照射影響を考慮したSCC評価手法の高度化に関する研究,2; 線照射下でのSUS316L鋼に形成する皮膜構造と環境因子

Research for the improvement of SCC evaluation method including the effect of radiation on water, 2; Oxide film structures and environmental parameters on type 316L stainless steel under -ray irradiation in high temperature water

加藤 千明   ; 中原 由紀夫 ; 山本 正弘 ; 塚田 隆 

Kato, Chiaki; Nakahara, Yukio; Yamamoto, Masahiro; Tsukada, Takashi

軽水炉などでは、水の放射線分解によりHO等の酸化剤が生成し、特にすき間部では生成した酸化剤の拡散が阻害されより厳しい腐食環境となっていることを報告してきた。今回、線照射下高温高圧水中にてすき間形状を有するステンレス鋼表面に生成した腐食生成物をレーザーラマン及びTEM分析を用いて皮膜構造の模式化を行った。また、高温水中におけるE-pH線図を用いて熱力学計算から得られる安定酸化物と環境条件(電位,pH)の関係から、すき間内環境の推定を行った。その結果、照射とすき間の複合的な要因によりすき間内のpHが低下する可能性が示された。

It is well known that the decomposition of water by irradiation results in the formation of oxidants, such as hydrogen peroxide and radical species. Inside crevices, the effect of diffusion restriction and surface reactions may become more significant, so that the environments are expected to be different from those in the outsides. Therefore the structural effects using crevice-like specimen have been discussed and corrosion acceleration effects were introduced. In this work, the effects of -ray irradiation and structure on the corrosion of Type 316L SS in high-temperature water of 288 C were examined. We also consider structures of the oxide film on the stainless steel using transmission electron microscope and Raman spectroscope in order to show the differences made by the irradiation and structure. In addition, the environment inside irradiated crevices was estimated from results of the modeling of the oxide film and stable oxide states based on the E-pH diagram.