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論文

A Raman spectroscopy study of bicarbonate effects on UO$$_{2+x}$$

McGrady, J.; 熊谷 友多; 渡邉 雅之; 桐島 陽*; 秋山 大輔*; 紀室 辰伍; 石寺 孝充

Journal of Nuclear Science and Technology, 60(12), p.1586 - 1594, 2023/12

https://doi.org/10.1080/00223131.2023.2236104
 被引用回数：2 パーセンタイル：33.46(Nuclear Science & Technology)

Raman spectroscopy was used to investigate the effect of bicarbonate solution on the hyperstoichiometric UO$$_{2+x}$$ surface oxide of UO$$_{2}$$ pellets. The hyperstoichiometry causes distortion of the UO$$_{2}$$ lattice, leading to the formation of defect peaks which arise in the Raman spectrum due to a loss of symmetry. By deconvolution of the defect peaks, the extent of oxygen inclusion and defect formation in the surface oxide as a function of bicarbonate concentration was investigated. Immersion in solution caused a reduction in the amount of interstitial oxygen due to dissolution U(V) and U(VI) in the UO$$_{2+x}$$ oxide surface. The defect concentration increased upon immersion due to the formation of an equilibrium between dissolution and reprecipitation. The bicarbonate concentration affected the defect content which was attributed to different forms of U in solution (hydrolysed UO$$_{2}$$$$^{2+}$$ and UO$$_{2}$$(CO$$_{3}$$)$$_{2}$$$$^{2-}$$) leading to different rates of reduction and precipitation.

論文

UO$$_{2}$$ dissolution in bicarbonate solution with H$$_{2}$$O$$_{2}$$; The Effect of temperature

McGrady, J.; 熊谷 友多; 北辻 章浩; 桐島 陽*; 秋山 大輔*; 渡邉 雅之

RSC Advances (Internet), 13(40), p.28021 - 28029, 2023/09

https://doi.org/10.1039/D2RA08131H
 被引用回数：2 パーセンタイル：22.69(Chemistry, Multidisciplinary)

使用済核燃料の埋設処分において、キャニスタが破損して核燃燃料が地下水と接触すると、水の放射線分解により発生した酸化性物質とUO$$_{2}$$が反応する。炭酸水素イオンが存在する地下水中での、H$$_{2}$$O$$_{2}$$によるUO$$_{2}$$の酸化溶解がこれまでに研究されてきた。埋設されたキャニスタ周辺の温度は、時間や配置場所により変化するが、これまでに酸化溶解の温度効果は明らかにされていない。種々の炭酸水素イオン濃度と温度条件下でのUO$$_{2}$$表面におけるH$$_{2}$$O$$_{2}$$の反応とU溶解を調べた。炭酸水素イオン濃度や温度によりUO$$_{2}$$表面でのH$$_{2}$$O$$_{2}$$の反応機構が変化し、これによりUO$$_{2}$$の溶解速度が変化することが分かった。これは、UO$$_{2}$$表面に生成される化学種の違いに起因することが示唆された。

論文

The Kinetics and mechanism of H$$_{2}$$O$$_{2}$$ decomposition at the U$$_{3}$$O$$_{8}$$ surface in bicarbonate solution

McGrady, J.; 熊谷 友多; 渡邉 雅之; 桐島 陽*; 秋山 大輔*; 北村 暁; 紀室 辰伍

RSC Advances (Internet), 11(46), p.28940 - 28948, 2021/08

https://doi.org/10.1039/D1RA05580A
 被引用回数：7 パーセンタイル：30.67(Chemistry, Multidisciplinary)

The rate of U release is affected by bicarbonate (HCO$$_{3}$$$$^{-}$$) concentrations in the groundwater, as well as H$$_{2}$$O$$_{2}$$ produced by water radiolysis. To understand the dissolution of U$$_{3}$$O$$_{8}$$ by H$$_{2}$$O$$_{2}$$ in bicarbonate solution (0.1 - 50 mM), dissolved U concentrations were measured upon H$$_{2}$$O$$_{2}$$ addition (300 $$mu$$M) to U$$_{3}$$O$$_{8}$$/bicarbonate mixtures. As the H$$_{2}$$O$$_{2}$$ decomposition mechanism is integral to U dissolution, the kinetics and mechanism of H$$_{2}$$O$$_{2}$$ decomposition at the U$$_{3}$$O$$_{8}$$ surface was investigated. The dissolution of U increased with bicarbonate concentration which was attributed to a change in the H$$_{2}$$O$$_{2}$$ decomposition mechanism from catalytic at low bicarbonate ($$leq$$ 5 mM HCO$$_{3}$$$$^{-}$$) to oxidative at high bicarbonate ($$geq$$ 10 mM HCO$$_{3}$$$$^{-}$$). Catalytic H$$_{2}$$O$$_{2}$$ at low bicarbonate was attributed to the formation of an oxidised surface layer.

口頭

アモルファス過酸化ウラニルの新しい生成経路の発見

McGrady, J.; 熊谷 友多; 日下 良二

no journal, , 

Two new pathways to the formation of amorphous uranyl peroxide under ambient conditions have been identified in this study. UO$$_{2}$$ powder was immersed in H$$_{2}$$O$$_{2}$$ solution, and in-situ Raman spectroscopy was used to analyse the surface oxide. At the interface uranyl peroxide was identified, yet underneath this surface amorphous uranyl peroxide was generated. The amorphous phase was found to be transient over time. Drying of the sample after immersion showed an enhanced Raman peak signal for the amorphous phase indicating significant generation, suggesting the formation mechanism involves dehydration. Addition of the amorphous uranyl peroxide into water showed decomposition of the amorphous phase by disappearance of the Raman peak, and the release of gas was observed via the Raman optical microscope which was thought to be O$$_{2}$$.

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