What does "upgrade the grid" mean to you?
Digging tons of rock and salts to store energy with batteries?
In Europe there are very few remaining sites to build hydro power, and those have serious ecological consequences too... I don't see to many alternatives. Biogas options are nearly tapped out. There is potential with geothermal using new digging techniques, but they're mostly in the testing stage still.
How is using batteries better than using said rocks to power nuclear reactors?
There is a limit to how much one can add uncontrollable energy sources to a grid...
While that is indeed not the most objective source, they are actually correct. Even if their stability argument didn't hold water (it does), they should keep the nuclear plants active and upgrade transmission lines to export to Germany through France and displace coal plants in Germany's electricity market... And literally save on radioactive waste which coal plants produce tons of.