A combination of electrochemical methods and X-ray photoelectron spectroscopy has been used to study the combined influence of H2O2 and dissolved H-2 on the oxidation of SIMFUEL (UO2 electrodes fabricated to simulate spent nuclear fuel without the accompanying radiation fields) electrodes in 0.1 mol/L KCl (pH 9.5) at 6 degrees C. The SIMFUEL electrodes contain REIII (where RE is rare earth) ions at U-IV lattice sites within the UO2 matrix and noble metal (epsilon) particles dispersed throughout the solid. Under Ar-purged conditions, UO2 can be oxidized by H2O2 by coupling to its direct reduction on the UO2 surface and on the noble metal particles that are galvanically coupled to the UO2 matrix. The OH center dot radicals formed on the noble metal particles can be scavenged by reaction with H-2 in H-2/Ar-purged solutions. Because the H2 concentration is many orders of magnitude greater than H2O2 concentrations, the rate of formation of H-center dot radicals on the noble metal surface exceeds that of OH center dot radicals, leading to the prevention, or even the reversal, of UO2 oxidation. A [H-2]/[H2O2] ratio >= 10(6) is sufficient to completely protect the UO2 surface from oxidation. (C) 2010 The Electrochemical Society. [DOI:10.1149/1.3446823] All rights reserved.