The preparation of UO₂ by fused salt electrolysis using UO₂ or UF₄ as starting material

Coarse crystalline uranium dioxide can be prepared by the electroreduction of UO₂Cl₂ or UO₂F₂ dissolved in fused chloride melts. The uranyl compounds are prepared in the melt by the treatment of UO₂ or UF₄ with a gas mixture of hydrogen chloride and oxygen. It is found that moisture accelerates the oxidation of the fluoride. Using the LiCl-KCl system, oxides with a composition ranging from UO_2.000 to UO_2.007 are obtained. The crystal form is affected by the degree of dryness of the melt and in the case of the LiCl-KCl-fluoride system also by the presence of chlorine in the melt. The presence of fluorides in the melt favourably influences the formation of cubeshaped UO₂ crystals. The oxides have densities varying between 10.85 and 10.98 (25° C).