REACTOR CAVITY FLOODING AS AN ACCIDENT MANAGEMENT STRATEGY

The impact of uncertainty in the parameters of deterministic models im portant to flooding the reactor cavity as an accident management strat egy on certainty of the outcome is evaluated. Among the possible param eters, only those that can significantly affect the output of the mode l were selected, based on several preliminary calculations (sensitivit y study for each parameter) and physics. For the selected parameters, probabilistic distributions which represent lack of knowledge were spe cified. It was found that when the reactor cavity is flooded to cool t he vessel lower head, the lower head shell may not melt through and fa il because of stress. Creep may be the only possible failure mechanism . When the reactor coolant system (RCS) is at high pressure, Vessel lo wer head failure is highly probable but the time of failure is uncerta in 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, the re is no load to cause creep. The vessel lower head would be stable. ( C) 1998. Published by Elsevier Science Limited.