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2 nd European Review Meeting on Severe Accident Research ERMSAR-2007 Karlsruhe, 12-14 June 2007

Achievements and status of Research Activities in the Corium area Christophe Journeau, Martin Steinbrück, Georges Repetto, Christian Duriez, Ma Weimin, Vincent Koundy, Manfred Bürger, Bertrand Spindler, Jean-Michel Bonnet + all the Corium topic partners.

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2 nd European Review Meeting on Severe Accident Research ERMSAR-2007 Karlsruhe, 12-14 June 2007

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  1. Achievements and status of Research Activities in the Corium areaChristophe Journeau, Martin Steinbrück, Georges Repetto, Christian Duriez, Ma Weimin, Vincent Koundy, Manfred Bürger, Bertrand Spindler, Jean-Michel Bonnet+ all the Corium topic partners 2nd European Review Meeting on Severe Accident Research ERMSAR-2007 Karlsruhe, 12-14 June 2007

  2. Outline of the Presentation • Generalities – Organization • WP 9: Early In Vessel Phases • WP10: Late In Vessel Phases • WP11: Ex-Vessel Phases • Cross-cutting Issues • Conclusions – Further research needs in the corium area

  3. The Corium Topic • 54 issues dealing with corium were selected in EURSAFE grouped in 11 of the 21 R&D items. • Organised in • 8 topical tasks, • 3 Work Packages • 1 cross-cutting task on thermodynamic and thermophysical properties

  4. About 50 full-time researchers devoted to corium topics in SARNET organizations Almost 10 equivalent full-time researchers in the SARNET joint programme of activities Link to EC-funded ISTC projects in Russia and Kazakhstan and to OECD/MCCI project in the USA. 20 organizations participating in the Corium Topic AECL Apologies for those whose research will not be cited due to time limitations !

  5. WP 9.1 : Hydrogen generation during core reflooding • Activity organized around QUENCH tests (and PARAMETER ISTC project). • QUENCH-11 Benchmark (separate presentation) • QUENCH-12 test with Zr-1%Nb VVER cladding • Need for data with Advanced Cladding Materials to complement the Zircaloy-based correlations in current codes Q06 Zry Intense oxide spalling

  6. WP 9.2 : Early core degradation and B4C effects • Largely devoted to the analysis of • Phébus FPT3 (presentation to come) • QUENCH 07/08. • 21 BECARRE Separate Effect Tests on B4C (+steel) oxidation • BOX Separate effect test in FZK • Literature review leading to proposal of a new oxidation correlation • Phenomena observed in BECARRE during the oxidation of a steel-5%B4C mixture at 1289°C • Formation of B2O3 +H2 • Evaporation of volatile boric acid • Formation of Fe3O4 layer

  7. WP 9.3: Zircaloy oxidation by air and steam-air mixture • Air ingress experiments have been conducted at IRSN, FZK and INR. • PSI has undertaken a state of the art review on air oxidation, showing that • the parabolic law is not conservative in case of air ingress. • an oxide scales breakaway model needed • RUB is analyzing CODEX AIT-1 test with ATHLET-CD • ENEA is analyzing IRSN tests with bare Zircaloy • The major issue is related to ruthenium release. (SARP High Priority issue)This has been confirmed by scenario analyses performed by EDF. • For more details, see coming presentation by Duriez et al. CANDU-type Zry-4 after oxidation in humid atmosphere at INR

  8. WP 10.1: Late phase core degradation and corium behavior in lower head • LIVE Experiments (FZK) on molten pool behaviour • Code Validation by CEA and IKE on LIVE tests • LIVE-2 Experiment with complex dissymetrical melt pouring Crust thickness => heat flux

  9. WP 10.1: Late phase core degradation and corium behavior in lower head (2) • Effective Conductivity-Convectivity Modelling (2D/3D) by KTH • Uses characteristic velocities instead of real velocities in convection equations • Validation on natural convection experiments • Applications to complex geometries, • e.g. unit volume around BWR guide tube

  10. WP 10.1: Late phase core degradation and corium behavior in lower head (3) • Modelling of FP release from molten pools • Calculation of FPT1 pool release with RELOS • Negligible in this case, except for Mo (0.2%)

  11. WP10.2: Vessel failure and corium release into cavity • Current focus on Vessel failure • Benchmark on the OECD - OLHF-1 creep rupture test • 6 partners participated in benchmark • To be presented in communication to come • FZD presented coupling of ECM model with mechanic code. • Link with accepted ISTC project (rupture of VVER vessel)

  12. WP11.1: Core and debris coolability during reflooding • Large experimental activity: STYX (VTT), POMECO, DEFOR (KTH), DEBRIS (IKE) • New proposed experiment at IRSN Cadarache on core debris coolability. • Nucl.Eng.Design. Special Issue on Debris Coolability published.

