融解亜鉛による核燃料の高温冶金処理

抄録

Interest in various pyrometallurgical processes of irradiated nuclear fuels has grown because they may serve as an aid to reduce fuel processing costs through the possibility of handling short-cooled fuels as well as the elimination of chemical conversions. As one of these pyrometallurgical processes, the fractional crystallization from low melting solvent metals using liquid zinc was investigated in this paper.
The process involves the dissolution of an irradiated material in zinc with some flux and subsequent separation through crystallization and precipitation of intermetallic compounds (U₂Zn₁₇). The required reduction in solubility was accomplished by temperature change from 750°C to 550°C.
Specimens used were artificial fissium alloys containing zirconium made by vacuum resistant-heat melting and injection casting.
The results of metallography and chemical analysis of slow cooled zinc ingots containing 3% uranium, showed the availability of the separation between solvent zinc and precipitated U₂Zn₁₇ phase by decantation. Thus separated cake whith mainly consisted of U₂Zn₁₇ containing from 6 % to 16 % uranium and the purified uranium sponges were recovered by vacuum distillation of these separated cakes at temperature 1000°C. The decontamination factors for zirconium obtained were 2.29.5. These decontamination factor were theoretically and experimentally confirmed to depend upon the uranium content in the separated cake.