The Guardian reports that "molten nuclear fuel in three reactors at the Fukushima Daiichi power plant is likely to have burned through pressure vessels, not just the cores, Japan has said in a report in which it also acknowledges it was unprepared for an accident of the severity of Fukushima. It is the first time Japanese authorities have admitted the possibility that the fuel suffered "melt-through" – a more serious scenario than a core meltdown.