nuclear fission 
noun [mass noun]
A nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy.It is irresponsible for scientists to suggest that the large tabulated total energy content of biomass, oil shale, oil sands, heavy oil, and nuclear fission can cover world energy demand for the longterm future....
- Well, we've got these different possible techniques - there's nuclear fusion, nuclear fission, solar power, tidal power and so on.
- The simple atom bomb owed its explosive power to the energy released by nuclear fission, or fusion.