Summary of SARNET Achievements

1. Summary of SARNET Achievements T. Albiol (IRSN) T. Haste (PSI), J.P. Van Dorsselaere (IRSN), C. Journeau (CEA), L. Meyer (FZK), B. Chaumont (IRSN), B.R. Sehgal (KTH), D. Beraha (GRS), A. Annunziato (JRC), R. Zeyen (JRC) ERMSAR 2008 Nesseber, Bulgaria, September 23-25, 2008

2. SARNET General Features SevereAccidentResearchNETwork of excellence 20 Countries (Europe plus Canada) • 51 organizations • 19 Research organizations • 10 Universities • 11 Industry organizations • 4 Utilities • 7 Safety authorities and Technical Safety Organizations • More than 230 researchers • About 20 PhD students • 800 to 900 person-months per year • About 10M€ effort per year (1.4M€ per year funded by the EC, since April 2004 to September 2008)

3. SARNET Main Objectives • Tackling the fragmentation that exists between the different R&D organizations, notably in defining common research programmes and developing/qualifying computer tools; • Harmonizing the methodologies applied for assessing risk and improve Level 2 Probabilistic Safety Assessment (PSA) tools; • Disseminating the knowledge to Newcomers to the European Union more efficiently and associating them with the definition and the conduct of research programmes more closely; • Bringing together top scientists in SA research to constitute a world leadership in advanced computer tools for SA risk assessment.

4. SARNET JPA Work Packages

5. SARNET Main Achievements: ACT and DATANET

6. SARNET Main Achievements: ASTEC • ASTEC capitalizes, in terms of models, the knowledge produced in the frame of the Network • 30 SARNET organizations involved in ASTEC  Use of the ACT, periodic users’ clubs, IRSN-GRS support to users, improved documentation, partners’ code assessment • Last version delivered in Dec. 2007 (V1.3 rev. 2) • Size: ~ 350 000 instructions • Maturity of the code has been reached: • Numerical robustness • Speed  real time • High quality models, in particular on Source Term • Extensive validation on 65 experiments: overall good results (except core late reflooding… like all other codes) • Many plant applications on PWRs and VVERs • Recently improved models: corium behaviour in lower head, vessel external cooling, ... • Underway actions (ASTEC V2, FP7 context) • Some new models proposed by partners (several on FP) in ASTEC V2.0 to be delivered in March 2009. • Work on BWR and CANDU applicability (all modules are already applicable except core degradation).

7. SARNET Main Achievements: Level 2 PSA • Description and comparison of the main PSA2 methods used by the partners. • Questionnaires set up and definition of harmonization steps based on the partners’ answers. • Cases studies for harmonization on specific issues: H2 combustion, iodine chemistry, MCCI, large early releases, reactor safe state definitions, PSA1 to PSA2 interfaces  a certain level of harmonization was reached leading to relevant recommendations. • SOAR on Dynamic Reliability methods issued. • Detailed examination of the benefits of one of these methods (Monte Carlo Dynamic Event Tree) for the station black out situation. • Benchmark exercise  comparison of classical and dynamic reliability methods. • Precise definition of ASTEC requirements for PSA2 needs and work on ASTEC coupling with probabilistic tools.

8. SARNET Main Achievements: Research Priorities • 6 issues remain open with high priority • core coolability during reflood and debris cooling • ex-vessel melt pool configuration during MCCI & ex-vessel corium coolability by top flooding • melt relocation into water & ex-vessel FCI • hydrogen mixing and combustion in containment (flame acceleration) • oxidising impact on source term (Ru oxidising conditions or air ingress for HBU and MOX fuel elements) • iodine chemistry in RCS & in containment • 4 issues are re-assessed with medium priority • hydrogen generation during reflood and melt relocation in vessel • corium coolability in lower head • integrity of RPV due to external vessel cooling • direct containment heating

9. SARNET Main Achievements: Research Priorities • 5 issues are assessed with low priority: • corium coolability in core catcher with external cooling • corium release following vessel rupture • crack formation and leakages in concrete containment • aerosol behaviour impact on source term (in steam generator tubes (SGT) and containment cracks) • core reflooding impact on source term • 3 issues are marked as ‘issue could be closed’: • integrity of reactor coolant system and heat distribution • ex-vessel core catcher and corium-ceramics interaction, cool-ing with water bottom injection • FCI incl. steam explosion in weakened vessel • Focus on few targeted research needs (experiments and interpretation of results), optimisation of resources and budgets. Work to be performed in SARNET2 and other international programmes

10. SARNET Main Achievements: Corium • Understanding of the oxidation phenomena has progressed and oxidation correlations have been validated  importance of material composition. • Data on B4C oxidation have been collected  common interpretation of the integral test PHEBUS FPT3. • Late-in-vessel LIVE experiments  new series of modelling and analytical work on in-vessel melt pool behaviour. • Comparison of the different models of vessel failure by creep rupture  common understanding of the OECD OLHF-1 test. • 2D debris bed coolability analyses for inhomogeneous bed structures showed an increased coolability compared to earlier 1D particle beds  new interest in this issue both experimentally and numerically including debris bed formation and coolability. • Unexpected results of the 2D MCCI test: marked ablation anisotropy for silica-rich materials  Interpretation and modelling to be pursued. • Core catcher concepts based on spreading (EPR) and bottom flooding (COMET, down-comers) studied  progress achieved in their modelling. • Extended validation of the chemical thermodynamics database NUCLEA  uncertainties of energy dispersive X-ray spectrometry (EDX) analyses qualified.

