Approach to Establish Flaw Evaluation Method for Class 2 and 3 Light Water Reactor Pipes

To achieve a rational maintenance program for aged Light Water Reactor components, it is important to establish and to improve the flaw evaluation criteria. The current flaw evaluation criteria such as ASME Boiler and Pressure Vessel Code Section XI are focused on Class 1 piping which usually shows relatively higher toughness. On the other hand, flaw evaluation criteria suitable for Class 2, 3 piping with moderate-toughness are also from the viewpoints of in-service inspection request, reduction of operating cost, and systematization of consistent code/standard. In this study, both analytical and experimental studies were conducted to provide the allowable flaw sizes for acceptance standards as well as the evaluation method of fracture loads for acceptance criteria for Class 2, 3 piping. An approach to identify the allowable flaw sizes for acceptance standards was newly proposed using the failure assessment curve, and allowable flaw sizes for Class 2 3 piping were tentatively derived based on the approach. Cracked pipe fracture tests together with finite element analysis and simplified fracture analysis were also conducted using typical moderate-toughness pipe materials. The experimental and analytical results were reduced to the Z-factor to predict fracture loads of Class 2, 3 cracked piping.