Breeder reactors are a type of nuclear reactor designed to generate more fissile material than they consume. They achieve this by converting non-fissile isotopes, like uranium-238 or thorium-232, into fissile isotopes, such as plutonium-239 or uranium-233. This process allows for more efficient use of nuclear fuel and can extend the availability of nuclear resources. These reactors operate by using a fast neutron spectrum, which enables the conversion process to occur. Breeder reactors can help address concerns about nuclear waste and fuel scarcity, making them an important area of research in the field of nuclear energy.