Things are starting to get more confusing as the news pours out of Japan. When I last wrote, things appeared relatively calm, as it looked like TEPCO had managed to get mobile electric generators on site and were keeping the reactors (mostly) cool through injection of seawater.
Then the hydrogen explosion that started on Unit 1 also happened on Units 2 and 3 (see bullet #1 from my previous post). The explosion from Unit 3 apparently knocked out some of the cooling pumps on Unit 2. There has been a very different type of explosion on Unit 2. And a fire broke out in or near the spent fuel pool of Unit 4. It's hard to keep it all straight, it's hard to follow along without spending hours sifting through all the reports. The TEPCO press releases aren't all that great, but I imagine they're putting every available resource on fixing the problem, not posting web pages.
NEI is reporting that radiation levels as high as 40 REM/hour were measured between Units 2 and 3. Yes, at that location, that's pretty high and I wouldn't want to stand there for very long. But to put that in perspective, it's still not a level that represents enough radioactivity that would threaten anyone outside the fence of Fukushima.
The most interesting tidbit, to me, is the explosion in Unit 2, and the hole that it created in the suppression pool. And this is where my knowledge of BWR's hits a wall: I don't fully understand the purpose, potential leakage paths, or impact of a hole in the suppression pool, so I'm not going to make any predictions about it. I'll be watching for updates on that today.
The reported fire at Unit 4 is scary at first because it was in a spent fuel pool, but it appears to have been put out. My guess is that oil or debris got in there and caught fire. I have seen analysis that all you really need to keep water in those pools is a garden hose, and that is sufficient to keep the spent fuel covered and cool.
TEPCO and the folks on the ground at Fukushima are doing a heroic job at trying to keep three nuclear reactors under control after a magnitude 8.9 earthquake. I'm sure all of them have families, all of them have relatives, all of them have lost something in this earthquake. And there's a lot more going on in Fukushima than just the reactors -- a water dam broke as a result of the earthquake and washed out 1800 homes -- but that doesn't seem to get much press coverage. If you want a calming, strong essay on why there's other, bigger things to worry about, go over and read this piece on Atomic Insights.