This paper describes how the Westinghouse Decision Advisor Process was employed to develop and quantitatively evaluate the financial merits of alternative strategies to address Alloy 600 (& 82/182) degradation issues at the higher-susceptibility locations throughout four Exelon Generation Company nuclear power units. The objective was to help Exelon focus its resources over both locations and time. Recommendations were also provided for the actions to resolve these issues at these highly susceptible locations. The paper describes the actions taken by Exelon that were supported by this study.
Certain nuclear power plants have “Rev B” reactor vessel upper internals guide tube support pins, commonly referred to as split pins, made from material with properties similar to Alloy 600 and known to be susceptible to primary water stress corrosion cracking (PWSCC). This paper describes a rigorous probabilistic methodology for evaluating the economics of a preemptive replacement of these split pins, and describes an application at four of Exelon Generation’s nuclear plants. The method uses Bayesian statistical reliability modeling to estimate a Weibull time-to-failure prediction model using limited historical failures, and a Westinghouse proactive aging management simulation tool called PAM to select a split pin replacement date that would maximize the net present value of cash flow to a plant. Also in this study is a sensitivity evaluation of the impact of zinc addition on split pin replacement timing. Plant decisions made based in part on results derived from applying this approach are noted.
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