  13. Debris Coolability issues • Previous works dealt with 1D homogeous, monodisperse debris bed • Since the start of SARNET, focus has been put on heterogeneous debris bed, closer to prototypic case. • Showed promises in term of Critical Heat Flux • Probabilistic Approach vs. Bounding Case • Need for further R&D to assess the coolability of debris bed • In the reactor core • In the lower head • In wet reactor pits (Nordic BWRs, e.g.) • SARP High priority issue

  14. WP11.2: Molten corium-concrete/ceramic interaction • 2D experiments • HECLA (VTT) Steel in concrete, transient • VULCANO Oxide then Oxide+Metal (CEA) • Benchmark of the 2-D COMET L1-L2 tests • See dedicated communication • New benchmark on reactor application oxide metal

  15. Further R&D needs on MCCI • High priority issue (SARP) • Concrete ablation isotropy with silica-rich concrete also observed at ANL was confirmed on Chernobyl data provided through ISTC-CHESS project. • Limestone-rich concrete ablation is isotropic – Behaviour consistent with OECD-MCCI project experimental results. • No predictive model currently available. • Further collaborative R&D is needed for current plant and should have application for Gen III+ corium recovery.

  16. Scenario MELCOR/CORCON ASTEC/MEDICIS TB2: no corium spreading no water injection 1.802 m 1.803 m TB3: corium spreading no water injection 0.780 m 0.940 m TB4: no corium spreading water injection 1.797 m 1.792 m TB5: corium spreading water injection 0.805 m 0.823 m WP11.3: Ex-vessel coolability • Modelling of reactor MCCI + Water cooling on VVER • Discussions (and coming benchmark) on a simplified Spreading model for ASTEC,

  17. WP11.3: Ex-vessel coolability • COMET concept • Post test calculations with WABE of VULCANO-COMET test

  18. WP 9/10/11: Thermodynamic and Thermophysical databases • Performance of dedicated experiments for the validation improvement of the NUCLEA Database • Comparisons exp. Calc. • Recommendations for database improvement • Round-robin exercise on material analyses of corium • CEA, ITU, UJV • Aim: quantification of uncertainties on the input data for database. • AECL is going to provide data on CANDU Thermophysical properties to be compared with LWR databases

  19. Link with EC-project PLINIUS FP6 • Access for visiting scientists from EU (except France) and Associated Countries to perform tests in PLINIUS facilities. • VULCANO, KROTOS, COLIMA, VITI • The EU will pay all facility costs + travel and expenses. Users pay only their salary(ies) . • 3 to 5 accesses will be funded by the EU. 4 year project • Formal link with SARNET through Selection Panel (1 delegate Mrs. Lindholm) – Part of the European Corium Research Area. • 1st Call for Proposal Deadline closed in May 2007 • 2nd Call for Proposal open till early 2008. Visit the www.plinius.eu site

  20. Summary of SARNET/Corium main achievements (1/2) • Understanding of the oxidation phenomena in steam and in air, validation of oxidation correlation. The importance of material composition has been demonstrated. Further research is required on new cladding materials, especially in relation to the hydrogen and fission product source term issues. • Collection of data on B4C oxidation, thanks to experiments at FZK and IRSN, which allows a common interpretation of the integral test PhébusFPT3. • The launching of the late-in-vessel LIVE experiments has started a new series of modelling and analytical work on in-vessel pool behavior. • The different models of vessel failure by creep rupture have been compared and a common understanding of the OECD OLHF-1 test has been achieved. Modelling of the crack evolution remains to be done.

  21. Summary of SARNET/Corium main achievements (2/2) • 2D Debris bed coolability analyses for inhomogeneous bed structures showed an increased coolability compared to earlier 1D particle beds. This launches a new interest in this issue both experimentally and numerically including a pursuit of the debris bed formation and its characteristics of coolability importance. • Likewise, the recent 2D Molten Core Concrete Interaction test resulted in unexpected results with a marked ablation anisotropy for silica-rich materials. Interpretation and modelling of this behaviour must be pursued. • Core catcher concepts based on spreading (EPR) and bottom flooding (COMET, downcomers) are being studied and progress has been achieved in their modelling.

  22. Conclusions • Joint activities through benchmarks, pre-post test calculations, transfers of codes, etc… has been found by researchers to have an important impact on the quality of their research. • The large R&D efforts devoted by SARNET partners to corium issues have led to significant achievements and some of the issues are about to be mostly closed. • Nevertheless, pursuing research on the issues related to corium recovery in the reactor pit is still of high priority, as well as, in-vessel coolability and advanced cladding degradation with air.

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