Flaw tolerance as an alternative approach for operating plant fatigue evaluation

In the design of Class 1 components for nuclear reactors, the ASME Boiler and Pressure Vessel Code requires that the suitability for cyclic operation be addressed to assure a fatigue-resistant design. During plant operation, the acceptability of the component may come in to question if new types of loading conditions are identified or if the number of plant cycles exceeds that considered in the original design. The most common approach for addressing this issue is by performing a revised fatigue evaluation, consistent with that considered in the original design. This paper presents an alternative approach for demonstrating acceptability for continued service using concepts from fracture mechanics