Addressing the fundamental issues in reliability evaluation of passive safety of AP1000 for a comparison with active safety of PWR

HASHIM Muhammad, YOSHIKAWA Hidekazu, and YANG Ming

College of Nuclear Science and Technology, Harbin Engineering University, 145-1 Nantong Street, Nangang District, Harbin, 150001, Heilongjiang, P.R. China (hashimsajid@yahoo.com, yosikawa@kib.biglobe.ne.jp, myang.heu@gmail.com)

Abstract: Passive safety systems adopted in advanced Pressurized Water Reactor (PWR), such as AP1000 and EPR, should attain higher reliability than the existing active safety systems of the conventional PWR. The objective of this study is to discuss the fundamental issues relating to the reliability evaluation of AP1000 passive safety systems for a comparison with the active safety systems of conventional PWR, based on several aspects. First, comparisons between conventional PWR and AP1000 are made from the both aspects of safety design and cost reduction. The main differences between these PWR plants exist in the configurations of safety systems: AP1000 employs the passive safety system while reducing the number of active systems. Second, the safety of AP1000 is discussed from the aspect of severe accident prevention in the event of large break loss of coolant accidents (LOCA). Third, detailed fundamental issues on reliability evaluation of AP1000 passive safety systems are discussed qualitatively by using single loop models of safety systems of both PWRs plants. Lastly, methodology to conduct quantitative estimation of dynamic reliability for AP1000 passive safety systems in LOCA condition is discussed, in order to evaluate the reliability of AP1000 in future by a success-path-based reliability analysis method (i.e., GO-FLOW).
Keywords: passive safety systems; active safety systems; AP1000; large break LOCA; GO-FLOW