Analysis of the effectiveness of in-vessel retention strategy under a three-layer corium pool configuration

To cope with the corium cooling issue in severe PWR accidents, Generation III reactors commonly employ the IVR (in-vessel retention) approach, which involves flooding the reactor cavity. The stratification of different melted core internals influences the temperature field and velocity field of the corium pool, thereby affecting the distribution of heat load on the reactor pressure vessel steel shell. The success criterion for the IVR strategy in present PWR safety assessments is that the local heat flux acting on the RPV wall from the molten corium must stay below the lower-head boiling CHF. In this paper, a CFD model is built to simulate the three-layer condition composed of metal and oxide, providing a basis for the further study of thermal-hydraulic phenomena in the corium pool and the integrity of the RPV lower head. Simulation findings indicate that adequate external cooling of the RPV vessel wall ensures the retention of lower head structural integrity under severe accident conditions.