LESSONS LEARNED FROM IMPLEMENTATION OF WESTINGHOUSE OWNERS GROUP RISK-INFORMED INSERVICE INSPECTION METHODOLOGY FOR PIPING

摘要

Risk-informed inservice inspection (ISI) programs have been in use for over seven years as an alternative to current regulatory requirements in the development and implementation of ISI programs for nuclear plant piping systems. Programs using the Westinghouse Owners Group (WOG) (now known as the Pressurized Water Reactor Owners Group - PWROG) risk-informed ISI methodology have been developed and implemented within the U.S. and several other countries. Additionally, many plants have conducted or are in the process of conducting updates to their risk-informed ISI programs. In the development and implementation of these risk-informed ISI programs and the associated updates to those programs, the following important lessons learned have been identified and are addressed. 1. Concepts such as "loss of inventory," which are typicallyrnnot modeled in a plant's probabilistic risk assessmentrn(PRA) model for all systems.rn2. The importance of considering operator actions in the identification of consequences associated with a piping failure and the categorization of segments as high safety significant (HSS) or low safety significant (LSS).rn3. The impact that the above considerations have had on the large early release frequency (LERF) and categorization of segments as HSS or LSS.rn4. The importance of automation.rn5. Making the update process more efficient to reduce costs associated with maintaining the risk-informed ISI program. The insights gained are associated with many of the stepsrnin the risk-informed ISI process including: development of the consequences associated with piping failures, categorization of segments, structural element selection and program updates. Many of these lessons learned have impacted the results of the risk-informed ISI programs and have impacted the updates to those programs. This paper summarizes the lessons learned and insights gained from the application of the WOG risk-informed ISI methodology in the U.S., Europe and Asia.