Oxidation of UO2 in molten alkali-metal carbonate mixtures: formation of uranates and diuranates

Abstract

The oxidation of UO2 in a variety of alkali-metal carbonate melts has been studied in the temperature range 723–1123 K. UO2 reacts with carbonate in the presence of oxygen to produce a mixture of mono- and di-uranates. The monouranate is favoured at high temperature. In the presence of alkali-metal nitrate salts the reaction rate is increased markedly: 100% oxidation of UO2 is possible at 723 K in 1 h. Oxygen stirring of the melt also increases the rate of oxidation over air stirring and simple stirring. The mechanism of oxidation of UO2 is dependent upon generation of peroxide and superoxide ions in the carbonate melt.