Impact of Stoichiometry on the Mechanism and Kinetics of Oxidative Dissolution of UO2 Induced by H2O2 and γ‑Irradiation

• Published in: Journal of physical chemistry. C 2019-04, Vol.123 (15), p.9919-9925
• Main Authors: Kumagai, Yuta, Barreiro Fidalgo, Alexandre, Jonsson, Mats
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.9b00862

Radiation-induced oxidative dissolution of uranium dioxide (UO2) is one of the most important chemical processes of U driven by redox reactions. We have examined the effect of UO2 stoichiometry on the oxidative dissolution of UO2 in aqueous sodium bicarbonate solution induced by hydrogen peroxide (H2O2) and γ-ray irradiation. By comparing the reaction kinetics of H2O2 between stoichiometric UO2.0 and hyper-stoichiometric UO2.3, we observed a significant difference in reaction speed and U dissolution kinetics. The stoichiometric UO2.0 reacted with H2O2 much faster than the hyper-stoichiometric UO2.3. The U dissolution from UO2.0 was initially much lower than that from UO2.3 but gradually increased as the oxidation by H2O2 proceeded. Increase in the initial H2O2 concentration caused decrease in the U dissolution yield with respect to the H2O2 consumption both for UO2.0 and UO2.3. This decrease in the U dissolution yield is attributed to the catalytic decomposition of H2O2 on the surface of UO2. The γ-ray irradiation induced the U dissolution that is analogous to the kinetics by the exposure to a low concentration (2 × 10–4 mol dm–3) of H2O2. The exposure to higher H2O2 concentrations caused lower U dissolution and resulted in deviation from the U dissolution behavior by γ-ray irradiation.