Level-1 PSA on large fast breeder reactor

Hioki, Kazumasa ; not registered ; not registered 

The Systems Analysis Section has performed a probabilistic Safety Assessment (PSA) on a large fast breeder reactor (FBR). The objective of the study is to apply the PSA method to a plant in a conceptual design stage, develop system models, perform quantitative analyses and systematic evaluation, supply valuable insights to enhance reliability and safety, and reflect them to the basic design. The plant analyzed is a 600MWe class large FBR designed by the Plant Engineering Section in the "Large FBR design study" that has been performed since JFY 1990. The report presents the results of level-1 PSA on internal events. The system models were constructed using fault trees and event trees and accident sequences which lead to core damage were identified and quantified. The systems and the components that are important to safety and the dominant accident sequences were identified based on the results of importance analyses and sensitivity studies. Insights were obtained through the systematic analyses that are effective for the enhancement of reliability and safety of the plant. As a result of the assessment based on the conceptual design the frequencies of LORL and ATWS are very low and the core damage frequency is dominated by PLOHS. The frequency of PLOHS is more than two orders of magnitude smaller based on the expected basic design and best estimate success criteria. The sensitivity study shows that the frequency decreases one more order if the Maintenance Cooling System has the same heat removal capability as one of the Auxiliary Cooling System loops.