One of the major tasks in a plant specific common cause failure (CCF) analysis is to determine the overall event applicability factors of the original CCF events. The overall event applicability factor of a CCF event, which is used for specializing the impact of the original event for a target system, should be determined by considering the target system’s defenses against such CCF. However, lack of currently available detailed guidelines made it difficult to determine the overall event applicability factors in a systematic and consistent manner. In this paper, practical procedures for plant specific CCF analysis were developed. Especially, guidelines and a set of criteria were developed for more systematic and consistent determination of the overall event applicability factors. Additional set of criteria was also developed especially for crediting plants with many years of operations for their enhanced defenses against CCFs based on accumulated operating experiences. The developed procedures were successfully implemented for three plant specific CCF analyses. It is believed that the use of the developed procedures would significantly facilitate a plant CCF analysis and produce consistent results.

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