Here is one...Eathquake anywhere on eastern region and south. East cost is 100% rock for the most part. We get a significant tremmor hundreds of miles south and game over. Earthquake closer and the waterway just off the ocean will make a tide that is way higher than the plants' design basis of 5 feet or so. How about a hurricane of serious proportions? We just need one to come up the east coast and bring us a nice tidal wave.
I am sure many will think that these are first time in history events...well...talk to those in Japan. It as the first of sorts for them too.
I'm trying to determine exactly which catastrophic event you think would cripple the plants be it Salem/Hope Creek or Oyster Creek. If you're saying a hurricane then for Salem/Hope Creek the diesel generators as well as the fuel are not exposed but in buildings. If you're worried about a tidal wave coming up the Delaware would have to be so massive as to be able to go get up 40 miles from the southern tip of NJ to even reach the plant which when you look at the shape of it would provide a natural storm break that would lessen the impact.
Back in 1962 LBI was flooded by one of the worst Nor'Easter's on record, putting much of the island under water and yet on the mainland there wasn't that much flooding, one of the positives of living near barrier islands.
Perhaps more of your energy should be directed at the federal government. After all every nuclear power plant as been paying into the spent fuel fund quarterly and yet they forced to hold the spent fuel on site.