Reactor Accidents

UPDATE, 11:30 am, Saturday, Official reports are that radiation levels have decreased from those reported below; however radiation monitoring systems are either still down or not available to the public.

UPDATE, 9:30 am, Saturday, An explosion has occurred at Fukushima Daiichi Unit 1. Video of the aftermath of the explosion shows that the containment building has been destroyed. In a General Electric Mark I reactor, the containment building is fairly weak and is considered the secondary containment. The primary containment is a steel liner that surrounds the reactor core. So far, video and photos have not been clear enough for us to determine whether this steel liner is intact.

UPDATE, 8 pm, Friday, Venting of the containment began at Fukushima Daiichi Unit 1 around 9:00 am Tokyo time. This will release some radiation into the air. Because radiation monitors at the site are inoperable (see below), it will be impossible to know how much radiation is being released.

UPDATE, 7:45 pm, Friday, An evacuation of a three kilometer zone has been ordered at a second reactor site in the Fukushima area. Apparently there are also problems cooling three of the four reactors at the Fukushima Daini site. All of these reactors are later model General Electric Boiling Water Reactors.

UPDATE, 7:30 pm, Friday, Units 1, 2 and 3 at the Fukushima Daiichi site have lost offsite power. Pressure is building up inside Unit 1 (a General Electric Mark I reactor, see below). The normal procedure to release the pressure is to vent the containment (a procedure that releases radiation into the air), but the utility has been unable to do so because of the lack of power. Plant workers may need to enter the containment to do so manually.

UPDATE, 6: 45 pm, Friday Numerous sources are reporting radiation levels at Fukushima to be 1,000 times higher than normal inside Unit-2 (though some sources have also reported high radiation levels inside Unit 1) and at least eight times higher than normal at the plant gates outside. The evacuation zone has been expanded to 10 kilometers (about 6 miles) from the Fukushima reactor site.

UPDATE, 3:30 pm, Friday, A Japanese Cabinet Office report released at 12:30 am Saturday, March 12, 2011 (Japanese time) predicts that fuel damage will occur at the Fukushima Daiichi Unit-2 reactor late Saturday night (Japan time, early Saturday morning US time) if cooling is not restored before then.

Activists believe this is indicative of an attempt to downplay potential radioactive releases, especially as Tepco says it plans to vent the containment to relieve pressure, which will cause release of radioactivity into the air. There are six nuclear reactors at the Fukushima Daiichi nuclear power site, located near the town of Okama in the Fukushima Prefecture. Another site in the same Prefecture, Fukushima Daini, contains four nuclear reactors. The sites are on the eastern Japanese coast about 200 miles north of Tokyo. All of these reactors are owned and operated by Tokyo Electric Power Co. (Tepco). The earthquake of appears to be causing the greatest problems for the Fukushima Daiichi reactors, although several reactors at both sites were affected by the earthquake. Specifically, Fukushima I-2 has lost backup power and necessary cooling capability. As of 11:30 am Eastern time March 11, cooling capability has not been restored.

This factsheet will be updated as new information becomes available. Michael Mariotte,