ASTEC application to in-vessel corium retention D. Tarabelli, G. Ratel, R. Pelisson – CEA

1. ASTEC application to in-vessel corium retention D. Tarabelli, G. Ratel, R. Pelisson – CEA M. Barnak, P. Matejovic - IVS

2. Corium retention strategy can be achieved by : Ex vessel spreading In-Vessel Retention ASTEC development and application for IVR analysis • DIVA : Corium behavior in the lower head • CESAR : Vessel cooling using an ERVC • ASTEC application on VVER440

3. Arbitrary corium configurations with : • Relevant heat transfer coefficient • Thermodynamic equilibrium situation • Correction of simplifications • Available in the ASTEC V1.3 reference code version From ASTEC V1.2 modeling to ASTEC V1.3 Restricted heat transfer correlations + minor simplifications A fixed configuration

4. Radiative heat transfer Light metal layer 2 layers out of thermodynamic equilibrium Molten oxide pool 2 layers in thermodynamic equilibrium Heavy metal layer ASTEC V1.3 modeling : general considerations So-called Masca configuration

5. BALI Jahn Globe & Dropkin Chawla & Chan BALI Steinberner & Reineke ASTEC V1.3 modeling : heat exchanges Basic assumptions No internal power With internal power

6. ASTEC V1.3 : status and perspectives • A postulate PWR application • Corium initial configuration (from bottom to top) • 5 tons of heavy metal • 120 tons of oxyde • 5 tons of light metal • Heavy metal and oxyde layers in thermodynamic equilibrium • fine meshing (R & Z) of the vessel may be necessary Qualification work to be performed on LIVE and SIMECO tests (JPA 3 and JPA4)

7. Vessel external cooling : objectives • CESAR module calculates two-phase flow in RCS  necessary adaptations • CESAR is coupled with DIVA to simulate the coupling between the external surface of the vessel and the coolant • The external circuit is calculated by CESAR as an independent channel (not connected to the primary or the secondary circuit. DIVA CESAR h,T F

8. Limitation for the DIVA - CESAR coupling • Due to Diva mesh number limitation a focus must be done on the position of the metal layer • Maximum number of cells in the radial direction is 5 • Maximum number of cells along the vessel 17 • This limitation can be important for the Vessel rupture • The vertical size of the cells in the lower head at the metal layer level must be lower than the metal layer thickness to avoid an averaging process which can hide the Foccussing effect • The radial size of the remaining cells in front of the metal layer must be high enough to be compatible with the DIVA rupture model of the vessel Metal layer Oxide layer

9. First CESAR stand alone evaluation • Vessel external cooling • Stand alone evaluation of CESAR • A vertical wall with a prescribed heat flux heats a channel (thickness 5cm, 6m high) belonging to a closed circuit : strong oscillations occur 1 bar Fixed flow rate • Works on heat transfer strongly reduced the oscillations • Conclusion : heat flux up to 1MW/m2 have been calculated, but in some calculation with a small thickness, numerical oscillations are severe. Fixed power

10. Sultan Qualification of CESAR Stand Alone mode (2) • Vessel external cooling • SULTAN experiment Calculation with CESAR (2) Prescribed Presure 1b Wall Prescibed power Comparison for for the pressure drop in the SULTAN channel as a function of the flow rate between Experiment and Cathare calculations (left) and CESAR calculations (right) (Ps=0.1MPa, vertical channel 15cm, 0.5MW/m2).

11. An example for the coupled tools with forced convection • DIVA/CESAR COUPLING Links between code are available VVER 440 Geometry, 3 layers, A forced convection open loop to model the External Vessel Cooling Circuit

12. steam/water vent molten metal l UO2 ZrO2 crust screening of impurities isolation valve ASTEC V1.2 application to VVER-440 • VVER-440/V213 design – candidate for IVR application: • low core power • no penetrations in RPV lower head • massive stainless steel internals …. • DIVA stand alone analyses performed using defined corium composition and decay heat • External cooling modelled using defined HTC and temperature water in confinement

13. Two results were used for benchmarking: - “Loviisa”configuration - used for IVR at Loviisa NPP (Finland); - ”ARVI” configuration – used in ARVI project, MVITA (KTH) calculation; • Thickness of upper metallic layer for “Loviisa” > “ARVI”

14. “Loviisa” configuration: heat flux and wall ablation – comparison of Finnish (green) and ASTEC (red) results

15. “ARVI” configuration: temperature field and heat flux distribution comparison of MVITA (green) and ASTEC (red) results.

16. Conclusions • The ASTEC modeling of the corium when located in the lower plenum has been massively rewritten. The new modeling allows: • Arbitrary layer configuration • Thermodynamic equilibrium • Up to date heat transfer coefficients between pools and between pools and the vessel • The coupling between CESAR and DIVA allows to compute more precisely the external cooling circuit. Forced convection are already possible but an improvement of the tools is necessary. • First ASTEC IVR applications performed to VVER-440 design – reasonable agreement obtained with the results of another analyses