stationary cathode surfaces, and it relies on ceramic “scrapers” to dislodge continuously electrodeposited uranium from these surfaces as the uranium accumulates. The dislodged uranium falls to the bottom of the cell and is captured by a bucket with a screen-covered bottom. The ability of these scrapers to remove the developing deposits is crucial to the continuous operation of the HTER because the accumulation of a significant mass of dense uranium deposit on the cathode surfaces leads to binding and stalling of the ACM anode rotor. In addition, this accumulated uranium can cause an electrical short between the anode and cathode, greatly decreasing the efficiency of the uranium recovery process.

In conjunction with work at ANL-W, ANL-E also modified the 10-inch (inner diameter) ACMs for the Mark-V electrorefiner to be used at ANL-W for processing experimental breeder reactor II (EBR-II) blanket fuel. The 10-inch ACM for use at ANL-W operates on the same basis as the 25-inch ACM but has only nine anode baskets and four cathode surfaces. ANL-E has attempted to mimic the operation of the 10-inch Mark-V HTER by using only the baskets in the two inner channels of the 25-inch HTER. ANL was able to achieve excellent uranium dissolution and zirconium retention by controlling the operating conditions of the HTER. However, desired objectives of 98% dissolution of uranium from the fuel segments with 80% retention of zirconium in the cladding hulls were not met when operating at anodic potentials less than 0.4 V.10

Unfortunately, two major problems were encountered. One was that a very dense deposit of uranium metal adhered to the cathodes in the HTER and made scraping impossible. A second was that the scrapers, which in the initial Mark-V design, and also on the 25-inch HTER at ANL-E, were mounted on the trailing edges of the anode baskets, caused hold-up of uranium metal in the space between the anode baskets. Additional scrapers were added and other modifications were made, including placing the scrapers on the leading edge of the baskets. In addition, current reversal (stripping) was carried out at periodic intervals to remove the high-density uranium metal from the cathode and deposit it on the anode basket. During the stripping cycle, these baskets were used as the cathode.

The problem with the hold-up of uranium has been a significant issue in the development of the ACM module. For example, the Argonne EMT Monthly Highlights for January 199811 describe efforts to reposition the ceramic scrapers from a trailing position to a leading position in order to provide more efficient removal of the electrodeposited uranium. The April 1998 EMT Monthly Highlights12 describe continued problems, including jamming of the redesigned anode rotor by accumulated dense, adherent uranium deposits.

Work at ANL-E in the electrorefiner area supports the EBR-II demonstration project. In addition, this work is also used in support of the development of a larger HTER that could be used in the pyrometallurgical processing of other DOE spent fuels,

10  

At less than 0.4 V, uranium dissolution is approximately 96% with approximately 70% retention of zirconium.

11  

Reprinted in Electrometallurgical Techniques for DOE Spent Fuel Treatment: Spring 1998 Status Report on Argonne National Laboratory's R&D Activity, National Academy Press, Washington, D.C., 1998, pp. 46-51.

12  

Reprinted in Electrometallurgical Techniques for DOE Spent Fuel Treatment: Spring 1998 Status Report on Argonne National Laboratory's R&D Activity, National Academy Press, Washington, D.C., 1998, pp. 60-65.



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