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論文

Distribution of studtite and metastudtite generated on the surface of U$$_{3}$$O$$_{8}$$; Application of Raman imaging technique to uranium compound

日下 良二; 熊谷 友多; 蓬田 匠; 高野 公秀; 渡邉 雅之; 佐々木 隆之*; 秋山 大輔*; 佐藤 修彰*; 桐島 陽*

Journal of Nuclear Science and Technology, 58(6), p.629 - 634, 2021/06

https://doi.org/10.1080/00223131.2020.1854881
 被引用回数：7 パーセンタイル：65.65(Nuclear Science & Technology)

Studtite and metastudtite are uranyl peroxides formed on nuclear fuel in water through the reaction with H$$_{2}$$O$$_{2}$$ produced by the radiolysis of water. However, it is unclear how the two types of uranyl peroxides are generated and distributed on the surface of nuclear fuel. Here, we used Raman imaging technique to exemplify distribution data of the two uranyl peroxides formed on the surface of a U$$_{3}$$O$$_{8}$$ pellet through immersion in a H$$_{2}$$O$$_{2}$$ aqueous solution. As a result, we observed that studtite and metastudtite are heterogeneously distributed on the U$$_{3}$$O$$_{8}$$ surface. No clear correlation between the distributions of studtite and metastudtite was observed, suggesting that the two uranyl peroxides are independently generated on the surface of U$$_{3}$$O$$_{8}$$. We anticipate that this Raman imaging technique could reveal how these uranyl peroxides are generated and distributed on the surface of the nuclear fuel debris in the Fukushima-Daiichi Nuclear Power Plants.

口頭

Surface alteration of simulated nuclear fuel debris containing Fe, Cr, and Ni in water; A Raman and M$"o$ssbauer spectroscopic study

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*

no journal, , 

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 M$"o$ssbauer 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 M$"o$ssbauer 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$$_{4}$$$$cdot$$4H$$_{2}$$O and UO$$_{4}$$$$cdot$$2H$$_{2}$$O. The formation of uranyl peroxides on the surface was clearly confirmed by the Raman spectroscopy. The $$^{57}$$Fe M$"o$ssbauer spectroscopy, in contrast, showed insignificant change between the spectra before and after the immersion. The result of $$^{57}$$Fe M$"o$ssbauer spectroscopy suggests that phases containing Fe are stable toward water and H$$_{2}$$O$$_{2}$$.

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