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High level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists as both raw waste such as spent raffinate and other waste streams created by nuclear reprocessing, and waste formed by vitrification of the raw waste.

Raw waste is typically held in underground tanks pending vitrification. Most of the high level waste created by the Manhattan project and the weapons programs of the cold war exists in this form, as funding for further processing was typically not part of the original weapons programs.

HLW contains many of the fission products and transuranic elements, predominantly the more alkaline ones, generated in the reactor core. HLW accounts for over 95% of the total radioactivity produced in nuclear reactions, but it represents a small portion of the overall waste generated during nuclear work. In other words, while most nuclear waste is low-level and intermediate-level waste such as protective clothing and equipment that have been contaminated with radiation, the majority of the radioactivity produced from nuclear reactions becomes high-level waste.

In the US, HLW from reprocessing of spent fuel from electrical power stations amounts to less than 1% of the total volume of US HLW; the rest is defense related.^[1] Some other countries, particularly France, reprocess commercial spent fuel.

High level waste is very radioactive and, therefore, requires special handling and transport. It also needs cooling, because it generates a great deal of heat. Most of the heat, for the first several hundred years, is from the medium-lived fission products cesium-137 and strontium-90.

A typical large nuclear reactor produces 25–30 tons of spent fuel per year. If the fuel were reprocessed and vitrified, the waste volume would be only about three cubic meters per year, but the decay heat would be almost the same.

It is generally accepted that the final waste will be disposed of in a deep geological repository, and many countries have developed plans for such a site, including France, Japan, and the United States (see also High-level radioactive waste management).

Definitions

High-level waste is the highly radioactive waste material resulting from the reprocessing of spent nuclear fuel, including liquid waste produced directly in reprocessing and any solid material derived from such liquid waste that contains fission products in sufficient concentrations; and other highly radioactive material that is determined, consistent with existing law, to require permanent isolation. Ref: Dept of Energy - RADIOACTIVE WASTE MANAGEMENT MANUAL - DOE M 435.1-1; http://www.directives.doe.gov/pdfs/doe/doetext/neword/435/m4351-1c1.html

Spent (used) reactor fuel.

• Spent nuclear fuel is used fuel from a reactor that is no longer efficient in creating electricity, because its fission process has slowed due to a build-up of reaction poisons. However, it is still thermally hot, highly radioactive, and potentially harmful.

Waste materials from reprocessing.

• Materials for nuclear weapons are acquired by reprocessing spent nuclear fuel. Reprocessing is a method of chemically treating spent fuel to separate out uranium and plutonium. The byproduct of reprocessing is a highly radioactive sludge residue.

Disposing of high-level wastes

Spent nuclear fuel is stored temporarily in spent fuel pools and in dry cask storage facilities when it is removed from the reactor.

In 1997, in the 20 countries which account for most of the world's nuclear power generation, spent fuel storage capacity at the reactors was 148,000 tonnes, with 59% of this utilized. Away-from-reactor storage capacity was 78,000 tonnes, with 44% utilised. With annual additions of about 12,000 tonnes, issues for final disposal are not urgent.

The status of disposal plans in various countries is described in the article High-level radioactive waste management.

External links

• NRC Backgrounder on Radioactive Waste

See also

• Radioactive waste
• low level waste
• transuranic waste
• spent nuclear fuel
• mixed waste

Notes

References

• Fentiman, Audeen W. and James H. Saling. Radioactive Waste Management. New York: Taylor & Francis, 2002. Second ed.

• Large, John H. Risks and Hazards arising the Transportation of Irradiated Fuel and Nuclear Materials in the United Kingdom R3144-A1, March 2006 [2]