Operational reliability of selected standby safety systems

The Idaho National Engineering Laboratory (INEL) over the past year has evaluated the operational reliability of several risk-significant standby safety systems as reflected in the operating experience at US commercial nuclear power plants. The reliability assessed was the functional probability that the system will perform its PRA defined safety function under accident conditions. The quantitative estimates of system reliability are expected to be useful in those applications of risk assessment or reliability engineering that are sensitive to the reliability of these risk-significant systems, including evaluations of Individual Plant Examinations (IPE) studies and risk-based prioritization of inspection activities. This paper provides an overview of the analysis methods and a results summary of four system reliability studies. Key characteristics include: (1) descriptions of the data collection and analysis methods, (2) the statistical methods employed to estimate operational unreliability, (3) a description of how the operational unreliability estimates were compared with typical PRA results, both overall and for each dominant failure mode, and (4) a results summary of the High Pressure Coolant Injection, Reactor Core Isolation Cooling, Auxiliary Feedwater, and Emergency Diesel Generator System Reliability Studies.