radioactive waste

radioactive waste material containing the unusable radioactive byproducts of the scientific, military, and industrial applications of nuclear energy. Since its radioactivity presents a serious health hazard (see radiation sickness ), disposing of such material is a great problem. Methods of disposal include dumping concrete-encased containers filled with radioactive waste in the ocean and burying the waste underground in old salt mines. In 1996 the United States opened a waste processing plant in Aiken, S.C. at the Savannah River nuclear-weapons complex. The waste will be converted into cylinders of radioactive glass, which will then be encased in steel containers that will be stored in an underground concrete vault. While the glass will still be radioactive, it will no longer be possible for the waste to leak into the soil, and there will be no possibility of a chemical explosion such as the one that occurred in the Soviet Union in the late 1950s. The United States has also agreed to accept about 20 tons of waste from research reactors in 41 countries. The spent nuclear fuel, supplied by the United States for medical and research purposes, includes about 5 tons of highly enriched uranium that could be extracted and used to produce nuclear weapons.

radioactive waste Any discarded substance that is radioactive. Wastes are classified as high-, intermediate-, or low-level according to their level of radioactivity. Low-level waste includes clothing and materials which have been used when handling radioactive sources, e.g. in hospitals. It can be safely buried in trenches 9 m deep beneath a covering of 2 m of clay; no alpha or beta radiation could penetrate the clay cover. Intermediate- and high-level wastes are mainly from the fission process in nuclear power stations or from military waste. High-level waste is hot and intensely radioactive. It is stored, usually in ponds of water, for up to 50 years, during which time it cools and its short-lived isotopes decay until it can be classed as intermediate-level. It can then be incorporated in a borosilicate glass or synthetic rock (a synrock), sealed in a container which corrodes at a known rate, and stored in a secure surface or underground facility. After 500 to 1000 years the radioactivity will have decayed sufficiently for the waste to emit no more radiation than many naturally occurring rocks.

radioactive waste Substances from nuclear processes which are contaminated and not reusable. Low-level waste includes clothing and materials which have been used when handling radioactive sources (e.g. in hospitals and research laboratories). High-level waste is mainly from the fission process in nuclear power stations or from military waste. The high level of radioactivity is caused by short-lived isotopes; their decay leads to lower levels of radioactivity, but from longer-lived isotopes with half lives of up to one million years (although, in most cases, their emissions fall to levels approximately equal to those of natural background radiation after about 500 years and it is not necessary to safeguard them for periods longer than this). During the first phase such waste is stored in corrosion-resistant containers, but the long-term requirement is to find geologically stable repositories so that any leakage will not return to the surface.