The influence of oxic (O-2-purged), anoxic (Ar-purged) and potentially reducing (5% H-2/95% Ar-purged) conditions on the corrosion of UO2 (nuclear fuel) has been studied on SIMFUEL specimens in 0.1 mol L-1 KCl (pH similar to 9.5) solutions at 60 C using corrosion potential measurements and X-ray photoelectron spectroscopy. A number of SIMFUEL specimens, doped to simulate various degrees of in-reactor burn-up were used. The doping yielded specimens containing REIII (rare-earth) ions at U-1V lattice sites within the UO2 matrix and noble metal (epsilon) particles interspersed throughout the solid. Under oxic and anoxic conditions, the corrosion potential and surface composition did not vary significantly with the degree of simulated burn-up. For potentially reducing conditions, both the corrosion potential and the extent of surface oxidation decreased as the degree of simulated burn-up increased. This was attributed to the increased number of noble metal particles on which H-2 oxidation is possible. Since these particles are galvanically coupled to the rare-earth doped UO2 matrix, this suppresses the corrosion potential of the matrix, thereby preventing its oxidation. (c) 2006 Elsevier B.V. All rights reserved.