'Melt-through' at Fukushima? / Govt report to IAEA suggests situation worse than meltdown
"Nuclear fuel in three reactors at the Fukushima No. 1 nuclear plant has possibly melted through pressure vessels and accumulated at the bottom of outer containment vessels, according to a government report obtained Tuesday by The Yomiuri Shimbun.
"A "melt-through"--when melted nuclear fuel leaks from the bottom of damaged reactor pressure vessels into containment vessels--is far worse than a core meltdown and is the worst possibility in a nuclear accident.
"The possibility of the situation at the plant's Nos. 1 to 3 reactors was raised in a report that is to be submitted to the International Atomic Energy Agency.
"If the report is released as is, it would be the first official recognition that a melt-through has occurred.
"It was revealed earlier that sections of the bottom of the pressure vessels where control rods go through have been damaged. Highly radioactive water from inside the pressure vessels was confirmed to have leaked out of the containment vessels, even outside the buildings that house the reactors.
"The report also acknowledges problems with the vertical administrative structure concerning nuclear safety regulations. As a result, the report says, who was responsible for keeping people safe in the event of a nuclear accident was not clear...."