Atoms are the particles that make up all objects in the universe. Atoms consist of neutrons, protons, and electrons. In nuclear fusion, energy is released when the nuclei of atoms are combined or fused together. This is how the sun produces energy. In nuclear fission, energy is released when the nuclei of atoms are split apart.
Nuclear fission is the only method currently used by nuclear plants to generate electricity.
The fuel most widely used by nuclear power plants for fissioning is uranium. Uranium is the heaviest of the 92 naturally occurring elements and is classified as a metal. It is also one of the few elements that is easily fissioned. Uranium was formed when the earth was created and is found in rocks all over the world. Rocks that contain a lot of uranium are called uranium ore, or pitch-blende.