THE FUTURE FOR BENEFICIAL USES
OF DEPLETED URANIUM
Charles E. Bradley, Jr.
Depleted Uranium Hexafluoride Management Program
Department of Energy
Cynthia A. Blaschke
The Department of Energy's Depleted Uranium Hexafluoride Management Program is developing long-range management strategy alternatives for its inventory of depleted uranium hexafluoride. One of these alternatives will be selected for implementation upon completion of a programmatic environmental impact statement (PEIS), now in preparation. The PEIS will contain assessments of the impacts of the alternative strategies. The Department's draft preferred alternative is to move as promptly as possible to begin conversion of the material to a more stable chemical form. To do this, we would seek to reduce the potential cost of conversion by reducing the per-unit conversion costs, increase the demand for the fluorine and uranium in the material, and expand program visibility through increased stakeholder awareness of the inventory's potential value. The Department would identify public and private-sector partners for cost-sharing agreements in order to develop new conversion technologies, to refine existing technologies, and to develop new uses for the component fluorine and uranium materials. This program would then provide a focal point, both in the United States and internationally, for the development of more efficient conversion technologies, and for the future development of beneficial uses for the depleted uranium hexafluoride and its components.
CYLINDER MANAGEMENT PROGRAM
The Office of Nuclear Energy is responsible for managing 560,000 metric tons of pure depleted uranium hexafluoride located at the three gaseous diffusion plant sites at Paducah, Kentucky, Portsmouth, Ohio, and the East Tennessee Technology Park (the former K-25 site) at Oak Ridge, Tennessee. The inventory is stored in 46,422 cylinders, which are 12 feet in length and four feet in diameter, with a capacity of ten to fourteen metric tons. There are 28,351 cylinders at Paducah, 13,388 at Portsmouth, and 4,683 at the East Tennessee Technology Park. The Department's inventory of depleted uranium hexafluoride was produced at these three plants during more than four decades of operation. The diffusion process was started during World War II at the Oak Ridge K-25 Site to produce material for nuclear weapons. In July 1993, the responsibility for providing enrichment services to make nuclear fuel for domestic and foreign reactors was passed to the U.S. Enrichment Corporation, created by the Energy Policy Act of 1992.
Depleted uranium hexafluoride is a product of an isotopic separation process of uranium enrichment called gaseous diffusion. In this enrichment process, a stream of gaseous uranium hexafluoride is separated into two components, one enriched (more than 0.711%) in the isotope U235, and the other depleted (less than 0.711%) in U235. The depleted uranium hexafluoride, a solid white crystalline compound, is stored in carbon steel cylinders, at ambient temperatures and below atmospheric pressure.
The Department's depleted uranium hexafluoride inventory is managed under the Depleted Uranium Hexafluoride Management Program, which consists of: 1) the safe and cost-effective management of the cylinders, and 2) the development of a long-term management strategy for the material. The Department spends approximately $15 million annually to maintain the safety basis of the cylinders, which includes monitoring and inspection, valve and plug repair, repainting, and refurbishment and construction of concrete cylinder yards. In an effort to reduce costs of maintaining the aging cylinders, Bechtel Nevada is currently identifying cylinder leaks and obtaining data on wall thickness and internal pressure by remote sensing techniques.
The Department began an initiative in the Fall of 1993 to identify several possible long-term management strategies for depleted uranium hexafluoride, with a goal of selecting one in 1998. In the Federal Register Notice (59 FR 56324) issued on November 10, 1994, the Department asked that the public and industry recommend possible uses, and technologies to facilitate its management.
The Draft Programmatic Environmental Impact Statement (PEIS) for Alternative Strategies for the Long-Term Management and Use of Depleted Uranium Hexafluoride, released in December 1997, assesses the impacts of several strategies, including continued long-term storage at the existing sites, storage as depleted uranium hexafluoride at a single site, storage at a single site after conversion to an oxide form, use as radiation shielding in a metal form, use as radiation shielding in an oxide form, disposal after conversion to uranium oxide, and a "hybrid" combination of several of these. The draft PEIS, which is available for public comment through April 23, 1998, will culminate with the Department's selection of a long-term management strategy that will be published in a Record of Decision, scheduled for the Fall of 1998.
