not an expert by any means, so take it for what it's worth...
Distance from a plant is (very) likely far less important than the prevailing wind direction - while you might be safe 10 mi. away if upwind after an "event", you may not be at 1000 mi. if downwind.
It would appear (and i would say very likely) that some amount of radiation from Fukushima has reached at least the western shore of the U.S.. Certainly the radiation from Chernobyl traveled thousands of miles and, even at that distance after dilution, was apparently at unsafe levels.
With that said, i would posit that your concern is less relevant than you probably think simply because we're all in danger, no matter where we live, and attempting to minimize the risk is largely dependent on the scale of the next accident, especially if you want to remain on the E. coast. I watch a couple of news feeds and, on average, i see about 1 to 1.5 events each week. Of course almost all of them "pose no threat to your safety", right?
http://thewatchers.adorraeli.com/category/nuclear-events/
http://fukushimaupdate.com/
http://hisz.rsoe.hu/