Strain Rate Calculation Approach in Environmental Fatigue Evaluations

Abstract

Fatigue usage factor evaluations including the effects of reactor water environment have been performed in numerous nuclear plant license renewal efforts. A large number of these evaluations have used the environmental fatigue penalty factor, Fen, approach prescribed in various regulatory documents. The Fen equations require input of strain rate, but the prescribing documents do not provide methodology or criteria for the quantification of the strain rate to be input. As a result, numerous approaches have been offered and studied. This paper presents an approach used by Westinghouse to include strain rate in an automated calculation of Fen based on the modified rate approach (MRA) to integrated strain rate applications. The starting point of the approach is ASME Code Section III NB3200 fatigue analysis. With environmental fatigue evaluations in new plant designs now emerging in ASME Code criteria, strain rate considerations remain part of the discussion. The intent of this paper is to provide further insight into this process.