Question

Explain the functions of a moderator and a control rod in a nuclear reactor.

Short answer

In a nuclear reactor, a moderator slows down the fast neutrons produced by nuclear fission, making it possible for more nuclear fissions to occur. Control rods, on the other hand, absorb neutrons to control the rate of nuclear fission, thereby regulating the amount of energy produced.

Step-by-step solution

Function of a Moderator

The moderator is responsible for slowing down the fast neutrons produced by nuclear fission. Doing this increases the possibility of more nuclear fissions occurring since slow neutrons are more likely to cause fission. Common moderators include light water, heavy water, or graphite.

Function of Control Rods

Control rods are used to control the fission rate of uranium and plutonium. They perform this function by absorbing the neutrons that are released during nuclear fission. By adjusting the height of the control rods inside the nuclear reactor, we can control the number of neutrons that participate in the chain reaction; therefore, the amount of energy produced can be regulated. Control rods are usually made of materials like boron, silver, indium and cadmium that are good neutron absorbers.

Balancing the Role of Moderator and Control Rods

Together, the moderator and control rods regulate the nuclear fission process inside a nuclear reactor. The moderator slows down the neutrons to make them suitable for causing additional fissions, while the control rods can absorb neutrons to decrease the fission rate when required. The balance between these two functions helps maintaining the chain reaction at a steady level, thus ensuring the controlled production of heat.