Nuclear Energy

Nuclear Energy -
the energy stored in the nucleus of an atom and released through fission, fusion, or radioactivity.In these processes a small amount of mass, equal to the difference in mass before and after the reaction, is converted to energy according to the relationship:

In fission processes, a fissionable nucleus absorbs a neutron, becomes unstable, and splits into two nearly equal nuclei. In fusion processes, two nuclei combine to form a single, heavier nucleus. Fission occurs for very heavy nuclei, while fusion occurs for the lightest nuclei. Nuclear fission was discovered in 1938 by Otto HAHN and Fritz Strassman,and was explained in 1939 by Lise MEITNER and Otto Frisch.

Fission energy can be obtained by bombarding the fissionable isotope URANIUM-235 with slow neutrons in order to split it. Because this reaction releases an average of 2.5 neutrons, a chain reaction is possible, provided at least one neutron per fission is captured by another nucleus and causes a second fission. In an ATOMIC BOMB the number of neutrons producing additional fission is greater than 1, and the reaction increases rapidly to an explosion.

In a NUCLEAR REACTOR, where the chain reaction is controlled, the number must be exactly 1 in order to maintain a steady reaction rate. Uranium-233 and PLUTONIUM-239 can also be used buT must be produced artificially. Moreover, the fuel for fusion reactors, deuterium, is readily available in large amounts. Temperatures greater than 1,000,000°C are required to initiate a fusion, or thermonuclear, reaction. In the HYDROGEN BOMB such temperatures are provided by the detonation of a fission bomb. Sustained, controlled fusion reactions, however, require the containment of the nuclear fuel at extremely high temperatures long enough to allow the reactions to take place. At these temperatures the fuel is a PLASMA, and magnetic fields have been used in attempts to contain this plasma. To produce fusion energy, scientists have also used high-powered laser beams aimed at tiny pellets of fission fuel.

In 1994 U.S. researchers achieved a fusion reaction that lasted about a second and generated about 10.7 million watts, using deuterium and tritium in a magnetically confined plasma. The use of tritium lowers the temperature required and increases the rate of the reaction, but it also increases the release of radioactive neutrons.
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