Dominant accident sequences derived from review of five PRA studies

This chapter reviews and compares the probabilistic risk assessment (PRA) studies conducted at the Big Rock Point, Zion, Limerick, Grand Gulf, and Arkansas Nuclear One reactors. The overall objective is to provide a summary of the studies together with an interpretation of the results that will help both technical specialists and management personnel understand the state-of-the-art in risk assessment, the validity of the methods employed, and the conclusions reached. An additional objective is to identify technical issues that are worthy of further discussion or in need of further research and development. It is determined that the long-term heat removal is the single largest functional contributor to core-melt frequency for both pressurized water reactors (PWRs) and boiling water reactors (BWRs). PWR accident sequences are dominated by small loss-of-coolant accidents (LOCAs) and transients. For BWRs, the dominant contributors are the transient events with LOCA sequences making only a minor contribution on the order of 10%