Comparison Between Fracture Mechanics Evaluation Methods in ASME Boiler & Pressure Vessel Code, Section XI and Those in JSME Leak-Before-Break Evaluation Guidelines for Sodium-Cooled Fast Reactors

Abstract

Abstract ASME Boiler and Pressure Vessel Code (BPVC), Section XI, Division 2 provides requirements for protecting passive components that affect reliability of the plant. It generally consists of technology-neutral common requirements, and additional ones for individual reactor types. Currently, an Appendix for sodium-cooled fast reactors (SFRs) is being developed based on Code Case N-875. In the Code Case, continuous leakage monitoring was employed as inspection method for components retaining liquid sodium. It is also important to introduce leak-before-break (LBB) assessment procedures in the Appendix because demonstration of LBB is necessary to show the adequacy of applying continuous leakage monitoring to the component of interest. However, LBB assessment method is not provided in ASME BPVC. On the other hand, recently, LBB assessment guidelines for SFRs has been developed by the Japan Society of Mechanical Engineers (JSME). It could be used to prepare LBB assessment procedures for the Appendix, but it needs to confirm the consistency with ASME BPVC Sec. XI. In this study, fracture evaluation methods for pipes with through-wall flaw are compared between the JSME LBB assessment guidelines and applicable evaluation method in ASME BPVC Sec. XI, Div. 1. There are limit load criteria and failure assessment diagram (FAD) approaches in both of them. Allowable flaw size evaluation methods in limit load criteria are almost same. In FAD approach, some differences exist. The FAD approach in the JSME LBB assessment guidelines is based on the R6 defect assessment procedures option 3 and constructed to be consistent with the Fitness-forservice code for light water reactors in JSME. In this study, fracture evaluation methods related to LBB assessment were compared in preparation for introducing LBB assessment procedures into ASME BPVC Sec. XI, Div. 2. Furthermore, effects of the differences were investigated. As a result, it was shown that there was not any significant difference between them except for the structural factors which need to be determined by considering the consistency with related provisions in individual codes.