Dependent failure analysis research for the US NRC Risk Methods Integration and Evaluation Program

The Risk Methods Integration and Evaluation Program (RMIEP), which is being performed for the Nuclear Regulatory Commission by Sandia National Laboratories, has the goals of developing new risk assessment methods and integrating the new and existing methods in a uniform procedure for performing an in-depth probabilistic risk assessment (PRA) with consistent levels of analysis for internal, external, and dependent failure scenarios. An important part of RMIEP is the recognition of the crucial importance of dependent common cause failures (CCFs) and the pressing need to develop effective methods for analyzing CCFs as part of a PRA. The NRC-sponsored Integrated Dependent Failure Methodology Program at Sandia is addressing this need. This paper presents a preliminary approach for analyzing CCFs as part of a PRA. A nine-step procedure for efficiently screening and analyzing dependent failure scenarios is presented, and each step is discussed