MH

9 ERMSAR 2012, Cologne March 21 – 23, 2012 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 ERI Topic Explanation Previous Status Revised Status 1,2Core 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. HH 1,3a Corium coolability in lower head Improve predictability of the thermal loading on RPV lower head to maintain their integrity. MH 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. MH

10 ERMSAR 2012, Cologne March 21 – 23, 2012 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 medium 10 ERI Topic ExplanationPrevious Status Revised Status 1,5 Integrity of RCSImprove predictability of heat distribution in the RCS to quantify the risk of RCS failure and possible containment bypass. CLM

11 ERMSAR 2012, Cologne March 21 – 23, 2012 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 investigate 11 ERI Topic Explanation Previous Status Revised Status 1,6 Corium release following vessel failure Improve predictability of mode and location of RPV failure to characterise the corium release into the containment. LL 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. HH 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. HH 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

12 ERMSAR 2012, Cologne March 21 – 23, 2012 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 ERI Topic Explanation Previous Status Revised Status 1,6 Corium release following vessel failure Improve predictability of mode and location of RPV failure to characterise the corium release into the containment. LL 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. HH 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. HH 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

13 ERMSAR 2012, Cologne March 21 – 23, 2012 ERI issues: MCCI and Corium Catcher 13 ERI Topic Explanation Previous Status Revised Status 1,3b External corium catcher device Improve predictability of corium catcher devices to maintain their integrity LL *) 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. HH 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 HH 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. CLL *) 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. CLL *) bilateral projects

14 ERMSAR 2012, Cologne March 21 – 23, 2012 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

15 ERMSAR 2012, Cologne March 21 – 23, 2012 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

16 ERMSAR 2012, Cologne March 21 – 23, 2012 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 ERI Topic Explanation Previous Status Revised Status 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 HH 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. MM

17 ERMSAR 2012, Cologne March 21 – 23, 2012 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 H 2 combustion (ERI 3,4) and melt injection (ERI 1,6) 17 ERI Topic Explanation Previous Status Revised Status 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 HH 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. MM

18 ERMSAR 2012, Cologne March 21 – 23, 2012 ERI issues: Leakage at penetrations SANDIA experiments available Candidate for closing 18 ERI Topic ExplanationPrevious Status Revised Status 3,5 Dynamic and static behaviour of containment, crack formation and leakage at penetrations Estimate the leakage of fission products to the environment LCL

19 ERMSAR 2012, Cologne March 21 – 23, 2012 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 potentia l 19 ERI Topic Explanation Previous Status Revised Status 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. HH 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

20 ERMSAR 2012, Cologne March 21 – 23, 2012 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 term 20 ERI Topic Explanation Previous Status Revised Status 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 HH 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. HH 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. LL

21 ERMSAR 2012, Cologne March 21 – 23, 2012 ERI issues: Source Term (Chemistry & Aerosols) (cont.) Certain link to Fukushima accident – Pool scrubbing – Influence on impurities on iodine behaviour and pool scrubbing 21 ERI Topic Explanation Previous Status Revised Status 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 HH 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. HH 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. LL

22 ERMSAR 2012, Cologne March 21 – 23, 2012 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

23 ERMSAR 2012, Cologne March 21 – 23, 2012 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

24 ERMSAR 2012, Cologne March 21 – 23, 2012 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

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