Nuclear energy is a kind of energy that comes from special atoms called atoms. The nucleus of an atom is very, very small. When the nuclei of certain atoms are split in a process called fission, they release a large amount of energy. This energy can be used to create electricity in special plants called nuclear power plants. In a nuclear power plant, the energy released by fission is used to heat up water and turn it into steam, which is used to turn big fans called turbines. The turbines can then create electricity for people to use.