High-Temperature Melter Tests for Vitrificationof BNFL High-Level Nuclear Wastes
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Mat. Res. Soc. Symp. Proc. Vol. 556 0 1999 Materials Research Society
In this work, continuously-fed melter tests were carried out using surrogate wastes of the current composition as well as potential feed stocks involving the zirconia-rich waste and the performance of the high-temperature technology with the two types of feed was investigated. The primary objectives of the melter runs were to determine, for each melt temperature and feed water content, the maximum achievable glass production rates, the conditions limiting the production rate, the quantity and characteristics of the resulting melter emissions. EXPERIMENT The melter system has been described previously 2 and consists of the feed system, the melter, and the off-gas system; for this work, a additional dry-feed system was added. The slurry feed system delivered the simulated wastes along with glass formers as dissolved or suspended chemicals in an acidic, aqueous slurry which is the favored method for radioactive waste melters operated in the United States. The dry feed system delivered dry mixed solids and is more consistent with the feed process employed at BNFL's Waste Vitrification Plant (WVP) at Sellafield. Figure I shows a schematic diagram of the minimelter system used for this work. The melter glass tank consists of a center chamber separated by conductive ceramic partitions from the two outer chambers, which contain the molybdenum electrodes that are used for SCRUBBER MIST ELIMINATOR joule heating 3' 4 . To a reasonable approximation, the glass melting process is the QUENCHER HEATER reaction of the feed material at the glass melt surface and therefore the melting rate is . Melter emissions sampling port BGOS roughly proportional to the s or BAGHOUSE melt surface area. As a general rule of thumb, the nominal melting rate for c dnh-bde unstirred slurry-fed joule CENTER HEPA FILTER heated waste melters is I CHAMBER I I about one metric ton of t1cmxl5cmxt2.5em 10cmxl5cmxt2.5cm Post-HEPA glass per square meter per 15cmxt5cmxt2.5cm sampling port > day. The surface area of the Figure 1 Schematic of High-Temperature Melter System center chamber of this melter is 194 cm2 and thus the corresponding nominal glass production rate is 19.4 kg/day. Three glass formulations were used in these tests. The first two formulations had 25 wt% waste oxide loadings of simulated Magnox/Oxide mixtures in which the radioactive constituents, trace elements, and the platinum group metals were excluded from the simulant recipe on the basis of cost. The most abundant rare earth elements in the waste (Pr and Sm) were substituted by lanthanum, which has similar properties at a reasonable cost. The simulant composition was then normalized to 100% to account for the remaining 4.1 wt% of oxides that were omitted from the recipe. The target composition expected from this formulation and the composition prior to normalization are presented in Table 1 as "BNFL". This first formulation was designed for a processing temperature range of 950 'C to 1050 'C and therefore could not be
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