Most nuclear reactors operate by allowing a radioactive element (usually plutonium or uranium) to decay and release neutrons. Some of these neutrons strike fuel atoms, causing them to decay and emit more neutrons, thus establishing a chain reaction. The heat generated in this reaction is absorbed by a circulating coolant and used to produce electricity. The reaction itself is controlled using rods made of material that absorbs neutrons called control rods. The breeder reactor (also called the fast reactor or the fast-breeder) does not use control rods, and so produces more fuel material than it consumes.