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ガンマ線照射下希釈人工海水中におけるSUS316L鋼の自然浸漬電位に及ぼすゼオライトの影響

Effect of zeolites on the corrosion potential of type 316L stainless steel in diluted artificial sea water under gamma-ray irradiation

加藤 千明; 佐藤 智徳; 上野 文義; 山岸 功; 山本 正弘

Kato, Chiaki; Sato, Tomonori; Ueno, Fumiyoshi; Yamagishi, Isao; Yamamoto, Masahiro

福島第一原子力発電所事故の汚染水処理に用いた使用済み吸着塔の局部腐食発生条件に関する基礎的検討として、ガンマ線照射下における人工海水を含んだゼオライト中のステンレス鋼(SUS316L)の電気化学試験を行った。ステンレス鋼の定常自然浸漬電位はガンマ線照射により貴化し、吸収線量率の増加に従いその電位が上昇した。一方、ゼオライト共存系ではガンマ線照射下の電位上昇が抑制された。ガンマ線照射下におけるステンレス鋼の電位上昇機構は放射線により生じるH$$_{2}$$O$$_{2}$$がステンレス鋼のカソード反応を活性化するためであり、ゼオライトはH$$_{2}$$O$$_{2}$$の生成を抑制するために電位が低下することを明らかにした。ステンレス鋼の局部腐食発生電位は、照射の有無、ゼオライトの種類や接触により大きく変化しないことから、ゼオライト共存はガンマ線照射下において定常自然浸漬電位を低下させ、局部腐食発生リスクを低減できることが期待できることを明らかにした。

In relation to the consideration for long-term storage of spent Cs adsorption vessels containing zeolites in the Fukushima Daiichi Nuclear Power Station, corrosion of the vessel material in the spent Cs adsorption vessel is one of important issues. We performed electrochemical tests of stainless steel (SUS 316L) in the zeolites containing artificial seawater under gamma-ray irradiation. The spontaneous potential (ESP) and critical pitting potential (VC), of SUS316L were measured to understand the corrosion resistance of the stainless steel in this study. The rest potential of the stainless steel increased with increasing time after gamma-ray irradiation. The ESP, defined as the steady rest potential, increased with increasing dose rate, while increasing ESP was suppressed by contact with the zeolites. Concentration of H$$_{2}$$O$$_{2}$$ in bulk water increased with increasing dose rate. The concentration increasing was suppressed by contact with the zeolites due to decomposition of H$$_{2}$$O$$_{2}$$. There was good relationship between ESP and the concentration of H$$_{2}$$O$$_{2}$$. The VC of SUS316L contacted with the zeolites decreased with increasing Cl$$^{-}$$ ion concentration and is slightly smaller than the VC in the bulk water. The contact with the zeolites causes the suppressant of increasing ESP under the irradiation. The contact with the zeolites can reduce probability in the localized corrosion for SUS316L.

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