The Department's preferred strategy for the long-term management of depleted uranium hexafluoride is to beneficially use the entire inventory of the material as soon as conversion is economical. The conversion of the depleted uranium to either an oxide or metal would result in the generation of fluorine gas or fluorine compounds, which have beneficial uses. The preferred alternative in the draft PEIS is to begin conversion of depleted uranium hexafluoride to a more stable oxide as soon as 2005, with a completion date in 2020.
In 1992, the state of Ohio issued to the Department a Notice of Violation alleging that the Portsmouth Site was storing solid waste in violation of Ohio's waste management regulations. Ohio argued that the material is a solid waste under the Resource Conservation and Recovery Act (RCRA), and as such, must be characterized to determine its hazardousness. In the Fall of 1997, the Department and the State signed an agreement wherein the Department would submit a cylinder management plan for the inventory, provide data on the depleted uranium hexafluoride, and would make a good-faith effort to find uses for the material and report on the results of that effort annually. These provisions are in exchange for a ten-year period granted by the State for the Department to seek uses for the inventory. Should the Department be successful in finding uses for the material instead of disposing of it as a waste, $2 billion in cost penalties could be avoided.
As a product of the nuclear age, extensive supplies of depleted uranium are in storage throughout the world. The Department's inventory of depleted uranium hexafluoride comprises approximately half of all the uranium ever mined in the world. Although depleted uranium is plentiful in supply, efforts to find beneficial, economical uses for the material other than fuel cycle applications, have been very limited.
Because depleted uranium has several properties that make it potentially very useful, it should be considered and managed as an asset.
Many organizations have searched for ways to use depleted uranium at periodic intervals over four decades. Today, material production and management circumstances have changed, and this program will be concentrating on what is achievable considering these changes. In 1993, the Department transferred enrichment responsibility to the U.S. Enrichment Corporation, while retaining the depleted uranium inventory. The Department would now concentrate on removing financial, regulatory, and institutional barriers that have thwarted the use of depleted uranium aiding the development of markets by industry.
As of today, however, only small amounts of depleted uranium have been beneficially used. Some historical uses for depleted uranium include use in nuclear reactor fuel, down-blending of high-enriched uranium, munitions, armor, radiation shielding, and aircraft counterweights.
Recently, several new beneficial uses of depleted uranium have been identified that could consume significant portions of the inventory. The production of a high-density concrete could be used to manufacture containers for radioactive material storage. The placement of depleted uranium oxide in a nuclear waste repository could buffer ground water against roll-front criticality, provide radiation shielding, and improve post-closure performance. Other possible applications include industrial counterweights, in shaped charges used in oil field development by the petroleum industry, as collars on drill platforms, and to weight sections of drill pipe.
Should the preferred alternative in the draft PEIS be selected, the Department would begin conversion of depleted uranium hexafluoride in or about 2005 if conversion could be done efficiently. Through a beneficial use program, the Department could avoid future costs of $15 million annually for the long-term storage of depleted uranium hexafluoride at the sites. The government's role would be to invest in removing barriers to the use of the depleted uranium in specialty markets, limited in scope to relatively narrow industrial and government applications. Such barriers include, for example, the lack of engineering code certification for structural uses, and financial inflexibility that inhibits capital investment by industry. Industry's role would be to develop markets for the material, and to help the government lower the barriers.
