Hi there,
It all depends on what you consider as nuclear energy. If you mean the amount of energy (thermal power) freed from the fission process, then the calculation is quite simple. Otherwise, you could also mean the net electrical output of the power plant, which there you would have to go for the effeciency of the power plant.
No matter which process you mean, the number of atoms that fission to create nuclear power is very little (everything in a relative sense), knowing that each fission liberates [tex]\sim 200MeV[/tex] of energy.
Now to give you a real answer to your question. In Europe (and I believe it's the same in America), the goal of a nuclear power plant is to produce a maximum of [tex]50\frac{m^3}{yr}[/tex] of radioactive waste for every [tex]1000kW[/tex] of net electrical power output.