Nuclear Fuel
To be a useful fuel for nuclear fission chain reactions, the material must:
- Be in the region of the binding energy curve where a fission chain reaction is possible (i.e. above radium)
- Have a high probability of fission on neutron capture
- Release two or more neutrons on average per neutron capture (which means a higher average number of them on each fission, to compensate for nonfissions, and absorptions in the moderator)
- Have a reasonably long half life
- Be available in suitable quantities
| Thermal neutrons | Epithermal neutrons | |||||
|---|---|---|---|---|---|---|
| σF | σγ | % | σF | σγ | % | |
| 531 | 46 | 8.0% | 233U | 760 | 140 | 16% |
| 585 | 99 | 14.5% | 235U | 275 | 140 | 34% |
| 750 | 271 | 26.5% | 239Pu | 300 | 200 | 40% |
| 1010 | 361 | 26.3% | 241Pu | 570 | 160 | 22% |
Fissile nuclides in nuclear fuels include:
- Uranium-235 which occurs in natural uranium and enriched uranium
- Plutonium-239 bred from uranium-238 by neutron capture
- Plutonium-241 bred from plutonium-240 by neutron capture. The Pu-240 comes from Pu-239 by the same process.
- Uranium-233 bred from thorium-232 by neutron capture
Fissile nuclides do not have a 100% chance of undergoing fission on absorption of a neutron. The chance is dependent on the nuclide as well as neutron energy. For low and medium-energy neutrons, the neutron capture cross sections for fission (σF), the cross section for neutron capture with emission of a gamma ray (σγ), and the percentage of non-fissions are in the table at right.
Read more about this topic: Fissile
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