According to reports, a seriously injured worker was trapped within Fukushima Daiichi unit 1 in the crane operating console of the exhaust stack and is now confirmed to have died. Four workers were injured by the explosion at the same reactor and have been taken to hospital. A contractor was found unconscious and taken to hospital. Two workers of a 'cooperative firm' were injured, said Tepco; one with a broken bone. At Fukushima Daiini unit 3 one worker received a radiation dose of 106 mSv. However, given the high levels of radiation inside the plant, and the opacity of information about what has actually gotten out, it is difficult to speculate at present on the true extent of radioactive contamination in the immediate and surrounding areas near the plant.
The Guardian is reporting that a Japanese seismologist Ishibashi Katsuhiko, warned long ago about the risks it faced in building nuclear plants in areas of intense seismic activity. Katsuhiko stated in 2007, specifically, that such an accident was highly likely to occur. Nuclear power plants in Japan have a "fundamental vulnerability" to major earthquakes. The government, the power industry and the academic community had seriously underestimated the potential risks posed by major quakes.
posted 11:10 AM EST "...the plan to flood the core with seawater and boric acid may be unprecedented and will effectively destroy the power plant. If the plan fails and the core does meltdown...the only thing left to do will be to "seal it up with concrete." NPR
Also see Keith Olbermann's opinion piece from yesterday: Time to shut down this nation’s nuclear energy program. For good...President Obama should officially reinstate the unofficial moratorium, and pledge to begin the process by which we dismantle these sleeping monsters.
The evacuation boundary has been extended to 20 km (13 miles). Japanese officials told the U.N.'s atomic watchdog they were making preparations to distribute iodine, which can be used to protect people from radioactive exposure to thyroid. Reuters Other forms of radiation exposure, however, would still be a worry.
The schematic diagram above shows the GE Mark I Boiling Water Reactor reactor building structure, the Fukushima Dai-ichi Unit 1.
The explosion at Fukushima has apparently disintegrated the upper third of the reactor building. The video and pictures currently available indicate that the "blow out panels" of the reactor building and roof cover were blown away by an energetic explosion likely due to a hydrogen gas detonation. The reactor core refuelling deck and the surface of the elevated irradiated nuclear fuel pool are now exposed to the atmosphere. Essentially, the photos show the remaining steel I-beam structure for the weather cover that was over the refueling deck and the top of the "spent fuel" pool. These panels are designed to "blow out" at overpressure.
The actual "pressure suppression system" structures credited for containment sit below this structure inside the concrete reactor building, namely the drywell and wetwell or "torus." The drywell is the large inverted lightbulb steel structure which is 100 feet tall and a nominal wall thickness of 1.5 inches. The reactor vessel sits inside this structure. In the event of a coremelt accident involving high pressure and high temperature, the highly radioactive steam and pressure would be vented into the drywell and then routed through the large diameter pipes to the "wet well" or "torus" which is the large 18 foot diameter hollow doughnut-shaped structure that surrounds the drywell. The torus contains approximately 1 million gallons of water and designed to receive the pressurized radioactive steam where it is supposed to be quenched and contained.
The status of the reactor containment in the reactor building remains unclear, but apparently remains intact. Fuel damage has apparently occurred because elevated levels of radioactive iodine and cesium are being monitored outside of reactor containment.
What is additionally unclear is how much cooling water is left in the fuel storage pools and whether or not there has been damage to irradiated fuel stored in that pool. There are reports of sea water being brought in to cool this facility.
Radiation levels are reported to have fallen following the explosion. David Lochbaum, Senior Reactor Safety Engineer for the Union Concerned Scientists, has reported that the explosion may acutally have occurred in the turbine hall building adjacent to the reactor building.
An anonymous Japanese government spokesperson has attributed the explosion to the buildup of a combination of hydrogen and oxygen that detonated inside the concrete reactor building but not the crdedited containment structure. Industry reports that the containment structure itself was not compromised or breached by the explosion.