UPDATE, 10:00 am, Wednesday, The situation at Fukushima Daiichi continues to deteriorate. All plant workers were evacuated for some hours due to extremely high radiation levels onsite, but a skeleton crew is said to have returned. Solid information is sketchy and even the Japanese government is publicly complaining about the quality and quantity of information coming from Tokyo Electric Power.

UPDATE, 6:15 pm, Tuesday, We have just learned that TEPCO has announced that at 5:45 am Tokyo time (4:45 pm eastern us time) flames have appeared again at the northwest side of Fukushima Daiichi (Unit 4). According to TEPCO, it is impossible to go near the fire since the radiation is so high.

UPDATE 8:15 am, Tuesday, The situation at Fukushima is going from bad to worse. There was briefly a fire in the irradiated fuel pool at Unit 4. The fire is said to be extinguished for now.

UPDATE 7:30 pm, Monday, Tokyo Electric Power is holding a press conference at this hour. NHK TV reports that there has been an explosion at Unit 2 at Fukushima Daiichi. There is speculation that this explosion has damaged the primary containment (inside the concrete containment building, which is the secondary containment. Tepco is evacuating some nonessential personnel from the reactor site. 2.5 meters of the core are currently uncovered by water—which means it is almost certainly melting. Winds from the site are currently blowing toward the North.

UPDATE 12:30 pm, Monday, According to our colleagues in Japan, Tokyo Electric Power states that Fukushima Daiichi-2 “has again lost its coolant (sea water was pumped in but is dropping). They cannot ease the reactor pressure because the relief valve is stuck closed. Air dose rate on site (outside the reactor building) was 3,130 at around 9:30pm.” We believe the 3,130 figure means 3130 MicroSievert/hour, which would be highest reading yet recorded—about 310 millirems/hour. For comparison, the U.S. EPA allowable dose to a member of the public from a single reactor is 25 millirems/year, the U.S. NRC’s allowable dose is 100 millirems/year from all nuclear sources. UPDATE 10:00 am, Monday, An explosion has occurred at Fukushima Daiichi Unit 3.

UPDATE 2:30 pm, Sunday, Tokyo Electric Power is reporting that some six feet of the core of Unit 3 remains uncovered and has been for some time despite efforts to pump water into the core. Tepco speculates there may be leaking pipes and water is not remaining in the core. A translation of part of the statement from our Japanese colleagues: "The fuel’s integrity has been considerably compromised. We are assessing a considerably serious situation."

UPDATE, 1 pm, Sunday, The International Atomic Energy Agency reports that a first-level (lowest-level) emergency has been declared at the three-unit Onagawa nuclear station north of Fukushima. Immediately after Friday’s earthquake a fire broke out at this facility, but it was said to have been extinguished fairly quickly. However, on Saturday, elevated radiation levels were measured at the Onagawa site (about 10 microSievert/hour or about 1 millirem/hour) for a few hours. The emergency was declared due to these elevated levels, but utility officials say the reactors there are under control.

Statement of Citizens’ Nuclear Information Center,