Latest SCC Issues of Core Shroud and Recirculation Piping in Japanese BWRs

摘要

This paper reports that a high incidence of stress corrosion cracking (SCC) cracks have been found in the core Shroudand PLR piping of several Japanese BWR plants. The results of investigations show the cracks to be of SCC type in316L stainless steel and with different characteristics from the type in 304 stainless steel. The cracks on the shroudsurface were mainly verified near the shroud ring weld line and core region weld line, and the crack shape could beclassified into two types: one type was circumferential cracking in the shroud ring, and the other was isolatedoccurrences of radial cracking in the core region. The structural integrity of those shrouds with cracks was evaluatedunder a conservative assumption and confirmed to be adequate. A relatively large error was identified in measuring thecrack depth in the PLR piping.