I'm confused about the fact that in a fission process the masses of the "products" are less than the mass of the "reactants". And in a fusion process the masses of the "products" are less than the masses of the "reactants".
My first question is then: Can I have an atom, fission it, then fusion it, then fission it, etc, etc,. And arrive at no mass and pure energy? I know this is wrong, but I don't know why so.
If you tell me this process is possible then how is it possible to recover a certain isotope of Uranium. I see this as a problem because having less mass in the "products" than in the "reactants" shows that nuclear processes aren't reversible, unless I inject mass in some way.
My second question is: Does the mass difference manifest itself as, e.g., "nucleons weigh less now", or as in "$x$ number of nucleons have disappeared".