control rods?

Question

what is the function of control rods in a nuclear reactor

Answer 1

Control rods contain a non-fissile material (e.g. cadmium) that can be inserted into a nuclear pile to damp the reaction by absorbing stray neutrons - they can thus control the intensity of the nuclear reaction by controlling the number of neutrons flying around. They can also be easily removed/inserted, allowing you to REVERSIBLY control the reaction (as opposed to in the case of an emergency, when you probably want to flood the pile with some non-fissile material to completely damp the reaction).

Answer 2

Control rods, usually made of graphite or boron, are used to absorb excess free Neutrons within the reactor.

This keeps enough neutrons available to maintain the chain reaction, but not enough so that another Chernobyl happens (this is when the chain reaction goes out of control and too much energy and heat are generated resulting in meltdown.)