A Liquid Metal Fast Breeder Reactor (LMFBR) is a type of nuclear reactor that uses liquid metal, typically sodium, as a coolant. This design allows for efficient heat transfer and enables the reactor to operate at high temperatures. LMFBRs are known for their ability to breed more fuel than they consume, making them a sustainable option for nuclear energy. In an LMFBR, fast neutrons are used to sustain the nuclear fission process, which is different from traditional reactors that use slow neutrons. The reactor's ability to convert non-fissile isotopes, like uranium-238, into fissile material, such as plutonium-239, enhances fuel efficiency and reduces nuclear waste.