Nuclear energy is energy released by reactions involving the nuclei of atoms. It can be from fission of the atoms or fusion.
Nuclear energy is energy released by reactions involving the nuclei of atoms. There is a difference between fission energy produced in nuclear power stations, released when the nucleus of a heavy atom splits into two or more lighter nuclei, and fusion energy released by the merging of light atoms, a technique which cannot yet be controlled on an industrial scale.
A natural power reactor existed naturally in OKLO, Gabon (reference: French Atomic Energy Commission).