Management of plant service life is a key issue for improving the safety of light water reactors. Some incidents of primary water stress corrosion cracking (PWSCC) of pressurized water reactor (PWR) components, such as a primary loop piping/nozzle weld, and intergranular stress corrosion cracking (IGSCC) of boiling water reactor (BWR) components, such as a shroud support weld, have been reported in the past. When a crack is detected, crack growth analysis is required as part of the structural integrity assessment of the component with the crack.

In Japan, the “Rules on Fitness-for-Service for Nuclear Power Plants” of the Japan Society of Mechanical Engineers (JSME FFS Code) describes the conventional methodology for analyzing crack growth. The methodology assumes a semi-elliptical crack shape and is based on crack growth calculation at only the deepest and surface points of the crack. However, the actual crack growth behavior is likely to be very different from that analyzed by the conventional methodology due to the complex distribution of residual stress and dependency of crack growth properties on the materials composing the weld joint, particularly in the case of cracks in a dissimilar metal weld. Recently, crack growth analysis techniques using finite element analysis (FEA) have been used to analyze crack growth behavior in more detail.

In this study, a program code was developed for SCC crack growth analysis that consists of fracture mechanics analysis by “ABAQUS”, crack growth calculation and automatic remesh of the FE model by in-house code. Case studies of SCC crack growth analysis for a dissimilar metal weld were performed and the analysis results were compared with those obtained by the conventional methodology. As a result, it was confirmed that the conventional methodology provides a conservative estimation of crack growth behavior. It was also found that the difference in crack growth properties of individual materials composing the weld joint had a significant effect on the crack growth behavior, particularly on a dissimilar metal weld. Furthermore, the effect of the material anisotropy of the SCC crack growth rate for the weld metal on the crack growth behavior was investigated.

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