A fast breeder reactor is a Nuclear reactor in which design tradeoffs have been made not to produce the ideal heat for power generation, but to produce reasonable heat but also a substantial amount of high-energy neutrons that will make ("breed") potential nuclear fuel of an appropriate plutonium isotope. Economically, it seems attractive when a reactor can produce 30 percent more fuel than it burns.[1] The reactor product is not immediately usable as fuel, but requires complex and hazardous Plutonium reprocessing.
There has been hesitancy to use this design, over concerns on weapons-grade plutonium becoming too widely available. Only two, neither of which is operational, have been built in the U.S.