Applying shutdown risk strategies to outage planning to minimize risk during shutdown outage activities

Shutdown risk analyses performed for U.S. and foreign nuclear power plants have suggested that accidents occurring during shutdown activities are significant contributors to a plant's overall total core damage frequency. Typically, during shutdown activities, fewer safety systems are available to mitigate the consequences of an accident. Shutdown operations also provide a greater opportunity for human error because of the numerous maintenance and operational activities that are carried out during outages and that may result in accident initiation or failure in recovering key safety systems. Risk during shutdown operations can be minimized by identifying potentially high-risk periods and ensuring that sufficient mitigation systems are readily available. Crucial to the analysis is the identification of the critical safety functions that must be maintained during shutdown operations. This paper reviews shutdown risk assessment activities associated with refueling and forced outages at the Palo Verde nuclear plant.