Great, just when I'm going to be in Vancouver for 3 weeks in April I agree, the graphic is way overblown. There isn't that much nuclear material there to start and meltdowns are by definition, MELT downs. They don't explode. The problem is the explosions caused by pressure venting oxygen and hydrogen. Those explosions cause the reactor damage that causes the meltdown. A meltdown is literally the reactor core turning into a pile of molten material that forms a big hot puddle. You don't want to go anywhere near it but it doesn't miraculously propel itself into the atmosphere.