Development of Treatment Process for Anode Residue from Molten Salt Electrorefining of Spent Metallic Fast Reactor Fuel

Abstract

A new treatment process was proposed for the anode residue from a molten salt electrorefining step in the pyrometallurgical reprocessing of spent metallic fast reactor fuel. This treatment process consists of two steps: (a) oxidation of the remaining actinides in the anode residue by the addition of CdCl2 and (b) removal of the accompanying chloride by high-temperature distillation. The oxidation of the remaining uranium by CdCl2 was studied using anode residue from previous electrorefining experiments using U-Zr alloys. The reaction between uranium and CdCl2 was completed in [approximately]2 days with a satisfactory chlorine balance among the species in the molten chlorides solvent. A high uranium oxidation rate was attained by appropriately controlling the rate of CdCl2 addition. The high-temperature distillation tests were carried out at 1473 K with pressure of [approximately]300 Pa to remove the solvent accompanying the anode residue. The chloride content in the anode residue was lowered to 1% to 2.5% by the distillation operation. Although the anode residue was heated to 1673 to 1773 K at a pressure of [approximately]50 kPa after the distillation, it was not melted completely. The remaining ratio of uranium after the electrorefining and the above treatment process was evaluated to be 0.04% to 0.20%. Material flow calculations were performed for a pyrometallurgical reprocessing facility equipped with the anode residue treatment process. It showed that (a) the chlorine and uranium supply/demand balance is maintained unless the remaining ratio of uranium after electrorefining exceeds a certain value and (b) the addition of the anode residue treatment process does not have an adverse effect on either the performance of the overall process or the facility design.