Analysis of concrete ablation depth by MCCI assuming top flooding condition of APR1400 NPP

Abstract

This study assesses whether the integrity of a containment maintains during ex-vessel cooling when a molten corium spreads on a dry reactor cavity floor and then it is cooled by top water flooding in the case of a postulated severe accident in an APR1400 nuclear power plant. The molten corium spreadability in the dry reactor cavity was calculated using CFD, and it was confirmed that the molten corium spreads uniformly on the reactor cavity floor under all assumed conditions. The concrete ablation depth during ex-vessel cooling was calculated using the CORQUENCH 3.03 code according to the reactor cavity flooding delay time from 0.5 hr to 9.0 hr for the dryout heat fluxes from 350 to 650 kW/m2. As a result, it is concluded that the containment of APR1400 NPP keeps its integrity during ex-vessel cooling if the reactor cavity is flooded within 9 hr after the reactor vessel failure.