# Nuclear reactor principle and working

Nuclear reactor :

Principle :

A nuclear reactor is a device in which nuclear fission can be carried out through a sustained and a controlled chain reaction. It is also called as atomic pile.

Nuclear fuel :

The fissionable material used in the reactor is called nuclear fuel. It generally contains natural uranium, enriched uranium, plutonium and $\textrm{}&space;U^{233}$ in the form of rods sealed in an aluminium cylinder. These cylinders are inserted in the holes drilled in the carbon blocks.

Moderators :

The purpose of the moderator is to slow down the fast-moving neutrons produced as a result of nuclear fission. Some of the suitable materials used as moderators are heavy water, carbon in the form of pure graphite, ordinary water, hydrocarbon plastics etc.

Control Rods :

These materials can absorb the neutrons and control the nuclear chain reaction. They absorb neutrons to such an extent that the chain reaction completely comes to a halt. Cadmium and Boron rods are generally used for this purpose.

Shielding :

Nuclear radiations like $\beta$ and $\gamma$ rays are emitted in addition to neutrons in fission. Suitable shielding such as steel, lead and concrete walls are provided around the reactor to reduce the intensity of radiation.

Coolant :

A large amount of heat is generated in the reactor due to chain reaction. Water or liquid sodium is used to remove the heat. These substances remove heat from the reactor and to keep it at a reasonably low temperature.

#### Working of nuclear reactor :

A single neutron starts fission of $\textrm{}&space;U^{235}$ or the nuclear fuel and the controlled chain reaction take places between of moderators and control rods. The heat generated here is absorbed by a suitable coolant and is carried to the boiler which in turn heat is the ordinary water and produce steam. This steam is made to rotate the steam turbine and thereby drive a generator for the production of electric power.

Uses of Nuclear reactor :

To generate electric power.

To produce nuclear fuel plutonium $\textrm{}&space;Pu^{239}$ and other radioisotopes which have many applications in the fields medicine, industry and research.