Backup diesel generators (nuclear power plants) were flooded with sea water, leading to the failure of the cooling system, core meltdown and a number of explosions.
Fukushima evacuation zone eventually reached 12 miles; 150,000 people.
NAIIC (investigation commission) found that the accident was foreseeable and preventable - failure of risk assessment and preparation ( sound familiar? Electrical Grid’s Susceptibility to EMP and solar storms )
ref: Arnie Gundersen and Mat Stein - Solar storms, EMP and grid vulnerability