SCC IN SHROUD SUPPORT CYLINDER VERTICAL WELD LINES (TOKAI-2)

摘要

SCC was found outer surface of shroud support cylinder vertical weld lines (V8) made of Nickel based alloy, Alloy 182, for Tokai-2 (BWR-5) operated since 1978. Three SCC among 4 weld lines of V8 were observed.rnThe material of Alloy 182 was known to have SCC potential in BWR environment. Based on the result of finite element method analysis, it was estimated that tensile circumferential stress generated at the upper corner of cylinder corresponding crack location when H7 welded.rnThe integrity assessment against seismic load in design was performed using shell model in finite element method analysis. It assumed conservatively that four vertical through wall cracks along whole length of V8 weld lines and four horizontal through wall partial cracks along H7 weld line at intersections of V8 and H7. The collapse load was estimated by twice slope method, a kind of limit load analysis. As the result of the integrity assessment, a critical horizontal through wall crack length along H7 weld line was about 1400mm per one crack (about 70% of all circumferences). SCC growth was evaluated to reach the critical length after about 20 years, where maximum crack growth rate, 63 mm/year was assumed. It is not judged that the immediate repair of vertical SCC is necessary.