Procedures for treating common cause failures in safety and reliability studies: Procedural framework and examples

This report presents a framework for the inclusion of the impact of common cause failures in risk and reliability evaluations. Common cause failures are defined as that cutset of dependent failures for which causes are not explicitly included in the logic model as basic events. The emphasis here is on providing procedures for a practical, systematic approach that can be used to perform and clearly document the analysis. The framework comprises four major stages: (1) System Logic Model Development; (2) Identification of Common Cause Component Groups; (3) Common Cause Modeling and Data Analysis; and (4) System Quantification and Interpretation of Results. The framework and the methods discussed for performing the different stages of the analysis integrate insights obtained from engineering assessments of the system and the historical evidence from multiple failure events into a systematic, reproducible, and defensible analysis. 22 figs., 34 tabs.