The core corium may melt through the reactor pressure vessel wall then lead to the failure of the second barrier during a serious accident. Core catcher can collect and cool the corium and prevent the development of severe accident.

This study aims to establish a computational model to explore the cooling process of crucible core catcher adopted by VVER (Vodo-Vodyanoi Energetichesky Reactor) designed by Russia.

According to the derived parameters based on VVER core catcher design data, non-isothermal flow calculation module of COMSOL was established to simulate the flow field, temperature field, and crust distribution of corium pool. The solidus temperature and liquidus temperature and the exponential form change of corium viscosity were referred to the research results of VULCANO item.

For the double layered structure of the corium pool in core catcher, the metal layer solidifies quickly after a core meltdown accident. Constantly changing natural convection flows are formed in the upper and middle part of the oxide layer and the temperature distribution is relatively uniform. No strong convection exists in the lower part of the oxide layer lead to obvious thermal stratification. Most of the corium cooled in the upper part of the oxide layer will transfer to the lower part by gravity and natural convection before full solidification, resulting in a slow increase in the thickness of the upper crust and a rapid increase in the bottom crust of the oxide layer.

The safety margin of crucible core catcher of VVER is sufficient, however the relevant equipment, support and auxiliary system are required to remain operational for a long time to realize the design function.