Nuclear reactor which uses fast neutrons to convert uranium to plutonium and which creates more fuel than it uses. A chain reaction is set up in which ²³⁸U, with an initial charge of ²³⁹Pu to begin the fission process, discards fast neutrons each of which induces fission in another nucleus. Excess ²³⁹Pu is produced where plutonium production exceeds rate of fission. About 60% of fuel elements in fast breeder reactors is converted to useful energy compared to 0.5–1% in burner reactors. Plutonium can be recycled, but other radioactive products are waste. See radioactive waste.