Loss of pressurizer water level during station blackout

Station blackout is the loss of all alternating current (ac) power to both the essential and nonessential electrical buses in a nuclear power plant. The US Nuclear Regulatory Commission (NRC) has proposed a requirement that all plants be capable of maintaining adequate core cooling during station blackout events lasting a specified duration. The NRC has also suggested acceptable specified durations of four or eight hours, depending on individual plant susceptibility to blackout events. In a pressurized water reactor (PWR), the occurrence of a station blackout event results in the functional loss of many plant components, including main feedwater, reactor coolant pumps, the emergency core cooling system, and pressurizer heaters and spray. Nevertheless, PWRs have the capability of removing decay heat for some period of time using steam-driven auxiliary feedwater pumps and the natural-circulation capability of the primary system. The purpose of this investigation is to determine the early response of a PWR to station blackout conditions. In particular, the effect of primary coolant shrinkage and inventory loss on pressurizer level is examined to gain insight into the operational and analytical issues associated with the proposed station blackout coping requirement.