Reactor cavity flooding as an accident management strategy

The impact of uncertainty in the parameters of deterministic models important to flooding the reactor cavity as an accident management strategy on certainty of the outcome is evaluated. Among the possible parameters, only those that can significantly affect the output of the model were selected, based on several preliminary calculations (sensitivity study for each parameter) and physics. For the selected parameters, probabilistic distributions which represent lack of knowledge were specified. It was found that when the reactor cavity is flooded to cool the vessel lower head, the lower head shell may not melt through and fail because of stress. Creep may be the only possible failure mechanism. When the reactor coolant system (RCS) is at high pressure, vessel lower head failure is highly probable but the time of failure is uncertain owing to uncertainty in the parameters in the model. If AC power is recovered before vessel failure, the RCS can be depressurized and the vessel lower head may be stable. When the RCS is at low pressure, there is no load to cause creep. The vessel lower head would be stable.