These rods absorb neutrons and stop the chain reaction to proceed further.. Some control rods are made from an alloy of silver and cadmium. Some are made from boron mixed with iron or carbon. The control rods are very good at absorbing neutrons. They reduce the number of neutrons available to continue the chain reaction. The control rods can be moved up and down inside the reactor core. As they are lifted up and out of the reactor, the less neutrons they absorb, the faster the chain reaction happens and the reactor gets hotter. The heat is then used to generate electricity. The further down the control rods go, the more neutrons they absorb, the slower the chain reaction happens and the reactor gets colder.The control rods can used to shut the reactor down completely.