A nuclear reactor using fast neutrons for fission, producing in breeding envelope more fissionable fuel than it consumes. A mixture of uranium and plutonium serves as fuel for fast neutron reactors. They don’t use a moderator and use molten sodium as a coolant. The main advantage of fast neutrons is that, after collision with depleted uranium, they could produce fissile plutonium. The core of such reactors is surrounded by a breeder blanket, where fission is almost non-existent. The resulting plutonium thus has the optimum isotope ratio for further use as fuel. If the reactor is set up to produce more plutonium than it consumes, we speak of a breeder. Fast breeder reactors can also fission actinides, the main component of high-level waste.

Schematic diagram of pool-type fast breeder reactor.

Schematic diagram of loop-type fast breeder reactor.