The energy liberated per nuclear fission is 200 MeV. If 1020 fissions occur per second the amount of power produced will be :
P=Etott= 1020 × 200 MeV1 = 2 × 1022 MeV/S = 2 × 1022 × 106 × 1.6 × 10−19 J/S = 32 × 108 W