The bad.

Okay, having explained why there's not going to be another Chernobyl at Fukushima, a few questions that were curiosities have slowly grown to become a bit more relevant.

The remaining of the three units that were in operation in Fukushima Daiichi reportedly blew a while back. This may, however, be worse.

Kyodo reported a while back:

The radiation level at the troubled nuclear plant in Fukushima Prefecture shot up to 8,217 micro sievert per hour temporarily Tuesday morning after an explosion was heard at its No. 2 reactor, Tokyo Electric Power Co. said.

The level as of 8:31 p.m. was more than eight times the 1,000 micro sievert level to which people are usually exposed in one year.

When you blow the lid off a reactor building when venting steam out of a partially melted reactor core, you're going to have elevated radiation readings. However, this is between one and two orders of magnitude more than the previous elevated readings, and getting into the unhealthy territory.

Now, this could be because reactor 2 has had worse core damage than reactors 1 and 3, or because they released more steam. But it can also be because the explosion damaged holding pools of fuel or waste, or because some part of containment is starting to give. The TEPCO press conference statement of unexplained "loss of pressure" seems to hint at that. The latest reports I'm reading suggest that unit 2 has breached at least one layer of containment and melted. Silver lining is that it's no MOX unit 3, which has nastier nasty stuff (more plutonium.)

We're still nowhere near Chernobyl.

Still, some questions that come up, aside from the obvious:

• ALL cooling redundancies at ALL THREE operational reactors failed. 1 and 2 are different GE designs, 3 is a Toshiba design, so this shouldn't be a monoculture issue. Was it bad design, follies in operation, or truly so monumentally unforeseen might of nature that it went beyond any imagined scenario for all three reactors?
  
• Reports of one loss of coolant episode, earlier today, was blamed on the pump running out of fuel. Really? You have an imminent meltdown of a nuclear reactor and you can't find fuel for a pump? That just makes no sense.
  
• People have been working on restoring cooling on these reactors for days now. I can understand that the situation got to where it is, but it is getting increasingly hard to understand why it hasn't gotten better.
  
• The implications of either layer of containment breaching will be, hopefully pretty severe, as it's one more thing in the "can't happen" chain of events and has repercussions to a lot of plants in a lot of places.
  


I think it's a foregone conclusion that this accident is by now far beyond the Three Mile Island one, though nowhere near Chernobyl or Kyshtym. Evacuation is looking like a very prudent measure, and wind direction begins to matter. Still, a lot depends on what happens now. It's still rather likely that this will be a major mess in Fukushima, but not a major health hazard to the population, thanks to the evacuation.

8000 microSieverts (8 milliSieverts, 8 one-thousands of a Sievert) is a lot, but nowhere lethal. Wikipedia tells us:



For acute (that is, received in a relatively short time, up to about one hour) full body equivalent dose, 1 Sv causes nausea, 2-5 Sv causes epilation or hair loss, hemorrhage and will cause death in many cases. More than 3 Sv will lead to LD 50/30 or death in 50% of cases within 30 days, and over 6 Sv survival is unlikely.



Following the news on what kind of readings we see, and what material is causing the readings, will tell more of the story.