Fission, in physics, is the process of splitting of heavy atomic nucleons into two or more fragments. A team of scientists in Chicago, U.S.A., led by the famous physicist Enrico Fermi, was the first to successfully demonstrate controlled nuclear fission. Under his direction, the so-called atomic pile or reactor was established in 1942 to release nuclear energy in a controlled manner. Do you know what are nuclear reactors? The nuclei of uranium are used as the main fuel to induce the split that release a large amount of heat energy. Nuclear reactors are the key units in nuclear power stations in which nuclear energy is produced in a controlled manner where fission takes place. Broadly, there are three types of reactors — thermal, fastbreeder and fusion. In thermal reactors controlled emission of neutrons to the core, by using moderators such as carbon or graphite increases the efficiency of fission process. They surround the neutron-absorbing rods in the reactor, made out of boron to release heat energy. Fast-breeding reactors have no moderators. In these cases, neutrons bring about fission and a mixture of plutonium and uranium oxide is used as fuel. While in operation, uranium is converted into plutonium. The plutonium is extracted and reused later as fuel. It is called fast-breeder because it produces more plutonium than it consumes. Fast-breeder reactors can extract about 60 times the amount of energy extracted from uranium in the thermal reactors. Fusion reactors are not yet in commercial production. Instead of splitting heavy atoms, they force very light atoms together. In all types of nuclear reactors, there is a coolant system in which ordinary water or gas like carbon dioxide is used. The heat produced in the reactors turns the water into steam that drives the generators to produce electricity. The greatest advantage of nuclear energy is that it produces a large amount of useful energy from a very small amount of fuel. It does not produce gases contributing to the ’Greenhouse Effect’. The disadvantage is that the radioactive nuclear waste produced is harmful to human beings and is difficult to store. There is always a risk of accident, which can be dangerous.