An explosion was reported at 0610 local time Tuesday morning at the Fukushima Daiichi nuclear power plant’s second reactor. The blast is feared to have breached the pressure chamber. Fukushima webcam, Fukushima Daiichi Nuclear Power Station
The explosion is thought to have been in the reactor’s “pressure suppression room” part of the cooling system. It damaged the area that contains water to cool the reactor, but it is not yet clear whether it affected the containment structure near the core.
Government officials have said that there was limited damage as a result of the explosion, and efforts to cool the reactor would go on, but nuclear industry executives in Japan have said that the situation is far worse, and other unnamed officials said the containment structure had been damaged, but did not say to what extent. In the wake of the explosion, officials at the Tokyo Electric Power Company (TEPCO), the plant’s operator, said for the first time a partial meltdown could be taking place within the reactor.
After the explosion, radiation levels near the facility rose from 1,941 to 8,712 microsieverts, a level still short of that required to cause immediate health effects, and radiation decreased again some time after the explosion. The legal limit for radiation in one year is a thousand microseiverts, but radiation sickness does not occur until a million microseiverts.
Prior to the explosion the fuel rods in the reactor reported to again be exposed after the pressure valve closed at 11pm local time, preventing pumping in cooling water.
“The reactor containment vessel, which is the last line of defence to contain the radiation, this may have experienced some damage…it seems that there are damages at several different places of these walls around radioactive substances.”