In case you are thinking of asking...
...Yes! The Laws of Thermodynamics also apply to the
potential nuclear-energy in matter; E = MC^2.
You cannot get more energy out of a "system" than you put into it.
How does that apply to the immense energy stored in nucear-fuel?
EXAMPLE: A graphite nuclear-reactor, and its control-rods, are the "SYSTEM". The ENERGY [stored] is contained in the [example]
uranium rods.
You cannot get more energy out of that reactor "system" than you
put in [the available energy in the uranium rods].