[UPDATE: Wow, minutes after I posted this, an explosion is being reported at the third reactor site. I mentioned in this post the third reactor was in trouble, so this may be another hydrogen combustion explosion as happened in the other two. I'll put more updates here as I find them.]
[UPDATE 2: The comments being posted below are contradictory, as I expected; news is coming quickly about the third explosion and speculation is flowing. I'll add that I freely admit things I wrote below may be in error; but they are based on what I've read and heard over the past few days. With news being as spotty as it is, that's inevitable. That's why I made the disclaimer I did in the post.]
[UPDATE 3: Alan Boyle at Cosmic Log has an excellent and calm discussion of what happened, including best and worst case scenarios.]
[UPDATE 4 (20:30 Mountain time): Yikes. The New York Times -- not generally known for breathless overreaction -- is reporting that the explosion from reactor 2 may have damaged the containment vessel of the nuclear core. The exact situation is still maddeningly unclear. Both best and worst case scenarios are being spun, but as usual I will wait for more information before drawing any conclusions. In the meantime, there may be evacuations of personnel from the plant. I hope that's not true; those people are the ones heroically working to keep this matter under control.]
[UPDATE 5 (March 15, 22:00 Mountain Time): I haven't updated today because until now not much news was coming out about the reactors, and some of the news I did see was clearly contradicted by other reports. However, The Associated Press is reporting that all the workers at the plant have been evacuated. This is bad news. Those people have been working heroically to keep things under control, despite some temporary but scary surges in radiation levels around the plant. The AP article itself has contradictory statements by experts -- one saying it's a matter of time now, and another saying there is minimal risk to the population. It was reporting like this that led me to write this article in the first place, and clearly some of the things on which I was basing my conclusions have changed. If there are any major developments, good or bad, I'll update here and most likely write a new post given what we've learned in the past few days.]
After the earthquake and tsunami in Japan, things over there are very, very bad. The pictures and video of the devastation are incredible… and before I go any further I will note that science and engineering mitigated this disaster by orders of magnitude. The Japanese have prepared for this type of event for decades, and it’s paid off. At this time, the number of dead is in the thousands… not the hundreds of thousands. I will not downplay the tragedy and loss, but it could’ve been far worse.
Still, there are many problems. One of the biggest* is the Fukushima Daiichi nuclear plant, which is facing a crisis with its reactors. While this situation is serious, let me be very clear: we are not facing a nuclear explosion, nor are we facing the release of a huge, deadly radioactive cloud (more on both of these below). The fear-mongering and misinformation on the web and in the news is rampant, and the last thing we need is people panicking because of it! The news is bad enough without exaggeration of it.
The best analysis I’ve seen so far is at Slate. An excellent summary is also on The Market Ticker. At reddit, a commenter gave a very short description, and Boing Boing also has a good piece. [Update: My friend Evelyn Mervine, who is a PhD candidate in geology, has a series of interview with her nuclear engineer father on her website.]
This situation is changing all the time, so please be aware that what I write here is based on what I’ve read in those articles, what I’ve seen in the news, and my own knowledge. With things being so fluid, caveat lector.
Here’s what happened: The plant has six reactors. The earthquake and subsequent tsunami severely damaged some of the reactors and hampered attempts to fix them. An explosion rocked the plant on Saturday, and another about a day later. These were not nuclear explosions! That is literally impossible from a fission reactor; the fuel is the wrong kind and doesn’t have sufficient quantities to explode like an atomic bomb. Instead, the explosions were due to hydrogen combustion, created when water came into contact with the extremely hot fuel cells. The cooling system was down, allowing the fuel cells to heat up. Hydrogen was released, and is extremely volatile. It volatilized.
The explosions destroyed the reactor buildings (basically an enclosure around the reactor itself to protect it from the elements), but far more importantly it appears the reactor housings are intact. Engineers are now using seawater to cool the reactors, which will ruin them for future use but should safely cool the fuel rods. This situation isn’t over yet (a third reactor is in trouble as well), but I’m cautiously optimistic this plant will be shut down safely. Ironically, it was two weeks from its scheduled 40 year decommissioning as it was.
That isn’t stopping the rampant speculation fueled by fear and ignorance of the real situation. For example, I’ve seen some people calling that blast a nuclear explosion, but it wasn’t. Again, it was hydrogen exploding when it reacted with air. A huge explosion, but not a nuclear one.