Practical Applications of Nuclear Fission

Nuclear reactor is a furnace or an equipment in which the nuclear chain reaction is carried out in a controlled manner and the heat energy so liberated is converted into electricity.

Boiling Water type Nuclear Reactor

Control Rods

To control the fission reaction, rods made of cadmium or boron is suspended between the fuel rods. These rods can be raised or lowered and thus check the reaction by absorbing the right number of neutrons. Hence they are called control rods. When the control rods are completely inserted into the fuel, i.e., inside the reactor all the neutrons are absorbed and the reaction does not start.

These rods are then slowly raised till they absorb the right number of neutrons and thus leaving behind just enough neutrons to sustain the chain reaction. That is, when the control rods absorb two neutrons leaving behind one neutron to bring about further fission reaction we say that the reactor has attained criticality. At this stage number of atoms getting fissioned in one second is constant which means that energy is generated at a constant rate

Moderator

The speed of the neutrons produced during the fission reaction has to be slowed down so that the neutrons are in contact with the fuel rods for sufficient time to bring about fission reaction. This is done by surrounding the fuel rods with graphite or heavy water. The material used to slow down the speed of neutrons is called a moderator. A moderator should absorb as few neutrons as possible and also slow down the neutron 

Coolant

The heat released during the fission reaction is carried away by liquid sodium or heavy water. The coolant enters from the base of the reactor core and leaves at the top. The heat carried away by the coolant is used for producing steam and the coolant is pumped back into the reactor core.

 Shielding

 The whole reactor core is covered with a thick coat of radiation absorbent material like lead and is enclosed in a heavy concrete or steel dome. This is done to protect the workers from dangerous radiations.