EP1000 shutdown safety evaluation

The EP1000 uses passive safety systems developed for the AP600 to enhance plant safety and to satisfy EUR requirements. The use of these passive safety systems has provided significant and measurable improvements in plant simplification, safety, reliability, investment protection and plant costs. As a part of the licensing review of the AP600, the US NRC required a systematic assessment of shutdown operations. The NRC reviewed this assessment and concluded that the AP600 is designed to mitigate all design basis events that could occur during shutdown operations and the risk of core damage as a result of an accident that may occur during shutdown operations is acceptably low. A preliminary shutdown safety assessment of the AP1000 has been performed. This assessment included an evaluation of the levels of defense during shutdown operation, an assessment of the design basis events, and evaluation / analysis of these design basis events. Based on this evaluation several shutdown events were identified that were not bounded by events initiating from at-power conditions. These limiting shutdown design basis events were analyzed and based on this analysis, some improvements to the actuation logic have been developed. The results of these analyses demonstrate the capability of the EP1000 passive safety features to provide effective core cooling during shutdown events. (author)