“TOKYO — Japan’s nuclear crisis intensified dramatically on Wednesday after the authorities announced that a second reactor unit at the stricken Fukushima Daiichi plant in northeastern Japan may have ruptured and appeared to be releasing radioactive steam.
Such were the radiation levels above the plant, moreover, that the Defense Force put off a highly unusual plan to dump water from military helicopters to lower temperatures in an overheating pool containing spent fuel rods, news reports said.
The development showed the seriousness of the challenges facing the authorities. The vessel that possibly ruptured had been seen as the last fully intact line of defense against large-scale releases of radioactive material from one of the stricken reactors, but it was not clear how serious the possible breach might be. The implications of overheating in the fuel rod pool at the plant’s No. 3 reactor unit also seemed perilous.”
The Mark I reactors in question were built back in