We develop an analytical model about concrete ablation during ex-vessel cooling in a pre-
flooded cavity. The model considers the melting of dry debris bed, the formation of crust, the
growth of crust and the thermal ablation of concrete. This model can obtain concrete ablation
depth during ex-vessel cooling. It is evaluated the adequacy of ex-vessel cooling in the pre-
flooded reactor cavity of Westinghouse 3-loop nuclear power plants. If the debris bed is
formed only in the zone directly below the reactor vessel narrowly and thickly, the …