"While most nuclear power plants in operation as of early 2000's were already designed with strong load following capabilities, they might have not been used as such for purely economic reasons: nuclear power generation is composed almost entirely of fixed and sunk costs so lowering the power output doesn't significantly reduce generating costs, so it is more effective to run them at full power most of the time.[10][11]"
https://en.wikipedia.org/wiki/Load-following_power_plant
France using Nuclear Power for load following is more a signal that they'd misjudged and significantly overbuilt nuclear capacity, not that it's a good idea. EDF has overwhemling financial problems and went spectacularly bankrupt in large part because unlike with, say, solar and wind - that spare capacity is very, very, very expensive.
tl;dr - as I said before, you technically can do it but it's absurdly expensive and just not worth it.