Risk-informed inservice inspection Original Research Article

The operational readiness and functional integrity of certain safety-related piping and associated structural elements such as piping supports are vital to the safety of operations in nuclear power plants. Inservice inspection (ISI) is one of the mechanisms used by the power plant owners to ensure piping integrity. Previously, the type and frequency of ISI have been based on the collective best judgment of the NRC and industry in a consensus code and rulemaking process. The ASME code-based ISI requirements and practices have not explicitly taken into consideration unique aspects of piping functions, piping degradation mechanisms, weld integrity, fabrication details, and the extent of the contribution to overall plant risk. Due to the general nature of the ASME code ISI requirements and non-reliance on quantification of risk estimates, current ISI requirements may unnecessarily emphasize inspection of less safety-significant piping segments, and thereby unnecessarily expose plant personnel to radiation exposure. Nuclear power plant owners are currently interested in optimizing inspection and testing by applying resources in more safety-significant areas. They are also interested in maintaining system availability and reducing overall maintenance costs which do not have any adverse effects on safety. The NRC has confirmed its intent of using probabilistic, as an adjunct to deterministic, techniques, to help define the scope, type, and frequency of ISI. The development of risk-informed inservice inspection programs (RI-ISI) has the potential to optimize the use of NRC and industry resources and to continue assuring adequate protection of the publicʹs health and safety. Currently there are two methodologies being proposed by the industry for the implementation of the RI-ISI programs. One is being developed jointly by the ASME Research and Westinghouse Owners Group (WOG) and the other by the Electric Power Research Institute (EPRI). Both methodologies will be implemented for pilot plant applications. Based on discussions with the interested licensees, the NRC staff has tentatively accepted Surry, ANO-2, and Fitzpatrick as the RI-ISI pilot plants. The Surry pilot application is based on the WOG methodology, whilst ANO-2 and Fitzpatrick are based on the EPRI methodology.