Depressurization to mitigate direct containment heating

Direct containment heating (DCH) can potentially occur during certain pressurized water reactor (PWR) severe accidents after core melt and high-pressure melt ejection from the reactor pressure vessel (RPV). Molten core material is dispersed into the containment and a rapid transfer of energy to the containment atmosphere follows. The resultant rise in the temperature and pressure could cause the containment to fail relatively early in the accident sequence. Depressurization of the reactor coolant system (RCS) is a proposed accident management strategy to reduce the DCH contribution to early containment failure. An analysis evaluating the effectiveness of this strategy has been conducted. The capability to depressurize a three-loop PWR during a TMLB' sequence (loss of alternating current power and feedwater) using the pressurizer power-operated relief valves (PORVs) and the RPV head vent was analyzed using the SCDAP/RELAP5 computer code