Breeder reactor - a nuclear fission reactor that is able to convert more than one atom of fertile material into fissile material for every atom of fissile material that undergoes fission.

Converter reactor - a nuclear fission reactor that can produce some new fissile material, but which does not achieve a one for one replacement of the fissile material used in fission.

Burner reactor - a nuclear reactor with little or no fertile material. There is no conversion of fertile material into fissile material.

Fissile material - isotopes that readily fissions with a low energy neutron. The most important fissile materials are U-233, U-235, and Pu-239. Any odd numbered isotope with atomic mass greater than 231 is also fissile.

Fertile material - isotopes that can become a fissile material after absorbing a neutron and undergoing a series of radioactive decays. The most abundant fertile isotopes are Th-232 and U-238.