Fertile material is a material that, while not itself fissionable by thermal neutrons, can be converted into a fissile material by neutron absorption and subsequent nuclei conversions. Naturally-occurring fertile materials that can be converted into a fissile material by irradiation in a reactor include:
- thorium-232 which converts into uranium-233
- uranium-234 which converts into uranium-235
- uranium-238 which converts into plutonium-239
Artificial isotopes formed in the reactor which can be converted into fissile material by one neutron capture include:
- plutonium-238 which converts into plutonium-239
- plutonium-240 which converts into plutonium-241
Some other actinides need more than one neutron capture before arriving at an isotope which is both fissile and long-lived enough to probably be able to capture another neutron and fission instead of decaying.
- plutonium-242 to americium-243 to curium-244 to curium-245
- uranium-236 to neptunium-237 to plutonium-238 to plutonium-239
- americium-241 to curium-242 to curium-243 (or, more likely, curium-242 decays to plutonium-238, which also requires one additional neutron to reach a fissile nuclide)
Since these require a total of 3 or 4 thermal neutrons to eventually fission, and a thermal neutron fission generates only about 2 to 3 neutrons, these nuclides represent a net loss of neutrons. In a fast reactor, they may require fewer neutrons to achieve fission, as well as producing more neutrons when they do fission.
A fast-neutron reactor, meaning one with little or no neutron moderator and hence utilising fast neutrons, can be configured as a breeder reactor, producing more fissile material than it consumes, using fertile material in a blanket around the core, or contained in special fuel rods. Since plutonium-238, plutonium-240 and plutonium-242 are fertile, accumulation of these and other nonfissile isotopes is less of a problem than in thermal reactors, which cannot burn them efficiently. Breeder reactors using thermal-spectrum neutrons are only practical if the thorium fuel cycle is used, as uranium-233 fissions far more reliably with thermal neutrons than plutonium-239.
Famous quotes containing the words fertile and/or material:
“Truly fertile Music, the only kind that will move us, that we shall truly appreciate, will be a Music conducive to Dream, which banishes all reason and analysis. One must not wish first to understand and then to feel. Art does not tolerate Reason.”
—Albert Camus (1913–1960)
“What persuades men and women to mistake each other from time to time for gods or vermin is ideology. One can understand well enough how human beings may struggle and murder for good material reasons—reasons connected, for instance, with their physical survival. It is much harder to grasp how they may come to do so in the name of something as apparently abstract as ideas. Yet ideas are what men and women live by, and will occasionally die for.”
—Terry Eagleton (b. 1943)