Nuclear fission

In nuclear fission, a very heavy nucleus splits into more stable nuclei of intermediate mass. This process releases enormous amounts of energy. Nuclear fission may occur spontaneously or when nuclei are bombarded by particles. When Uranium-235 is bombarded with slow neutrons, a uranium nucleus can capture one of the neutrons, making it very unstable.

Nuclear chain reaction

A chain reaction is a reaction in which the material that starts the reaction is also one of the products and can start another reaction. These neutrons can cause the fission of other Uranium-235 nuclei. Again neutrons are emitted, which can cause the fission of still other Uranium-235 nuclei.

The minimum amount of nuclide that provides the number of neutrons needed to sustain a chain reaction is called the critical mass. Uncontrolled chain reactions give the explosive energy to atomic bombs. Nuclear reactors use controlled-fission chain reactions to produce energy and radioactive nuclides.

Nuclear power plants

Nuclear power plants use energy as heat from nuclear reactors to produce electrical energy. They have five main components: shielding, fuel, control rods, moderator, and coolant. The components, are surrounded by shielding. Shielding is radiation-absorbing material that is used to decrease exposure to radiation, especially gamma rays, from nuclear reactors. Uranium-235 is typically used as the fissile fuel to produce energy as heat, which is absorbed by the coolant. Nuclear power plants can provide competitively priced electricity without emitting greenhouse gases or particulates.

Nuclear fusion

In nuclear fusion, low-mass nuclei combine to form a heavier, more stable nucleus. Nuclear fusion releases even more energy per gram of fuel than nuclear fission. In our sun and stars that are similar to the sun, hydrogen nuclei combine at extremely high temperature and pressure to form a helium nucleus with a loss of mass and release of energy.

Fusion is appealing as an energy source because of the availability of light isotopes on Earth and because fusion products are generally not radioactive. Despite this fact, fusion is not presently used to generate energy. Fusion reactions are therefore also known as thermonuclear reactions.