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When fission reaction occurs tremendous amount of energy is liberated. While some energy appears as radiation, most of the energy is in the form of kinetic energy of the fragments. The fragments dissipates most of their kinetic energy as heat, which can be used to boil water and the resulting steam can be used to turn turbines to generate electricity. The following are the stages in the working of a power reactor. |
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The percentage of  U in the naturally occurring uranium is only about 0.7%. In a nuclear reactor, the percentage of U-235 is increased by a process called enrichment . This is usually achieved either by gaseous diffusion or by a centrifuge. In the diffusion process, natural uranium, which is first converted to gaseous uranium hexafluorid (UF  ) is passed through a series of semi-porus membranes which permit passage of the gas that contains the lighter U-235 but not the component containing the heavier isotope U-238. The technique is somewhat inefficient and it requires several stages of diffusion barriers to achieve the desired concentration of about 4 to 5% of U-235. In the centrifuge technique the natural UF is spun at high speed which separates the heavier and the lighter components as they are subjected to different centrifugal forces. Newer techniques of enrichment using lasers are now available. |
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The core is the centre of the reactor which contains the fuel which is used in running the reactor. Control rods to absorb excess neutrons are introduced into the core. Usually a heavy steel vessel surrounds the core. A reactor which produces enough neutrons to sustain controlled chain reaction is called critical . Criticality not only depends on the nuclear reaction producing neutrons but also depends on availability of enough uranium which must absorb a released neutron. Enrichment of the fuel ensures this for a reactor. The mass of the fissile material required to sustain chain reaction is said to be critical mass . If a reactor cannot sustain chain reaction, it is called sub-critical. On the other hand if the chain reaction proceeds uncontrolled, as in an atom bomb, the reactor is called supercritical . |
