The majority of United States Commercial Nuclear Power Plants (CNPP) within the next 10 years will reach the end of their license to operate and can be renewed per the “Atomic Energy Act” of 1954. This act allowed the commission to issue commercial electric power nuclear plants a license to operate (“licensed, but not to exceed 40 years, and maybe renewed upon the expiration of such period, (Chapter 10, Sec. 103(c))).” These CNPP licenses are also governed by the NSSS vendor specification requirements and by the American Society of Mechanical Engineers (ASME) design code standards. This connection is in the form of a stress report that defines the “cyclic life” adequacy criteria for this operational limit of 40 years. The license extension subsequently requires a reconstitution of the initial design stress report input parameters per ASME IWA-4120, 4223 & 4311 (e) for the renewal period extension. This requirement can entail an analysis of the operating conditions and cycles to demonstrate the material elasticity is maintained. The proposed approach for this reconstitution effort was a reanalysis in the form of a study of the Nuclear Steam System Supplier (NSSS) vendors’ original methodology to determine the NSSS vendor specification requirement for ASME code compliance and “cyclic life” adequacy. The information acquired from this evaluation has demonstrated the application to be a complex and simplistic approach. This effort to unravel the composite loading (thermal and pressure transients) condition in relation to specific plant and incident cycles provides both an understanding of component end-of-life limits and supports a comprehensive template for future fatigue life management programs. This paper summarizes this reconstituting effort that utilizes the original vessel stress analysis report to support the license renewal effort, provides a template for future fatigue management programs, demonstrates the conservatism of design, and offers an insight into the design philosophy revealing an elegant process that assures against failures.

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