You're forgetting the mass-energy equivalence, E = mc^2. Both fission and fusion are elaborate ways of converting a small fraction of the mass of the fuel to e

You're forgetting the mass-energy equivalence, E = mc^2. Both fission and fusion are elaborate ways of converting a small fraction of the mass of the fuel to energy. Also, "you can't get more than you put in" applies to closed systems. Reactors are open systems.