A nuclear control rod is removed from or inserted into the core of a nuclear reactor in order to increase or decrease the number of neutrons which will split further uranium atoms. This in turn affects the heat of the reactor, the amount of steam generated, and hence the electricity produced. Nuclear power station at Leibstadt, Switzerland. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 939. ... General Name, Symbol, Number Uranium, U, 92 Chemical series Actinides Period, Block 7, f Density, Hardness 19050 kg/m3, 6 Appearance silvery-white metal Atomic properties Atomic weight 238. ... Electricity is a property of certain subatomic particles (e. ...

Originally the control rods hung above the reactor, suspended by a rope. In an emergency a person assigned to the job would take a fire axe and cut the rope, allowing the rods in fall into the reactor and stop the fission. At some point the title of the person assigned this duty was given as SCRAM, or Safety Control Rod Ax Man. This term continues in use today as the phrase "scram" to describe a shutting down of a reactor by dropping the control rods. For other uses, see Axe (disambiguation). ... Sketch of induced nuclear fission, a neutron (n) strikes a uranium nucleus which splits into similar products (F. P.), and releases more neutrons to continue the process, and energy in the form of gamma and other radiation. ...

Modern reactor designs use an electromagnetic system to raise and lower the rods, therefore the reactor will scram due to gravity in the case of a power failure, preventing overheating.