Whenever there's a maintenance or refuelling operation, comparatively large amounts of power generation goes offline for weeks.
While this can be dealt with through careful planning, the elephant in the room for France is the age of their nuclear reactors. The vast majority or reactors is 40 years old or reaches the end of their design-life within this decade. Even with ten year extensions, about more than half of all French reactors will have reached EOL by 2035.
At the same time there's only a single new reactor under construction right now.
Given that it takes about a decade for a nuclear reactor to go from start of construction to commercial operation, France should really start building about a dozen new reactors within the next 5 years...