High-level waste

High-level waste (HLW) is a type of nuclear waste created by the reprocessing of spent nuclear fuel.[1] It exists in two main forms:

See also: High-level radioactive waste management
The Hanford site represents 7-9 percent of America's high-level radioactive waste by volume. Nuclear reactors line the riverbank at the Hanford Site along the Columbia River in January 1960.

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 [2] 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 reactor core and is the type of nuclear waste with the highest activity. 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 comes from 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.[3] Some other countries, particularly France, reprocess commercial spent fuel.

High-level waste is very radioactive and, therefore, requires special shielding during handling and transport. Initially it also needs cooling, because it generates a great deal of heat. Most of the heat, at least after short-lived nuclides have decayed, is from the medium-lived fission products caesium-137 and strontium-90, which have half-lives on the order of 30 years.

A typical large 1000 MWe nuclear reactor produces 25–30 tons of spent fuel per year.[4] 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 Finland, France, Japan, United States and Sweden.

Definitions
Long-lived fission products
Nuclide t​1⁄2 Yield Decay
energy[a 1]		 Decay
mode
(Ma) (%)[a 2] (keV)
99Tc0.2116.1385294β
126Sn0.2300.10844050[a 3]βγ
79Se0.3270.0447151β
93Zr1.535.457591βγ
135Cs2.36.9110[a 4]269β
107Pd6.51.249933β
129I15.70.8410194βγ
  1. Decay energy is split among β, neutrino, and γ if any.
  2. Per 65 thermal-neutron fissions of U-235 and 35 of Pu-239.
  3. Has decay energy 380 keV,
    but decay product Sb-126 has decay energy 3.67 MeV.
  4. Lower in thermal reactor because predecessor absorbs neutrons.
Medium-lived
fission products
Prop:
Unit:		 t½
(a)		 Yield
(%)		 Q *
(keV)		 βγ *
155Eu 4.76 0.0803 252 βγ
85Kr 10.76 0.2180 687 βγ
113mCd 14.1 0.0008 316 β
90Sr 28.9 4.505 2826 β
137Cs 30.23 6.337 1176 βγ
121mSn 43.9 0.00005 390 βγ
151Sm 88.8 0.5314 77 β

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.[5]

Spent (used) reactor fuel.

  • Spent nuclear fuel is used reactor fuel 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.






Disposal
Main article: High-level radioactive waste management
Spent fuel pool

High-level radioactive waste is stored for 10 or 20 years in spent fuel pools, and then can be put 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% utilized.[6] With annual additions of about 12,000 tonnes, issues for final disposal are not urgent.

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See also

Notes
  1. M.I. Ojovan and W.E. Lee. An Introduction to Nuclear Waste Immobilisation. Elsevier, Amsterdam (2005)
  2. Radioactive Waste Management
  3. US EPA, Spent Nuclear Fuel and High-Level Radioactive Waste, www.epa.gov
  4. WNO radwaste management
  5. Dept of Energy - RADIOACTIVE WASTE MANAGEMENT MANUAL - DOE M 435.1-1
  6. "Radioactive waste". martinfrost.ws. Archived from the original on 3 December 2012. Retrieved 16 April 2013.

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
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