URANIUM TRANSPORT IN A HIGH-THROUGHPUT ELECTROREFINER FOR EBR-II BLANKET FUEL

摘要

A unique high-throughput Mk-V electrorefiner is being used in the electrometallurgical treatment of the metallic sodium-bonded blanket fuel from the Experimental Breeder Reactor II. Over many cycles, it transports uranium back and forth between the anodic fuel dissolution baskets and the cathode tubes until, because of imperfect adherence of the dendrites, it all ends up in the product collector at the bottom. The transport behavior of uranium in the high-throughput electrorefiner can be understood in terms of the sticking coefficients for uranium adherence to the cathode tubes in the forward direction and to the dissolution baskets in the reverse direction. The sticking coefficients are inferred from the experimental voltage and current traces and are correlated in terms of a single parameter representing the ratio of the cell current to the limiting current at the surface acting as the cathode. The correlations are incorporated into an engineering model that calculates the transport of uranium in the different modes of operation. The model also uses the experimentally derived electrorefiner operating maps that describe the relationship between the cell voltage and the cell current for the three principal transport modes. It is shown that the model correctly simulates the cycle-to-cycle variation of the voltage and current profiles. The model is used to conduct a parametric study of electrorefiner throughput rate as a function of the principal operating parameters. The throughput rate is found to improve with lowering of the basket rotation speed, reduction of UCl_3 concentration in salt, and increasing the maximum cell current or cut-off voltage. Operating conditions are identified that can improve the throughput rate by 60 to 70% over that achieved at present.