Thermal properties of simulated Hanford waste glasses

Abstract

The Hanford Tank Waste Treatment and Immobilization Plant will vitrify the mixed hazardous wastes generated from 45 years of plutonium production at the Hanford Site in Washington State. The molten glasses will be poured into stainless steel containers or canisters and subsequently cooled for storage and disposal. For appropriate facility design and operations to handle such highly energy‐consuming processes, knowledge of the material properties is required. The thermal properties (heat capacity, thermal diffusivity, and thermal conductivity) of representative high‐level and low‐activity waste glasses were studied as functions of temperature in the range of 200°C‐800°C (relevant to the cooling process). Simultaneous differential scanning calorimetry‐thermal gravimetry (DSC‐TGA), Xe‐flash diffusivity, pycnometry, and dilatometry were implemented. The study showed that simultaneous DSC‐TGA would be a reliable method for obtaining the heat capacity of various glasses in the temperature range of interest. Accurate thermal properties from this study were shown to provide a more realistic guideline for capacity and time constraints of the heat removal process when compared to the original conservative design‐basis engineering estimates. The estimates, though useful for design in the absence of measured physical properties, can now be supplanted and the measured thermal properties can be used in design verification activities.

Thermal properties of sodium borosilicate glasses as a function of sulfur content

“…This is an increase of ~11% for a 1.18 mass% increase in measured SO 3 in the bulk glass. These values were similar to previous values reported for waste glasses . The rate of increase in thermal diffusivity decreases with increasing SO 3 additions, becoming somewhat invariant in the three glasses that exceeded the sulfur solubility (>2.0 mass% SO 3 additions).…”

“…All samples exhibited a ~25% increase in heat capacity with a 375°C increase in temperature. This was consistent with the literature and also indicated that the temperature range of measurement was below the Debye temperature . At the Debye temperature, all phonon modes would be active, and the relative heat capacity increase with temperature would drastically reduce.…”

“…Heat capacity values had a higher variability (± 5%) than found for thermal diffusivity, but the overall increase was still larger than the variability. The reported values were similar to those reported for other borosilicate waste glasses in the literature . Figure showed the heat capacity for the NBS glasses as a function of temperature.…”

“…These values were T A B L E 3 Fractional assessment of each bonding unit type determined from peak fitting analysis and assessment of boron network cross- similar to previous values reported for waste glasses. 43 The rate of increase in thermal diffusivity decreases with increasing SO 3 additions, becoming somewhat invariant in the three glasses that exceeded the sulfur solubility (>2.0 mass% SO 3 additions). Measurements were highly reproducible, with a standard deviation of one in the fourth decimal place over three measurements.…”

“…The reported values were similar to those reported for other borosilicate waste glasses in the literature. 30,43 Figure 7 showed the heat capacity for the NBS glasses as a function of temperature. Heat capacity increased with increasing temperature for all compositions and the effect of SO 3 loading did not change with temperature.…”