Purity isn’t really important. We need to decarbonise as much of our energy grid as we can as quickly as possible since cumulative carbon emissions matter.

Does it make sense for France to replace their existing nuclear power plants with new ones? Possibly, since the existing power generation is clean so there is less rush.

Does spending the effort on building new nuclear outweigh the opportunity costs for others? Given new nuclear plants in Europe are taking 20 years to build I have strong doubts. It seems absolutely clear that wind/solar + batteries can get most countries to 80-90% clean energy faster and at lower cost. And after that happens nuclear seems a very awkward addition to the mix since it is not cost effective to run when it’s power is only needed 10-20% of the time.