Question

If the energy released in the fission of one uranium nucleus is 200 MeV, then the number of fissions per second required to produce 20 MW is:

• A. $25 \times 10^{17}$
• B. $6.25 \times 10^{17}$
• C. $12.5 \times 10^{17}$
• D. $3.125 \times 10^{17}$

Hint:

Convert MeV → Joules: $1 \text{ MeV} = 1.6 \times 10^{-13}$ J.
Number of fissions = Power / Energy per fission.
Check units carefully: W = J/s.
Always round to match option format.

Answer 1

The Correct Option is B

• Energy per fission: $E = 200$ MeV = $200 \times 1.6 \times 10^{-13}$ J = $3.2 \times 10^{-11}$ J.
• Required power $P = 20$ MW = $2 \times 10^7$ W = $2 \times 10^7$ J/s.
• Number of fissions per second: $n = P / E = 2 \times 10^7 / 3.2 \times 10^{-11} \approx 6.25 \times 10^{17}$.
• Hence correct answer = $6.25 \times 10^{17$}.