Details from the Washington Post on the partial meltdown at the Fukushima Daichi complex number 1 reactor:
Tokyo Electric Power Co., owner of two heavily damaged nuclear power complexes near the center of Friday’s earthquake, told Japanese regulators Sunday that it faced a new emergency at one of its 10 reactors, even as it struggled to bring several others under control.
Earlier, the big electric utility took the unprecedented step of pumping seawater mixed with boric acid into the core of Fukushima Daiichi’s unit 1 reactor to tame ultra-high temperatures from fuel rods that had been partially exposed….
While Japanese authorities tried to calm citizens, they also began evacuating more than 200,000 residents from a 12.5-mile radius around two nuclear power complexes, made preparations to distribute potassium iodide pills, and warned people in the vicinity to stay inside and cover their mouths if they ventured outdoors. Federal safety agency officials said that as many as 160 people had been exposed to radiation from the plants.
“Only the gravest danger would justify an evacuation at such a moment,” said Peter Bradford, a former commissioner at the U.S. Nuclear Regulatory Commission.
The evacuation, wider than announced the day before, followed an explosion Saturday that destroyed a building that housed both the reactor vessel and its containment building. Four workers were injured, but Japanese authorities said the containment building was intact.
The explosion was yet another indicator of dire problems inside Fukushima Daiichi unit 1, problems that might be plaguing other units as well. The explosion was caused by hydrogen, which nuclear experts said could only have been produced from inside the reactor vessel by the exposure of zirconium cladding that surrounds the fuel rods. Those rods are supposed to be covered by water, but at extremely high temperatures, steam reacts with the zirconium and produces hydrogen.
Video of the explosion from AP:
Even though this looks pretty scary, the reactor’s container is still sound.
CNN reports (hat tip BoingBoing) that the authorities believe a meltdown may be underway at reactor 3 as well due to the inability to cool the reactor’s core:
Chief Cabinet Secretary Yukio Edano told reporters there is a “possibility” of a meltdown at the plant’s No. 1 reactor, adding, “It is inside the reactor. We can’t see.” He then added that authorities are also “assuming the possibility of a meltdown” at the facility’s No. 3 reactor.
Later reports indicate that the emergency cooling system had stopped working at reactor 3, and that efforts were in progress to flood it with water as had been done with reactor 1, which would necessitate a release of steam that would have very small amounts of radiation.
The New York Times notes cooling is impaired at three reactors in a second nuclear plant, which may also require emergency intervention:
The cooling systems at three other reactors at a second nuclear plant had also failed, officials said. While backup systems might still be revived, if they could not, these reactors too could require emergency cooling, they said.
It also has this cheery news:
Japanese nuclear safety officials and international experts said that because of crucial design differences, the release of radiation at Daiichi would most likely be much smaller than at Chernobyl even if the plant had a complete core meltdown, which they said it had not.
Background and assessment from a member of the Union of Concerned Scientists via Rachel Maddow (hat tip reader Sufferin’ Succotash):
Update 5:30 AM: The Wall Street Journal reports (hat tip reader furzy mouse) that reactor 1 was safety tested assuming a maximum earthquake less powerful than the one that struck last week:
Separately, company documents show that Tokyo Electric tested the Fukushima plant to withstand a maximum seismic jolt lower than Friday’s 8.9 earthquake. Tepco’s last safety test of nuclear power plant Number 1—one that is currently in danger of meltdown—was done at a seismic magnitude the company considered the highest possible, but in fact turned out to be lower than Friday’s quake. The information comes from the company’s “Fukushima No. 1 and No. 2 Updated Safety Measures” documents written in Japanese in 2010 and 2009. The documents were reviewed by Dow Jones.
The company said in the documents that 7.9 was the highest magnitude for which they tested the safety for their No. 1 and No. 2 nuclear power plants in Fukushima.
Simultaneous seismic activity along the three tectonic plates in the sea east of the plants—the epicenter of Friday’s quake—wouldn’t surpass 7.9, according to the company’s presentation.
The company based its models partly on previous seismic activity in the area, including a 7.0 earthquake in May 1938 and two simultaneous earthquakes of 7.3 and 7.5 on November 5 of the same year.
As some readers have surmised, this was a classic underestimation of tail risk. The Journal article also has a nice interactive graphic and contains reassurances by officials that the vapor released contained “minimal” amounts of radiation and that the container was intact. The before and after shots from ABC (Australia, hat tip reader furzy mouse) are dramatic.