Development of metal fuel fabrication technology for irradiation test in JOYO. Production of uranium-plutonium alloy by electrochemical reduction

U-Pu ingots were produced for following fabrication tests of U-Pu-Zr metallic fuel by means of electrochemical reduction of U-60 wt% Pu mixed oxide in molten LiCl-Li2O. Sintered pellets with a low density of 60-70%, relative to the theoretical density were placed on a tungsten mesh basket and used as the cathode of the electrochemical reduction at 923 K. After the electrochemical reduction, shiny metallic color was observed on the whole porous cross section of the pellets. That suggests the pellets of the U-Pu mixed oxide were reduced in the size of 10 mm in diameter and 4 mm in thickness. The porous U-Pu alloy was heated to melt at 1123 K and then the atmosphere was evacuated to around 30 Pa of an absolute vacuum pressure to remove an accompanying electrolyte salt by distillation. A U-Pu ingot of 10 g was successfully recovered as a dense material, in which oxygen contamination was less than 1000 wt ppm. More than 99% of U and Pu that initially loaded in the mixed oxide pellets were recovered in the U-Pu ingot, suggesting that the operation of this study works very well. (author)