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for Safe Long Term Operation (LTO)
Development of Technical Guidelines
Methodology for Risked Informed in-service inspection programmes of in Nuclear Power Plant
Risk-informed inspection is one strategy for improving the effectiveness of ISI and is based on the combination of independent assessments of the probability of failure of components and the consequences of those failures. It was started for NPP in the US and is currently spreading towards other developed countries.
This document will inform managers, ISI supervisors, and lead ISI engineers of NPPs and TSOs with regard to the technology. It describes RI-ISI process, application status, technological issues, and on-going development activities. It will be helpful for regulator staff related to ISI program.
The ISI scope and interval for the inspection items in many developing countries are still determined based on the pressure vessel and boiler industries’ experience and intuitive engineering judgment on safety importance – deterministic approach. State-of-the-art information on best practices on Risked Informed ISI from the Agency will improve allocation of the ISI resources to better ensure the SSC integrity and enhance lifetime management of NPP.
A pilot study on Risk Informed In-Service Inspection for WWER NPPs was carried out in co-operation with Nuclear Research Institute of Czech republic. The EPRI methodology on RI-ISI was tested on primary piping and pressurizer surge line of WWER-440 Dukovany NPP. 119 welds were assigned to risk category IV and 5 welds to risk category II among a total number of 124 welds per WWER-440 unit. Based on RI-ISI optimization procedure, 12 welds of Category IV and 2 welds of Category II were selected for inspection, while the current inspection programme covers 66 welds. This means a one fourth to one fifth reduction of inspection scope (14 vs. 66 welds), while the safety level is still maintained.
On March 10-12, 2008, the 2nd CS meeting was held in VIC, Vienna to develop a guidance document on risk-informed in-service inspection (RI-ISI) of piping systems of NPP. This meeting has expanded the outline of document, which was agreed in the previous meeting of last year.
In order to find out the current status of the technology in NPP-operating countries, a questionnaire will be sent out to collect the information and opinions of the industries and regulators. The 3rd Cs meeting is planned on 22-24 September 2008 in Vienna to resolve all the issues and finalize the document.
References:
- Improvement of In-service Inspection in Nuclear Power Plants Details , IAEA TECDOC-1400, IAEA, Vienna (2004)
- Maintenance, Surveillance and In-Service Inspection in Nuclear Power Plants, Safety Standards Series No. NS-G-2.6, IAEA, Vienna (2002)