Radioactive waste

Radioactive waste is generated during the production of electricity by nuclear power plants, by the eventual disposal of those facilities, and during the manufacturing and disposal of nuclear weapons and machines used in medical diagnosis and treatments, academic and industrial research, and certain industrial applications. Radioactive waste produces ionizing radiation , which can damage or destroy living tissues. Ionizing radiation transfers energy when it encounters biochemicals, causing them to become electrically charged, or ionized, which can damage their essential metabolic function.

Unlike conventionally toxic chemicals, the degree of danger from radioactive waste decreases over time. The half-life of a radioactive substance (or radioisotope) is the time required for one-half of an initial quantity to decay to other isotopes. Each radioisotope has a unique half-life, which can be only fractions of a second long, or as great as billions of years. The longer the half-life of a radioisotope, the longer is the period for which it must be safely stored or disposed until it is no longer hazardous.

Types of radioactive waste

Radioactive wastes are grouped into three categories: high-level waste, low-level waste, and transuranic waste. High-level waste emits intense levels of ionizing radiation for a relatively short time, and then emits lower levels for a much longer time. Most high-level waste is used nuclear fuel rods, which must be removed from the reactor core about every 2–4 years. Large quantities of high-level wastes are also associated with the production and disposal of nuclear weapons. In 2000, about 44,000 tons (40,000 tonnes) of spent fuel were stored at commercial nuclear power sites in the United States, a quantity expected to rise to 116,000 tons (105,000 tonnes) by 2035.

Low-level waste emits small amounts of ionizing radiation, usually for a long time, and it tends to be a high-volume waste. Low-level waste is produced from a variety of sources, such as filters and other cleaning material from nuclear plants, and used low-level radioisotopes from hospitals, universities, and industry. For example, in nuclear generating stations, tiny quantities of some radioactive materials may leak from the reactor. To protect the workers and the ambient environment, this radioactivity is removed with filters, which must periodically be replaced, becoming low-level waste.

Transuranic waste results primarily from the fabrication of plutonium as well as research activities at defense installations. Transuranics are elements, not found in nature, that are heavier than uranium . Most transuranics have special properties that increase the probability of causing damage to living tissue . Transuranic elements are found in both high-level and low-level radioactive waste. They can be separated from low-level waste, and are then treated as high-level waste.

Storage of radioactive waste

Storage can be defined as "a method of containment with a provision for retrieval." High-level and transuranic wastes are typically stored in on-site, deep-water storage ponds with thick, stainless steel-lined concrete walls. After about five years, the spent fuel has lost much of its radioactivity and can be moved into dry storage facilities. These are usually on-site, above-ground facilities in which the waste is stored in thick, concrete canisters.

Low-level waste is stored in concrete cylinders in shallow burial sites at nuclear plants or at designated waste sites. Since these wastes are not as much of a concern as high-level wastes, the regulations for their storage are not as strict. Basically, the waste must be covered and stored so that contact with ambient water is minimal.

Transportation of radioactive waste

The regulations for transporting radioactive waste are stringent due to the possibility of a transportation accident. Various containers are used for transporting specific kinds of waste. High-level waste has the most rigorous standards, and the containers in which it is shipped must be capable of withstanding tremendous pressure , impact, and heat , and are waterproof. There have been accidents in North America involving trucks and trains carrying radioactive waste, but no significant amount of radioactivity has ever been released to the environment as a result.

Treatment of radioactive waste

High-level radioactive waste can be treated by fuel reprocessing, which separates still-useful fuel isotopes from the rest of the waste. The useful isotopes can then be sent to a fabrication plant, which produces new nuclear fuel. Some technologists view this strategy as an excellent alternative to long-term storage, since it is essentially a re-use practice as opposed to disposal. Fuel reprocessing plants exist in Britain, France, Japan, Germany, India, and Russia. The United States, Canada, Spain, and Sweden do not have reprocessing plants, and are planning on long-term storage of their spent fuel.

Low-level radioactive waste is commonly a high-volume material, which can often be reduced prior to storage, transport, or disposal. It can be concentrated by filtering and removing the liquid portion, so only the solid residue remains for disposal. Alternatively, the material may be solidified by fusing it into glass or ceramic, which are highly stable materials.

Disposal of radioactive waste

Radioactive waste disposal refers to the long-term removal of the waste, and is designed to have minimal contact with organisms and the ambient environment. The safe disposal of high-level and transuranic wastes from nuclear power plants and nuclear weapons facilities has been the center of vigorous debate for more than 50 years, and researchers and policy-makers have yet to come up with politically acceptable solutions.

The most widely supported plan involves the burial of high-level waste deep underground in a stable geological formation. Less-popular ideas include burial under a stable glacier, or dumping into a deep oceanic trench. Part of the problem with any of these ideas is that disposal requires that the site will be secure for tens of thousands of years. This probably exceeds the time for which present governmental and social institutions will persist, so far-future generations may have to deal with the high-level nuclear wastes of the present ones. Moreover, nature can be a changeable, unpredictable, and powerful force , so there are unknown risks associated with all disposal options, and long-term, absolute guarantees cannot be given.

