User blog comment:Mr.Xeight/Forum for the Federation of Greece in the Universe of 1983:Doomsday/@comment-1593341-20100823175855

With Hiroshima and Nagasaki though, they remained habited even after the bombings. And yes the 10 megaton bombs would of course leave much more devastation, but the vast majority of strikes were of 1MT or under. So if the Hiroshima/Nagasaki ones took 2 weeks to reach safe levels, and the bombs used are 100x more powerful, that would mean 200 weeks, or 4 years.