If 200MeV energy is released per fission of U235 nuclei. Find the mass of U235 consumed (in mg) per day in a reactor of power 1MW assuming its efficiency is 80%.

Energy produced in one day =106×24×60×60 joule η=0.8= output energy  input energy =106×24×60×60 input energy  So input energy =106×24×60×600.8=10.8×1010 J Energy released in one fission =200×106×1.6×10−19=3.2×10−11 J No. of fissions per day =10.8×10103.2×10−11=3.375×1021 Mass of U235 consumed per day = no. of nuclei disintegrating per day × mass of U235=3.375×1021×235×1.67×10−27=1.324mg