Ever since Fukushima, I think we've all had a nasty firsthand wake-up call to potentially the worst after-effect of a CME event--potentially hundreds of nuclear reactors melting down at the same time.

Even if they are able to scram a reactor in time, unless the grid is able to resume providing power afterwards, or the grid is able to function enough to keep refineries going and new fuel deliveries flowing for the pumps/generators for weeks or months or possibly years, it's another Fukushima.

I wouldn't want to be in a nuclear-dense country like France or Japan if that happens.