Definition of Nuclear Reactor

A nuclear reactor is a device in which the nuclear fission reaction is carried out at a controlled rate so that the liberated energy can be utilised for constructive purposes.

Components of a nuclear reactor and its functions

Controlled fission reaction is carried out in a specially designed plant called nuclear reactor or nuclear power plant.

Nuclear reactor consists of:

1. Reactor core
2. Fuel element
3. Moderator
4. Control rods
5. Coolant
6. Protective shield
7. Heat-exchanger
8. Turbine

1. Reactor core

The reactor core is the principal component of a nuclear reactor. It is that part where controlled fission reaction is made to occur and where heat energy is liberated. It consists of an assembly of fuel elements, moderator, coolant and control rods.

2. Fuel element

The commonly used fissionable element which is used in a nuclear reactor is U²³⁵ isotope. Since it is very costly, U²³⁸ enriched with U²³⁵ is used in the reactor. The heat energy and neutrons produced by the fission of U²³⁵ start the chain reaction.

3. Moderator

The substances used to slow down or moderates the neutrons are called moderator. Neutrons slow down by losing energy due to collision with moderator.

The most commonly used moderator is ordinary water. Graphite, heavy water and beryllium are also used as moderators.

The main purpose to use moderator is to slow down the fast fission neutrons.

4. Control rods

The control rods are movable rods which control the rate of fission of  U²³⁵ which are suspended between the fuel rods. Cadmium or boron rods are used as control rods.

These rods absorb the excess neutrons and thus remove them which in turn make the reaction proceed at a steady speed.

Rods deeply inserted in the reactor = reaction is slow (as absorb more neutrons).

Rods pushed outside the reactor = reaction is fast (as absorb less neutrons).

5. Coolant

Coolant is a substance which cools the fuel core by removing the heat produced by fission. In most successful reactors, liquid sodium metal is used as the coolant.

In some reactors, CO₂ gas, ordinary water, heavy water, organic compounds like polyphenyls are used as coolants.

The function of a coolant is to remove the intense heat produced in the reactor.

6. Protective shield

The reactor is enclosed in a thick wall made of steel shields and concrete. These walls stop the nuclear radiations produced in the reactor to go out of the reactor. Thus, it protects the operating personal and environment from harmful radiation.

7. Heat exchanger

It transfers the heat liberated from the reactor core to boil water and gets steam at about 400°kg/cm².

8. Turbine

The steam at high pressure, generated in the heat-exchanger is used to operate a steam turbine which drives the generator to produce electricity.

Read More Topics

Classification of nuclear reactor

Nuclear chain reaction

Types of electrochemical corrosion