A very interesting question. At Fukushima, I think the earthquake didn't do anything really massive to the nuclear plants. And I think the tsunami didn't do anything really massive to the nuclear plants. But those events did create a power outage and the power outage led to meltdowns.
I don't think Japan expected such a turn of events, and it is not clear to me that America has either.
The Japanese had an advantage - they had back-up generators that worked for a while. In a US EMP attack that might not be the case.