[...]
1) Nanotechnology is hypothetical. If sustainable autoreplication by means
of machine-phase processes is impossible, we're stuck with solvated
(bio)polymer autoreplicator-based form of molecular manufacturing
(which is almost certainly possible), while significantly less powerful.
2) If nanotechnology _can_ work, it can do very little to increase safety
of nuclear processes. At best, you can expect a near 100% rate of
waste isotope reclaiming. Otoh rad damage seems to be incompatible with
'living' nano devices, and will certainly drastically reduce lifetimes
of nonliving ones.
3) There are alcohol-metabolizing fuel cells out there. If it is just the
heat you are after, there also portable catalytic ovens.
ciao,
'gene