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.