Proceedings of the Seventh International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components.\n12-14 May 2009 - Yokohama, Japan

In 2005, the Joint Research Centre of the European Commission (JRC) together with the Nuclear Energy Agency of the OECD (NEA) launched a project for benchmarking various risk-informed in-service inspection (RI-ISI) methodologies. The project, called RISMET, had more than twenty participating organizations from Europe, U.S., Canada and Japan. The JRC acted as the technical coordinator of the project, and the NEA provided secretariat support.\nThe overall objective of the project was to apply, for the first time, various RI-ISI methodologies to the same case, i.e. selected piping systems in one nuclear power plant, with the idea of verifying whether they would lead to significantly different results. Also, a benchmarking exercise would ideally result in the identification of those phases in a methodology with the greatest potential to affect the outcome, and might suggest areas for further improvement.\nFour systems from the Swedish PWR Ringhals 4 were selected for the benchmark exercise. The following criteria were used for selecting these systems: All safety classes should be covered; a variety of degradation mechanisms should be covered; good coverage of risk categories should be achieved; systems with a significant increase or decrease in the new inspection program (before/after applying RI-ISI) should be included; and balance between initiating and mitigating systems should be ensured. Based on these criteria, the following systems were suggested by Ringhals and approved by the project team as the scope of the exercise: 1) Reactor coolant system, 2) Residual heat removal system, 3) Main steam system and 4) Condensate system.\nThe following approaches to define the ISI program were considered in the benchmark exercise: 1) Swedish regulatory requirements ("SKIFS"); 2) PWROG methodology; 3) PWROG methodology adapted to Swedish regulations ("PWROG Swedish"); 4) EPRI methodology; 5) Code Case N-716, "streamlined RI-ISI"; and 6) ASME Section XI (deterministic).\nThe application results were evaluated by five groups concentrating on the following issues: 1) Scope of application; 2) Failure Probability Analyses; 3) Consequence analyses; 4) Risk ranking, classification and selection of segments/sites to be included in inspection programs; and 5) Regulatory aspects. The evaluation included the identification of differences in the RI-ISI applications, the analysis of the importance of identified differences, and the comparison between RI-ISI and "traditional" inspection programs.\nEven if the scope of the benchmark was limited to four systems, the variety regarding safety class, potential degradation mechanisms and pipe break consequences ensured a good coverage of issues for a comparative study. The risk-informed methodologies showed some significant differences and resulted in slightly different risk ranking and selection of inspection sites. However, the results of the benchmark indicated that the risk impact of these differences is small, and the RI-ISI approaches identify safety important piping segments that are ignored by approaches not using the probabilistic safety assessment (PSA). The results of the benchmark exercise RISMET improve the knowledge on differences in approaches and their impact on plant safety, and promote the use of risk-informed ISI.\nThis paper summarizes the results of the RISMET benchmark exercise.

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