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Entombment (also referred to as safe enclosure) of a nuclear reactor is a method of nuclear decommissioning in which radioactive contaminants are encased in a structurally long-lived material, such as concrete, that will last for a period of time to ensure the remaining radioactivity is no longer of significant concern. The entombment structure is appropriately maintained and continued surveillance is carried out until the radioactivity is no longer a major concern, permitting decommissioning and ultimate unrestricted release of the property.
Whether or not the radioactivity is of 'major concern' is mostly a financial question. Highly contaminated sites can only be decommissioned using remotely operated tools, and this is often very expensive. After waiting a certain amount of years, the amount of short lived radioisotopes has significantly reduced, making the final decommissioning process also cheaper. At the same time, nuclear decommissioning funds, which are often collected during the operation of a nuclear power plant, have a possibility to collect interest, making more funds available for final decommission.
There are some public doubts on nuclear entombment, as it does not uphold the polluter pays principle. It is often not possible to make an exact estimate of total decommissioning costs, leaving a certain financial liability for a future generation. It is also difficult to guarantee that the necessary expertise for final decommissioning will be available in due time, or that the decommissioning fund has earned sufficient interest. In the United States, Nuclear Regulatory Commission rules limit licensees to 60 years to decontaminate an installation to background levels. Long-lived isotopes in reactors do not decay to background level in only sixty years.
- Lucens, Switzerland - initially entombed in a cavern and later decontaminated.
- Dodewaard, the Netherlands - entombed for 40 years, awaiting final decommissioning. Also referred to as 'safe enclosure'.
- Boiling Nuclear Superheater (BONUS) Reactor Facility, Rincón, Puerto Rico
- Hallam Nuclear Power Facility, Hallam, NE, USA
- Piqua Nuclear Generating Station, Piqua, OH, USA
- US NRC 2008-2009 Information Digest, Government Printing Office, pp 113-114