Answer:
The correct answer is - control rods.
Step-by-step explanation:
Control rods are filled with special absorbing agents such as boron, cadmium, silver, and others to absorb as many neutrons as to control the fission reaction by moving them up and down in between uranium rods.
These control rods are used to prevent the nuclear reaction from getting out of control in the nuclear plant or reactor by absorbing the neutrons and prevent uranium to convert.