The discovery and the development of nuclear energy technology, has been a breakthrough in science. Nuclear power is a sustainable source of energy and it provides about 13-14% of the world’s electricity. The US, France and Japan together account for 50% of the world’s nuclear generated electricity. Commercial production of nuclear power started in the mid 1950s. While it is a clean source of energy with no carbon emissions, nuclear power may also pose threats to people and environment. Thus, there is an ongoing debate about the large scale use of nuclear power.

Nuclear energy or atomic energy is the energy released by the nucleus of an atom when it undergoes fission, fusion or radioactive decay. The nucleus of an atom is made up of protons and neutrons and they are tightly bound together with a force, which is 10³⁹ times stronger compared to gravitational force. Nuclear fission refers to a process in which the nucleus of an atom splits into smaller parts, often with the production of free neutrons or gamma rays and release of large amount of energy. Gamma rays are the most energetic form of light and are usually produced by the hottest regions of space.

Nuclear Fission

Nuclear power is produced by sustained nuclear fission. The fission process is initiated by an impact with a slow neutron of energy about 1electronVolt. A chain nuclear reaction can be sustained if at least one neutron from each fission reaction strikes another nucleus and initiates another fission. The chemical element isotopes that can sustain chain reactions are used as nuclear fuels and one of the most common nuclear fuels is U-235, which is uranium with an atomic number 235 (92 protons + 143 neutrons). When uranium undergoes fission,

the sum of the masses of the daughter nuclei on the right side is less than the sum of masses on the left side. This difference in mass before and after appears as the fission energy. The energy release is based on the famous Mass-Energy equivalence relation by Einstein, E = mc², where E is the energy released for a mass m, and c = 3×10⁸ m/s, is the velocity of light. More precisely, 0.1% of the mass of the uranium-235 nucleus appears as the fission energy, which is about 200×10⁶ electron Volts. This typically comes as the kinetic energy of the daughter nuclei and other fission fragments. In nuclear reactors, this energy is converted into heat as the particles collide with the atoms that make up the reactor, usually in the reactor core or it’s shielding. This heat is used to produce steam by boiling water, which in turn is used to turn a turbine and run the generator to produce electricity. In nuclear reactors, the fission fragment’s kinetic energy remains as low-temperature heat, therefore causes little or no ionization. Control rods are used in reactors to capture extra neutrons produced in the fission processes to maintain the fission as a controlled chain reaction. However, in an atomic bomb, the chain reaction is uncontrolled and it may raise the temperature of the bomb core to a 100 million Kelvin and cause secondary emission of soft X-rays, which convert some of this energy to ionizing radiation.

The amount of energy released by the nuclear fission of a given mass of uranium is about 2,500,000 times greater than that released by the combustion of an equal mass of carbon. The energy equivalent of one kilogram of mass could supply the needs of about 180,000 for one year, or the needs of a US city of one million for over two months! So for a country like India, where per capita energy consumption is considerably lower, nuclear power can be a cheap and environment-friendly substitute.

As far as nuclear fusion is concerned, the amount of energy released by nuclear fusion of a given mass of deuterium is about 400 times greater that that released by the nuclear fission of an equal mass of uranium. Current technology uses mainly nuclear fission as the source of nuclear energy, since nuclear fusion of light elements has yet to be harnessed for electricity generation.