During the course of conversion of depleted uranium hexafluoride, fluorine gas and hydrofluoric acid are key components in conversion cost offsets. The two-step conversion process which is described in The Engineering Analysis Report for the Long-Term Management of Depleted Uranium Hexafluoride is similar to existing industrial practice in France. The conversion process to chemically stable oxides or metal would produce either fluorine gas or a fluorine compound as a co-product. About 180,000 metric tons of fluorine would be available from the depleted uranium hexafluoride at the three sites. Further conversion of the fluorine would yield about 190,000 metric tons of anhydrous hydrogen fluoride. The current market price of anhydrous hydrogen fluoride is about $1400 per metric ton. Uses for fluorine exists now in the aluminum, chemical, steel and glass industries. The program has recently been studying potential applications for the fluorine, and meeting with chemical industry representatives.
There is a potential market for depleted uranium in radiation shielding applications. If depleted uranium were converted to an oxide, it could be used as a component of the primary shielding material in containers designed to store, transport, and dispose of spent nuclear fuel, low-level, or high-level radioactive wastes. Another shielding application involves using the depleted uranium as a substitute for the aggregate component in concrete. If a depleted uranium compound is used in the concrete, the thickness of the shielding material could be reduced by 50%.
Depleted Uranium Aggregate
Depleted uranium aggregate - or DUAGG - is made from uranium dioxide (UO2) that is formed into briquettes, and sintered. This application has been under development for several years and sponsored by the Department's Office of Environmental Management. DUAGG is composed of 80% UO2 (by volume) and 20% additives, which include soil, clay, mill additives and boron. DUAGG density of approximately 8.5 grams-per-cubic centimeter and a porosity of less than 2% has been reached in bench-scale tests. In Fiscal Year 1996, development concentrated on aggregate composition, while Fiscal Year 1997 developments concentrated on aggregate production. DUAGG oxidation testing is scheduled for the future. The use of depleted uranium aggregate in high-density shielding has the potential of consuming the entire depleted uranium inventory.
By combining DUAGG with conventional concrete materials, a dense concrete called
DUCRETETM has been patented by Lockheed Martin Idaho Technologies, the operating contractor at Idaho National Engineering and Environmental Laboratory (INEEL) and licensed exclusively to Starmet, Inc., (formerly Nuclear Metals, Inc.) of Concord, Massachusetts, to commercialize the DUCRETETM process, including the installation of a pilot project at Starmet's subsidiary, Carolina Metals, Inc., located in Barnwell, South Carolina. Strength tests were completed in 1997, and shielding tests are scheduled in the future. Several applications have been proposed for DUCRETETM including the production of 2,000 self-shielded storage boxes for radioactive wastes at Fernald, and additional shielded containers for INEEL, as well as the dry spent fuel storage shields for on-site storage of spent civilian reactor fuel.
Oak Ridge National Laboratory has been developing a new technology for spent nuclear fuel package fill in which depleted uranium dioxide is placed in the voids of spent nuclear fuel waste containers for storage, transport, or disposal. Depleted uranium would be used as a canister fill for isotopic dilution of highly enriched uranium in order to reduce criticality concerns. Approximately 5,000 metric tons of depleted uranium would be required in the waste packages to dilute 150 metric tons of the highly enriched uranium. Another application would make use of 4,000 metric tons for transportation casks. The use of DUAGG for inverts or backfill within the repository could reduce criticality issues.
The use of depleted uranium for industrial counterweights appears to have potential. Several entities are in the process of collaborating in the production of a prototype forklift using steel-clad depleted uranium as a counterweight. Due to its density (e.g., iron weighs 437 pounds per cubic foot, lead weighs 708 pounds per cubic foot, uranium metal weighs 1186 pounds per cubic foot), depleted uranium metal offers unique benefits in storage space efficiency by reducing the turning radius required within warehouse aisles. A shorter turning radius is achieved by decreasing the length of the machine by up to 19 inches, thus making as much as 10% more floor space available for material storage. Such machines might first be operated in unlicensed facilities, such as in the government. If successful, they might then be made available in the private sector. If the design were adopted for use throughout the industry, it could take advantage of most of the inventory.
Uranium Metal as an Alloy
The Department has an extensive knowledge base on the properties of uranium metal. Initially, most of this information was classified, but recently some information has been declassified. Since much of the research done on uranium development was completed over 30 years ago, it is important to capture the institutional memory before it disappears.
