According to the 2018 Report from the Electromagnetic Defense Task Force, authored by Maj David Stuckenberg, Amb. R. James Woolsey, and Col Douglas DeMaio; US nuclear power plants are not hardened against an EMP (Electrical Magnetic Pulse).
If N Korea or Iran fired 3 missiles with nuclear warheads that detonated high above the US, the EMP would shut down the electrical power grid in the US for up to two years.
Using their batteries, all 97 nuclear power plants East of the Rocky Mountains (only 2 West of the Rockies) would automatically SCRAM their nuclear cores. But since it takes 5 years to cool a nuclear core, it is essential that the cooling pumps keep operating continuously during that time. Unfortunately, neither the backup generators, the controlling electronics, nor the pumps are protected from an EMP. And even if the backup generators, the controlling electronics, and the pumps were hardened against an EMP, all the nuclear power plants have only a 4 day supply of fuel for the generators. And since the EMP would take out the country’s communication system, fuel processing plants, pumping stations, storage facilities, and the transportation system; a four day supply of fuel for nuclear power plants is nothing more than a gesture of safety.
If a nuclear power plant is without power for just 24 hours, the core will start melting and enough radioactive hydrogen will be released to cause the containment structure to explosively fail. But let’s not forget about the 20 to 40 used nuclear cores quietly sitting in the near by cooling ponds at all nuclear power plants. Without operational cooling pumps, the water will evaporate and those cores will all spontaneously catch on fire.
A single breached nuclear core, as demonstrated by the Chernobyl accident, will make an area half the size of Pennsylvania uninhabitable. And since it took the peacetime resources of an entire country to contain the emissions of that one nuclear core, it would be impossible for the US to contain the emissions of 99 active cores and over 1,500 used nuclear cores all failing at the same time.
I suggest hardening all nuclear power plants against an EMP, increasing the size of their backup generator fuel tanks by a factor of 10, and design an operational system that would allow the nuclear power plants to quickly restart and provide enough internal power to operate the cooling pumps.
Failing to take these simple steps runs the risk of making all the land East of the Rocky Mountains both in the (US and Canida) uninhabitable for hundreds of years.