How Nuclear Reactor Works

Nuclear Reactor

A device containing fissionable material in sufficient quantity and so arranged as to be capable of maintaining a controlled, self-sustaining nuclear fission chain reaction is known as a nuclear reactor.

Principle

The fact that the fission process releases several neutrons making possible a series of chain of self-sustained neutron induced fission, i.e, one neutron from a fission event triggers the fission of the another nucleus and so on. The environment of the fissioning nuclei is controlled in such a way that one and only one neutron triggers another event. Thus controlled fission chain reaction is the principle of the nuclear reactor.

Construction

• Core

It is the main part of the nuclear reactor. Here the fuel is kept in the shape of cylindrical tubes. Uranium was used as a fuel in the elementary reactors but know a days plutonium is also used as fuel in the nuclear reactor.

• Moderator 

The fuel rods are placed in a substance of small atomic weight, such as water, heavy water, carbon, and hydrocarbons, etc. These substances are called moderators. The function of these moderators is to slow down the speed of the neutrons produced during the fission process and to direct them towards the fuel. The neutrons produced in the fission reaction are very fast and energetic and are not suitable for producing fission in reactor fuel like uranium. For this purpose, slow neutrons are more useful. To achieve this moderator are used.

• Absorbing Rods

There are neutron absorbing rods which control the number of neutrons which produce nuclear fission reaction. For this purpose, cadmium or boron materials are used. These materials have a property of absorbing fast moving neutrons. These control rods are moved in or out of the reactor core to control the neutrons that can initiate a further fission reaction. In this way, the speed of the chain reaction is kept under control. In the case of emergency or for repair purposes control rods are allow to fall back into the reactor and thus stop the chain reaction and shut down the reactor.

Heat Exchanger

Due to controlled fission chain, reaction in the core of the reactor heat is produced. The temperature of the core, therefore, rise to about 1200 C. To produce steam from this heat, it is transported to a heat exchanger with the help of water, heavy water or any other liquid under great pressure. In the heat exchanger, this heat is used to produce steam from ordinary water. The steam is then used to run the turbine which in turn rotates the generator to produce electricity. The temperature of steam coming out of the turbine is about 300 C. This is further cooled to convert it into the water again.