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Effects of temperature on the corrosion potential of stainless steel under $$gamma$$-ray irradiation

$$gamma$$線照射下でのステンレス鋼の腐食電位への温度の影響

佐藤 智徳; 加藤 千明; 上野 文義

Sato, Tomonori; Kato, Chiaki; Ueno, Fumiyoshi

福島第一原子力発電所の機器構造材は$$gamma$$線照射kの腐食環境にさらされている。照射下でのステンレス鋼の腐食における温度の影響を決定するために、$$gamma$$線照射下でのステンレス鋼の腐食電位測定を実施した。その結果、照射による、腐食電位の上昇が確認された。そこで、水の放射線分解解析を実施して、照射下の腐食環境を解析した結果、数ppmの過酸化水素が生成されていることを示し、過酸化水素の生成量は$$gamma$$線の線量より初期溶存酸素濃度により決定されることを示した。さらに、この解析結果を用いて、照射下での腐食電位測定結果を解析し、照射下での電位の上昇が、過酸化水素に起因することを示した。また照射下での腐食電位の温度依存性が、非照射下での腐食電位と同様に、溶存酸素濃度の温度依存性により決定されることを示した。

The structural materials of the instruments used in Fukushima Daiichi Nuclear Power Station are exposed to the corrosive condition under the $$gamma$$-ray irradiation. In order to determine the effects of the temperature of water under $$gamma$$-ray irradiation on the corrosion potential of stainless steel, the measurements of the corrosion potential under $$gamma$$-ray irradiation condition was performed. The dissolved oxygen concentration was aerated condition in each temperature in this study. And the corrosive condition under the irradiation was evaluated by the water radiolysis calculation and the measurements of the included hydrogen peroxide in the water after the irradiation. As parameters, the temperature of water and the $$gamma$$-ray dose rate were changed. The major results are listed as follows; (1) The corrosion potentials rose about 400 mV by the $$gamma$$-ray irradiation in all temperature conditions. (2) The potential was low with higher temperature under irradiation with the aerated condition. It was assumed that the lower dissolved oxygen concentration with higher temperature will cause the dependency of the corrosion potential on the temperature under irradiation. (3) The generation of some ppm of hydrogen peroxide was confirmed by the measurements of hydrogen peroxide concentration. It was indicated that the increase of the corrosion potential by the irradiation was caused by the generation of the high concentration of hydrogen peroxide. (4) It was confirmed that the generation of hydrogen peroxide was lower in higher temperature condition due to the lower dissolved oxygen concentration in high temperature. It was indicated that lower potential in high temperature water was caused by not only lower dissolved oxygen but also lower generation of hydrogen peroxide.

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