Radioactive Waste Management/High Level Waste

High level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel. It exists in two main forms:

• First and second cycle raffinate and other waste streams created by nuclear reprocessing.

• Waste formed by Radioactive waste#Vitrification|vitrification of liquid high level waste.

Liquid high level waste is typically held temporarily 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 because funding for further processing was typically not part of the original weapons programs. Both spent nuclear fuel and vitrified waste are considered l as suitable forms for long term disposal, after a period of temporary storage in the case of spent nuclear fuel.

HLW contains many of the fission products and transuranic elements, generated in the Nuclear reactor core|reactor core and is the highest activity type of nuclear waste. HLW accounts for over 95% of the total radioactivity produced in the nuclear power process. 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 the nuclear power generation process 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 defence related. Some other countries, particularly France, reprocess commercial spent fuel.

High level waste is very radioactive and, therefore, requires special shielding during 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 nuclear fuel|spent fuel per year. If the fuel were nuclear reprocessing|reprocessed and Radioactive waste#Vitrification|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.

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 Nuclear poison|reaction poisons. However, it is still Decay heat|thermally hot, highly radioactive, and potentially harmful.

Waste materials from reprocessing.

• Materials for nuclear weapons are acquired by Nuclear reprocessing|reprocessing spent nuclear fuel from breeder reactors. 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

High-level radioactive waste is stored temporarily in spent fuel pools and in dry cask storage facilities.

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.