Determination of electrochemical corrosion potential along the JMTR in-pile loop, 1; Evaluation of ECP of stainless steel in high-temperature water as a function of oxidant concentrations and exposure time

JMTRインパイルループ中の腐食電位の決定,1; 酸化種濃度と浸漬時間の関数としての高温水中のステンレス鋼の腐食電位評価

内田 俊介; 塙 悟史 ; 西山 裕孝 ; 中村 武彦 ; 佐藤 智徳  ; 塚田 隆 ; Kysela, J.*

Uchida, Shunsuke; Hanawa, Satoshi; Nishiyama, Yutaka; Nakamura, Takehiko; Sato, Tomonori; Tsukada, Takashi; Kysela, J.*

高温水中の酸素,過酸化水素にさらされたステンレス鋼の腐食挙動についてのin-situ測定に基づいて、腐食電位,金属の表面条件,その他環境条件の相関を求めた。この相関に基づき、電気化学モデルと二層酸化皮膜モデルを結合させた腐食電位評価モデルを開発した。本評価モデルにより得られた結果は以下の通りである。(1)酸素と過酸化水素により腐食電位の差異は、主として内装酸化皮膜の厚さと成長速度によって決まる。(2)計算された腐食電位、すなわち、酸素と過酸化水素のレスポンスの差異、ヒステリシス及びメモリ効果、は実測値とよく一致する。(3)中性子照射は酸化皮膜の照射誘起拡散の結果、腐食電位を低下させる。本腐食電位評価モデルは、JMTRインパイルループの腐食環境評価に適用可能である。

In-pile loop experiments are one of the key technologies which can provide an understanding of corrosion behaviors of structural materials in nuclear power plants (NPPs). The experiments should be supported not only by reliable measurement tools to confirm corrosive conditions under neutron and ray irradiations but also by theoretical models for extrapolating the measured data to predict corrosion behaviors in NPPs. The relationships among electrochemical corrosion potential (ECP), metal surface conditions, exposure time and other environmental conditions have been determined from in situ measurements of corrosion behaviors of stainless steel specimens exposed to HO and O in high temperature water. Based on the relationships, a model to evaluate ECP of stainless steel was developed by coupling an electrochemical model and a double oxide layer model. Major conclusions obtained from the evaluation model are as follows. (1) The difference in ECP behaviors of the specimens exposed to HO and O were mainly from the thickness and developing rate of the inner oxide layers. (2) Calculated ECP behaviors, e.g., the different responses to HO and O and hysteresis and memory effects, agreed with the measured ones. (3) Neutron exposure might decrease ECP due to radiation-induced diffusion in the oxide layer. The ECP evaluation model will be applied to evaluation of corrosive conditions in the JMTR in-pile loop.