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Cold Crucible Vitrification of Uranium-Bearing High Level Waste Surrogate
Published online by Cambridge University Press: 01 February 2011
Abstract
Three tests on vitrification of U-bearing DWPF SB2 and SB4 waste surrogates (40-50 wt% waste loading) in a lab-scale (56 mm inner diameter) copper cold crucible with melt surface area of 24.6 cm2 energized from a 5.28 MHz/10 kW generator were conducted. At the feeding of the air-dry batch (3-5 wt% moisture) glass productivity and specific melt productivity achieved under steady-state conditions were 0.64 kg/h and 256 kg/(m2×h) [6150 kg/(m2×day)], respectively. Similar to previously prepared U-free products, the U-bearing vitrified SB2 (highferrous) waste product was composed of U-enriched glassy matrix and high-ferrous spinel structure phase. As expected, the vitreous phase in the vitrified SB2 waste surrogate was enriched with Na, Al, Si, P, S, Ca, Sr, Pb, U oxides and Cl, whereas spinel preferentially accumulated transition metals (iron group elements: Mn, Fe, Ni) as well as Cu and Zn oxides. Iron oxide content in the spinel phase was ∼67–71 wt %. This result was consistent with XRD data and implies that this spinel was close to magnetite with respect to chemical composition and structure. This was consistent with our previous data on characterization of glass crystalline materials containing both U-bearing and U-free SB2 waste surrogate produced in resistive furnace and cold crucibles. The vitrified SB4 (high-alumina) waste products were predominantly amorphous at waste loading of up to 50 wt %. Traces of quartz occurred in the “skull” zone. In all the products, uranium was found to be uniformly distributed within the vitreous phase. Leach rates of Na, Si, Fe, and U from the vitrified SB2 waste surrogate (50 wt % waste loading) determined by a SPFT procedure were found to be 1.38, 1.42, 0.122, and 0.841 (g×m−2×d−1), respectively.
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- Copyright © Materials Research Society 2008
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