Fusion energy is released when two light nuclei combine to form a single heavier one (nuclear fusion reaction). Fusion energy-based power generation (fusion power plant) uses the energy generated when deuterium and tritium combine to form helium. Fusion energy is released when two light nuclei combine to form a single heavier one (nuclear fusion reaction). Fusion energy-based power generation (fusion power plant) uses the energy generated when deuterium and tritium combine to form helium. Plasma Physics Phys.org – latest science and technology news stories