![]() Typically, when uranium 235 nucleus undergoes fission, the nucleus splits into two smaller nuclei (triple fission can also rarely occur), along with a few neutrons (the average is 2.43 neutrons per fission by thermal neutron) and release of energy in the form of heat and gamma rays. ![]() About 85% of all absorption reactions result in fission. Therefore about 15% of all absorption reactions result in radiative capture of neutron. The cross-section for radiative capture for thermal neutrons is about 99 barns (for 0.0253 eV neutron). Most of absorption reactions result in fission reaction, but a minority results in radiative capture forming 236U. For fast neutrons its fission cross-section is on the order of barns. Uranium 235 is a fissile isotope and its fission cross-section for thermal neutrons is about 585 barns (for 0.0253 eV neutron). Since a typical fuel cycle takes about 320 days (12-month fuel cycle), the annual fuel consumption is about:ģ.14 kg/day x 320 days = 1 005 kg of 235U Since each atom of 235U has a mass of 235u x 1.66 x 10 -27 kg/u = 3.9 x 10 -25 kg, the daily consumption of a reactor is:ĩ.33 x 10 19 fissions/sec x 3.9 x 10 -25 kg x 86400 sec/day = 3.14 kg/dayįor comparison, a 1000 MWe coal-fired power plant burns about 10 000 tons (about 10 million kg) of coal per day. Since we know that each second we need 3000 MJ of energy, the required reaction rate can be determined directly as: The average recoverable energy per 235U fission is about E r = 200.7 MeV/fission. For the reactor of power of 3000MW th, determine the consumption of 235U that must undergo fission each day to provide this thermal power. A typical thermal reactor contains about 100 tons of uranium with an average enrichment of 2% (do not confuse it with the enrichment of the fresh fuel, that is about 4%).
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