High-level waste (HLW) is a type ofnuclear waste created by the reprocessing of spent nuclear fuel.[1] It exists in two main forms:
Liquid high-level waste is typically held temporarily in underground tanks pending vitrification. Most of the high-level waste created by theManhattan Project and the weapons programs of theCold 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 thefission products andtransuranic elements generated in thereactor 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 theradioactivity produced from the nuclear power generation process comes from high-level waste.
Some 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 themedium-lived fission productscaesium-137 andstrontium-90, which have half-lives on the order of 30 years.
A typical large 1000 MWe nuclear reactor produces 25–30 tons ofspent fuel per year.[3] If the fuel werereprocessed andvitrified, the waste volume would be only about three cubic meters per year, but thedecay heat would be almost the same.
It is generally accepted that the final waste will be disposed of in adeep geological repository, and many countries have developed plans for such a site, includingFinland,France,Japan,United States andSweden.
| Nuclide | t1⁄2 | Yield | Q[a 1] | βγ |
|---|---|---|---|---|
| (Ma) | (%)[a 2] | (keV) | ||
| 99Tc | 0.211 | 6.1385 | 294 | β |
| 126Sn | 0.230 | 0.1084 | 4050[a 3] | βγ |
| 79Se | 0.327 | 0.0447 | 151 | β |
| 135Cs | 1.33 | 6.9110[a 4] | 269 | β |
| 93Zr | 1.61 | 5.4575 | 91 | βγ |
| 107Pd | 6.5 | 1.2499 | 33 | β |
| 129I | 16.14 | 0.8410 | 194 | βγ |
| t½ (year) | 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 | 94.6 | 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.[4]
Spent (used) reactor fuel.
Waste materials from reprocessing.
High-level radioactive waste is stored for 10 or 20 years inspent fuel pools, and then can be put indry 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.[5]
