How difficult would it be to use nuclear power to make synthetic hydrocarbons?
One could get (much) higher efficiency by using the heat from a nuclear power plant directly (never producing electricity) but I guess that would have to be a completely custom design.
If you have spare electricity (from any source), it's easy. Just capture some CO2 and react it with hydrogen with specific catalysts and at a high pressure. You can get methanol directly this way.
It's more expensive than fossil fuels at the current prices, so nobody cares.