Surface alteration of simulated nuclear fuel debris containing Fe, Cr, and Ni in water; A Raman and Mssbauer spectroscopic study

ステンレス鋼成分を含む模擬デブリの水中での表面変質; ラマン分光法・メスバウアー分光法による研究

熊谷友多 ; 日下良二 ; 中田正美 ; 渡邉雅之 ; 桐島陽*; 秋山大輔*; 佐藤修彰*; 佐々木隆之*

Kumagai, Yuta; Kusaka, Ryoji; Nakada, Masami; Watanabe, Masayuki; Kirishima, Akira*; Akiyama, Daisuke*; Sato, Nobuaki*; Sasaki, Takayuki*

Fuel debris generated in the Fukushima Daiichi NPS accident remains in the damaged reactors and substantial time and effort will be required until the retrieval of the debris. The debris is most likely contacted with water since the accident. The contact with water has possibility to induce degradation of the debris. According to the researches of uranium oxides and spent fuels, the uranium oxide matrix of fuels is oxidized and gradually dissolved as a consequence of water radiolysis. This oxidative dissolution process must be associated with surface alteration. In order to examine these possible degradation processes, we have conducted leaching experiments using simulated fuel debris combined with surface analysis by Raman spectroscopy and $^{57}$ Fe Mssbauer spectroscopy in backscatter geometry. The simulated fuel debris used in this study was prepared from powders of UO $_{2}$ and stainless steel (1 : 1 in atomic ratio of U : Fe + Cr + Ni) by heat treatments. The samples were immersed in pure water or aqueous H $_{2}$ O $_{2}$ solution for up to 30 days. Aqueous H $_{2}$ O $_{2}$ solution was used to simulate the water radiolysis. After certain periods of immersion, the samples were analyzed by Raman spectroscopy and Mssbauer spectroscopy as well as chemical analysis of leached elements. The analysis of leached elements showed a selective dissolution of U from the samples. The U dissolution was facilitated by the reaction of H $_{2}$ O $_{2}$ . The reaction of H $_{2}$ O $_{2}$ also resulted in formation of solid uranyl peroxides, UO $_{4}$ 4H $_{2}$ O and UO $_{4}$ 2H $_{2}$ O. The formation of uranyl peroxides on the surface was clearly confirmed by the Raman spectroscopy. The $^{57}$ Fe Mssbauer spectroscopy, in contrast, showed insignificant change between the spectra before and after the immersion. The result of $^{57}$ Fe Mssbauer spectroscopy suggests that phases containing Fe are stable toward water and H $_{2}$ O $_{2}$ .

使用言語	:	English
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発表会議名	:	International Chemical Congress of Pacific Basin Societies 2021 (Pacifichem 2021)
開催年月	:	2021/12
開催都市	:	Honolulu
開催国	:	U.S.A.
キーワード	:	燃料デブリ; ラマン分光法; メスバウアー分光法; 過酸化ウラニル; 福島第一原子力発電所事故; Fukushima Daiichi Nuclear Power Station Accident

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使用施設	:	第4研究棟
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受委託・共同研究相手機関	:	東北大学

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