Nuclear Power is produced when a nucleus absorbs a neutron and splits into two lighter nuclei. This releases enormous amounts of energy which in turn produces heat. In fact the Uranium, which is the most common element used to produce nuclear power today, has an energy content about 3 million times greater than that of fossil fuel. Consequently 1 gram of Uranium is equivalent to approximately 3 tones of coal. Nuclear reactors harness the heat which is produced from the energy released when the atom splits and convert it into electrical energy. Current Nuclear Power plants require the the use of the rare Uranium isotope U-235 and consequently only use one fifth of the total energy content. Next generation reactors forecast to be available in 2020's will use all the energy in Uranium or the more abundant Thorium.
Nuclear reactors produce vast amounts of radioactive waste including large amounts of very long lived radioactive atoms. These radioactive particles are a product of the splitting of the atom. We are constantly exposed to low-level radioactivity from cosmic rays from outer space and naturally occurring radioactive isotopes which in general do not cause any harm. However at high levels of exposure there are numerous biological effects of radiation. These cause cell death, cancer induction and can cause genetic damage. The waste of nuclear reactors is highly radioactive and long lived, and as a consequence must be isolated from humans for around 100,000 years. The current consensus is that Nuclear Waste should be disposed in secure containers and placed deep underground. Future technology promises to turn the long lived radioactive particles into shorter lived