Removal of Zirconium in Electrometallurgical Treatment of Experimental Breeder Reactor II Spent Fuel

During electrorefining of irradiated, binary U-Zr Experimental Breeder Reactor II fuel, a portion of zirconium is found to dissolve along with uranium. It accumulates in the cadmium pool both as dissolved zirconium and as a zirconium-cadmium intermetallic precipitate. Two electrochemical methods of removing zirconium from the electrorefiner have been evaluated. The first is a three-step method consisting of chemical oxidation of zirconium by CdCl₂ addition, depletion of zirconium from the cadmium pool by electrotransport, and drawdown of zirconium from the LiCl-KCl eutectic salt by using a different electrorefiner configuration. A transport model is employed to determine the cell operating conditions for growing pure zirconium deposits and the throughput rate. The second method eliminates the chemical oxidation step and permits codeposition of uranium and zirconium onto the solid cathode. The transport model is used to assess the level of uranium impurity in the cathode product; an additional step is proposed to reoxidize uranium in the deposit. The two methods are compared from the standpoints of throughput, deposit composition, deposit adherence to a solid cathode mandrel, and the underlying uncertainties. A brief review is given of the related past laboratory work on removal of zirconium from the electrorefiner.