Estimation of common cause failure parameters for essential service water system pump using the CAFE-PSA

This paper presents the estimation results of the common cause failure (CCF) parameters of essential service water system (ESWS) pump failure to run for KX nuclear power plant (NPP) in Korea. Until now, the generic values of the CCF parameters have been mainly used in most probabilistic safety assessment (PSA) projects for the Korean NPPs. The PSA results for KX NPP showed that the CCF events of ESWS pump failure to run was identified as one of dominant contributors to its internal event core damage frequency (CDF). Thus, we performed the plant specific detailed CCF analysis to estimate CCF parameters of ESWS pump failure to run for KX NPP with the CAFE-PSA, a program to analyze CCF events in the ICDE database. Reasonable values of CCF parameters were obtained through performing plant specific detailed CCF analysis. The estimated Alpha Factor with three out of three failure criterion was about one half of that for recent US NRC CCF parameters. The re-quantification results on the CDF of KX NPP with the new estimated Alpha Factor showed that originally estimated CDF with generic Alpha Factor decreased by 16.84% and the contribution of the sum of cutsets for the CCF events of ESWS pump failure to run to internal event CDF decreased from 20% to 3.29%.