A rod of neutron-absorbing material used to control nuclear reactor power. The intensity of the fission reaction depends on the number of neutrons participating in the reaction. If the number of neutrons is reduced, the reaction slows down and the reactor power decreases. In contrast, if the number of involved neutrons increases, the reaction becomes more intense and the reactor power increases. By retracting and extending the control rods with a neutron absorber, the number of neutrons and thus the intensity of fission can be regulated. The typical regulating rods are made of steel alloyed with boron and containing cadmium or hafnium.