This is loosely measured by EROI (energy return on invested). Concrete muddies the water slightly as it's a non-energy ghg emitter. The answer is definitely to

This is loosely measured by EROI (energy return on invested). Concrete muddies the water slightly as it's a non-energy ghg emitter. The answer is definitely to the first part. By what ratio depends on who you ask. The nuclear lobby claims 50-80x. Most other people say it's in the 10-20x range. This is about as good as to somewhat better than wind, but at some point between 2012 and 2030 solar has surpassed/is going to surpass it by whichever measure you choose. Of course once the steel/silicon/composite/etc comes from low carbon sources, then the embodied carbon reduces as well. To the second part (while being profitable), no new nuclear build can be profitable, so no.