title: Effects of Fe(II) and hydrogen peroxide interaction upon dissolving UO2 under geologic repository conditions.
abstract: Iron redox cycling is supposed to be one of the major mechanisms that control the geochemical boundary conditions in the near field of a geologic repository for UO2 spent nuclear fuel. This work investigates the impact of reactions between hydrogen peroxide (H2O2) and iron (Fe2+/Fe3+) on UO2 dissolution. The reaction partners were contacted with UO2 in oxygen-free batch reactor tests. The interaction in absence of UO2 gives a stoichiometric redox reaction of Fe2+ and H2O2 when the reactants are present in equal concentration. Predomination of H202 results in its delayed catalytic decomposition. With UO2 present, its dissolution is controlled by either a slow mechanism (as typical for anoxic environments) or uranium peroxide precipitation, depending strongly on the reactant ratio. Uranium peroxide (UO4 x nH2O, m-studtite), detected on UO2 surfaces after exposure to H2O2, was not found on the surfaces exposed to solutions with stoichometric Fe(II)/ H2O2 ratios. This suggests that H2O2 was deactivated in redox reactions before a formation of UO4 took place. ESR measurements employing the spin trapping technique revealed only the DMPO-OH adduct within the first minutes after the reaction start (high initial concentrations of the OH radical); however, in the case of Fe(II) and H2O2 reacting at 10(-4) mol/L with UO2, dissolved oxygen and Fe2+ concentrations indicate the participation of further Fe intermediates and, therefore, Fenton redox activities.
authors.affiliation: European Commission, Joint Research Centre, Institute for Transuranium Elements, 76125 Karlsruhe, Germany. amme@itu.fzk.de
authors.forename: M
authors.initials: M
authors.lastname: Amme
authors.forename: W
authors.initials: W
authors.lastname: Bors
authors.forename: C
authors.initials: C
authors.lastname: Michel
authors.forename: K
authors.initials: K
authors.lastname: Stettmaier
authors.forename: G
authors.initials: G
authors.lastname: Rasmussen
authors.forename: M
authors.initials: M
authors.lastname: Betti
mesh_terms: D055593:Geological Phenomena; D005844:Geology; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D016877:Oxidants / Q000737:chemistry*; D010084:Oxidation-Reduction; D011850:Radioactive Waste; D012995:Solubility; D017974:Uranium Compounds / Q000737:chemistry*
chemical_list: D016877:Oxidants; D011850:Radioactive Waste; D017974:Uranium Compounds; D006861:Hydrogen Peroxide; D007501:Iron; C012597:uranium dioxide