Cold crucible vitrification of the Savannah River Site SB2 HLW surrogate at high waste loading

摘要

Test vitrification of Savannah River Site sludge batch 2 (SB2) high level waste (HLW) surrogate was undertaken in the Radon full scale vitrification plant using a 418 mm inner diameter cold crucible energised from a 160 kW high frequency (1·76 MHz) generator. Waste loading in the glass ranged between ∼52-53 wt% and ∼60 wt%. Commercially available alkali borosilicate Frit 320 was used as a glass forming additive. In total 1319·2 kg of feed was vitrified and 317·9 kg of glass was produced. The average AC power was 148·5 kW. The average slurry feeding rate was 25·6 kg/h, while the average glass production rate was 6·2 kg/h. Specific power consumption for slurry feeding was 5·8 kWh/kg, while the specific power consumption for glass production (melting ratio) was 24·0 kWh/kg. The specific glass production rate was 1084·8 kg/(m2d). Maximum slurry feeding and glass production rates were achieved by processing a slurry that had a water content of approximately 65 wt%. The products consisted of a vitreous matrix with a spinel structure magnetite type phase distributed in the matrix. The average degree of crystallinity ranged between 6 vol% at ∼52-53 wt% waste loading to 18 vol% at ∼60 wt% waste loading in the glassy product. The spinel phase was strongly enriched with iron and other transition elements (Cr, Mn, Ni, Cu, Zn) as well as Mg, whereas alkali, alkali earth elements and Zr, Pb, S, Cl entered the vitreous phase. At the highest waste loadings (55-57 wt% and above) an extra nepheline phase was produced. The major cations in the nepheline phase were Na, Al, Si and the minor ones were Fe, K, Sr, and Mg. A decrease in the silica content of the composition and nepheline formation in the resulting glass probably caused the decrease in chemical durability seen in the glass products with high waste loadings.