BackgroundIn-vessel Retention (IVR) refers to the prevention of pressure vessel melt-through failure by injecting cooling water into the gap between the pressure vessel and the heat insulation layer during a serious accident in a nuclear power plant. When the double-layer corium pool formed in the lower head of the reactor pressure vessel (RPV), the lower head in contact with the metal layer may fail due to the heat accumulation in the metal layer.PurposeThis study aims to build a computational model by numerical simulation to investigate the thermal hydraulic characteristics of the double-layer corium pool in pressurized water reactor (PWR).MethodsBased on the design parameters of current large third generation PWR, the calculation model of the fluid-heat-solid coupling double-layer corium pool was established by using COMSOL Multiphysics code. The upper surface of metal layer was considered as the radiation boundary condition, and the outside of the lower head was set as forced convection cooling.ResultsSimulation results show that a natural convection main flow forms in the oxide layer in stable two-layer corium pool, and a mass of vortexes exist in the metal layer. The lower head in contact with the oxide layer does not melt obviously whilst significant melting occurs in the lower head area in contact with the metal layer due to the rising temperature. The completeness of the pressure vessel is maintained under normal cooling conditions.ConclusionsThe IVR design is proved efficient to protect the pressure vessel form melt failure during a serious accident.