A total of approximately 2,000 metric tons of SNF—broadly classified as production fuels, special fuels, or naval fuels—has accumulated throughout the DOE complex.4

The EMT process developed by ANL and originally proposed for the treatment of all DOE SNF is potentially applicable to a fairly wide variety of spent fuel types besides the EBR-II used by Argonne in its development and demonstration of the technology. For example, Fermi-1 blanket fuel and Fast Flux Test Facility sodium-bonded fuel are SNFs that can potentially be treated using EMT. DOE initially proposed that the EBR-II driver fuel and at least half of the blanket fuel be treated via the process.5 For most fuels, such as oxides, the fuel would first have to be converted to a suitable metallic form before the electrorefining could be applied.

Electrometallurgical technology for treatment of DOE spent fuel evolved from ANL’s work on the Advanced Liquid-Metal Reactor Integral Fast Reactor (ALMR/IFR).6 With the termination of the ALMR/IFR project, this process, with some modification, served as the basis for ANL’s January 1995 proposal, which included the use of the electrometallurgical process for the treatment of EBR-II spent nuclear fuel. The proposal was accepted by DOE and was to include treatment of both reactor driver fuel and uranium blanket material. The present committee as part of its task was asked to evaluate the ongoing work on electrometallurgical technology at ANL.

During its second year of operation, the committee was asked to evaluate the scientific and technological issues associated with extending ANL’s electrometallurgical program to handle plutonium, in the event that DOE might pursue an electrometallurgical treatment option for the disposition of excess weapons plutonium (WPu). The committee concluded that disposition of WPu would involve different feeds for use in SNF processing, raising several concerns with respect to electrometallurgical processing, zeolite loading, and waste form performance.

THE ELECTROMETALLURGICAL PROCESS AT ANL

The electrometallurgical treatment process for spent fuel at ANL consists of several distinct steps: chopping the fuel elements, electrorefining the driver and blanket fuel, removing entrained salt from uranium electrodeposits and consolidating dendritic deposits in a cathode processor, casting separately into ingots the uranium metal from the cathode and the metal residue from the anode, and, finally, mixing, heating, and pressing the salt electrolyte with zeolite to form a ceramic waste.

The electrorefining step is the heart of the EMT process. The fuel element choppers are pneumatic punch presses that have been modified with blades for shearing driver and blanket fuel elements into segments for loading into the anode compartments of the Mark-IV electrorefiner (for driver fuel) and the Mark-V electrorefiner (for blanket fuel) developed at ANL. As part of ANL’s demonstration project criterion that required a blanket throughput rate of 150 kg per month sustained for 1 month,7 the blanket element chopper was used to process 3.5 blanket fuel assemblies or 66 blanket fuel elements, for a total of 164.4 kg of uranium.

The Mark-IV electrorefiner has an overall anode batch size of 16 kg and was designed for processing driver fuel. The efficiency of the overall electrorefining operation is enhanced by using a second cathode inserted into melt through the fourth port. The cadmium pool in the bottom of the Mark-IV catches and dissolves any of the uranium deposits that either fall off the cathode or are scraped off the cathode by the scrapers during the electro-deposition process.

During the repeatability phase of the demonstration project, the Mark-IV electrorefiner was used to treat 12 driver assemblies at an average rate of 24 kg of uranium per month over a 3-month period compared to the target of 16 kg (~4 driver assemblies) per month over a 3-month period.8

4  

Argonne National Laboratory, Proposal for Development of Electrometallurgical Technology for Treatment of DOE Spent Nuclear Fuel, Argonne National Laboratory, Argonne, IL, 1995.

5  

Argonne National Laboratory, Proposal for Development of Electrometallurgical Technology for Treatment of DOE Spent Nuclear Fuel, Argonne National Laboratory, Idaho Falls, ID, 1995.

6  

National Research Council, Nuclear Wastes: Technologies for Separations and Transmutation, National Academy Press, Washington, D.C., 1996, pp. 27-28, 43, 155-158.

7  

The full success criteria for the demonstration project, along with the goals to meet them, are included in Chapter 6.

8  

R.D. Mariani, D. Vaden, B.R. Westphal, D.V. Laug, S.S. Cunningham, S.X. Li, T.A. Johnson, J.R. Krsul, and M.J. Lambregts, Process Description for Driver Fuel Treatment Operations, NT Technical Memorandum No. 111, Argonne National Laboratory, Argonne, IL, 1999.



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