Probabilistic accident analysis: ATWS

Using operational experience for plant parameters, the probability that the peak reactor coolant system pressure will exceed allowable pressure has been evaluated for the Loss of Feedwater (LOFW) Anticipated Transient Without Scram (ATWS) for the Standard 3800 MWt, 205 fuel assembly, Babcock and Wilcox reactor. The probabilistic approach to ATWS is reviewed including current estimates of anticipated transients' frequency, probability of scram system failure, and probability of excessive peak pressure. The result of the present study is a best estimate probability of 0.18 that an allowable pressure of 3750 psia would be exceeded if an ATWS were to occur and 0.6 that 3200 psia would be exceeded. Considering all uncertainties and using estimates of transient frequency and scram system failure, it is found that the frequency of significant ATWS events is smaller than 1.1 x 10/sup -6/ per reactor per year. Thus it is concluded that the ATWS safety goal of approximately 10/sup -6/ per reactor per year has been met with the current design. A proposed redundant Backup Scram System (BUSS) to the present generation reactor protection system would reduce the estimate to approximately 7.8 x 10/sup -7/ per reactor per year. Therefore, compliance with th ATWS safety goalmore » is demonstrated.« less