The Fast Breeder Reactor
A fast breeder reactor converts non – fissionable U - 238 with 99.3% natural abundance, to plutonium – 239, which may undergo fission. Some of the neutrons emitted by the fission of U – 235 are absorbed by U – 238 and after the following series reactions Plutonium – 239 is produced.
the Plutonium – 239 isotope is a fissionable material that produces about three neutrons per fission and can serve as a nuclear fuel for sustained fission reactions.
In a breeder reactor, one neutron released by Plutonium – 239 produces another fission. A second neutron is absorbed by a Uranium – 238 nucleus and produces a new Plutonium – 239 nucleus. In this way the concentration of the Plutonium – 239 fuel remains constant. If the third neutron is also absorbed by Uranium – 238, two Plutonium nuclei are produced for each Plutonium – 239 fission. Since more fuel is produced than is consumed, the reactor is said to breed nuclear fuel. Breeding fissionable Plutonium – 239 from non – fissionable Uranium – 238 increases the supply of fissionable material by a factor of more than 100. Without the breeding described above, only 0.7% of natural Uranium is fissionable. If we are allowed to use this method, it is all fissionable.