Industry Performance of Relief Valves at U.S. Commercial Nuclear Power Plants through 2007

NUREG/CR-7037 characterizes current industry average performance for relief valves at U.S. commercial nuclear power plants using data through 2007. It uses data obtained from the Institute for Nuclear Power Operation‘s Equipment Performance and Information Exchange (EPIX) database and Licensee Event Reports (LERs). It describes the parameter estimation process used to derive the failure probabilities on demand (using beta distributions), failure rates (using gamma distributions), maintenance unavailabilities, and initiating event frequencies for use in Level 1 Standardized Plant Analysis Risk (SPAR) models of U.S. commercial nuclear power plants. The methods employed in this report are conventional estimation methods as documented in NUREG/CR-6823, "Handbook for Parameter Estimation for Probabilistic Risk Assessment."

The characterization of current industry average performance is an important step in maintaining up-to-date risk models. Studies have indicated that industry performance of most components has improved since the 1980s and early 1990s. For most relief valve component performance estimates, data for 1997–2007 are used to characterize current industry average performance. However, data from 1987 to 2007 are used to characterize relief valve response to unplanned shutdown events.