Application of shutdown probabilistic safety assessment

Abstract Shutdown probabilistic safety assessment represents an extension of probabilistic safety assessment performed for other plant operating states, excluding power operation, which is covered in probabilistic safety assessment. The objective is to present the method of shutdown probabilistic safety assessment and its application on real nuclear power plant example model to evaluate the feasibility of the future wider use. The main methods are similar to conventional probabilistic safety assessment including the fault tree analysis, the event tree analysis, the common cause failures analysis, the human reliability analysis and the probabilistic data collection and analysis. Results interpretation reveals differences between power and other operating states probabilistic safety assessment. Most of the results have been expected including notable or significant differences among the plat operating states regarding the minimal cut sets, regarding the main risk contributors, regarding the importance factors for equipment, regarding the variability of initiating events contributions which are easily explained due to the differences among the plant operating states. The results revealed a variability of durations of the plant operating states among different shutdowns, which causes large differences in risk results among different shutdowns and different overall risk. Such variability may require the adjustment of risk informed decision making methods.