clear what the purity of the uranium deposit on the cathode mandrel will be, nor what will happen to plutonium and the other elements present.

The committee notes that the difference between demonstrating the viability of the process and optimizing the process seems to be blurred. The committee believes that ANL should be clear about directing its efforts to the former. The committee makes this observation in light of what it perceives to be significant effort devoted to various electrorefiner designs, and it questions whether they are required for experimental verification or for optimization.

Process Development

Process development work being carried out in the Mark IV has involved both irradiated and unirradiated materials and has used both depleted uranium and depleted uranium with zirconium metal present.3 The presence of zirconium metal appears to improve both uranium collection efficiency and the nature of the uranium deposit. The electrorefining process is being carried out at constant current to a fixed voltage cutoff. ANL fully understands the importance of establishing and stabilizing the process operating conditions that will permit anodizing the uranium while leaving the zirconium mostly in the anodization baskets, and it has made good progress in this area.

ANL is studying a number of important process operating parameters, such as rotation rates, scraper configuration, and current densities, on all of the electrorefiners. One parameter specific to the Mark IV is the “path” followed by the uranium during its deposition. The first path is what ANL calls “direct.” In this path, uranium in the chopped driver fuel is anodized from anode baskets into the melt, followed by its reduction and deposition as metallic uranium at the cathode. The second path ANL calls “deposition.” In this path, the uranium in the chopped driver fuel is anodized from the anode basket into the molten process salt, reduced to metal into the cadmium pool (which is operated as a cathode), anodized back into the process salt from the cadmium pool (which is now operated as an anode), and finally reduced and deposited as metallic uranium at the cathode. CdCl2 is added to the electrorefiner to oxidize the uranium in the cadmium to U(III) so as to effect its transfer to the process salt. Care must be taken because an excess of the cadmium salt apparently can corrode iron components of the electrorefiner.

Electrorefiner operating results of particular interest are the morphologies of the uranium deposits and the uranium collection efficiencies. The morphologies of the deposits as shown in several photographs of the cathodes from the Mark IV electrorefiner appear more dendritic than the deposits seen by the committee at ANL-E. However, since the uranium deposits are treated further in the cathode processor and the casting furnace, this does not appear to be a serious problem.

One possible benefit of the Mark V electrorefiner would be the elimination of the casting furnace process step because the cathode processor, operating on uranium scraped from the cathode, can produce

3  

Argonne National Laboratory, Nuclear Technology, EBR-II Spent Fuel Treatment Program Monthly Report, March 1997.



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