An ASME Section III Task Group (TG) was formed in 2012 to develop alternate rules for the design assessment of Section III Class 1 nuclear components subject to fatigue service with environmental effects. A Section III Code Case has been proposed with the purpose of providing a method for performing fatigue evaluations of Class 1 components when the effects of a light water reactor environment on fatigue life are judged to be significant and cumulative usage factor (CUF) limits may not be satisfied. The Code Case implements a flaw tolerance approach by postulating that a fatigue crack initiates at the beginning of life and is subjected to fatigue crack growth under the specified design cycles. It must be demonstrated that the crack would remain stable with set margin throughout the design life of the component or part under consideration, and would remain confined to an acceptable fraction of the wall thickness. At this time, the application is limited to type 304/304L and 316/316L austenitic steel. This paper discusses the methodology and technical background of the proposed Code Case.

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