沸騰硝酸溶液中でのSUS304ULC鋼の過不働態域での腐食挙動

Corrosion of SUS304ULC stainless steel at transpassive region in boiling nitric acid solution

山本 正弘 ; 内山 洋平; 上野 文義  ; 加藤 千明   ; 本岡 隆文

Yamamoto, Masahiro; Uchiyama, Yohei; Ueno, Fumiyoshi; Kato, Chiaki; Motooka, Takafumi

核燃料再処理施設では、耐粒界腐食性を向上させたSUS304ULC鋼が沸騰硝酸中で用いられている。この際に沸騰部や共存イオンによる電位上昇が腐食を加速することが知られている。そこで、沸騰硝酸中での電気化学的評価を行い、同鋼の過不働態域での腐食挙動を解析した。酸素発生反応は溶液種などの影響を受けるが、金属の溶解反応は電位のみにほぼ依存する。腐食形態は粒界腐食であり、腐食形態に及ぼす溶液種の影響は小さい。溶出イオンは、過不働態域では母材と同等の比率で溶出していた。

SUS304ULC which had been designed stainless steel was used for a nuclear fuel reprocessing plant. SUS304ULC stainless steel which had been designed to improve the anti-corrosion properties for intergranular corrosion was used for a nuclear fuel reprocessing plant. It has been, however, known that the boiling and/or co-existence of oxidizing ions conditions accelerated the corrosion rates of the material. We examined the electrochemical evaluation of the steel at transpassive region in the boiling nitric acid solution. Although oxygen evolution reaction was influenced by the solutions, metal dissolution reaction was mainly depended by the corrosion potential of the material. Corrosion features were intergranular corrosion and were not influenced by the kinds of solutions. The ratio of the dissolved ions was same as that of the bulk steel composition.