Deep geological repository

A deep geological repository is a nuclear waste repository excavated deep within a stable geologic environment (typically below 300 m or 1000 feet). It entails a combination of waste form, waste package, engineered seals and geology that is suited to provide a high level of long-term isolation and containment without future maintenance. The Waste Isolation Pilot Plant, under construction in the USA, is the only one which actually contains nuclear waste. But the facility suffered a chemical explosion which led to a serious radiological accident in 2014.

The most long-lived radioactive wastes, including spent nuclear fuel, must be contained and isolated from humans and the environment for a very long time. Disposal of these wastes in engineered facilities, or repositories, located deep underground in suitable geologic formations is seen as the reference solution. The International Panel on Fissile Materials has said:

It is widely accepted that spent nuclear fuel and high-level reprocessing and plutonium wastes require well-designed storage for periods ranging from tens of thousands to a million years, to minimize releases of the contained radioactivity into the environment. Safeguards are also required to ensure that neither plutonium nor highly enriched uranium is diverted to weapon use. There is general agreement that placing spent nuclear fuel in repositories hundreds of meters below the surface would be safer than indefinite storage of spent fuel on the surface.

However, even a storage space hundreds of metres below the ground would, in many parts of the developed world, have to be able to withstand the pressures of one or more future glaciations with thick sheets of ice resting on top of the rock, deforming it and creating internal strains, which is being taken into consideration by agencies preparing for long-term waste repositories in Sweden, Finland, Canada and some other countries that would have to expect a reneved ice age.

Common elements of repositories include the radioactive waste, the containers enclosing the waste, other engineered barriers or seals around the containers, the tunnels housing the containers, and the geologic makeup of the surrounding area.

The ability of natural geologic barriers to isolate radioactive waste is demonstrated by the natural nuclear fission reactors at Oklo, Gabon. During their long reaction period about 5.4 tonnes of fission products as well as 1.5 tonnes of plutonium together with other transuranic elements were generated in the uranium ore body. This plutonium and the other transuranics remained immobile until the present day, a span of almost 2 billion years. This is quite remarkable in view of the fact that ground water had ready access to the deposits and they were not in a chemically inert form, such as glass.

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Wikipedia