Why is energy released during nuclear fission?

[Boomka]

When a massive nucleus splits, it forms two smaller fragments. For Uranium, we have A=235, and the typical fragments are A=140 and A=95. Looking at the binding energy curve, these two fragments have greater binding energy per nucleon than the original uranium nucleus. Hence, if the uranium nucleus splits in this way, energy will be released.

I think i do understand why the binding energy is higher for the fragments, however I don't understand why energy is released.

Could someone please explain in simple language.

Thank you

 

[Meir Achuz]

Binding energy is not what determines the available energy.
The available energy/c^2 equals the nuclear mass of Uranium minus the masses of the two fragments and the neutrons released.

 

[Bill_K]

Boomka, the mass-energy of a nucleus is approximately A (Mc² - B) where A is the atomic weight, M is the mass of a nucleon and B is the binding energy per nucleon. When a nucleus fissions, the total mass-energy of the two daughter nuclei will be A₁ (Mc² - B₁) + A₂ (Mc² - B₂). Ignoring the few neutrons that escape ("fast neutrons"), A = A₁ + A₂. We still have the same number of nucleons, so the Mc²'s on both sides cancel. And since B₁ ≈ B₂, we find that the energy released will be A (B₁ - B). As you point out, B₁ > B, so the energy released is positive.