One of the standard common cause failure models used in US NPPs is the alpha factor model. The alpha factor model uses the multi-parameter generalizations of event-based parameters directly to estimate the common cause basic event probabilities. NUREG/CR-5485 provides a discussion on the alpha factor model but explicitly distinguishes the CCF probability estimates based on a selected test scheme, namely, staggered or non-staggered testing. It is noted that an explicit form for the alpha factors for non-staggered testing is explicitly provided, whereas an equivalence for staggered testing is not detailed. Various white papers have been developed which the importance of the test scheme on the alpha factors and the difficulty in developing detailed estimates given the currently available data. This paper discusses the development of staggered alpha factor parameter estimates for a subset of important plant equipment.

Key Words: PRA, Common Cause Failure, Alpha Factor Model, Staggered