11. SARNET Main Achievements: Containment • ENACEFF experimental programme performed and analyzed  some weakness in the combustion models for negative H2 gradients. • REKO-3 experimental programme performed and analyzed  results to be used for the validation of codes dealing with H2 recombiners. • Containment sprays experiments performed and analyzed (TOSQAN, MISTRA)  atmosphere depressurization and stratification break-up well calculated by CFD and lumped parameter codes. • CFD simulations of operation of recombiners in simplified 2D containment models  first step to comprehensive calculation in real containments. • CONAN condensation experiments  comparison and assessment of steam condensation models. • SERENA OECD programme + MISTEE, DEFOR and KROTOS experiments  • In vessel steam explosion would not induce failure of the vessel  issue closed • Ex-vessel steam explosion may damage the cavity  large uncertainties to be addressed in SERENA2 and SARNET2 • DCH consequences linked to the geometry of the cavity  • issue considered as closed for EPR and VVER1000 plants • Needs of improvement in modelling (debris dispersion, oxidation and H2 combustion)

12. SARNET Main Achievements: Source Term • Effect of air ingress on FP release and transport  Ru release occurs in oxide form, following full oxidation of fuel and cladding. Oxide forms can be transported to the containment... On going tests • Strong orientation by SARNET of the test matrices of ISTC project EVAN (iodine chemistry) and proposal VERONIKA (FP release) • Understanding FP transport from Phebus FP and VERCORS HT results  • Under reducing conditions (and without absorber material), iodine is transported mainly as CsI • Under oxidizing conditions, either iodine is transported mainly as CsI or as other metal iodides, or as HI (still to be confirmed  CHIP programme) • Measurement of release following control rod failure (QUENCH13, plus use of EMAIC and Phebus FP)  improvement of models expected • Aerosol retention under SGTR conditions (PSAERO/HORIZON, PECA/SGTR, ARTIST)  • Effective scrubbing in wet scenarios, much less in dry conditions. • Study of aerosol retention in containment cracks  development of models • Iodine behaviour  • Data book compiled, including all available results • Some models (e.g. mass transfer) improved in ASTEC • Other studies (effect of radiation, effect of impurities, speciation of iodine, organic iodides,... ) still on going

13. SARNET Main Achievements: Integration of Research Activities • Collaborations on pre and post calculations of experiments: e.g. PSI performed pre and post-test calculations of the FZK QUENCH tests, • Joint realization of experiments: e.g. experimentalists from VTT have installed and operates specific instrumentation on the IRSN CHIP experiments, • Joint definition and interpretation of experiments (many “interpretation circles” created and really active), • Benchmarking of codes, • Distribution of codes to partners in order to achieve a common understanding of experimental phenomena (ASTEC modules), • Exchanges on the application of R&D results to the reactor scale, • Round-robin exercise on EDX analyses of a prototypic corium sample by three European laboratories (Cadarache, France; Karlsruhe, Germany; Rez, Czech Republic), • Yearly technical meetings in each of the three topical areas (corium behaviour, containment integrity and source term), complemented by a large number of specialists’ meetings.

14. SARNET Main Achievements: Spreading of Excellence • Three courses (5 days each) successfully organised in January 2006 (Cadarache), March 2007 (Cadarache) and April 2008 (Budapest). Two courses targeted to students and young researchers, one more targeted to severe accident specialists. 40 to 100 attendees to each course. • Mobility programme, under which students and researchers can go into different laboratories of SARNET for training: 33 mobilities, with an average duration of 3 months, have been funded by SARNET. • Three conferences (European Review Meetings on Severe Accident Research – ERMSAR) organized in France, Germany and Bulgaria as a forum to the Severe Accident community. About 100 attendees to each conference. These conferences are becoming one of the major events in the world on the severe Accident topic. • THE LWR Severe Accident Safety Book. Text book of about 450 pages. Draft now ready. Final version to be edited and published in 2009. • SARNET WEB site operational, to be improved in SARNET2. • About 300 SARNET papers in conferences and/or journals. Complete set of papers will be provided as an appendix of the final public SARNET synthesis report.

15. SARNET Main Achievements: Conclusions • Important objective  achieving a sustainable integration of the European severe accident research capacities. • ASTEC and DATANET  preservation of the knowledge produced by thousands of person-years of research and dissemination to end-users. • Collaborative work on PSA2 first steps towards harmonization of methods within Europe (continuation through the ASAM-PSA2 EC project). • Spreading of Excellence activities  efficient transfer of knowledge to younger generations. • Collaborative work on Corium, Containment and Source Term  large progress to solve remaining outstanding issues, and to provide model recommendations for ASTEC. • Research Priorities  direct impact on national programmes and associated budgets; optimisation of the European (and worldwide) Resources • SARNET2 in final negotiation phase with the EC  Follow-up of the SARNET NoE with a major self-sustainability objective... See next specific SARNET2 presentation.

16. Thank-you for your attention.