In a nuclear reactor U235 undergoes fission liberating 200MeV of energy. The reactor has a 10% efficiency and produces 1000MW power. If the reactor is to function for 10 years, find the total mass of uranium needed.
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Total energy produced by the reactor in time t=10 years,
Efficiency=output energyinput energy
⇒ Input energy caused by fission =output energyefficiency=3.15×1017(10/100)=3.15×1018J
Energy produced by 1 fission of 235U=200MeV=200×1.6×10−13J=3.2×10−11J
Therefore, number of fissions required =Total energyEnergy per fission=3.15×10183.2×10−11≈9.8×1028