SULFATE RETENTION IN HIGH LEVEL WASTE SLUDGE BATCH 4 GLASSES: A PRELIMINARY ASSESSMENT

Early projections of the Sludge Batch 4 (SB4) composition predicted relatively high concentrations of alumina (Al{sub 2}O{sub 3}, 23.5 wt%) and sulfate (SO{sub 4}{sup 2-}, 1.2 wt%) in the sludge. A high concentration of Al{sub 2}O{sub 3} in the sludge, combined with Na{sub 2}O additions in the frit, raises the potential for nepheline crystallization in the glass. However, strategic frit development efforts at the Savannah River National Laboratory (SRNL) have shown that frits containing a relatively high concentration of B{sub 2}O{sub 3} can both suppress nepheline crystallization and improve melt rates. A high sulfate concentration is a concern to the DWPF as it can lead to the formation of sulfate inclusions in the glass and/or the formation of a molten, sulfate-rich phase atop the melt pool. To avoid these issues, a sulfate concentration limit of 0.4 wt% SO{sub 4}{sup 2-} in glass was originally set in the Product Composition Control System (PCCS) used at DWPF. It was later shown that this limit could be increased to 0.6 wt% SO{sub 4}{sup 2-} in glass for the Frit 418, Sludge Batch 3 (SB3) system