Nuclear Technology / Volume 162 / Number 2 / May 2008 / Pages 169-178
Technical Paper / First International Pyroprocessing Research Conference / dx.doi.org/10.13182/NT162-169
The electrochemical reduction process has been recently developed for converting oxide nuclear fuels to metals. In order to characterize the reduction mechanism and to investigate appropriate conditions for improving the reduction rate, several reduction tests were conducted in a LiCl-Li2O electrolyte at 650°C using various types of cathode baskets containing 10 to 100 g of UO2. The reduction progressed from the outside to the center of the cathode basket, and the reduction rate might be determined by the transportation of oxygen ion to the bulk salt. It was verified that feeding in small UO2 particles and reducing the thickness of the UO2 layer in the cathode basket improved the reduction rate. The completion of UO2 reduction was indicated by the open circuit potential of the cathode basket exhibiting lithium deposition potential for a long time. A salt distillation test was conducted using the reduction product comprising a mixture of porous uranium metal particles and the electrolyte. The reduction product loaded in an yttria crucible was heated to 1400°C in an argon stream. The residue in the crucible consisted of a uranium metal ingot and a small amount of dross. The adhering LiCl seemed to be completely removed. Consequently, it was demonstrated in the electrochemical reduction followed by the salt distillation that a uranium metal ingot could be produced from the UO2 feed with a high degree of efficiency.