Control rods made from neutron-absorbing materials regulate the speed of the nuclear chain reaction.

Control rods composed of materials like cadmium, silver, or boron can be inserted into or withdrawn from the reactor core. By absorbing excess neutrons, they reduce the number available to continue the chain reaction, slowing or stopping the fission process. This provides a critical safety mechanism to keep the reactor operating at a safe, steady power output or to shut it down in emergencies.