COG Risk-Informed In-Service Inspection (RI-ISI) Project

In 2009, the Canadian Nuclear Safety Commission (CNSC) prepared “Guidelines for Risk-Informed In-service Inspection for Piping,” which provided guidance and acceptance criteria for licensees to develop an RI-ISI program as an alternate to the current CSA N285.4 and augmented programs for piping inspection. A project was initiated by the CANDU Owners Group (COG) to develop a best-fit RI-ISI methodology for the CANDU design and evaluate plant risk levels between current and RI-ISI inspection programs. The traditional EPRI RI-ISI methodology was selected as a starting point, and four plant systems were evaluated. Both failure potential and consequence of failure were used to establish the risk significance for all in-scope piping components. Once the risk associated with each component was established, elements were selected for inspection based upon the sampling percentages of the EPRI RI-ISI methodology, and as a final check a comparison was made between plant risk under the current CSA N285.4 (and augmented) inspection program and under RI-ISI. The project was successfully concluded in 2011, and results confirmed that the EPRI RI-ISI methodology can be adapted to the CANDU design and the degradation mechanisms evaluated under RI-ISI are consistent with CANDU operating experience. The original CSA N285.4 basis for the CANDU Periodic Inspection Program (PIP) was validated, and potential improvements to the station inspection programs were identified.