Fast reactors are a type of nuclear reactor that use fast neutrons to sustain the fission process. Unlike traditional thermal reactors, which slow down neutrons using moderators, fast reactors can efficiently utilize a wider range of nuclear fuels, including plutonium and uranium. This allows them to generate more energy and reduce nuclear waste. These reactors are designed to be more sustainable by recycling spent fuel and producing less long-lived radioactive waste. Fast reactors can also help in closing the nuclear fuel cycle, making them an important option for future energy production and nuclear safety advancements.