The discovery of leaking cracks in Alloy 82/182 bimetal welds at the V.C. Summer Nuclear Station has lead the industry to reassess the Leak-Before-Break (LBB) analysis of the reactor coolant system pressure boundary piping components involving Alloy 600 base metals and Alloy 82/182 welds. The leaking cracks were attributed to primary-water-stress-corrosion-cracking (PWSCC). To-date, LBB analysis submittals to the NRC have not considered PWSCC cracks in bimetal welds or Alloy 600 base metals and the leak rate calculations have only considered the conventional fatigue crack morphology. There are limited observed in-service leakage cracks of Alloy 82/182 pipe butt welds with plant measured leak rate data. Effects of PWSCC induced crack morphology involving these welds is investigated through various modeling techniques. The differences in leakage prediction when evaluating as a fatigue crack versus assessing as a PWSCC crack is addressed for various PWR LBB piping systems. The impact of this finding to the overall LBB assessment is discussed. Additionally, the LBB results are compared against the results from another paper.

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