Tweetmeltdown is when they cannot cool off the rods
the rods burn up, but the water that usually cools it turns to steam too quickly
alot of radiation in a meltdown is quickly disipated like smoke in a log fire
not usually that high
the problem is not getting it under control, otherwise you have a big concrete block of radioactivity that can't be touched, thus, the whole site ends up being worthless
per the pictures i've seen they have like 8 rod submersion buildings
i'd imagine one or two more goes and the whole thing is junk, although not a health risk unless some mega 10 quak hits and splits open the buildings which propably have several feet thick re-inforced concrete
the real issue is where do u get new electricity for 400k homes would be my guess