Nuclear fission is the division dl nucleus of an atom by its bombardment with neutrons. On the contrary, nuclear fusion is the process of joining of two atomic nuclei collide and fuse to form heavier atomic nuclei. Nuclear fission is carried out in reactors using natural uranium as fuel or enriched. This reaction generates a huge amount of energy. For example, the fission of one kilogram of uranium releases 18.7 million kilowatt hours. On the other hand, frees fission neutrons, colliding with other nuclei, causing further fissions, creating what is called a chain reaction. The reactors must be cooled during fission because of the high heat it generates. This uses various elements such as light-water or heavy water. The first is pressurized tap water is passed through the reactor core. Another coolant, developed in Canada, is the deuterium dioxide, generally known as heavy water.
Nuclear Fusion:
The Sun is composed mostly of hydrogen. At its center, huge temperatures and pressures fuse the nuclei of atoms to form the nucleus of a helium atom. Released large amounts of energy that emerge from the Sun mainly as heat and light. You can also release a neutron to continue the reaction. As the nuclei are fused together or, in this process is called nuclear fusion.
Nuclear fission:
A neutron destroy the nucleus of an atom of uranium. The core is divided into two parts. This releases large amounts of heat, and also two neutrons which move very quickly, crashing against more uranium nuclei, and so on in a chain reaction. The division of the nucleus is called nuclear fission. During this process, pieces of matter cease to exist and are transformed into vast amounts of energy.
In the case of fission nuclear bulges caused by a reaction can not be controlled. In contrast, in the reactors is controlled through the use of substances called moderators, for example, graphite.