Assessment of Environmental Fatigue (F_EN) Approaches

Since 1998, many U. S. utilities have embarked upon efforts to renew their nuclear plant operating licenses. One of the key areas of uncertainty relates to fatigue of pressure boundary components. Although the Nuclear Regulatory Commission (NRC) has determined that fatigue is not a significant contributor to core damage frequency, they believe that the frequency of pipe leakage may increase significantly with operating time. Therefore, as a part of the license renewal process, the NRC has requested that license renewal applicants perform an engineering assessment to determine the effects of reactor water coolant environment on fatigue and, where appropriate, manage this effect during the license renewal period. As the license renewal application process progressed starting in 1998, utilities have committed significant resources to license renewal activities related to fatigue. In response to this, several possible approaches have emerged from a variety of industry efforts that may be taken to address fatigue environmental effects in a license renewal application. This paper summarizes an assessment that was performed under funding by the Materials Reliability Program (MRP) for several of the currently-documented environmental fatigue (F_en) approaches. Practical application of these F_en approaches was performed for typical power plant components. In addition to the results obtained from this assessment, this paper summarizes several issues associated with the practical application of these methods to typical power plant components. For some of these issues, recommended solutions are proposed to satisfactorily apply the methods. For remaining issues, recommendations for further studies are provided that would assist in the development of refined methods and guidance to eliminate the issues.