The Effect of Adding Crystalline Silicotitanate on the Durability, Liquidus, and Viscosity of Simulated High-Level Waste
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J. R. HARBOUR, T. B. EDWARDS, R. J. WORKMAN Westinghouse Savannah River Company, Aiken, SC 29808, iohn.harbourisrs.gov ABSTRACT This report provides a summary of the results obtained for a limited variability study for glasses containing Crystalline Silicotitanate (CST), Monosodium Titanate (MST), and either simulated Purex or HM sludge. Twenty-two glasses containing Purex sludge and three glasses containing HM sludge were fabricated and tested. The fabricated glasses were tested for durability using the 7-day Product Consistency Test (PCT) and characterized by measuring the viscosity at 1150'C and by determining an approximate, bounding liquidus temperature. The current models used by Defense Waste Processing Facility (DWPF) for predicting durability, viscosity, and liquidus temperature were applied to all 25 glasses. The goal of this work was to identify any major-problems from a glass perspective, within the scope of this effort, which could potentially preclude the use of CST at DWPF. INTRODUCTION One of the alternative salt disposition flowsheets being considered by Savannah River Site (SRS) would require that the Defense Waste Processing Facility (DWPF) vitrify a coupled feed containing High Level Waste (HLW) and Crystalline Silicotitanate (CST). A glass variability study was therefore conducted to explore the processibility and product quality of the glass composition region for this alternative to the In-Tank Precipitation (ITP) Process. The objective of this study was to obtain information on the feasibility of incorporating anticipated levels of CST into DWPF glass with and without doubling the nominal levels of Monosodium Titanate
(MST). The glasses for this study were selected from a set of candidate glasses that involved Purex and HM sludge types, covered sludge loadings (in the glass) of 22, 26, and 30 oxide weight percent (wt%), utilized CST loadings (in the glass) of 3, 6, and 9 oxide wt%, and included MST concentrations (in the glass) at 1.25 and 2.5 wt%. For each composition, the remainder of the glass consisted of a proprietary glass former composition developed by M. K. Andrews of Savannah River Technology Center (SRTC). The selection of Purex sludge for this study was based on the knowledge that this sludge type has historically been the most difficult sludge to incorporate into glass. Depleted uranium was introduced into the simulated Purex sludge to represent the uranium content (- 9 wt% oxide) of actual sludge. One of the major elements of concern for this study was titanium, which the DWPF currently restricts to a value of less than I wt% TiO 2 in glass. The introduction of CST and MST in this study results in TiO 2 levels in the glasses that significantly exceed the current limit. Furthermore, CST introduces proprietary components with unknown impact on glass quality and processing properties.
659 Mat. Res. Soc. Symp. Proc. Vol. 608 @ 2000 Materials Research Society
The primary property of interest in this study was the durability (as measured by the 7-day Product Consistency Test, PCT
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