Equivalent Margins Analysis (EMA) involves the calculation of an alternative minimum reactor pressure vessel (RPV) upper shelf energy (USE) when the projected value falls below current limits codified in Title 10, Code of Federal Regulations, Part 50 (10 CFR 50), Appendix G. One set of calculation methodologies for performing the analysis are provided in the Nuclear Regulatory Commission’s (NRC’s) Regulatory Guide (RG) 1.161 and American Society of Mechanical Engineers Boiler & Pressure Vessel Code (ASME Code), Section XI, nonmandatory Appendix K. Careful application of fracture mechanics principles is necessary in order to properly carry out the evaluation. This is particularly the case for demonstrating compliance with the ductile crack growth stability criterion. This paper discusses robust implementation of EMA calculations and identifies recommended changes to RG 1.161 and ASME Code, Section XI, nonmandatory Appendix K.

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