Process Chemistry and Engineering
The 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 Cycle
Used 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 Uranium
The 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.
Contact
Monica Regalbuto, Manager
Process Chemistry and Engineering
Chemical Sciences and Engineering Division
Argonne National Laboratory, Bldg. 205
9700 South Cass Avenue
Argonne, IL 60439 USA
phone: 630/252-1540
fax: 630/972-4495
e-mail: regalbuto@anl.gov
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