Question
What are the utilities of moderator, coolant and controlling rods with reference to nuclear reactor.
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Answer
Moderator : In the fission of uranium, fast neutrons of energy 2 MeV are released. These fast neutrons have more tendency to escape instead of triggering another fission reaction. Also, slow neutrons are more efficient in inducing fission in ${ }_{92}^{235} Ur$ nuclei than fast neutrons. By the use of a moderator, the fast neutrons are slowed to thermal velocities. Usually, heavy water, graphite and beryllium oxide are used as moderators.
Control rods : To start, stop or control the chain reaction, rods of neutron absorbing material like cadmium or boron are inserted into the reactor core. The rate of neutron production is controlled by adjusting the depth of control rods.
Coolant : It is the material used to cool the fuel rods and the moderator and is capable of carrying away large amount of heat produced in the fission process. The coolant transfers heat to the working liquid like water and produces steam. The steam drives a turbine which, in turn, runs a generator to generate electric power. The coolant must have high boiling point and high specific heat. Heavy water and liquid sodium are good coolants.
Control rods : To start, stop or control the chain reaction, rods of neutron absorbing material like cadmium or boron are inserted into the reactor core. The rate of neutron production is controlled by adjusting the depth of control rods.
Coolant : It is the material used to cool the fuel rods and the moderator and is capable of carrying away large amount of heat produced in the fission process. The coolant transfers heat to the working liquid like water and produces steam. The steam drives a turbine which, in turn, runs a generator to generate electric power. The coolant must have high boiling point and high specific heat. Heavy water and liquid sodium are good coolants.
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