Like other industrial processes, generating electricity from nuclear power or making nuclear weapons creates waste. These radioactive and chemically toxic wastes result from the mining and processing of uranium as well as from storing or reprocessing spent reactor fuel.
Figure 1 – Containment Site on the Colorado River near Moab, Utah
Courtesy of WISE Uranium Project
Waste from Conversion, Enrichment, and Fuel Fabrication Processes
Waste from Reactors
Waste from Nuclear Power Generation – The Open Fuel Cycle
Figure 2 – Storage of Spent Fuel at the Reactor
Courtesy of the Union of Concerned Scientists
After a minimum of one year, the rods may be removed from the pool and placed in a cylinder in a chemically inert atmosphere of helium gas (Figure 3). The cylinder is then sealed and encased in steel and concrete to contain the radiation and enhance security for storage or transportation to a permanent repository. In 2008 there were 160,000 assemblies containing 45,000 tons of spent fuel from nuclear power reactors in the United States. The majority of these are stored at the reactor sites in reactor pools with only about 5 percent in dry casks. Each year about 7,800 additional used fuel assemblies are placed into storage. If all of the current assemblies were collected in a single location they would cover a football field to about a height of five and half yards.
Figure 3 – Dry Cast Storage
Courtesy of the U. S. Nuclear Regulatory Commission
Waste from Reprocessing Spent Fuel – The Closed Fuel Cycle
Waste from Nuclear Weapons Production
Figure 4 - Waste Storage Tank
(Courtesy Department of Energy)
The U.S. Department of Energy has begun a process of mixing this waste with sand at high temperatures to form a liquid glass mixture, which is poured into stainless steel canisters where it solidifies and is sealed for permanent storage. This method of stabilization, known as vitrification, has also been used to process waste from power reactors.
Types of Nuclear Waste
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.
High-level waste is the highly radioactive waste resulting from spent nuclear fuel from production or power reactors, as well as from 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 U235 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 (Figure 5).
Figure 5 – Radioactive Decay of High-level Waste from Reprocessing One Tonne of Spent Reactor Fuel
(Courtesy OECD NEA)
Transuranic (TRU) waste contains alpha-emitting transuranic elements or actinides with half-lives of greater than 20 years and a combined activity of greater than 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 Pu-238, Pu-239, Pu-240, Pu-241, Pu-242, Am-241, and Cu-244. TRU waste results from the fabrication of plutonium components, recycling of plutonium from scrap, retired weapons, and chemical separation of plutonium. Unlike high-level waste, which 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 cannot 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.
Mixed low-level waste contains both chemically hazardous waste subject to the Resource Conservation and Recovery Act (RCRA) and radioactive 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.
Waste Repositories in the United States
Figure 6 -WIPP
Figure 7 – Yucca Mountain Site in Nevada
Courtesy of the U.S. Department of Defense
As the licensing agency, the NRC will use standards currently being developed by the U.S. Environmental Protection Agency. However, conflicting scientific and technical information as well as strong political opposition from Nevada cloud the future of the site.
Complete Bibliography on Nuclear Waste from the Alsos Digital Library for Nuclear Issues
|2005-2009 Kennesaw State University
Principal Investigator Laurence Peterson
Project Director Matthew Hermes