control rod

In nuclear physics, control rods are essential components used to regulate the rate of nuclear fission within a nuclear reactor. These rods are made of neutron-absorbing materials, such as boron carbide.1

Nuclear reactors operate on the principle of a controlled fission chain reaction, where neutrons released from splitting atoms cause further fissions. Control rods manage this process by absorbing excess neutrons.2

There are typically three types of rods:
* Safety rods: Used for starting up, shutting down, and in emergencies, designed to fall into the core if power fails.3
* Regulating rods: Fine-tune the reactor's power level.3
* Shim rods: Compensate for changes in reactivity as fuel is consumed over time.3

By inserting or withdrawing these rods, operators can maintain the reactor in a critical state for steady operation or shut it down by making it subcritical.2