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Investigation of the effects of irradiation on corrosive environments using in-situ electrochemical measurements during $$gamma$$-ray irradiation

電気化学測定による$$gamma$$線照射下での腐食環境への照射影響に関する研究

佐藤 智徳  ; 上野 文義  

Sato, Tomonori; Ueno, Fumiyoshi

福島第一原子力発電所の構造材は照射下でかつ、海水成分などの多量の不純物を含む腐食環境にさらされている。格納容器材である炭素鋼の腐食は照射下では加速されることが報告されており、このような照射下での腐食メカニズムの理解には、腐食環境の照射下での変化に関する定量的な評価が不可欠である。そこで、$$gamma$$線照射下でのサイクリックボルタンメトリーの連続測定を実施し、$$gamma$$線照射による腐食環境変化のその場測定評価を実施した。線量率は3kGy/hとし、温度は50$$^{circ}$$Cで試験を実施した。その結果、カソード電流において、照射開始直後に減少し、その後増加して一定値となるような変化を示すことが分かった。最終的に、カソード電流は照射前と比較すると、約2割増加した。一方でアノード電流は照射とともに増加する結果となった。また、炭素鋼の電気化学インピーダンス測定結果の時間変化から、炭素鋼の分極抵抗は、照射開始直後は、カソード電流の照射影響による変化で決定されるが、被膜の成長とともに表面酸化被膜の寄与が大きくなり、40時間程度で皮膜の影響は表れ始めることが分かった。

The structural materials used in Fukushima-Daiichi Nuclear Power Plant are exposed to the water containing some impurities, e.g., seawater components, under irradiation. The hydrogen peroxide and hydrogen generated by water radiolysis under irradiation condition. It was reported that $$gamma$$-ray irradiation enhanced the corrosion of carbon steel by the weight loss measurements in the immersion test of carbon steel under irradiation. The in-situ measurement of the electrochemical parameter during irradiation is one of the most effective approaches to investigate the effects of irradiation on the corrosion. In this study, to investigate the effects of $$gamma$$-ray irradiation on the corrosive condition and corrosion phenomena, the in-situ electrochemical measurement method during irradiation was constructed, and the cyclic voltammetry (CV) was performed in the diluted artificial seawater under $$gamma$$-ray irradiation conditions. The dose rate of $$gamma$$-ray was 3.3 kGy/h, and the temperature was fixed at 50 degrees centigrade. Obtained major results are in follows;(1) The in-situ electrochemical measurements were successfully performed in this study. (2) The diffusion limiting current in the cathodic region decreased just after the start of irradiation. And then the cathodic current increased. This tendency indicated that the dissolved oxygen was consumed rapidly by the irradiation. The consumed dissolved oxygen contributed to the generation of hydrogen peroxide. (3) The cathodic current under irradiation was 20 percents larger than that before irradiation. (4) The anodic current increased just after the start of irradiation by the generation of hydrogen and hydrogen peroxide.

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