Differences between Nuclear Fission and Nuclear Fusion reaction

Nuclear Fission	Nuclear Fusion
Breaking of heavy atom into two or greater smaller ones.	Two or more small atoms combine together to form one large atom.
It does not normally occur in nature.	It occurs in stars, such as the sun.
It does not require a lot of energy to split heavy atom into two small one.	It requires a lot of heat and pressure for the process to happen.
The energy released with the aid of   fission is decrease than the energy released by the fusion reaction.	The energy released by fusion is three to four times greater than the energy released by the fission reaction.
It produces many highly radioactive particles.	Few radioactive particles are produced by fusion reaction.
Critical mass of the substance and high speed neutrons are required.	High density, high temperature environment is required.
The principle of atom bomb is based on nuclear fission.	One class of nuclear weapon is the hydrogen bomb, which uses a fission reaction to trigger a fusion reaction.
Fission is used in nuclear power plants. Uranium is the primary fuel used in power plants.	Fusion is an experimental technology for producing power. Hydrogen isotopes are the primary fuel used in experimental fusion power plants.