A Fast Reactor is a type of nuclear reactor that uses fast neutrons to sustain the fission process. Unlike traditional reactors, which use slow neutrons, fast reactors can efficiently convert fertile materials, like uranium-238, into fissile materials, such as plutonium-239. This allows for better fuel utilization and the potential for breeding more fuel than they consume. Fast reactors can also help manage nuclear waste by transmuting long-lived isotopes into shorter-lived ones. They are considered a key technology for the future of nuclear energy, promoting sustainability and reducing the environmental impact of nuclear power generation.