Abstract: The Reactor Coolant System (RCS) piping of a pressurized water reactor (PWR) plant is probably the best in terms of resistance to known degradation mechanisms of passive components. However, a failure in the RCS piping is extremely important in terms of safety and economic significance. Therefore, an effective management tool is needed to mitigate the potential effects of degradation due to aging or other effects such that plant reliability and availability are not affected. Currently, the RCS piping of all US PWR plants is being subjected to inservice inspection (ISI) based upon certain deterministics criteria set by the ASME code and the NRC regulatory guide. Even though the history of large RCS piping has not shown any degradation, the ISI continues at many locations at greta expense to the plant owners whereas, there can be only a few locations of relatively high vulnerability. A risk based ISI can provide an alternative and cost-effective solution in this situation. Pressurizer surge line is a unique segment in the RCS which is subjected to significant transient loadings due to stratification and striping during the normal heatup and cooldown processes. Therefore, the surge line is considered for illustration. Examples of structural reliability studies of pressurizer surge lines in four PWR units are presented in this paper to demonstrate possible reduction of ISI and significant cost saving without reduction of plant safety or reliability. !6
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