Overview of results and perspectives from the Shoreham major common-cause initiating events study

This study represents the continuation of a large effort by LILCO to fully understand the potential hazards posed by future operation of the Shoreham Nuclear Power Stations (SNPS). The Shoreham Probabilistic Risk Assessment, a level 3 PRA without external events, provided a characterization of the accident sequences that could leave the core in a condition in which it would be vulnerable to severe damage if further mitigating actions were not taken. It estimated the frequency and magnitude of the potential radioactivity releases associated with such sequences. The study was limited to accident sequences initiated by so called internal events to the plant including a loss of offsite power. It also characterized the public risk associated with those accident sequences. The ''Major Common-Cause Initiating Events Study'' (MCCI) for the Shoreham plant was performed to obtain insights into the plant's susceptibility to, and inherent defenses against, certain MCCIs. Major common-cause initiating events are occurrences which have the potential to initiate a plant transient or LOCA and, also, damage one or more plant systems needed to mitigate the effects of a transient or LOCA. The scope of the MCCI study included detailed analyses of seismic events and fires through the severe core damage and bounding analyses of aircraft crashes, windstorms, turbine missiles and release of hazardous materials near the plant