The Electrochemical Reactivity of 6.0 wt% Gd-Doped UO2 in Aqueous Carbonate/Bicarbonate Solutions

The effect of gadolinium doping on the anodic reactivity of UO2 in aqueous carbonate solutions has been investigated voltammetrically, potentiostatically, by Raman spectroscopy and X-ray photoelectron spectroscopy. The mechanism of oxidation/dissolution is the same as on undoped UO2 and lightly doped SIMFUEL (doped UO2) but the reactivity is significantly reduced. This is attributed to the formation of Gd-III-Oxygen vacancy (O-V) clusters which limits the availability of these vacancies required to accommodate excess O2- during matrix oxidation to (U1-2 lambda U2xO2+x)-U-IV-O-v. The subsequent reaction of this oxidized surface layer to (UO3 center dot yH2O)-O-VI/(UO2)-O-VI(CO3)(x)((2-2x)+) is also suppressed by Gd-doping. The overall oxidation/alteration (dissolution) reaction appears to be kinetically controlled by the creation of U-VI surface species prior to dissolution. (C) 2014 The Electrochemical Society.