Fission Or Fusion :: essays research papers

Fission or Fusion     I think that right now, fission is the only way that we can get more power out of a nuclear reaction than we put in. First, the energy per fissionis very large. In practical units, the fission of 1 kg (2.2 lb) of uranium-235releases 18.7 million kilowatt-hours as heat. Second, the fission processinitiated by the absorption of one neutron in uranium-235 releases about 2.5neutrons, on the average, from the split nuclei. The neutrons released in thismanner quickly cause the fission of 2 more atoms, thereby releasing four ormore additional neutrons and initiating a self-sustaining series of nuclearfissions, or a chain reaction, which results in continuous release of nuclearenergy. Naturally occurring uranium contains only 0.71 percent uranium-235 theremainder is the non-fissile isotope uranium-238. A mass of natural uranium byitself, no consider how large, cannot sustain a chain reaction because only theuranium-235 is easily fissionable. The probability that a fission neutron withan initial energy of about 1 MeV will tow fission is rather low, but can beincreased by a factor of hundreds when the neutron is slowed down through aseries of elastic collisions with come nuclei such as hydrogen, deuterium, orcarbon. This fact is the basis for the design of practical energy-producingfission reactors.     In December 1942 at the University of Chicago, the Italian physicistEnrico Fermi succeeded in producing the prototypal nuclear chain reaction. This wasdone with an arrangement of natural uranium lumps distributed within a largestack of pure graphite, a form of carbon. In Fermis "pile," or nuclear reactor,the graphite moderator served to slow the neutrons.     Nuclear fusion was first achieved on earth in the early 1930s bybombarding a target containing deuterium, the mass-2 isotope of hydrogen, with high-voltage deuterons in a cyclotron. To accelerate the deuteron beam a great deal of energy is required, most of which appeared as heat in the target. As aresult, no net useful energy was produced. In the 1950s the first large-scalebut uncontrolled release of fusion energy was demonstrated in the tests of nuclear weapons by the United States, the USSR, Great Britain, and France.This was such a brief and uncontrolled release that it could not be used for theproduction of electric power.     In the fission reactions I discussed earlier, the neutron, which has noelectric charge, can easily approach and react with a fissionable nucleus ,forexample, uranium-235. In the typical fusion reaction, however, the reactingnuclei both acquit a positive electric charge, and the natural repulsion betweenthem, called Coulomb repulsion, must be overcome before they can join.