Deconversion of Depleted Uranium
As uranium-235 (U235) is extracted, converted, and enriched in the uranium recovery, conversion, and enrichment processes for use in fabricating fuel for nuclear reactors, large quantities of depleted uranium hexafluoride (DUF6), or “tailings,” are produced. These tailings are transferred into 14-ton cylinders which are stored in large yards near the enrichment facilities. A process called "deconversion" is then used to chemically extract the fluoride from the DUF6 stored in the cylinders. This deconversion process produces stable compounds, known as uranium oxides, which are generally suitable for disposal as low-level radioactive waste. For additional information, see the following topics on this page:
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Benefits of Deconversion
Enriching 1,000 kilograms (kg) of natural uranium to 5% U235 produces 85 kg of enriched uranium hexafluoride (UF6) and about 915 kg of DUF6 (0.3 percent U235). As a result, enrichment processes in the United States produce approximately 12,000 – 15,000 tons of DUF6 tailings per year, which are then transferred to storage cylinders. The uranium in these cylinders consists of high purity U238 with less than 0.7% other uranium isotopes (e.g., U234 and U235). In addition the cylinders contain small quantities of impurities resulting from the natural radioactive decay of the uranium. The high purity of the U238 and self-shielding of the bulk material limit the radiological hazard from the full cylinders. Nonetheless, DUF6 represents a chemical hazard if it is released to the environment.
The deconversion process significantly reduces the chemical hazards associated with DUF6 by extracting the fluoride atoms and replacing them with oxygen. This deconversion process results in depleted uranium dioxide (DUO2) and depleted triuranium octoxide (DU3O8) compounds. These compounds are chemically stable, compared to DUF6, and are generally suitable for disposal as low-level radioactive waste. These oxides are similar to the chemical form of uranium in nature. Depleted uranium has a lower specific radioactivity per mass than natural uranium because the enrichment process reduces the percentage of other isotopes, e.g. U234 and U235. The specific radioactivity of the storage containers increases over time as the daughter products, removed during uranium recovery and conversion processes, return to natural levels due to radioactive decay. Most of the daughter products return to natural levels over the course of several million years.
Deconversion also enables the recovery of high purity fluoride compounds which have commercial value. These fluoride compounds are used in the production of refrigerants, herbicides, pharmaceuticals, high-octane gasoline, aluminum, plastics, electrical components, and fluorescent light bulbs.
Hazards of Deconversion
Chemical exposure is the dominant hazard at deconversion facilities because uranium and fluoride compounds (such as hydrogen fluoride) are hazardous at low levels of exposure. In particular, these compounds have the following characteristics:
- When DUF6 comes in contact with moisture in the air, it reacts to form hydrogen fluoride and uranyl fluoride.
- Uranium is a heavy metal, which can be toxic to the kidneys when ingested.
- Hydrogen fluoride is a corrosive acid, which can be very dangerous if inhaled.
Deconversion facilities are designed to reduce the likelihood and consequences of accidental releases of hazardous radiological and chemical compounds through safety systems, onsite and offsite monitoring, and emergency planning.
Deconversion Facilities in the United States
Currently, the United States has one operating deconversion facility, which is regulated by the State of Tennessee under an Agreement State license in accordance with Title 10, Part 40, of the Code of Federal Regulations (10 CFR Part 40), “Domestic Licensing of Source Material.” At this facility in Jonesborough, Tennessee, Aerojet Ordnance Tennessee, Inc., fabricates uranium metal for the U.S. Army to use as antitank rounds. This fabrication involves deconverting depleted UF4 using a process that does not produce significant quantities of fluorine or hydrogen fluoride as reaction products.
As directed by Congress, the U.S. Department of Energy (DOE) is constructing two depleted uranium deconversion facilities next to the existing gaseous diffusion uranium enrichment plants (GDP) in Paducah, Kentucky, and the Portsmouth GDP (near in Piketon, Ohio). The plants are projected to be completed in mid-year 2010.1 Together, these plants will deconvert more than 700,000 metric tons (771,000 U.S. tons) of depleted UF6 in storage in the DOE inventory. This inventory is projected to require 15–20 years to deconvert once the facilities become operational. DOE plans to dispose of the 551,000 metric tons of depleted uranium oxide as low-level radioactive waste at an estimated cost of about $428 million. See Depleted UF6 Management for additional detail regarding the DOE program.
In addition, on December 30, 2009, International Isotopes Fluorine Products, Inc. (IIFP, a subsidiary of International Isotopes, Inc.) submitted an application to the U.S. Nuclear Regulatory Commission (NRC), seeking a license to construct and operate a Fluorine Extraction Process and Depleted Uranium Deconversion (FEP/DUP) Plant near Hobbs, New Mexico. If approved, the FEP/DUP Plant will be the first major commercial deconversion facility licensed by the NRC to convert depleted UF6 to a uranium oxide for the purpose of recovering the fluoride products. The NRC's licensing safety review and development of the environmental impact statement are scheduled to be completed in 2012. This schedule may change based on the quality of the applicant’s license application, its responsiveness to requests for additional information, and unanticipated higher-priority operational safety work.
For additional information, see our Frequently Asked Questions About Depleted Uranium Deconversion Facilities.
1 “Audit Report: Potential Uses for Depleted Uranium Oxide,” U.S. Department of Energy, Office of the Inspector General, Office of Audit Services, DOE/IG-0810, January 2009.