Definitely nuclear. But you need to have a plant size that is right. That is, you shouldn't have grid scale reactors for this, as the power source has to be wit

Definitely nuclear. But you need to have a plant size that is right. That is, you shouldn't have grid scale reactors for this, as the power source has to be within a couple of miles of the factory/process location. So the size of the reactor has to be on the order of 10 to 50 mW. And you need a good method for getting the heat there - probably a molten salt intermediate heat transfer system... There are a couple of nuclear companies doing this seriously.