抄録
A high incidence of Stress Corrosion Cracking (SCC) has been found in the Core Shroud and PLR piping of several Japanese BWR plants. The investigation results show the cracks to be of SCC type in 316L stainless steel and with different characteristics from the type in 304 stainless steel. The cracks on the shroud surface were mainly verified near the shroud ring weld line and core region weld line, and the crack shape could be classified into two types:one type was circumferential cracking in the shroud ring, and the other was isolated occurrences of radial cracking in the core region. The structural integrity of those shrouds with cracks was evaluated under a conservative assumption and confirmed to be adequate. On the other hand, cracks of PLR pipings were found to have an uncertainty of crack depth measurement and the improved UT technique is to be expected for this matter.
