I just read a great post somewhere else from a guy who said he was an actual nuclear engineer. He seemed legit enough. I lost the post but he made some really good points in that
1) The reactors in Japan simply will not blow up, no matter how much news hype wills them to. Reactor fuel is 4-5% pure typically, while a nuclear bomb is 90% pure.
2) The reactors in Japan simply cannot turn into another Chernobyl. Not only was Chernobyl a completely different type of reactor (thus preventing this in the first place) but they also had very awful containment policies in that accident, of which Japan has plenty of good ones, regardless of what disaster strikes. Chernobyl was handled by covering the reactor core (yes, the core itself) with massive amounts of lead and sand, which is ultimately one of the primary reasons it blew.
3) If the cooling systems just completely fail from here on out, while it is a "race against time" like the media says, it's not as bad as it sounds, because the reactors have already shut down, which means they're going to cool off later on regardless of speeding up the process with generators activating the main cooling system.
4) The worst possible scenario is that the containment vessel for the core pops like a balloon. If it does that, it will be a horribleterrible mess to clean up, and will take a very long time, but no thing such as the surrounding environment becoming uninhabited will happen. It will just be a large, internal, frustrating clusterfuck.
5) The radiation "leaks" are being done (only one is confirmed now, and the intentional/unintentional status of it is current up to debate) to prevent #4 from happening. And yet, at the same time, if #4 does happen, there are precautions in place to handle it. However, it would be several times worse than releasing a small amount of radiation to the surrounding areas.
It's not word for word (due to my more limited terminology) but that's basically what he said, i tried to get it as close as possible without making stuff up, which I didn't. Don't trust everything here, but I think this guy seems legit, again. At least more knowledgeable than most.