As plants prepare for license renewal, extending their original operating licenses from 40 years to 60 years of plant operation, various tasks are required to be performed. Some of the required tasks include validation of the current fatigue evaluations for ASME Class 1 components, evaluation of environmental affects for a subset of those components, and calculation of revised component life to demonstrate acceptability for the entire license renewal period. Validation of the current fatigue evaluations is a significant challenge for older-vintage plants because the documentation of transient parameters and event severity was often not rigorous, especially during the early years of plant operation. This is primarily because historical data gathered in the early years was difficult to obtain before the implementation of modern computer systems and was therefore only collected at limiting times and locations. As a result, transients were typically considered to be full design basis severity events. Also, the design basis transient definitions, as defined in the original Final Safety Analysis Report (FSAR), were limited to a simpler, bounding set to help simplify the process. Whereas these simplifications are typically conservative and make it easier for the staff implementing plant procedures, they can challenge the ability of utilities to be able to demonstrate long-term acceptability for license renewal where additional margins are required. The purpose of this paper is to provide an example of the efforts expended on this issue for the Pilgrim Nuclear Power Station (PNPS). The intent is to educate the reader on the efforts involved, the vast array of input that is needed, and the possible hurdles that may be encountered for the validation and re-evaluation of Class 1 component fatigue for license renewal. Prior to starting work on the fatigue analysis, PNPS requested that SI develop a design specification for the fatigue reevaluation project. The importance of this document is that it maintained consistency and documented methods to be used along with design inputs.

This content is only available via PDF.
You do not currently have access to this content.