CHOOSE EXPERTS, FIND PARTNERS Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Philippe Dejardin ERMSAR 2012, Cologne March 21 – 23, 2012

2 TABLE OF CONTENT Objectives and methodology Cases definitions, results and findings -Base cases & foreseen parametric cases -Additional parametric cases Conclusions and recommendations Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4 ERMSAR 2012, Cologne March 21 – 23, 2012

3 TABLE OF CONTENT Objectives and methodology Cases definitions, results and findings -Base cases & foreseen parametric cases -Additional parametric cases Conclusions and recommendations ERMSAR 2012, Cologne March 21 – 23, Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4

4 OBJECTIVES & METHODOLOGY Objectives -Derive parameters of importance for reactor cases under dry MCCI conditions -Achievement of clear conclusions and recommendations for future work -Contribution to the international effort Methodology -Use of the ASTEC / MEDICIS module in stand-alone -Definition of a parametric study considering both siliceous and limestone-common-sand concretes types under dry cavity conditions -Base cases + several foreseen parametric cases investigating 3 axes of interest Intrinsic initial parameters of the reactor cavity Scenario-dependent parameters affecting the initial state of the MCCI Physical model parameters involved in some MCCI phenomena ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

5 TABLE OF CONTENT Objectives and methodology Cases definitions, results and findings -Base cases & foreseen parametric cases -Additional parametric cases Conclusions and recommendations ERMSAR 2012, Cologne March 21 – 23, Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4

Concrete composition SILLCS Al %2.54% CaO9.97%35.31% CO %22.51% H2OH2O9.58%7.54% SiO %32.10% Corium composition Masses [T] UO ZrO Zr8.0 Fe14.2 Cr3.4 Ni m 9.0 m 3.5 m Z r 6 REACTOR CASES - BASE CASE / DEFINITION Cavity geometry and concrete composition Corium initial conditions -80 tons UO 2 / 20 tons Zr (60% ox.) / 20 tons stainless steel -Stratified initial configuration with initial temperature = 2400°C Solid oxide layer at the bottom / Liquid metal layer at the top Boundary conditions -Decay heat evolution with MCCI onset 1.5 h after SCRAM -Constant cavity environment: 1700°C / 1.5 bar abs Physical model parameters -Stratification evolution parameter: b_HS = m/s -γ = 0.2  T_solidif = 0.2 T_solidus T_liquidus Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

7 FORESEEN PARAMETRIC CASES - DEFINITIONS Case Initial cavity parametersScenario dependent parameters Physical model parameters concretegeometrycorium compositionboundary conditions typedensityT_ablaΔh_ablaradius stainless steel mass ZrO2/Zr oxidation ratio cavity temperature delay between SCRAM and MCCI b_HSgamma [kg/m^3][K][J/kg][m][tons][%][K][h] [BC]SIL E [P1]SIL E [P2]SIL E [P3]SIL E [P4]SIL E [P5]SIL E [P6]SIL E [P7]SIL E [P8]SIL E [P9]SIL E [P10]SIL E [P11]SIL E [P12]SIL E Calculation matrix – SIL concrete Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

8 BASE CASES & FORESEEN PARAMETRIC CASES - RESULTS (1/2) Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

9 BASE CASES & FORESEEN PARAMETRIC CASES - RESULTS (2/2) Homogeneous – isotropic global ablation behaviour Example for SIL base case -Radial / axial ratio ~ 1.2 -Slight anisotropy due to initial radial ablation by top metal layer -BMMT after 7.08 days (3.5 m)  axial ablation ~ 2 cm/h ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

10 Rather homogeneous ablation and long BMMT times (4 to 9.5 days for 3.5 m) -No occurrence of a stratified configuration with a bottom metal layer -Important conclusion regarding safety as base cases developed based on best estimate values of the different parameters + foreseen parametric cases considering plausible variations of these parameters -To be nuanced in view of remaining uncertainties and possible parameters combinations Gas content in concrete is expected to play a fundamental role -Rather high H 2 O content (9.58 wt%) in considered SIL concrete compared to some other studies for which a stratified configuration was observed  cliff-edge effect suspected -Strong recommendation = to study the impact of the gas content (H 2 O and CO 2 ) BASE CASES & FORESEEN PARAMETRIC CASES - CONCLUSIONS ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

11 TABLE OF CONTENT Objectives and methodology Cases definitions, results and findings -Base cases & foreseen parametric cases -Additional parametric cases Conclusions and recommendations ERMSAR 2012, Cologne March 21 – 23, Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4

12 ADDITIONAL PARAMETRIC CASES - DEFINITIONS Several additional parametric cases based on previous recommendation -Base case of SIL concrete adapted to consider a theoretical concrete composition with varying H 2 O content (instead of 9.58%) -H 2 O content varied between 4 and 10 wt% -Other species normalized over the remaining fraction -Very low CO 2 content in theoretical concrete considered (< 1%) -Global composition is theoretical and may not be representative of an actual reactor case All other parameters identical to the base case for the SIL concrete Theoretical concrete composition Example: Mod. SIL 5% Al % CaO10.473% CO % H2OH2O5.000% SiO % ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

13 ADDITIONAL PARAMETRIC CASES - RESULTS (1/3) Cliff-edge effect between 5.5 and 7.0 wt% of H 2 O 2 driving phenomena -Impact on the gas superficial velocity -Impact on the metal inventory Remark -Stratification stabilized as opposite evolution precluded in calculation Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

14 ADDITIONAL PARAMETRIC CASES - RESULTS (2/3) Short term example with 5 wt% of H 2 O content -Predominant axial ablation -Faster MCCI kinetics leading to BMMT after only 20.5 h -Explanation of fast axial ablation to be found in the geometrical effect linked to the very thin metal layer thickness Contact with cavity walls for a short duration Continuous contact with basemat Axial ablation kinetics -Stratified  3.5 m in 20.5 h  ~ 17 cm / h ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

15 ADDITIONAL PARAMETRIC CASES - RESULTS (3/3) Medium term example with 6.5 wt% of H 2 O content -Predominant axial ablation stopped at around 0.8 days  configuration switch after ~ 2 m of ablation -Rest of ablation is “homogeneous”  BMMT retarded until 3.09 days Axial ablation kinetics -Stratified  2 m in 0.8 days  ~ 10.4 cm / h -Homogeneous  1.5 m in 2.29 days  ~ 2.75 cm / h ERMSAR 2012, Cologne March 21 – 23, 2012 Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper

16 TABLE OF CONTENT Objectives and methodology Cases definitions, results and findings -Base cases & foreseen parametric cases -Additional parametric cases Conclusions and recommendations ERMSAR 2012, Cologne March 21 – 23, Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4

17 CONCLUSIONS AND RECOMMENDATIONS Two main conclusions -Rather homogeneous ablation without any stratification for all the best estimate cases foreseen  more favourable from a safety point of view as longer BMMT times -Fundamental role of the concrete gas content on the occurrence of a stratified configuration  additional parametric cases with theoretical concretes having lower H 2 O contents  evidence of a cliff-edge effect regarding the BMMT time One main recommendation -Study further the impact of the concrete gas content in future work (H 2 O and CO 2 ). First step has been performed regarding the cliff-edge effect linked to the H 2 O content Including increasing our knowledge of concrete gas content in actual power plants ERMSAR 2012, Cologne March 21 – 23, Parametrical study on MCCI reactor cases under dry cavity conditions for assessment of parameters of importance Session 4 “Ex-vessel corium behaviour” – Paper 4.4