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Fusion Science and Technology
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Glass strategy: Hanford’s enhanced waste glass program
The mission of the Department of Energy’s Office of River Protection (ORP) is to complete the safe cleanup of waste resulting from decades of nuclear weapons development. One of the most technologically challenging responsibilities is the safe disposition of approximately 56 million gallons of radioactive waste historically stored in 177 tanks at the Hanford Site in Washington state.
ORP has a clear incentive to reduce the overall mission duration and cost. One pathway is to develop and deploy innovative technical solutions that can advance baseline flow sheets toward higher efficiency operations while reducing identified risks without compromising safety. Vitrification is the baseline process that will convert both high-level and low-level radioactive waste at Hanford into a stable glass waste form for long-term storage and disposal.
Although vitrification is a mature technology, there are key areas where technology can further reduce operational risks, advance baseline processes to maximize waste throughput, and provide the underpinning to enhance operational flexibility; all steps in reducing mission duration and cost.
D. R. Harding, D. Whitaker, C. Fella
Fusion Science and Technology | Volume 70 | Number 2 | August-September 2016 | Pages 173-183
Technical Paper | doi.org/10.13182/FST15-211
Articles are hosted by Taylor and Francis Online.
The accepted mechanism for the formation of a deuterium-tritium (D-T) ice layer is that mass evaporates (sublimes) from the warmer regions of the shell and deposits in the cooler regions. Recent observations of the early-stage formation of single-crystal ice layers in OMEGA targets show that the rate and direction of crystal growth are influenced by liquid wicking to the crystal growth surface. This behavior is attributed to the ice-liquid interface possessing a lower surface energy than the ice-vapor interface, and the amount of liquid transported by this process is determined by the size, position, and growth rate of the initial seed crystal. Appreciating this behavior allowed us to define an improved cooling ramp that balances the rate at which heat was removed from the target with the supply of liquid to the crystal growth surface. The time and temperature parameters used to form a seed crystal and then grow the crystal into a complete ice layer are presented. One benefit of this process may be fewer defects in the ice layer. The target was cooled to 0.6 K below the temperature where it was formed before strain-induced crystallographic features developed. An estimate of the extent of fractionation of D2, D-T, and T2 isotopes during the freezing cycle was based on the thickness uniformity of the ice layer and how the crystal grew. The region where the ice layer initially formed was 4% thinner than the region where its formation was complete. The alignment of this perturbation to the ice layer with the growth axis of the crystal suggests, to a first-order approximation, that the area of the crystal that first formed possessed a higher fraction (~4%) of tritium atoms.