Complex sentence: This is because the amount of revenue generated from a nuclear powerplant with a given thermal reactor power is proportional to the efficiency of the power conversion; that is, how much heat is actually converted to electricity to feed into the grid.
Split into simpler sentences: This is because the amount of revenue generated from a nuclear powerplant with a given thermal reactor power is proportional to the efficiency of the power conversion. That is, how much heat is actually converted to electricity to feed into the grid.