To generate a power of 3.2 mega watt, the number of fissions of $U^{235}$ per minute is (Energy released per fission = 200 MeV, 1 eV = $1.6 \times 10^{-19}$ J)

$6 × 10^{18}$

Number of fissions per second $=\frac{\text { Power output }}{\text { Energy released per fission }}$

$=\frac{3.2 \times 10^6}{200 \times 10^6 \times 1.6 \times 10^{-19}}=1 \times 10^{17}$

⇒ Number of fission per minute = $60 \times 10^{17}=6 \times 10^{18}$