Nuclear Chemistry
Nuclear and Chemical Wastes

Dr. Frank Settle


    According to the U.S. Department of Energy (DOE), the four major elements of the environmental legacy of nuclear weapons production are

    • waste,
    • contaminated environmental media,
    • surplus facilities, and
    • materials in inventory.

    We will focus on the first two components. As we have seen in previous modules, nuclear weapons production in the United States was a complex series of manufacturing operations that generated large quantities of nuclear and chemical wastes. The term "waste" is defined as solids or liquids that are radioactive, chemically hazardous, or both. This waste consists of materials that have been disposed of previously, await disposal, or have been retrieved in site cleanups and are currently in storage. Waste is measured in terms of its volume (cubic meters) and its radioactivity (curies). Waste from nuclear weapons production managed by DOE includes 24 million cubic meters containing 900 million curies.

    Hanford B reactor and waste barrels
    (Courtesy of the Department of Energy)

    The major categories of waste are

    • high-level waste,
    • transuranic waste,
    • low-level waste,
    • mixed low-level waste,
    • 11e(2) byproduct material,
    • hazardous waste, and
    • other waste.

    High-level waste is the highly radioactive waste resulting from spent nuclear fuel, as well as the chemical processing of spent nuclear fuel and irradiated target assemblies. The radioactivity comes from fission fragments and their daughter products resulting from the fission of U-235 in production reactors. Although radiation from short-lived fission products (fragments and their daughters) will decrease dramatically in the next hundred years, radiation risks associated with the long-lived products will remain high for thousands of years. In the initial decay period, most of the radioactivity is due to Cs-137, Sr-90, and their short-lived daughter products. Plutonium, americium, uranium, and their daughter products are the major contributors to long-term radioactivity.

    The Hanford, Washington, site manages the largest volume of high-level waste, but the Savannah River site in South Carolina contains more total radioactivity. At Hanford, high-level waste alkaline liquid, salt cake, and sludge are stored in 149 single-shell and 28 double-shell underground tanks. Double-shell underground tanks are also used to store waste at the Savannah River site. Hanford waste is less radioactive than Savannah River waste because much of the radioactive Cs and Sr has been removed, the waste is older and has had more time to decay, and it has been mixed with less radioactive waste.

    Transuranic (TRU) waste contains alpha-emitting transuranic elements with half-lives of greater than 20 years and a combined activity of 100 nanocuries per gram of waste. Because of the long half-lives of many TRU isotopes, TRU waste can remain radioactive for hundreds of thousands of years. Some common isotopes found in TRU are plutonium-239, -240, -241, -238, and -242; americium-241; and curium-244. TRU waste from weapons production results from the fabrication of plutonium components, recycling of plutonium from scrap, retired weapons, and chemical separation of plutonium. Unlike high-level waste that results from a few specific processes with a narrow range of physical matrices and chemical characteristics, TRU waste exists in many forms with a spectrum of chemical properties.

    A small percentage of TRU waste exhibits high direct exposure hazards and is referred to as "remote-handled" TRU waste. The majority of TRU waste emits low levels of direct radiation and is called "contact-handled" waste. The chief hazard of "contact-handled" waste is due to alpha radiation. Alpha particles can not penetrate the skin but cause serious localized tissue damage when inhaled or ingested. When inhaled, TRU elements tend to accumulate in the lungs; soluble TRU compounds migrate through the body, accumulating in the bone marrow and liver.

    DOE classifies the tailings or waste produced by the extraction or concentration of uranium or thorium from their ores as 11e(2) byproduct material. More than 200 pounds of byproduct material are typically produced for each pound of uranium. After extraction of uranium from the ore, the tailings contain much of their original radioactivity in the form of alpha-emitting uranium, thorium-230, radium-226, and daughter products such as radon-222 gas. The total radioactivity present in mill tailings can exceed 1,000 picocurie per gram. Toxic heavy metals, including chromium, lead, molybdenum, and vanadium, are also present in this byproduct material in low, but significant, concentrations.

    Mixed low-level waste contains both hazardous waste subject to the Resource Conservation and Recovery Act (RCRA) and nuclear materials. The radioactive component of mixed low-level waste is similar to low-level waste and thus less radioactive than high-level or TRU waste. Hazardous chemical components present in mixed waste include toxic heavy metals, explosives, halogenated organic compounds, and acids.

    The other two categories are defined by government regulations. A variety of materials not covered previously fall into these categories. These materials include polychlorinated biphenyls, asbestos, and byproduct materials that have been mixed with chemically hazardous substances.

    Waste Isolation Pilot Plant site in New Mexico
    (Courtesy of the Department of Energy)

    Waste storage
    (Courtesy of the Uranium Information Center)

    Waste Storage Facilities in the United States

    Two locations in the United States have been identified to dispose of nuclear waste: one has been permitted for waste that results from defense activities (e.g., nuclear weapons development), while the other is proposed for waste from commercial activities (e.g., nuclear power generation).  The Waste Isolation Pilot Plant (WIPP) located in southeastern New Mexico is a geologic repository for the disposal of defense-related waste such as clothing, equipment, rags, and other itemscontaminated with transuranic (TRU) elements.  This TRU waste is defined as having activity greater than 100 nanocuries per gram due to transuranic isotopes. These isotopes have longer half-lives, extending from 20 to thousands of years. The waste is packaged in containers and emplaced in salt beds approximately 2,000 feet below ground. The salt will slowly close around the waste, permanently isolating it from the accessible environment.

    The Yucca Mountain site, located about 100 miles northwest of Las Vegas, Nevada, will be a geological repository for high-level spent nuclear fuel from civilian power plants and defense-related activities. This site is being studied carefully by DOE to ensure public health and safety. If DOE determines that the site is suitable, it will submit a construction application to the Nuclear Regulatory Commission (NRC). As the licensing agency, the NRC will use the standards currently being developed by the U.S. Environmental Protection Agency. Assuming all goes as planned, Yucca Mountain will receive the first waste shipments in 2007. In the meantime, the high-level waste will remain in storage at individual reactor and chemical processing sites throughout the country.

    Map of Nevada

    Yucca Mountain Site in Nevada
    (Courtesy of the Department of Energy)

     Complete Bibliography on Nuclear Waste from the ALSOS Digital Library for Nuclear Issues


     

©2003 Kennesaw State University
Principal Investigator Laurence Peterson
Project Director Matthew Hermes