Nuclear power is derived from the transformation of a mass of matter. This phenomenon occurs as a result of fission or fusion. The fission of the atom is the division of its nucleus, which happens to bombard it with neutrons, this procedure results in a huge release of energy. The nuclear power reactors produce energy by fission. Fusion is the reverse reaction, because it combines two atomic nuclei to form a larger one. Like fission, it releases a large amount of heat. But unlike the first, yet could not be controlled by man because reactors to generate it is been found experimentally. The fusion process is one that is unleashed when a bomb explodes.
The fuel that is most often used in nuclear plants is uranium 235 (U-235), an isotope of the element uranium.
If by accident a nuclear reactor released radiation, pollutes the environment to the point of causing the death of living beings. So nuclear power plants are in remote locations, their constructions are special to protect the surrounding environment and have many security measures.