From 1940–1970, most low-level wastes were placed into steel drums and dumped into the ocean or into pits on land. However, there has been inevitable leakage from the drums, and environmentalists and the public objected to this method of disposal. Since 1970, the United States has been disposing its low-level waste at government-regulated disposal sites. In June 1990, the U. S. Nuclear Regulatory Commission (NRC) proposed that low-level radioactive waste be handled as regular garbage, due to its supposed low health risk. Epidemiologists calculated that implementing this policy might have caused 2,500 American deaths, but the NRC believed this risk was acceptable because it would save the nuclear power industry many millions of dollars every year. However, this proposal did not fully take account of recent research indicating that low-level radiation risks may be about 30 times higher than previously estimated.

Current problems in radioactive waste

The biggest technological challenge presently facing the nuclear industry is the long-term, safe disposal of high-level waste. The current preferred disposal option is to bury it deep underground. The Department of Energy proposed in 1983 that nine sites in geologically diverse locations be studied for suitability as one of two potential waste repositories. In 1987, Congress amended the Nuclear Waste Policy Act to redirect the Department of Energy to focus site characterization activities only at Yucca Mountain, Nevada. Huge sums of money have been spent in planning for this disposal option, but it remains controversial and is not yet built. The Department of Energy does predict, however, that the site will be available for disposal activities in the year 2010.

Political and scientific disagreements between the State of Nevada and the federal government have delayed the process, as have arguments presented by environmental groups. Opponents have complained that the site selection process has been dominated by political decision making rather than scientific reason. Technical concerns largely center on the geological stability of the area and the potential for water infiltration into the repository causing the release of radioactive material into the environment. Moreover, there are relatively young volcanoes nearby, several faults near the site, and the potential for climate change to cause ground-water levels to rise and inundate the repository horizon. Further complicating the issue is the fact that the proposed site lies adjacent to the Nevada Test Site (NTS), the location at which approximately one thousand nuclear weapons tests have been conducted. Some have argued that the extensive radioactive contamination associated with testing at the NTS makes the Yucca Mountain site more favorable for waste disposal. They suggest that the existing, uncontrolled contamination is unlikely to be significantly worsened by the proposed disposal of nuclear wastes in a controlled, engineered system and that localization of the wastes in a previously contaminated area is preferable to the contamination of a new site.

Despite the controversy, in February 2002, the Secretary of Energy recommended to the President that the Yucca Mountain site be selected as the nation's high-level nuclear waste repository. The President followed the Secretary's recommendation and approved the site, only to be vetoed by the Governor of the State of Nevada. However, the U.S. Congress voted to override the veto in July 2002. The State of Nevada has since filed lawsuits to stop the project and will very likely fight the licensing application with the NRC prior to the receipt of waste and operation of the repository. It seems that the only certainty is that the safe, long-term disposal of high-level radioactive wastes will continue to be an extreme challenge for technologists, and for society.

See also Nuclear reactor; Radiation.

Resources

books

Cohen, B. L. The Nuclear Energy Option: An Alternative for the 90s. New York: Plenum Press, 1990.

Keller, Edward. Environmental Geology. Upper Saddle River, NJ: Prentice-Hall, Inc., 2000.

Miller, G. T., Jr. Environmental Science: Sustaining the Earth. 3rd ed. Belmont, CA: Wadsworth Publishing Company, 1991.

Price, J. The Antinuclear Movement. rev. ed. Boston, MA: Twayne Publishers, 1990.

United States Department of Energy, Office of Civilian Radioactive Waste Management. Final Environmental Impact Statement for a Geologic Repository for the Disposal of Spent Nuclear Fuel and High-Level Radioactive Waste at Yucca Mountain, Nye County, Nevada North Las Vegas, NV: U.S. Dept. of Energy, Office of Civilian Radioactive Waste Management, 2002.

United States Department of Energy, Office of Civilian Radioactive Waste Management. Program Plan, Revision 3. North Las Vegas, NV: U.S. Dept. of Energy, Office of Civilian Radioactive Waste Management, 2000.

United States Department of Energy, Office of Civilian Radioactive Waste Management. Site Characterization Progress Report, Yucca Mountain, Nevada. North Las Vegas, NV: U.S. Dept. of Energy, Office of Civilian Radioactive Waste Management, 2001.

organizations

Nuclear Regulatory Commission [cited October 17, 2002] <http://www.nrc.gov/>.

State of Nevada Nuclear Water Project Office. [cited October 17, 2002) <http://www.state.nv.us/nucwaste/>.

other

The Yucca Mountain Project. United States Department of Energy, Office of Civilian Radioactive Waste Management [cited October 17, 2002]. <http://www.ymp.gov/>.

Yucca Mountain Standards. United States Environmental Protection Agency [cited October 17, 2002]. <http://www.epa.gov/radiation/yucca/>.

Jennifer LeBlanc

KEY TERMS

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Half-life

—The time required for one-half of an initial quantity of a radioactive substance to disintegrate.

High-level waste

—Waste that emits intense levels of ionizing radiation for a short time, and then lower levels for a much longer time.

Ionizing radiation

—Radiation that can cause tissue damage or death.

Low-level waste

—Waste that emits small amounts of ionizing radiation, often for a long time.

Radioisotope

—A type of atom or isotope, such as strontium-90, that exhibits radioactivity.

Transuranic waste

—A special category of waste produced during the fabrication of plutonium as well as research activities at defense installations, involving non-natural elements heavier than uranium.