Nuclear Energy: Nuclear Energy is energy derived from nuclear reactions either by the fission of heavy nuclei into lighter ones or by fusion of light nuclei into heavier ones. In principles, the binding energy of a system of particles forming an atomic nucleus is nuclear energy. It results from changes in the nucleus of atoms. Scientists and engineers have found many uses for this energy, especially in producing electricity. But they do not yet have the ability to make full use of nuclear power. If nuclear energy were fully developed, it could supply all the world’s electricity for millions of years. A nucleus make up most of the mass of every atom and this nucleus is held together by an extremely powerful force. A huge amount of energy is concentrated in the nucleus because of this force. Scientists first released nuclear energy on a large scale at the University of Chicago in 1942, three years after World War II began. This achievement led to the development of the atomic bomb. It is since 1945 that nuclear energy has been put to peaceful uses such as production of electricity. Einstein pointed out that if the energy of a body changes by an amount E, its mass changes by an amount m given by the equation, E = mc2. The implication is that any reaction in which there is a decrease of mass, called a mass defect, is a source of energy. The energy and mass changes in physical and chemical changes are very small; those in some nuclear reactions, such as radioactive decay, are millions of times greater. The sum of the masses of the products of a nuclear reaction is less than the sum of the masses of the reacting particles. This lost mass is converted into energy.