Evaluation of ATWS core damage frequency for a BWR/4

This paper reports a study performed to evaluate the core damage frequency contribution from Anticipated Transient Without Scram (ATWS) in a BWR/4 plant. Discussions on improvements in the design and operation of BWR plants to reduce the likelihood of occurrence and core damage frequency of ATWS have continued for years. In November 1981, subsequent to the issuance of three alternate proposed ATWS rules, the Nuclear Regulatory Commission invited comments on these rules. In June 1984, a final rule on the reduction of risk from ATWS events was issued. In the study, it is assumed that the BWR/4 reactor is of an earlier vintage. However, only two of the modifications have been implemented in accordance with the final rule: a diverse scram system and automatic recirculation pump trip. It is further assumed that the setpoint for Main Steam Isolation Valves (MSIVs) closure is at reactor pressure vessel (RPV) water level 1 and that the BWR emergency procedure guidelines are implemented.