The United States is the first country in the world to have begun operating a deep geological repository for radioactive waste. The Waste Isolation Pilot Plant (WIPP) in Carlsbad, in south-eastern New Mexico, is currently the only underground waste disposal facility of the type in existence. This depot for military transuranium waste (TRU in US nomenclature), excavated in a deep-lying salt formation, entered service in 1999.
Defence-related TRU waste is so named because it is from materials that have been contaminated with plutonium. It includes protective clothing: coveralls, gloves, shoe covers, etc. Other sources include, dismantled machine tools, workshop demolition rubble and sludge contaminated with radioactive substances from US nuclear weapon plants.
In order to manufacture the US arsenal of thousands of plutonium-containing nuclear weapons, dozens of tonnes of this heavy transuranium element (thus described due to its position after uranium in the periodic table) were synthesised and then machined. From a radiation protection perspective, plutonium and the other transuranium elements are alpha emitters, and radiotoxic if ingested. They have long half-lives.
Under the French system, the waste at WIPP would be classified as intermediate-level, long-lived waste (ILW-LL). Under federal law, WIPP is not licensed to accept high-level waste or spent nuclear fuel intended for disposal at the Yucca Mountain repository in the Nevada desert.
WIPP is located in a sparsely-populated desert area. Waste is disposed of in salt domes. The salt formations, the top of which lies 305 m below the surface, are 650 m thick. Salt is considered to be a good medium for repositories, as it is free from water. The geology of the salt formations at the WIPP has been stable for 200 million years. The facilities are located 635 m below the surface. They include four shafts and 10 waste disposal areas.
The National Defence argument undoubtedly played a role in surmounting the many procedural obstacles that had to be overcome before the site opened. Twenty years elapsed (1979-1999) between the initial license granted for WIPP by Congress and the final operating license issued by the New Mexico Department of the Environment.
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