It is now clear that the second explosion at the Fukushima Dai-ichi plant was at reactor Number 3 on March 14, two days after the first explosion at reactor Number 1. Reactor Number 3 is of special concern because, unlike the other two which use standard uranium fuel, it contains “mixed oxide” or MOX fuel—a mixture of uranium and plutonium reprocessed from spent uranium, and significantly more toxic than standard uranium fuel. Safety concerns have long made MOX reactors controversial, and Number 3 may have already started to melt down.
Reactor Number 2 also remains dangerously overheated, with water evaporating so quickly in the chamber that its fuel rods were probably fully exposed—although with monitoring equipment down, what is really going on in the reactor chamber cannot be determined with certainty.
Radiation levels at the site remain a source of controversy, with reports wildly fluctuating since the crisis began on March 10. The US-based Nuclear Information and Resource Service (NIRS), citing official sources in Japan, reports levels as high as 3,000 micro-sieverts over the past 24 hours. The Kyodo news agency reported a radiation level of 1,557 micro-sieverts per hour on March 13—roughly equivalent to one chest X-ray. At least 19 people from the areas around Fukushima have been hospitalized for radiation exposure. Evacuees have been given instructions to “close doors and windows; place a wet towel over the nose and mouth; cover up as much as possible.” Far greater radiation still would be released in the event of a meltdown.
Electricity has still not been restored to the site, and fire trucks were evidently employed to flood the reactors with seawater. This was obviously a last-ditch effort to prevent a meltdown, as untreated seawater has a corrosive effect on reactors, which basically means they are being written off for any future use. The seawater is presumably being turned into (radioactive) steam, or released (with much radioactivity) back into the sea. (San Francisco Chronicle, CNET, BBC News, The Journal, Ireland, NIRS, March 14; NYT, March 12)
See our last posts on the crisis at Fukushima.