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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.
Nader M. A. Mohamed
Nuclear Science and Engineering | Volume 173 | Number 2 | February 2013 | Pages 172-181
Technical Paper | doi.org/10.13182/NSE11-77
Articles are hosted by Taylor and Francis Online.
Zirconium is studied in this paper as a reflector for light water reactors. An exploratory analysis of using zirconium as a reflector for two simple reactor core models was carried out. The study showed that use of zirconium as a reflector has a valuable impact on the core reactivity. The study also showed that zirconium-water reflector is more effective than water reflector or stainless steel-water reflector. A typical Westinghouse 1150-MW(electric) pressurized water reactor was simulated using the Monte Carlo code MCNP5 as a case study. The simulation was carried out at the beginning of the core cycle of three batch cores with 235U enrichments of 2.25, 2.8, and 3.3 wt%. The simulation showed that use of Zircaloy-4 reflector between the fuel assemblies and the core barrel adds a positive reactivity Δkeff of 0.00686, while use of stainless steel reflector adds a positive reactivity Δkeff of 0.0037.Use of Zircaloy-4 reflector increases the relative power density in the peripheral assemblies by ˜38%. The power peaking factor is shifted from the center toward the periphery, and the assembly power peaking factor is reduced by ˜13%. The use of Zircaloy-4 reflector with this increase of the reactivity of the peripheral assemblies increases the fast neutron current (E > 0.5 MeV) that reaches the reactor pressure vessel (RPV) by 70%, while the use of stainless steel reflector reduces it by 44%.Adjusting the 235U enrichment in the peripheral assemblies batch to compensate for the excess reactivity caused by using Zircaloy-4 reflector reduces the 235U enrichment by 8.5% in this batch. This means a reduction of 3.35% of the core 235U average enrichment can be achieved by the use of Zircaloy-4 reflector. This reduction in the 235U enrichment reduces the increase of the fast neutron current that reaches the RPV to 23%. In this case, increasing the water gap between the core barrel and the RPV by 3 cm reduces the fast neutron current that reaches the RPV to 95% of that of the basic case. The use of Zircaloy-4 reflector has a good effect on flattening the fission density distribution in the peripheral assemblies batch both before and after reducing 235U enrichment.
