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Graphite Anodes for Electroreduction of Uranium Oxide

Tuesday, 26 May 2015: 15:10
PDR 3 (Hilton Chicago)
P. Motsegood, J. Willit, and M. A. Williamson (Argonne National Laboratory)
Recycling of used nuclear oxide fuel is under investigation using pyrochemical methods, which involve a series of molten salt processes performed at elevated temperatures and result in the separation of actinides from fission products. During this process, used fuel oxides are electrochemically reduced to metals prior to electrochemical separation of the actinides from fission products in a subsequent process step. This electroreduction is typically performed at 650C in LiCl-Li2O. Reduction of UO2, the primary component of used nuclear fuel, has been successfully demonstrated at the kilogram-scale using platinum anodes1-2, but progression toward larger scales presents different requirements for anode materials.

Carbon (graphite) is commonly used in commercial molten salt processes within the ore refining industry. It is cost effective, readily available, and a logical choice for scale-up needs. However, different chemistries in molten LiCl-Li2O result from this change of anode material in both the salt and off-gas streams. Instead of forming oxygen at a platinum anode, the byproduct gas becomes CO and CO2. Although slightly soluble, these species can react with Li2O to form Li2CO3 as a result of residence time within the salt. The carbonate concentration can build up in the salt during the reduction process, which is problematic because of potential reaction between actinides and carbonate ions to form undesired byproducts in the reduced product.

This report will discuss use of carbon as an anode material for the electroreduction of UO2 to uranium metal in molten LiCl-Li2O at 650C. We will present design challenges and a discussion of salt chemistry with respect to carbonate formation in the system, along with results on reduction efficiency.

References:

  1. Laszlo Redey and Karthick Gourishankar, “Direct Electrochemical Reduction of Metal-Oxides” US Patent US6540902 B1, Granted April 1, 2003
  2. S. D. Herrmann, S. X. Li, M. F. Simpson and S. Phongikaroon, Separation Science and Technology 2006, 41, 1965-1983.

The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.