Many examinations concerning the fatigue life reduction for structural materials of nuclear power plants in water simulated LWR coolants had been carried out after the first paper had been recognized in Japan [1, 2]. Based on these results, the method to evaluate the fatigue damage for the materials exposed to the LWR coolant had been developed. After 1990s in Japan, the Environmental Fatigue Data Committee (EFD) of the Thermal and Nuclear Power Engineering Society (TENPES), the Project on Environmental Fatigue Testing (EFT) supported by the Japan Power Engineering and Inspection Corporation (JAPEIC) and the Japan Nuclear Energy Safety Organization (JNES) and some utility joint studies have investigated the environmental fatigue. In September 2000, the Nuclear Power Generation Safety Management Division of the Agency for Natural Resources and Energy, Ministry of International Trade and Industry issued “Guidelines for Evaluating Fatigue Initiation Life Reduction in the LWR Environment” (hereafter, called “the MITI Guidelines”) [3]. These guidelines include an equation to evaluate environmental fatigue and require electric utilities to consider the environmental effects in their Plant Life Management (PLM) activities. However, the MITI Guidelines do not provide specific and practical techniques for evaluating environmental fatigue under actual plant conditions. Accordingly, TENPES took on the task to produce one. In 2002 TENPES issued the “Guidelines on Environmental Fatigue Evaluation for LWR Component” [4, 5] (hereafter, called “the TENPES Guidelines”) based on the techniques developed by the EFD Committee. A set of Rules, called the Environmental Fatigue Evaluation Method (EFEM), was established in the Codes for Nuclear Power Generation Facilities - Environmental Fatigue Evaluation Method for Nuclear Power Plants (JSME S NF1-2006, EFEM-2006)[6], which was issued in March 2006 by reviewing the equations for the environmental fatigue life correction factor, Fen, specified in the MITI Guidelines, and the techniques for evaluating environmental fatigue specified in the TENPES Guidelines, and considering the new environmental fatigue data including JNES-SS report (August 2005) [7]. The EFEM revised version has been drafted by incorporating the updated knowledge described in JNES-SS report (April 2007) [8] and is scheduled to be issued by the end of 2009. This paper introduces the revision in it and their technical basis. Additionally, future issues are addressed to be considered in the improvement of the EFEM.

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