Kinetics of Reaction of Oxygen with Uranium(IV) Chloride in Alkali Chloride Melts

Abstract

Reaction of oxygen with solutions of uranium tetrachloride in molten alkali chlorides was studied. The experiments were performed in LiCl–KCl, NaCl–KCl–CsCl, and NaCl–CsCl eutectic based melts at 450–750oC. Pure oxygen and argon–oxygen mixtures (containing ca. 1 and 10% O2) were used. Amount of oxygen passed through the melt varied from less than one to over 100 moles per mole of uranium present. In addition the reaction of oxygen with the melts containing a mixture of uranium(IV) and neodymium chlorides was investigated. The course of the reactions was followed by in situ electronic absorption spectroscopy measurements with the spectra recorded at the certain time intervals. Depending on temperature, cationic melt composition, and oxygen-to-uranium molar ratio, the reaction resulted in oxidation of uranium(IV) to soluble uranyl chloride and/or precipitation of uranium oxide. Analysis of the spectra provided the information on kinetics of U(IV) concentration change and the reaction rates were determined. Increasing temperature, O2 : U(IV) molar ratio or decreasing mean radius of alkali cations of the solvent melt resulted in faster decrease of U(IV) concentration in the melt.