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Chemical Sciences and Engineering Division |
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Process Chemistry and EngineeringThe Process Chemistry and Engineering Department conducts research that supports closing the nuclear fuel cycle, and eliminating the use of highly enriched uranium in civil research programs throughout the world. Closing the Nuclear Fuel CycleUsed nuclear fuel and high-level radioactive waste are materials produced by nuclear power plants or from government defense programs. These materials contain highly radioactive isotopes of elements, such as cesium, strontium, technetium, plutonium, and neptunium. Some of these elements will remain radioactive for a few years or decades, while others will be radioactive for millions of years. Scientists worldwide agree that the safest way to manage these materials is to dispose of them deep underground in what is called a geologic repository. Currently, used nuclear fuel is stored in specially designed pools at individual reactor sites around the country while high-level radioactive waste is stored at government facilities. The current baseline approach is to package the used fuel and to vitrify the waste for placement in the proposed Yucca Mountain geologic repository for permanent disposal. The behavior of waste materials following their disposal in the repository has been a focus of significant research. An alternative approach under consideration is aqueous reprocessing of the used fuel. The overall toxicity, fissile content and volume of the used fuel is reduced while the fissionable elements are recycled for energy production,. Nearly all of the risk associated with the disposal of spent fuel comes from approximately 1 percent of its content—primarily the transuranic elements: plutonium, neptunium, americium, and curium, and the long-lived isotopes of iodine and technetium. In a recycle approach, the transuranics will be separated from spent fuel and destroyed in advanced reactors, while the Tc and I will be placed into waste forms specifically tailored to retain these elements. With the key elements removed, the toxicity of the remaining 99 percent of the waste drops below that of natural uranium ore in about 1,000 years. If in addition, strontium and cesium are removed, the decay heat from the final waste form is also greatly reduced, which means that waste packages can be stored closer together, effectively expanding the repository's capacity. Under the Department of Energy's Global Nuclear Energy Partnership (GNEP), Argonne is leading development of the UREX+ aqueous separations, a multi-step process for separating out the high-risk elements of spent nuclear fuel. Argonne has successfully demonstrated the entire process using prototypic process equipment and is supporting scale-up demonstrations in partnership with other national laboratories. A key research thrust has been the development of detailed models of the chemistry of these aqueous processes, which is the basis for their design. These models are incorporated into codes that generate process flows and equipment designs that in turn feed into an overall plant design. As chemical data and process concepts are developed, the codes are refined to incorporate new findings. Argonne is also heading the effort to apply advanced computational techniques to the design and implementation of processes like UREX+ in the next generation recycling facility and to ensure that the facilities are safe and secure. Since treating and disposing of nuclear waste is a key element of the nuclear fuel cycle, we are active in projects focused on waste processing and disposal. DOE is preparing a license application for submittal to the Nuclear Regulatory Commission to construct the Yucca Mountain geological repository for disposal of the nation’s spent nuclear fuel and other highly radioactive waste materials. We are providing support to DOE by using scientific understanding and data developed through experimental studies (both here at Argonne and elsewhere) to develop and refine computer models that DOE can use to assess the repository’s long-term performance. A number of reprocessing product streams require conversion to waste forms
that can retain specific fission products. We have been developing waste forms
for Cs, Sr, Tc, and I, as well as, the processes for their production. This
effort involves evaluation of candidate materials, spectroscopy of natural
analogs, and lab-scale synthesis and testing. Much of the work meshes with the
efforts to develop the advanced separations process from which the streams
spring. Eliminating the Use of Highly Enriched UraniumThe U.S. Department of Energy initiated the Reduced Enrichment for Research and Test Reactors (RERTR) Program in 1978 with the mission of developing the technologies necessary to convert research and test reactors from the use of fuels and targets containing highly-enriched uranium (HEU, 20% or more U-235) to the use of fuels and targets containing low enriched uranium (LEU, less than 20% U-235). This mission is consistent with the U.S. nonproliferation policy goal of minimizing and, to the extent possible, eliminating the use of highly enriched uranium in civil programs worldwide. The CSE Division supports the RERTR Program at Argonne by developing new processes that allow the production of molybdenum-99 (the most commonly used medical isotope in the world) from low-enriched uranium targets. The Division's Remote Handling Mockup Facility is a valuable tool in our research, allowing us to carry out and refine planned handling of radioactive isotopes in preparation for hot-cell experiments, saving considerable time and expense. ContactMonica Regalbuto, Manager |
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