The atoms of a few elements such as radium and uranium act as natural source of energy. Atoms of these elements spontaneously undergo changes in which the nucleus of the atom disintegrates.
A large amount of energy is stored in the nucleus of every atom. The energy stored in the nuclei of atoms can be released by breaking a heavy nucleus such as uranium into two lighter nuclei. The splitting of the nucleus of an atom into fragments that are roughly equal in mass with the release of energy is called nuclear fission.
A small amount of each fission mass vanishes, in releasing huge amounts of energy as per E = mc2, where m is the missing mass and c is the velocity of light.
When a free neutron strikes a Uranium (235) nucleus at a correct speed, it gets absorbed. A Uranium (235) nucleus on absorbing a neutron becomes highly unstable and splits into nuclei of smaller atoms releasing huge amount of energy in the process. During this process, a few neutrons are also released. These neutrons split other nuclei of the Uranium (235). The reaction continues rapidly and is known as the chain reaction.
In this process, a large amount of energy is released. This energy is used for boiling water till it becomes steam. Steam so generated is used to drive a turbine which helps in generating electrical energy.
The fission reaction is carried out in a controlled and regulated manner in nuclear reactors. Else, they would explode like bombs with an uncontrolled chain reaction. In order to control the fission reaction, some of the neutrons released by the reaction are absorbed by the control rods made of boron or cadmium.
If the nuclear chain reaction is uncontrolled, all the nuclei in the piece of uranium split in a fraction of a second and this may cause a devastating explosion - such as those of the atom bombs dropped on Hiroshima and Nagasaki in Japan by America.
Energy is also produced when two light nuclei such as deuterium (heavy hydrogen) combine together to form a heavy nucleus. A process in which the nuclei of light atoms are combined to form a nucleus of a heavier atom with the release of energy is called nuclear fusion.
Nuclear fusion requires very high temperature, of the order of 4 million degree Celsius (4000000 °C). This is the mechanism through which energy is produced in stars, including the Sun. This reaction has been used to make hydrogen bombs.
Nuclear energy is non-renewable as the uranium fuels used are consumed in the fission reaction and hence are non replenishable. Nevertheless, nuclear energy has many uses:
On one side nuclear energy seems to be an alternative to fossil fuels, on the other, it can also be hazardous. Nuclear radiations and the radioactive wastes are two major hazards that accompany production of nuclear energy.
In the process of producing nuclear energy, harmful nuclear radiations may get accidentally leaked or released which can penetrate human bodies and cause irreparable damage to cells. For preventing this from happening, nuclear reactors are covered with a thick shell of radiation absorbent material such as lead.
1. However, accidental releases of these extremely harmful radiations into the environment pose a constant threat to those inhabiting the surrounding areas. The two major accidents in nuclear power plants - one at the Three Mile Island (U.S.A.) and the other at Chernobyl (the then Soviet Union). The immediate devastation caused in these two accidents through the release of harmful nuclear radiations was huge and its full extent is yet to be assessed.
2. Another hazard relate to the problems involving disposal of harmful radiant wastes mainly spent fuels produced in the fission process. During nuclear reactions, a number of harmful substances capable of emitting nuclear radiations are generated. These substances are called nuclear wastes. Presently, most of the nuclear waste generated in nuclear power plants is simply being stored underground in strong lead containers.