http://www.businessinsider.com/french-heat-wave-one-tumultou...
> France imports UK electricity as summer heatwave puts a third of its nukes out of action
https://thinkprogress.org/france-imports-uk-electricity-as-s...
> Germany powers France in cold despite nuclear u-turn
https://www.reuters.com/article/europe-power-supply/germany-...
> France was heavily dependent on power imports from Germany during the first cold spell of this winter, despite the fact that most of the country’s nuclear reactors are back online
France cannot react to a fluctuating power demand like Germany can and Germany simply takes over the French excess power. You cannot power down a (French) nuclear plant as quick as you can spin up a (German) gas turbine. So Germany operates on a stable power source of less than they actually need and import from France but if more power is needed, Germany quickly spins up their gas turbines for the time it takes to power up the coal plants. France' power plants normally run at full power and if the demand falls off, they are in a bit of trouble and rely on Germany to help them out. Be it by taking over electricity (most of the time) or delivering electricity (sometimes).
If Germany didn't take the excess electricity, France would have to burn it off.