1. ERMSAR 2012, Cologne March 21 – 23, 2012 A SARNET Benchmark on two VULCANO Molten Core Concrete Interaction Tests C. Journeau 1, J.F Haquet 1, B. Letexier 1, A. Greco 1, B. Spindler 2, R. Gencheva 3, P. Groudev 3, D. Dimov 4, A. Fargette 5, J. Foit 6, B. Michel 7, C. Mun 7, T. Sevon 8, C. Spengler 9, F. Polidoro 10 1 CEA, Cadarache (FR)2 CEA, Grenoble (FR) 3 INRNE, Sofia (BG)4 Energy Inst., Sofia (BG) 5 AREVA NP, Erlangen (DE)6 KIT, Karlsruhe (DE) 7 IRSN, Cadarache (FR)8 VTT, Espoo (FI) 9 GRS, Cologne (DE)10 RSE, Milan (IT)

2. ERMSAR 2012, Cologne March 21 – 23, 2012 Outline 1. Test presentation 2. Benchmark characteristics 3. Calculations vs. Experiment 4. Synthesis, conclusions and perspectives

3. ERMSAR 2012, Cologne March 21 – 23, 2012 Main Test characteristics Limestone rich concrete (VB-U6) - Silica rich concrete (VB-U5) Corium masses 31 kg (U6) – 28 kg (U5) Net power ~ 9kW (U6) - 11.5 kW (U5)  1 kW (Side View) TEST SECTION (Cross View)

4. ERMSAR 2012, Cologne March 21 – 23, 2012 Concretes Concrete F- VB-U5 Concrete G VB-U6 SiO 2 64.725 CaO16.441 Al 2 O 3 5.12 CO 2 9.325 H2OH2O3.17 Fe 2 O 3 1.40 Concrete – corium pseudobinary phase diagrams

5. ERMSAR 2012, Cologne March 21 – 23, 2012 Partners and codes In this benchmark nine organisations from 5 different EU countries have been involved. They simulate main MCCI phenomena in VB-U5 and VB-U6 tests using different codes as it is pointed bellow: – MEDICIS (ASTECv2) code used by IRSN, France, GRS, Germany, EI, Bulgaria and INRNE, Bulgaria; – TOLBIAC-ICB v3.2 code used by CEA-Cadarache, France and CEA-Grenoble, France; – CORQUENCH 3.03 code used by VTT, Finland; – COSACO code used by AREVA, Germany; – WECHSL code used by KIT (FZK), Germany; – CORIUM2D code used by RSE, Italy The purpose of these analyses is to compare code results with the results obtained by the tests, to compare the best-estimated assumptions and to synthesize conclusions

6. ERMSAR 2012, Cologne March 21 – 23, 2012 Ablation Rate VB-U6 (limestone-rich) Models consider either isotropic ablation for VB-U6 or have standard correlation for each direction 2 types of modelling: With initial transient (thermal inertia) ~constant ablation rate (TOLBIAC) Average ablation rate ~2 cm/s

7. ERMSAR 2012, Cologne March 21 – 23, 2012 VB-U6 Ablation shape CEA Grenoble 3 (anisotropic ablation) indeed shows a too large radial ablation. VB-U6 is indeed rather isotropic. KIT and RSE exhibit too small lateral ablation/ too large axial All the others provide a reasonably good fit.

8. ERMSAR 2012, Cologne March 21 – 23, 2012 VB-U5 Ablation (silica-rich) Various approaches – No coefficient to model anisotropy: Too large axial ablation – No coefficient but different h : VTT/CORQUENCH: good shape – Empirical coefficient added: leads to rather good fit of curves  Predictive nature of the empirical coefficients to be assessed

9. ERMSAR 2012, Cologne March 21 – 23, 2012 VB-U5 Ablated volumes Rather good fit of results Major uncertainty lies with axial/lateral ablation anisotropy

10. ERMSAR 2012, Cologne March 21 – 23, 2012 Corium Pool Temperatures Few measurements available (improved in recent tests) Uncertainty: <200 K RSE overestimates temperatures (linked with too, small ablation) Approaches with T interface =T solid underestimate the pool temperature by several 100s K. Models with T interface ~T liquidus provide better simulation. – TOLBIAC (CEA) – AREVA (U6), EI (U5) – TOLBIAC with macrosegregation gives too low temperature.

11. ERMSAR 2012, Cologne March 21 – 23, 2012 Pool composition UO2 wt% Analyses: 40-53wt% UO2 in central part of pool TOLBIAC do not model well final composition – CEA_gre: Macrosegregation: crusts enriched in UO2-ZrO2 – CEA_cad: crust at pool composition at the time of deposit Even if there are crusts, they must be remelted when ablation progresses and be at a composition close to the final melt pool composition. Exp. value

12. ERMSAR 2012, Cologne March 21 – 23, 2012 Synthesis 10 partners – 6 code benchmark was a key point in EU networking on MCCI. Cavity volume and shape are roughly well predicted – VB-U5 needs to take into account anisotropy, either explicitly or implicitly (CORQUENCH). – Axial ablation is generally overestimated Assuming an interface temperature around liquidus provides better estimates of the pool temperature Crusts, if they exist, shall have a composition close to the current pool composition.

13. ERMSAR 2012, Cologne March 21 – 23, 2012 Conclusions Up to now, it is still not possible to propose a comprehensive modelling of MCCI that could predict the observed anisotropy and all the parameters of the experiment. No single calculation has been able to compute all the parameters of the experiments. But we are using multi 0D quasi-steady state modelling to model an intermittent ablation process – complex geometry both at the interface – complex convection pattern in the pool because of combined effects of gas bubbling and solutal convection. Nevertheless, reasonably good estimates of ablation volume and profile.

14. ERMSAR 2012, Cologne March 21 – 23, 2012 Conclusions - Perspectives VB-U5 and VB-U6 were within the first VULCANO MCCI experiments They used typical Gen 2 plant concretes and prototypical corium Latest VULCANO tests have better measurements – Better estimation of radiated and ablated powers – Valid measurement of temperature every ~10 min Coming SARNET-VULCANO tests shall eliminate initial transient crusts (by introduction of Zr) SARNET is in parallel writing a State of the Art report.