Reactor Cavity Flooding as an Accident Management Strategy

This study deals with the uncertainty in the parameters of deterministic models important to flooding the reactor cavity as an accident management strategy. Among the parameters, a few 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 due to stress. Creep may be the only possible failure mechanism. When the RCS is at high pressure, vessel lower head failure is highly probable but the time of the failure is uncertain due to uncertainty in the parameters in the model. if AC power is recovered before vessel failure, the RCS can be de-pressurized and the level lower head may be stable. A further study of the availability of a system for depressurization at AC power recovery timing is needed. When the RCS is at low pressure, there is no load to cause creep. The vessel lower head would be stable