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Oral presentation

Effects of hyperstoichiometry and adsorption of phthalic acid on oxidative dissolution of uranium oxide

Kumagai, Yuta; Fidalgo, A. B.*; Jonsson, M.*

no journal, , 

Radiation-induced oxidative dissolution of nuclear fuel is anticipated in the geological repository of spent fuel and after severe accidents, where the fuel would be in direct contact with water. Therefore, understanding of the oxidative dissolution of UO$$_{2}$$ is indispensable to estimate radioactive release. This study has addressed effects of hyperstoichiometry of UO$$_{2}$$ and adsorption of organic compounds on the process. Comparison between hyperstoichiometric UO$$_{2.3}$$ and stoichiometric UO$$_{2.0}$$ demonstrated that the reactivity of UO$$_{2.0}$$ approaches that of UO$$_{2.3}$$ by the H$$_{2}$$O$$_{2}$$ reaction. The result indicates formation of hyperstoichiometric surface layer during the oxidative dissolution. Phthalic acid, which was used as a model compound, suppressed the U dissolution by $$gamma$$-ray irradiation but had little involvement in the H$$_{2}$$O$$_{2}$$ reaction, in spite of adsorption exceeding 1 molecule/nm$$^{2}$$. The results suggest an involvement of radical intermediate derived from phthalic acid in the surface reaction.

Oral presentation

Oxidative uranium dissolution from UO$$_{2}$$ in the presence of adsorbed phthalic acid

Kumagai, Yuta; Jonsson, M.*

no journal, , 

Contact of water with spent nuclear fuel is anticipated in scenarios of failure of the repository system for the direct disposal of spent fuel. Upon the direct contact of water, the UO$$_{2}$$ matrix of the fuel is expected to gradually dissolve due to oxidation of uranium by the action of ionizing radiation. In this study, we examined effects of organic acid on the UO$$_{2}$$ dissolution by using phthalic acid as a model compound. We investigated oxidation of UO$$_{2}$$ by exposure to H$$_{2}$$O$$_{2}$$ in aqueous solution containing phthalic acid. Significant adsorption of phthalic acid on UO$$_{2}$$ was observed. The coverage of the surface was estimated to reach 80 %. The H$$_{2}$$O$$_{2}$$-exposure experiments revealed that adsorbed phthalic acid has no significant effect on the redox reaction by H$$_{2}$$O$$_{2}$$ on the UO$$_{2}$$ surface, despite the high surface density. H$$_{2}$$O$$_{2}$$ oxidation of UO$$_{2}$$ with adsorbed phthalic acid resulted in U dissolution to similar extents with the U dissolution measured in aqueous bicarbonate solutions.

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