Japan Nuclear Crisis

Though I know that two posts in one day is recently unprecedented, I've been meaning to post about the Japan nuclear crisis for a few days. The various major news outlets are doing a good job, or so it seems, of keeping us informed of the events going on over there. However, I found myself rather puzzled over the physics of what was happening. From the news articles I was unable to figure out what was actually causing the meltdown, beyond some problem with the cooling. As a postdoc in my lab asked, "Isn't all they have to do drop the control rods and the reaction ends?" So I decided to do a little digging. I've found a couple of places that do a nice job of explain some of the physics of what is actually happening, nature news (not sure if the nature blogs are behind a paywall), and scientific american (not up on current events, but a nice summary of what can/might go wrong). I'm sure there are many other places doing a good job of explaining things, but these are the ones and I found, and hopefully they help clarify what is actually happening.