High-level radioactive waste consists of spent fuel elements from nuclear reactors, waste produced from reprocessing, and waste generated from the manufacture of nuclear weapons. All these wastes are highly regulated and controlled due to the dangerously high levels of radiation and the security issues caused by their plutonium content. Strict licensing requirements for the storage of spent nuclear fuel and high-level radioactive waste are specified in 10 CFR Part 72.
Spent nuclear fuel has been withdrawn from a reactor, has undergone at least one year of decay since being used as an energy source in a power reactor, and has not undergone chemical reprocessing. Spent fuel is normally stored on-site at nuclear power plants in an independent spent fuel storage installation (ISFSI). An ISFSI is defined in 10 CFR Part 72 as a complex designed and constructed for the interim storage of spent nuclear fuel and other radioactive materials associated with spent fuel storage.
Spent fuel reprocessing was discontinued in the United States in 1972, except for the DOE, which continues to reprocess most of its spent fuel. France, Germany and several other major nuclear power producers also reprocess their spent fuel. Reprocessing improves the cost effectiveness of nuclear power by recycling recovered uranium and plutonium. The reprocessing of spent fuel, using the PUREX process developed in the United States, involves dissolution in large volumes of acid, liquid/liquid extraction, chemical reduction, and precipitation (Lanham & Runiou 1949, Flagg 1961, Koch 1979). The highly radioactive waste produced from reprocessing is classified by the NRC as a highlevel radioactive waste or HLW in 10 CFR Part 72.
Spent fuel elements, HLW, and other highly radioactive wastes, such as transuranic wastes, require permanent containment. The disposal method must be designed to allow decay of the longest-lived radionuclides present in significant amounts in the waste. This means a time period of several hundreds of thousands of years.
Burial in engineered geological repositories is the only current option being seriously considered on a worldwide basis. Except for TRU waste, no site has been selected in the U.S., making it necessary for power plants and the DOE to continue storing waste on site. TRU waste generated by the DOE from various weapons programs is being disposed of at the waste isolation pilot plant (WIPP), a geological repository constructed in a bedded salt dome in New Mexico (Kohn 1987).
Many books and publications are available on the subject of HLW and the reader is referred to these for further details (Delange 1987, IAE 1981, Gertz 1989).
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