Pressurized thermal shock analysis of a reactor pressure vessel for optimizing the maintenance strategy: Effect of asymmetric reactor cooling

Abstract

The structural integrity of a reactor pressure vessel (RPV) is significant for nuclear plant safety. In assessing the integrity of the RPV, one of the most severe situations to be considered is pressurized thermal shock (PTS) during emergency water cooling. Many efforts have been made to understand this PTS, and these efforts assumed symmetric reactor cooling injection. However, once extreme circumstances occur, such as a major earthquake, some of the cooling injections will fail. This failure makes symmetric injection impossible, leading to more serious conditions. In this study, the effect of asymmetric reactor cooling was investigated using three-dimensional computational fluid dynamics and the finite element method. Our results indicate that the most asymmetric injections provide approximately 30% more serious situations than symmetric injections. Additionally, a risk-based methodology was proposed for optimizing the maintenance strategy of an emergency cooling system, where the probabilities of the occurrence of RPV fracture are used as indicators representing the risk.