Question

Why does it take less binding force to hold the two atoms that a uranium atom has split into?

Answer 1

I think this

When a Uranium atom splits into two there is a little bit of mass left that is equivalent to a big amount of energy (e=mc^2) and it explodes in fission

It takes less binding force to keep the two atoms together than it does with the original atom

Answer 2

Binding energy is the net energy that is the result of the balance with the strong force and the repulsiveforce, and this is the amount of energy that holds the nucleus together.