Generic and profile specific feeder stress analysis


Flow assisted corrosion (FAC) caused wall thinning has been observed on CANDU feeder pipes. Thinning in general occurs in the first two bends near the Grayloc fitting. In a fitness for service analysis of thinned feeders, the inspected or predicted minimum thicknesses are often used in the stress analysis. The determination of the exact location of the thin spot, axially and circumferentially, is dose intensive during inspection. In view of urgency during an outage to disposition measured thicknesses, two types of stress analysis approaches are developed. Type A analysis, also named here as the "Average- Minimum-Average" or generic approach provides requirements on minimum wall thickness as well as average wall thickness. The required minimum wall thickness is not location specific and can reside anywhere within the first two bends. It provides great flexibility to disposition feeders with either general or local thinning. On the other hand, Type B analysis is conducted with the exact thickness profile. Type B analysis is performed on feeders which do not pass Type A analysis. The two approaches have been demonstrated in Darlington feeders, where the majority (413 out of 480) of feeders has Type A requirements, while 67 out of 480 have Type B requirements. Type A requirements provide a greater flexibility to disposition local thinning on feeder pipes.

Publication Title

Canadian Nuclear Society - 29th Annual Conference of the Canadian Nuclear Society and 32nd CNS/CNA Student Conference 2008

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