Concepts for Dry Processing of Spent Nuclear Fuel for Recycling to Light-Water Reactors
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fuel composition would require even more fresh feed (50% by volume at 17% enrichment). As long as the uranium enrichment remains below 20%, it is considered proliferation resistant. In order to make dry recycle more efficient and economical, a reasonable goal would be to reduce the feed enrichment and/or the feed volume percent. Reduction of the feed enrichment or volume percent requires a reduction in the spent nuclear fuel poison concentrations or the total negative reactivity. In essence, this is the additionally neutron capture attributed to the presence of fission products. In 20-year-old spent PWR fuel, the largest elemental negative reactivity contributors are the rare earth fission product elements. These include Sm, Gd, Nd, Eu. The elements contribute 22.8%, 13.2%, 12.7%, and 4.6% of the total spent fuel negative fission product reactivity, respectively, or 54.2% of the total. The next largest contributor of negative reactivity in the spent fuel is from the metallic inclusions composed of Mo, Ru, Rh, Tc, and Pd. The stable rhodium isotope (Rh-103) alone accounts for 11.8% of the total negative reactivity. The following sections look at the potential use of magnetic and electrostatic separation techniques to extract both rare earth fission products and the metallic inclusions from the spent fuel based on their differences in magnetic susceptibility and electrical conductivity relative to UO. Standard industrial magnetic and electrostatic separation techniques anticipated for these separations are discussed elsewhere [1,2]. We survey the material properties of the rare earth oxides and metallic inclusions and evaluate separation applicability. Separation Analysis Magnetic Separation of Rare Earth Elements The rare earth oxides are unfortunately distributed more or less uniformly as a solid solution throughout the spent nuclear fuel urania matrix. In addition, the rare earth oxides and urania are all paramagnetic materials. Separation using standard magnetic separation techniques would be virtually impossible, despite the fact that the magnetic susceptibilities of the rare earth oxides are significantly higher than that of U0 2 . The rare earth oxides susceptibilities range from a factor of 5-25 greater than the uranium oxide. Despite these significant differences in susceptibilities, the rare earth oxides mixed uniformly throughout the urania make magnetic separation ineffectual. However, recent developments [31 in the oxidation of U0 2 to U30 8 followed by further heating at higher temperatures (1000 to 1600 C) can lead to a rare earth-rich fluorite phase and a rare earth-poor phase in the U30 8 . Use of this heat treatment technique may allow for the application of a magnetic separation technique. Further investigation is required. Magnetic Separation of Rhodium Rhodium does not form an oxide like the rare earth elements, but rather has an affinity to accumulate with other noble metals in intermetallic inclusions or precipitates. These metallic inclusions or "white inclusions", as they are referred to becaus
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