In Japan, they found at one point that there was a possibility of it *seriously* going to hell in a hand basket.
If the wind had been really wrong, it would have put serious fallout over Tokyo; which would have been really, really, really bad. While few people would have died, the economic disruption would have been (without any hyperbole) unbelievably stupendous.
You can tell me all you want that this kind of accident can never happen, but I just don't believe it. We have no reason to think that Chernobyl or Fukushima were the worse cases, nor that these kinds of failures cannot happen again worse.