Analysis of AP1000 containment passive cooling system during a loss-of-coolant accident

A loss-of-coolant accident (LOCA) is one of the design basis accidents (DBAs) in nuclear power plant safety. DBAs may cause containment failure as a result of high temperature or pressure from LOCAs. This study investigates the integrity of the protective mechanism of the AP1000 containment system during a LOCA. The performance of the passive containment cooling system (PCCS) and the ability to perform decay heat removal for long-term cooling are evaluated in this study. The PCCS utilizes gravity-driven natural convection and naturally induced passive safety devices to move the decay heat of fuels to the atmosphere. In this study, two accidents are selected for analysis: a double-ended guillotine of a hot leg and a double-ended break of a main steam line. The analytical results are compared with the corresponding results provided in the AP1000 “Design Control Document” (DCD). The short-term calculations and comparisons with the DCD suggest that GOTHIC 7.2a with a natural convection model may properly represent the phenomenon of passive, safe heat removal. This paper also simulates the long-term calculations of spraying the outer primary containment with a water film and the steam condensation of the inner containment.