21.7+Nuclear+Fission

=Chapter 21 = =Nuclear Fission =

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Exothermic chemical processes always release energy in the form of heat to their surroundings. Nuclear fission and fusion are both nuclear reactions that are highly exothermic in nature. Fission specifically is the release of energy through the splitting of heavy atomic nuclei, which occurs when fission occurs when nuclei of heavy atoms are struck by slow moving neutrons. The products of fission vary greatly, many of which are dangerously radioactive for inhabited biological environments. ======



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Fission occurs in a manner referred to as a chain reaction, in which neutrons released from the splitting of nuclei cause other nuclei to undergo fission. The amount of fissionable material large enough to maintain such a sustained reaction process is known as its critical mass. If the material is of subcritical mass a chain reaction may not occur, but if it is of supercritical mass, rapid multiplication of the number of fissions taking place simultaneously may result in a nuclear explosion. ======

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As nuclear fission releases large amounts of energy, this energy can be captured and utilized as a source of power. Uranium-235 is commonly enriched and used as the fissionable substance in these nuclear reactors. Control rods regulate the flow of neutrons into the reactor core, maintaining a self- sustaining reactor and preventing any possible over- heating that may occur. The reactor core also contains a neutron- emitting source, a moderator, and a cooling liquid that passes through the reactor to carry away any energy produced in the form of heat. The excess heat of the cooling liquid is then used to generate high pressure steam in a heat exchanger. The steam is then used to drive a series of turbines connected to an electrical generator which transports electrical energy away from the reactor site. Recondensing the steam using additional cooling water requires such nuclear power plants to be located near streams or rivers to provide extra water for cooling purposes (Gas based cooling systems are more recent solution to the limitation on where such plants must be located). ======



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Radioactivity of many byproducts of nuclear fission present an environmental bio-hazard which must be overcome if nuclear power is to become a major player amongst the various alternative energy sources currently on trial. Current disposal methods of nuclear wastes require burial of radioactive materials with long half- lives deep underground for many years. Although initially developed for the purpose of weaponry, nuclear fission has an important future in science and energy production. ======

Additional Links

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References

 * 1) Brown, Theodore L., H. Eugene Lemay Jr., Bruce E. Bursten, and Catherine J. Murphy. "21.7 Nuclear Fission." Chemistry: The Central Science. AP ed. Upper Saddle River, NJ: Pearson Prentice Hall, 2009. Print.
 * 2) "Fission Reactors." Welcome to Waterloo Science | UW Faculty of Science. Web. 23 Mar. 2011. .