Nuclear fission is used to generate electricity, for the destructive component of nuclear weapons and to break down radioactive elements into other elements. In nuclear fission, a radioactive element is broken down into lighter elements. This process releases nuclear energy.
Fission is an efficient way to generate electricity; 7 to 8 million volts of electrical input generates 200 million volts of electrical output. Despite its efficiency, nuclear fission power is not widely deployed due to safety concerns. The risks of nuclear fission power are accidents and radiation leaks while the reactors are in use, as well as hazards associated with disposing of leftover nuclear materials.
While the risks of nuclear reactors are real, it is not possible for a reactor accident to cause the same damage a nuclear weapon does. This is because the radioactive materials in weapons are enriched to provide more power in a single explosion; the nuclear fuel in a power plant is intended to yield energy through many reactions over time. This same enrichment process means that the payload of a nuclear weapon is not a viable source of energy generation.
The opposite of nuclear fission is nuclear fusion. In this process, two lighter elements combine to form a heavier element. Fusion reactions produce a great deal of energy without leaving behind dangerous radioactive waste but are not possible in conditions on Earth. Fusion reactions require high temperatures and pressures, such as those found in the sun.