Intentional depressurization accident management strategy for pressurized water reactors

In a previous investigation of the Surry nuclear power station, it was concluded that intentional depressurization of the reactor coolant system (RCS) could prevent or mitigate the effects of direct containment heating (DCH) during a station blackout transient. Two strategies, early and late depressurization, were investigated as methods to mitigate DCH. The investigation concluded that since there are greater opportunities to recover plant functions before core damage occurs and operator response uncertainties are lessened, the strategy of late depressurization is preferred over early depressurization. The results of the Surry analysis were extended to other US pressurized water reactors (PWRS) in order to evaluate their capability to successfully employ the late depressurization strategy to prevent or mitigate DCH. By applying appropriate scaling factors to the selected key parameters, this evaluation resulted in the categorization of four PWR groups based upon their perceived late depressurization capability. In this report, a PWR representative of each of the four PWR groups was chosen for detailed analysis of its capability to intentionally depressurize employing the late depressurization strategy. The phenomenological behavior, hardware performance, and operational performance of these PWRs during the intentional depressurization strategy were considered. The phenomenological behavior was analyzed using the SCDAP/RELAP5/MOD3 severemore » accident analysis code. The results of these evaluations were then extended to the remaining PWRs comprising each PWR group.« less