The problem as I see it is the nuclear power plants. So many in the eastern half of the US. So many all over Europe. Most all will be safely shut down in the event of a CME, because the staff will be on site and able to deal with getting the generators online (diesels are impervious to CME/EMP, and can be rigged to start after pulling any failed electronic controllers). So that’s not the worry.
I also don’t worry so much about the spent storage pools. Again, most staff will be on site and people will figure out that 90% of what’s in the pool is cold enough to be pulled and laid on the ground once it becomes clear this is a long term event. What remains will do just fine in the remaining water without the external water cooling system. As long as water is replenished the process can be managed until the remaining rods are cool enough to be left exposed to air. By then there won’t be power to run the equipment to pull them, but the staff will have spaced them out in the pool so they have adequate distance and air circulation. So most plants will wind up safely shut down. Basically, each plant will become a dead zone all to itself, but fairly limited in reach.
Most.
Not all.
Some plants won’t have smart enough, or motivated enough staff, to see that proactively managing the cooling pools is essential for regional safety. Those plants will see cooling pool failures and the resulting fires and smoke will spread lethal plumes downwind. Farmland, cropland, transportation routes, population centers will be depopulated and unusable for centuries.
Not all.
Some.
So here’s the real problem: Which ones will fail? Where will the dead zones occur?