The anodic dissolution of SIMFUEL (UO_2) in slightly alkaline sodium carbonate/bicarbonate solutions

摘要

The corrosion of nuclear fuel under waste disposal conditions is likely to be influenced by the bicarbonate/carbonate content of the groundwater since it increases the solubility of the U~(VI) corrosion product, [UO_2]~(2+). As one of the half reactions involved in the corrosion process, the anodic dissolution of SIMFUEL (UO_2) has been studied in bicarbonate/carbonate solutions (pH 9.8) using voltammetric and potentiostatic techniques and electrochemical impedance spectroscopy. The reaction proceeds by two consecutive one electron transfer reactions (U~(IV) → U~V → U~(VI)). At low potentials (≤250mV (vs. SCE) the rate of the first electron transfer reaction is rate determining irrespective of the total carbonate concentration. At potentials >250mV (vs. SCE) the formation of a U~(VI)O_2CO_3 surface layer begins to inhibit the dissolution rate and the current becomes independent of potential indicating rate control by the chemical dissolution of this layer.