The pilot plant production of electrolytic uranium dioxide

Abstract

The pilot plant production of uranium dioxide crystals by a fused salt electrolytic process is described. The electrolyte, containing uranyl chloride dissolved in molten NaCl KCl eutectic, is obtained by the direct chlorination of uranium oxide in situ in the fused salt, and electrolysis between graphite electrodes forms a crystalline deposit of UO 2 at the cathode. The deposition is carried out with either horizontally or vertically disposed electrodes, but the latter are preferred from the point of view of simplicity. An alternative process, using uranium ore concentrate as the starting material and involving three electrolytic stages is also described. The bulk of the impurities are removed in the first electrolysis in which anodic chlorination is used to improve the efficiency of the stage. The product, 99% pure, is then treated in the same way as the pure oxide starting material, but a third electrodeposition, in which the UO 2 plated cathode is used as a soluble anode, is necessary to achieve the purity level required for nuclear fuel applications. The impurities found in the product are discussed in the context of their origin and their behaviour in the process, particular reference being made to the rare earths. The process has been found capable of producing oxides within the range of composition UO 2 to UO 2.5, and the conditions affecting this variation are described.