France claims two things:
- Reactors are seasonally idle and will ramp back up for winter
- During this normally idle time, they do maintenance
https://abcnews.go.com/International/wireStory/minister-fren...
Perhaps this idea that "half of France's reactors are idle" is partly true, partly scare tactics from the "anti-nuke" group?
Nuclear reactors require vast amounts of cooling water so timing your "down time" to coincide with low water levels does make sense.
Here(Ontario) we build them on the shores of Lake Ontario and the intake pipe extends far into the lake to avoid any sort of water level fluctuations impacting power production.