This is current as March 15th, 6pm or so EDT. Summarized from a more technical JAIF publication.
Update, 9:50am, March 16: Here is the latest technical publication from JAIF. The situation has become slightly worse over the past 12 hours, with more damage to spent fuel pools and more damage to primary plant integrity than my above chart.
- Fuel: This is the current condition of the fuel in the reactor vessel. Units 1, 2, and 3 have had some level of core damage because of the falling water levels (I'm making an educated guess at Unit 2 for simplicity). Melting core means the release of radioactive fission products, and these now get released when they burp the reactor to relieve pressure. This is what US Navy ships and others in the area are detecting. The release of radiation is a bad mark on the industry, but it still has no measurable impact on human health. This kind of thing happens all the time in the chemical industry (each one of those words is a link to a separate incident!!!); the nuclear industry is held to a sterling standard.
- The primary plant integrity is questionable on Unit 2 because of the unexplained explosion (the one inside the reactor building, not the ones that blew the top off the buildings) and related drop in pressure. This is usually indicative of a hole opening up. I haven't been able to determine if the torus is isolable from the reactor or not.
- In the case of Unit 1, not only are they trying to fill up the reactor vessel and cover the core, they're also trying (or were trying) to fill up the primary containment as an additional cooling measure. This will require millions of gallons of seawater, and will take a while.
- Vent to atmosphere: all three reactor plants have been burped at least once.
- Spent Fuel: Unit 4 did not have any fuel in its reactor vessel -- it was all located in the spent fuel pool for tests. Which caught fire. OK, this is bad. I'm not sure how the operators allowed the pool level to get that low: the pool is 45 feet deep, and the fuel elements are about 12 feet tall, leaving over 30 feet of water to go. A lot of water has to boil off before you expose the fuel elements, but apparently that's what happened. That caused additional radiation to be released, but still not enough to affect the area outside of the nuclear plant facility.
Core cooling efforts will continue. There is probably a small slurry of reactor fuel, cladding, control rods, and core structural material in the reactor vessel. This is similar to what happened at Three Mile Island. By keeping water on the cores, they're keeping it from melting any further. Unit 1 was scheduled for retirement on March 26th, 2011, so that was very near the end of its useful life anyhow. Units 2 and 3 will never operate again; cleanup is going to be too hard and too expensive to get them back into working condition again.
TEPCO is calling in helicopters to dump water on the spent fuel pools to prevent them from catching fire again. I'm still shocked that happened in the first place.
There remains at least 6 inches of reactor vessel steel and about 6 feet of steel reinforced concrete that is keeping the worst of the stuff inside. Occasional burps of steam and gas may occur, and these are sent through "scrubbers" and filters before they are released. Some radioactivity will still be in there, though.
3. Stop the Hysteria.
A dose rate of 40 REM/hour was measured between Units 2 and 3 sometime yesterday. This is pretty hot for a localized spot. But a single location DOES NOT endanger the entire island of Japan. I'm sick and tired of reputable news organizations linking the awful conditions in Japan with the nuclear incident -- while this is an unprecedented situation with 3 reactors having core damage, the situation has not had one iota of impact on the health and safety of the residents of Japan.
Personally, I believe people are being evacuated out of an overabundance of caution. In the interest of full disclosure / total honesty, there is a possibility that the Japanese government knows of large cracks in the 6 foot thick containment walls due to the magnitude 8.9 earthquake. (I was told that the design basis earthquake was 8.2, which means the actual quake was 7x larger than design.) If history shows that the government or other authorities were trying to keep something like that secret, the political and regulatory impacts would be terrible.
There is NO chance of hazardous material raining out across the Pacific or endangering the US. The hysterics and comparisons to Hiroshima are unwarranted. And newer designs will only weather this kind of event better, with built-in passive safety systems that don't need offsite power to work.
As part of all this, I've discovered other bloggers who have been doing fantastic jobs getting out information in a clear, easy-to-understand manner. Reward these folks by hitting their site, too:
- The Neutron Economy. I love that name.
- Futurejacked. Also a nuclear engineer who has similar socioeconomic interests as I do.
- Brave New Climate.
And that's about it. Thanks to everyone for the emails, comments, and input. I'm glad to help where I can.