Numerical investigation of corium coolability in core catcher: sensitivity to modeling parameters

To avoid settling of molten materials directly on the vessel wall in severe accident sequences, using of a 'core catcher' device in the lower plenum of sodium fast reactor designs is considered. The device is to collect, retain and cool the debris, created when the corium falls down and accumulates in the core catcher, while interacting with surrounding coolant. This Fuel-Coolant Interaction (FCI) leads to an energetic heat and mass transfer process and may threaten vessel integrity. For simulation of severe accidents, including FCI, the SIMMER code is employed at KIT. SIMMER is an advanced tool for CDA analysis of liquid-metal fast reactors (LMFRs) and other GEN-IV systems. It is a multi-velocity-field, multiphase, multicomponent, Eulerian, fluid dynamics code coupled with a fuel-pin model and a space- and energy-dependent neutron kinetics model. However, the experience of SIMMER application to simulation of corium relocation and related FCI is limited. To verify the code applicability to FCI in a large system, an in-vessel model based on European Sodium Fast Reactor (ESFR) was established and calculated by the SIMMER code. In addition, a sensitivity analysis on some modeling parameters is also conducted to examine their impacts. The characteristics of the debris in the core catcher region, such as debris mass and composition are compared. Besides that, the pressure history in this region, the mass of boiling sodium vapor and average temperature of liquid sodium, which can be treated as FCI quantitative parameters, are also discussed. It is expected that the present study can provide some numerical experience of the SIMMER code in plant-scale corium relocation and related FCI simulation.