Numerical simulation of relocation behavior of molten debris in reactor pressure vessel on severe accident

Yamashita, Susumu   ; Takase, Kazuyuki; Yoshida, Hiroyuki  

In order to understand phenomenologically, we have been developing the numerical simulation method for predicting the melting core behavior including solidification and relocation based on the multi-phase thermal-hydraulic simulation models. In this code, each of gas, liquid and solid phase are treated individually, and interface between two phases are simulated directly. In this paper, the developed code was applied to numerical simulations of the melting behavior of the simulated fuel assemblies and reactor structures. In the simulation, complicated structures in the BWR lower plenum were simply modeled. From the present numerical results, it was confirmed that relocation of molten debris in the RPV can be simulated by the currently developed code including effects of melting and solidification of debris in two components flow simulation. And it was also confirmed that relocation of molten debris with decay heat could be simulated in three components flow simulation.