Question

which are the control rods in a nuclear power plant?

Answer 1

Control rods are used in nuclear reactors to control the fission rate of uranium and plutonium. They are composed of chemical elements such as boron, silver, indium and cadmium that are capable of absorbing many neutrons without themselves fissioning.
Nuclear reactors also have control rods, which you stick down into the fuel to absorb neutrons, to slow the reaction down, or withdraw to speed the reaction up.