Improved Alumina Loading in High-Level Waste Glasses
- Pacific Northwest National Laboratory, Richland, WA (United States)
- Savannah River National Laboratory, Aiken, SC (United States)
- V.G. Khlopin Radium Institute, St. Petersburg (Russian Federation)
- EM-21, Office of Waste Processing, U.S. Department of Energy, Washington, DC (United States)
Recent tank retrieval, blending, and treatment strategies at both the Savannah River Site (SRS) and Hanford have identified increased amounts of high-Al{sub 2}O{sub 3} waste streams that are scheduled to be processed through their respective high-level waste (HLW) vitrification facilities. It is well known that the addition of small amounts of Al{sub 2}O{sub 3} to borosilicate glasses generally enhances the durability of the waste glasses. However, at higher Al{sub 2}O{sub 3} concentrations nepheline (NaAlSiO{sub 4}) formation can result in a severe deterioration of the chemical durability of the slowly cooled glass near the center of the canister. Additionally, higher concentrations of Al{sub 2}O{sub 3} generally increase the liquidus temperature of the melt and decrease the processing rate. Pacific Northwest National Laboratory (PNNL), Savannah River National Laboratory (SRNL), and Khlopin Radium Institute (KRI) are jointly performing laboratory and scaled-melter tests, through US Department of Energy, EM-21 Office of Waste Processing program, to develop glass formulations with increased Al{sub 2}O{sub 3} concentrations. These glasses are formulated for specific DOE waste compositions at Hanford and Savannah River Site. The objectives are to avoid nepheline formation while maintaining or meeting waste loading and/or waste throughput expectations as well as satisfying critical process and product performance related constraints such as viscosity, liquidus temperature, and glass durability. This paper summarizes the results of recent tests of simulated Hanford HLW glasses containing up to 26 wt% Al{sub 2}O{sub 3} in glass. In summary: Glasses with Al{sub 2}O{sub 3} loading ranging from 25 to 27 wt% were formulated and tested at a crucible scale. Successful glass formulations with up to 26 wt% Al{sub 2}O{sub 3} that do not precipitate nepheline during CCC treatment and had spinel crystals 1 vol% or less after 24 hr heat treatment at 950 deg. C were obtained. The selected glass, HAL-17 with 26 wt% Al{sub 2}O{sub 3}, had viscosity and electrical conductivity within the boundaries for adequate processing in the Joule heated melters operated at 1150 deg. C. This HAL-17 glass was successfully processed using small-scale (SMK) and larger scale (EP-5) melters. There was no indication of spinel settling during processing. The product glass samples from these melter tests contained 1 to 4 vol% spinel crystals that are likely formed during cooling. The PCT tests on the product glasses are underway. The present study demonstrated that it is possible to formulate the glasses with up to 26 wt% Al{sub 2}O{sub 3} that satisfy the property requirements and is processable with Joule-heated melters operated at 1150 deg. C. The 'nepheline discriminator' for HAL-17 glass is 0.45, which supports that claim that the current rule ('nepheline discriminator' < 0.62) is too restrictive. Considering that the cost of HLW treatment is highly dependent on loading of waste in glass, this result provides a potential for significant cost saving for Hanford. The maximum Al{sub 2}O{sub 3} loading that can be achieved will also depend on concentrations of other components in wastes. For example, the loading of waste used in this study was also limited by the spinel crystallization after 950 deg. C 24 hr heat treatment, which suggests that the concentrations of spinel-forming components such as Fe{sub 2}O{sub 3}, Cr{sub 2}O{sub 3}, NiO, ZnO, and MnO would be critical in addition to Al{sub 2}O{sub 3} for the maximum Al{sub 2}O{sub 3} loading achievable. The observed glass production rate per unit melter surface area of 0.75 MT/(d.m{sup 2}) for SMK test is comparable to the design capacity of WTP HLW melters at 0.8 MT/(d.m{sup 2}). However, the test with EP-5 melter achieved 0.38 MT/(d.m{sup 2}), which is roughly a half of the WTP design capacity. This result may imply that the glass with 26 wt% Al{sub 2}O{sub 3} may not achieve the WTP design production rate. However, this hypothesis is not conclusive because of unknown effects of melter size and operational differences. Further testing is needed to quantify the effect of high Al{sub 2}O{sub 3} loading on glass production rate. (authors)
- Research Organization:
- WM Symposia, 1628 E. Southern Avenue, Suite 9 - 332, Tempe, AZ 85282 (United States)
- OSTI ID:
- 21326171
- Report Number(s):
- INIS-US-10-WM-08460; TRN: US10V0632067536
- Resource Relation:
- Conference: WM'08: Waste Management Symposium 2008 - HLW, TRU, LLW/ILW, Mixed, Hazardous Wastes and Environmental Management - Phoenix Rising: Moving Forward in Waste Management, Phoenix, AZ (United States), 24-28 Feb 2008; Other Information: Country of input: France; 13 refs
- Country of Publication:
- United States
- Language:
- English
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