If there's enough waste heat from a reactor to do something with it seems like making electricity with it is the thing to do since that's what the reactor is there for. Bleeding off some of the available heat to make hydrogen instead of electric isn't really saving anything.
Cogeneration is pretty common and extremely efficient. In a rankine cycle engine, all the energy than can be converted to electricity is, but the "spent" steam coming through the back of the turbines is still extremely hot and must be cooled and condensed to reduce the entropy levels. In some plants, they just use cooling towers. Where they can, though, the steam is used for building heat, as it's too cold for use as much else, but works great as a heater; extremely high efficiencies are gained from electric/steam heat cogeneration. If some of this waste heat can be used for processing oil shale into oil, or water into hydrogen, it's essentially free energy.
