Fission energy is the thermal and radiative energy released during nuclear fission, a nuclear reaction in which a heavy atomic nucleus splits into lighter nuclei, releasing a significant amount of energy and neutrons. As an academic concept and field of research, it investigates the physics of the fission process, the dynamics and control of self-sustaining nuclear chain reactions, the properties and behavior of fissile and fertile materials, the safe management of radioactive byproducts, and the engineering principles for harnessing this energy, primarily for electricity generation in nuclear reactors.