It's not an easy thing to retrofit into an existing plant though: first of all France isn't the US and even though it's the biggest country in western Europe, it's relatively space constrained, especially in the places where plants are built, so most exiting sites are already quite cramped (even just post-Fukushima external diesel generators gave headache to my wife's colleagues in her plant site). Also in France we have a lot of reactors, on very few rivers (Rhône and Loire river have like a dozen reactor on each) so there's less margin than what we'd like.