controlestaven

Controlestaven are neutron-absorbing rods used to regulate the rate of fission in a nuclear reactor. Inserted into the reactor core among the fuel assemblies, they control reactivity by capturing neutrons that would otherwise sustain the chain reaction. The term controlestaven is used in several languages and corresponds to what in English is called control rods or reactor control rods.

Construction and materials: most controlestaven consist of a neutron-absorbing material such as boron carbide, hafnium, cadmium, indium, or silver–indium–cadmium alloys, enclosed in corrosion-resistant cladding made of stainless steel or a similar alloy. The rods are mounted in guide tubes and moved by mechanical drives, hydraulics, or servo motors. In some reactor designs, soluble neutron absorbers (for example boric acid in the reactor coolant) provide an additional layer of reactivity control, though these are not a substitute for solid controlestaven in many systems.

Operation and purpose: by adjusting the insertion depth of the rods, operators increase or decrease reactivity. A higher insertion reduces neutron flux and reactor power; withdrawal increases it. In emergency situations, rapid insertion of all controlestaven, known as a scram, aims to halt the fission chain reaction as quickly as possible.

Technical considerations: the worth of each rod segment depends on reactor design, fuel burnup, temperature, and neutron spectrum. Controlestaven are subject to aging, wear, swelling, and corrosion, requiring regular inspection, calibration, and replacement as part of safe reactor operation.

History and significance: controlestaven date to the early development of nuclear reactors and remain a central safety and control feature in most commercial reactors today, especially pressurized and boiling water reactors. See also nuclear reactor, reactivity, scram, and neutron absorber.