Big Disagreement

US Nuclear Regulatory Chairman Gregory Jaczko said today in testimony to Congress that all the water in Fukushima reactor #4's spent fuel pool had boiled off, and he urged Americans in the area to evacuate.

I'm in touch by e-mail with a number of nuclear experts, and what I conclude from what I've heard is that Jaczko is wrong. That's what Japanese officials are saying, too.

I'll keep looking into this. I've gotten feedback from readers and tweeps that it would be a good idea to write some more about radiation dose, and that is part of understanding whether it's likely that the situation is as dire as Chairman Jaczko testified. Radiation outside the reactors are going up AND DOWN. They wouldn't go down if material from the fuel rods were being spread around.

Radiation levels were as high as 10 millisieverts per hour today, the equivalent of getting a CT scan for every hour of exposure. Radiation levels have since dropped and the plant workers are planning to return to work, officials said.

I'll post as soon as I can, but it's likely to be tomorrow morning.