What safety feature works to slow down nuclear fission chain reaction?

A key safety feature that slows down a nuclear fission chain reaction is the use of control rods, which are made of materials that absorb neutrons, such as boron or cadmium. By inserting these control rods into the reactor core, they reduce the number of free neutrons available to sustain the fission process, effectively slowing down or stopping the chain reaction. Additionally, coolant systems can also help manage the reactor's temperature and prevent overheating.