The energy released during a nuclear reaction is called nuclear energy.
Nuclear energy can be obtained by two types of nuclear reactions:
Nuclear fission, and
In a process called nuclear fission, the nucleus of a heavy atom, when bombarded with low energy neutrons, gets split into lighter atoms with the release of tremendous amount of energy.
This can be harnessed to generate electricity. This is called nuclear energy.
The process in which the heavy nucleus of a radioactive atom (such as uranium, plutonium or thorium) splits up into smaller nuclei when bombarded with low energy neutrons, is called nuclear fission.
A tremendous amount of energy is produced in the nuclear fission process.
When uranium-235 atoms are bombarded with slow moving neutrons, the heavy uranium nucleus breaks up to produce two medium –weight atoms, barium-139 and krypton-94, with the emission of 3 neutrons. A tremendous amount of energy is produced during the fission of uranium.
This fission reaction can be represented in the form of a nuclear equation as:
The energy produced during nuclear fission reactions is used for generating electricity at nuclear power plants.
When all the neutrons produced during fission of uranium-235 are allowed to cause further fission, then so much energy is produced in a very short time that it cannot be controlled and leads to an explosion called atom bomb.
We can, however, control a nuclear fission reaction by using control rods made of boron.
Boron has a property that it can absorb neutrons.
So, when a nuclear fission reaction is carried out in the presence of boron rods, the excess neutrons produced during successive fissions of uranium-235 atoms are absorbed by boron rods and hence not available to cause further fission.
Due to this a controlled fission reaction of uranium-235 takes place liberating heat energy at a slow, steady and manageable rate which can be used for generating electricity at a nuclear power plant.
Nuclear fusion reactions of hydrogen are the source of sun’s energy. Other stars also obtain their energy from the nuclear fusion reactions of hydrogen.
An advantage of nuclear fusion reactions over nuclear fission for producing electricity is that the amount of energy released in a fusion reaction is much more than that liberated in a fission reaction.
ADVANTAGES OF NUCLEAR ENERGY
It produces a large amount of useful energy from a very small amount of a nuclear fuel (like uranium-235).
Once the nuclear fuel (like uranium-235) is loaded into the reactor, the nuclear power plant can go on producing electricity for two to three years at a stretch. Thus, no need for putting in nuclear fuel again and again.
It does not produce gases like carbon dioxide which contribute to greenhouse effect or sulphur dioxide which causes acid rain.
DISADVANTAGES OF NUCLEAR ENERGY
The waste products of nuclear fission reaction (produced at nuclear power plants) are radioactive which keep on emitting harmful nuclear radiations for thousands of years.
So, it is very difficult to store or dispose of nuclear wastes safely.
Improper nuclear waste storage or disposal can pollute the environment.
There is the risk of accidents in nuclear reactors (especially the old nuclear reactors).
Such accidents lead to the leakage of radioactive materials which can cause serious damage to the plants, animals (including human beings) and the environment.
The high cost of installation of nuclear power plants and the limited availability of uranium fuel make the large scale use of nuclear energy prohibitive.