Radioactive waste

Radioactive waste is any waste material that is radioactive, meaning it contains radionuclides, or atoms with unstable nuclei. This waste may be the radioactive material left over after the completion of a procedure involving a nuclear reaction, or it may simply be any material that has come into contact with other radioactive material and must be disposed of. There has been considerable debate over how best to dispose of radioactive waste, as, depending on the material, its radioactivity may not dissipate for thousands or even millions of years.

Overview

Radioactivity is produced by a variety of activities. One major source of radioactive waste is the generation of nuclear energy, including the nuclear fuel cycle, which produces different types of waste at several stages in the process, such as depleted uranium and spent fuel rods. Other waste-generating activities include the medical use of radioisotopes, the processing of mineral ore, the production of weapons for defense programs, and the decommissioning of nuclear facilities.

The International Atomic Energy Agency (IAEA) divides radioactive waste into six categories: exempt waste (EW), very short-lived waste (VSLW), very low-level waste (VLLW), low-level waste (LLW), intermediate-level waste (ILW), and high-level waste (HLW). Strictly speaking, EW is not considered radioactive waste, as its radioactivity levels are so low that it is exempt from regulatory control. VSLW is radioactive material with a very short half-life, typically less than a year but very occasionally several years. VLLW is waste that does not qualify as EW but still has low enough levels of radioactivity to pose minimal risk. LLW has high levels of radioactivity, but the vast majority of its radionuclides have short half-lives. ILW contains high levels of radioactivity and long-lived radionuclides, but containing it does not require provisions for heat dissipation. HLW is material that contains a significant amount of long-lived radionuclides and is radioactive enough to generate significant heat. The US government uses a slightly different classification system, one that does not use the ILW category but does include the category of transuranic waste (TRUW), which refers to any waste that has been contaminated with alpha-emitting transuranic radionuclides above a certain concentration and with a half-life of more than twenty years.

The IAEA recommends different methods of radioactive-waste management depending on the type of waste being managed. VSLW need only be stored for a short period of time, until its radionuclides decay to a safe level, at which point it can be disposed of without issue. VLLW does not require high-level containment and can be disposed of in covered trenches, though measures should be taken to protect against radiation while it is being processed. All other types of radioactive waste must be isolated from the environment and are typically stored in underground facilities of varying depths and levels of shielding. LLW can be kept in near-surface facilities and must remain isolated for some time, often as long as several hundred years. ILW may require extra shielding and is typically stored at greater depths than LLW.

The management of HLW is a special case and the source of much debate. HLW must be both shielded and cooled, and it is often cooled for several years or even decades in specialized facilities before being transferred to a different location for storage, where it continues to be cooled by means of either cooling pools or specially engineered vaults. The IAEA notes that permanent underground storage of HLW in deep geological repositories, at depths of one thousand feet (three hundred meters) or greater, is generally regarded as ideal; however, because of the vast time scales on which the longest-lived radionuclides in HLW decay—iodine-129, for example, has a half-life of 15.7 million years—as of 2015, no such underground repository has been constructed, and all HLW remains in interim storage facilities aboveground.

Bibliography

Alexander, W. R., and L. E. McKinley, eds. Deep Geological Disposal of Radioactive Waste. Oxford: Elsevier, 2007. Print.

Alley, William M., and Rosemarie Alley. Too Hot to Touch: The Problem of High-Level Nuclear Waste. New York: Cambridge UP, 2013. Print.

Freiesleben, H. “Final Disposal of Radioactive Waste.” EPJ Web of Conferences 54 (2013): 1–17. Print.

International Atomic Energy Agency. Classification of Radioactive Waste: General Safety Guide. Vienna: IAEA, 2009. PDF file.

International Atomic Energy Agency. Policies and Strategies for Radioactive Waste Management. Vienna: IAEA, 2009. PDF file.

McCombie, Charles. “Evaluating Solutions to the Nuclear Waste Problem.” Bulletin of the Atomic Scientists Nov.–Dec. 2009: 42–48. Web. 26 Sept. 2013.

Pusch, Roland. Geological Storage of Radioactive Waste. Berlin: Springer, 2010. Print.

Wagman, David. “Nuclear Waste Disposal Sites Still Rare after All These Years.” Power Apr. 2013: 67–72. Print.