Fission and Fusion 

 Nuclear Fission

Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into smaller parts (lighter nuclei), often producing free neutrons and photons as well. Fission of heavy elements is an exothermic reaction which can release large amounts of energy both as electromagnetic radiation and as kinetic energy of the fragments (heating the bulk material where fission takes place). For fission to produce energy, the total binding energy of the resulting elements has to be higher than that of the starting element.

 Nuclear Fusion

       Nuclear fusion is the process by which two or more atomic nuclei join together, or "fuse", to form a single heavier nucleus. This is usually accompanied by the release or absorption of large quantities of energy. Large-scale thermonuclear fusion processes, involving many nuclei fusing at once, must occur in matter at very high densities and temperatures (like in stars going nova).

       The fusion of two nuclei with lower masses than iron (which, along with nickel, has the largest binding energy per nucleon) generally releases energy while the fusion of nuclei heavier than iron absorbs energy. The opposite is true for the reverse process, nuclear fission.

Nuclear Reactors 

 A nuclear reactor produces and controls the release of energy from splitting the atoms of certain elements. In a nuclear power reactor, the energy released is used as heat to make steam to generate electricity. (In a research reactor the main purpose is to utilize the actual neutrons produced in the core. In most naval reactors, steam drives a turbine directly for propulsion.)

The principles for using nuclear power to produce electricity are the same for most types of reactor. The energy released from continuous fission of the atoms of the fuel is harnessed as heat in either a gas or water, and is used to produce steam. The steam is used to drive the turbines which produce electricity (as in most fossil fuel plants).

Fission =  The splitting of the atom, the most common form of nuclear reactions (every atom is trying to decay to Iron, fission is taking a large atom and make it a smaller atom)

Fusion = Combine atoms together, not as common as fission because the atom is getting large.

For Nuclear Reactors

 There are currently no nuclear power plants that use Fusion.... fusion reactors are a sort of holy grail for nuclear power plants, over a billion of dollars have been spent trying to create a fusion power plant, the largest of these projects is the tokamak).  Why we (as scientist) obsessed about fusion power.

                  -  Safety, the fusion reactor is supposed to not produce radioactive waste

                  -  Cheaper, fuel for the fusion reactors is plentiful, with salt water being the preferred source.

Nuclear Power: