The postulated core disruptive accidents (CDAs) are regarded as particular difficulties in the safety analysis of liquid-metal fast reactors (LMFRs). In the CDAs, core debris may settle on the core-support structure and form conic bed mounds. Heat convection and vaporization of coolant sodium will level the debris bed, which is named “self-leveling behavior” of debris bed. To reasonably simulate such transient behavior, as well as thermal-hydraulic phenomena occurring during a CDA, a comprehensive computational tool is needed. The SIMMER code is a successful computer code developed as an advanced tool for CDA analysis of LMFRs. 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. Until now, the code has been successfully applied to simulations of key thermal-hydraulic phenomena involved in CDAs as well as reactor safety assessment. However, strong interactions among rich solid particles as well as particle characteristics in multiphase flows were not taken into consideration for its fluid-dynamics models. Therefore, a hybrid computational method was developed by combining the discrete element method (DEM) with the multi-fluid models to reasonably simulate the particle behaviors, as well as the thermal-hydraulic phenomena of multiphase fluid flows. In this study, 3D numerical simulation of a simplified self-leveling experiment is performed using the hybrid method. Reasonable agreement between simulation results and corresponding experimental data demonstrated the validity of the present method in simulating the self-leveling behavior of debris bed.

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