I can't say if this question is asked in good faith.

Pretty obviously it's better than what the other European countries have been doing.

someone could calculate the savings in CO2 emissions over all the power generated by nuclear energy each year in France, since the power stations were built, vs coal plants (which would have been the alternative at the time)

They replaced oil burning plants in France, when the global oil supply got disrupted.

If France had coal to burn they wouldn't have been burning oil in the first place.

France being about 1% of world's population, any effort won't make a huge dent in a global phenomenon. Also, that 1% pollutes a lot more than the average, so the efforts made on the electricity front are offset by other issues.