https://www.lemonde.fr/planete/article/2016/03/04/un-inciden...
It is in French, but it is saying that nothing was out of control and out of ordinary small issues. The temperature was a little bit out of the normal during the operations but that is quite common. And they used Boron because it was the adequate procedure in this case but again not out of ordinary. They decided to not use the control rodes that were not operating 'automaticaly' because of the disruption of the flooded system. But manual control was still available if they wanted to. And at the same time, like in a space shuttle, every electric control circuits are mirrored for safety. So the control room A was affected by the flooding but the control room B and the B circuits were ok, unaffected and operational as designed!
https://en.wikipedia.org/wiki/Fessenheim_Nuclear_Power_Plant...
Official report says it wasn't tried and remained a last line of defense. http://www.french-nuclear-safety.fr/Media/Files/Technical-no...
Also it was 2014, not 2016.
They assigned the incident level 1, the lowest one, in order to cover it up.
France has huge power demands in cold weather due to badly isolated houses heated with electricity. The power grid is already unstable, France cannot afford to loose much generator power, as they have nothing to replace it with - very few renewables.