Microstructural Analyses of hardened surface in BWR core shroud made of 316L
末石 裕一郎 Yuichiro SUEISHI 香山 晃 Akira KHOYAMA 木下 博嗣 Hiroshi KINOSHITA 鳴井 實 Minoru NARUI 福元 謙一 Kenichi FUKUMOTO
Boiling Water Reactor Core Shroud Stress Corrosion Cracking surface machining
To verify the effect of hardened surface on stress corrosion cracking (SCC) of 316L, characteristics of cracked BWR core shroud have been investigated by means of microstructures. At the inner surface of core shroud where grinding was done, fine grains were observed at the surface thin layer. Furthermore, deformation-induced slip-line field including extensive deformation-twins was observed in the harden ed surface region. In contact with corrosion products on the shroud surface, intensive Ni enrichment and Fe, Cr, Mn depletion was detected at the grain boundary. It is suggested that corrosion occurs with Nio formation and Fe, Cr, Mn elution. Since SCC found was initiated at hardened surface, deformation-induced microstructures and/or corrosion behaviors found could have affected the cracking initiation.