In the generation of Nuclear Power, fissionable products may be created by neutron collisions with non-fissionable isotopes. Plutonium for nuclear weapons is created by this means. Since plutonium is also useful as fuel in a reactor, it is possible to build reactors which convert non-fissionable materials into fissionable materials faster than the fissionable materials are used. These are called breeder reactors. Breeder reactors have the characteristic that they can use natural uranium as fuel thereby skipping the enrichment step.

The first large scale breeder reactor entered service in France in 1984. It uses liquid sodium instead of water as a heat transfer medium. Various environmental and non-proliferation concerns have discouraged wide-spread development of breeder reactors.