radioactive waste

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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.

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