another idea that popped to my mind....
there isnt a the
fuel resource, or even anything that is just fuel.
everything you can mine is fuel, of varying efficiency.
so while you can use anything you mine as fuel, not everything is equally efficient.
this could tie in with the ubiquitous frequency mechanic,
every mineral has its own spectrum and reactors have their absorbtion spectra.
the total produced energy depends on how much of the emission spectrum of the fuel lies beneath the absorption spectrum of the reactor.
any spectral parts that "stick out" of the reactors spectrum are wasted
any "empty" parts in the generator spectrum are unused potential
very potent fuels would have very high peaks, but would need a specialised reactor to be utilised fully
less potent fuels would have broader spectra, but could be utilised better by a larger range of reactors
same with reactors, potent ones have high peaks, but relatively low absorbtion in bands other than their specialisation
and generalist generators would have broad spectra, but less total power
this way everything could be used as emergency fuel source, but producing and transporting fuel is still worthwile