An electrochemical and radiolytic study of the effects of H2 on the corrosion of UO2-based materials

Highlights: • H₂ effect in suppressing UO₂ corrosion was studied by producing H radicals. • Reactive H radicals were produced electrochemically and radiolytically. • H radicals produced by H₂O reduction lead to the reduction of U^V states in UO₂. • The combination of γ-irradiation and H₂ lead to the reduction of UO₂. The influence of γ-radiation in the presence of dissolved hydrogen on the corrosion of uranium dioxide has been compared to the electrochemical behavior of uranium dioxide in aqueous chloride solutions. Hydrogen atoms, produced either electrochemically or by water radiolysis were shown to reduce U^V in the oxide leading to suppression of its corrosion. The removal of electrochemical polarization, and of hydrogen when γ-radiation was present, allowed re-oxidation of the uranium dioxide accompanied by the reformation of hydrogen. These results are consistent with published studies which show the corrosion of spent nuclear fuel can be suppressed in the presence of hydrogen. H₂ effect in suppressing the corrosion of UO₂-based materials without catalysis of noble metal particles is studied by producing H radicals electrochemically and radiolytically. Reactive H radicals produced by H₂O reduction at cathodic potentials, lead to the reduction of U^V states which are present due either to the Dy^III doping or the non-stoichiometry within the UO₂ based materials. When the cathodic potential is switched to open circuit, the relaxation of E_CORR (corrosion potential) indicates that the electrochemically reduced surface is unstable. The combination of γ-irradiation and H₂ can also lead to the reduction of UO₂. In the absence of dissolved H₂, a similar relaxation of E_CORR indicates that reactive H radicals produced electrochemically or radiolytically are responsible for the reduction of the UO₂ matrix.