Uranium has some unique properties. The metal is very dense, strong, ductile, and hard. It can be heat-treated and welded. Studies are underway on the benefits of using uranium alloys. With these properties, and controlling its pyrophoricity, uranium alloys could be used in machine tools, pressure vessels, and structural members.
Before widespread use of uranium metal as an engineering material will be possible, it will be necessary to meet permit requirements and to be included in design standards and handbooks by professional societies.
The Petroleum Industry
Several published studies describe oil field applications for depleted uranium. Well casings and country rock are perforated much easier using depleted uranium shape charges for hydraulic fracture, with penetration two to three times deeper than standard charges. World market estimates vary regarding the amount of depleted uranium used, but the amount could be 3,000 to 40,000 metric tons per year. e
Another petroleum industry use would be as drill collars and as heavily-weighted sections of drill pipe to increase the down force on drill bits. Estimates vary on the amount of depleted uranium used this way, but there may be a potential market ranging between 9,000 to 1.3 million metric tons per year. f Costs range between $1 million and $6 million to drill one well. Using a smaller, heavier depleted uranium drill collar would reduce drill hole size, increase drilling speed, and reduce drilling costs by 50%. g Depleted uranium drill collars would require cladding to control oxidation and radiation. To ensure the product meets industry standards and regulatory requirements, additional development will be required.
APPROACH TO SUCCESS
The Depleted Uranium Hexafluoride Management Program has included private industry since its inception. There have been regular discussions with domestic and foreign companies to discuss conversion, use, and other management processes and procedures. In November 1994, the Department requested recommendations for alternative management strategies and uses for depleted uranium from a variety of organizations, including industry and the general public. Fifty-seven responses were received, which included a total of 70 recommendations.
This spring of 1998, the program will be hosting public hearings to receive comment on its programmatic EIS at the gaseous diffusion plant sites and in Washington, D.C.. We also plan to meet with industry representatives. We believe that if there is a potential to use the inventory, industry and government cooperation will be required to realize it. Industry's role will be to find value in the material and take advantage of that value. Government's role will be to facilitate industry's role, by reducing barriers. It is now up to the Department to identify and develop the necessary incentives.
Declassification of information concerning the unique properties of uranium could aid in certifying the use of depleted uranium metal in structural applications by the American Society of Testing and Materials. Currently, steel (or another approved material) is required as the structural component in spent fuel storage and transportation casks. Depleted uranium metal may only be used as shielding. It is possible to achieve an 11% weight reduction in these applications if a structural alloy of depleted uranium metal cask were certified. To accomplish this, the Department would need to sponsor the appropriate regulatory changes and initiate code cases for its acceptance.
Historically, depleted uranium has been regulated as a "source material" under the Atomic Energy Act of 1954. In addition, federal statutes from the Nuclear Regulatory Agency and the Environmental Protection Agency are applicable. State and federal regulations cover the ownership, production, and use of depleted uranium, while the Code of Federal Regulations Title 10, Part 40, describes the requirements for obtaining a Radioactive Materials License. Generally, a license from the Nuclear Regulatory Commission is required for the possession of more than 6.8 kilograms of depleted uranium, with licenses granted only when requirements for technical competency are satisfied. The Nuclear Regulatory Commission requires that any licensing exemption request include a detailed "cradle-to-grave" risk assessment covering the manufacture, storage, use, and disposal of the product. The Nuclear Regulatory Commission also requires that depleted uranium be disposed of in a licensed facility.
This program's approach to promoting the affordable conversion of the material is to focus on overcoming the barriers that have previously been roadblocks to the use of depleted uranium. Flexible thinking will be the key regarding use possibilities. We have confidence in "Yankee" ingenuity to provide solutions for materials which may soon be available to the public from the Department's stockpile of materials. With the determined partnership of the Department, the national laboratories, and industry, we foresee a new and successful use of these materials for the future.