The rules on fitness for service for nuclear power plants of JSME are applied for flaw evaluation after detecting defects in the operating nuclear plants in Japan. The rules mainly focus on simple geometry such as straight pipes or vessels and do not provide the evaluation procedure for complex structures. The authors made a draft of flaw acceptance rule for J-groove weld of a bottom mounted instrumentation nozzle at application of the cap repair. The rule contains flaw modeling, fatigue and SCC crack growth calculation and flaw instability assessment. After detecting a defect on a J-groove weld, a flaw will be modeled in the whole of J-groove weld region because of fast SCC crack propagation in the weld region. Due to complex configuration of the evaluation location, FE analysis is needed for obtaining stress intensity factors (Ks) to calculate the crack growth and flaw instability. The proposed rule has a guidance for K calculation by FE analysis with the aim of decreasing dependence of individuals for calculation. The authors performed benchmark analyses to confirm the guidance applicability. The calculation results by three participants agreed within several percent.

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