Effects of Fe(II) and Hydrogen Peroxide Interaction Upon the Dissolution of UO2 in Simulated Geologic Repository Conditions

Iron redox cycling is supposed to be one of the major mechanismsthatcontrol the geochemical boundary conditions in the near field of a geologic repository for UOj spent nuclear fuel. This work investigates the impact of reactions between hydrogen peroxide (H2O2) and iron (Fe/Fe34) 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 FB2 and H202 when the reactants are present in equal concentration. Predomination of H2O2 results in its delayed catalytic decomposition. With UOj 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 (UOnHzO, rn-studtite), detected on UO2 surfaces after exposure to HjO, was not found on the surfaces exposed to solutions with stoichometric Fe(ll)/ H2O2 ratios. This suggests that HjO; was deactivated in redox reactions before a formation of DO, took place. ESR measurements employing the spin trapping technique revealed only the DMPO-QHattduct within the first minutes after the reaction start (high initial concentrations of the OH radical); however, in the case of Fe(ll) and H2O2 reacting at 1Q 4 mol/L with UO2, dissolved oxygen and Fe4-concentrations indicate the participation of further Fe intermediates and, therefore, Fenton redox activities.

AMME Marcus;  BORS W.;  MICHEL C.;  STETTMAIER K.;  RASMUSSEN Gert;  BETTI Maria; 

2005-09-12

AMER CHEMICAL SOC

JRC30448

https://publications.jrc.ec.europa.eu/repository/handle/JRC30448,   

10.1021/es040034x,