These reactors were doomed as soon as they used seawater to try to cool them off.
Japan may have lost race to save nuclear reactor
Fukushima meltdown fears rise after radioactive core melts through vessel – but 'no danger of Chernobyl-style catastrophe'
• In pictures: Fukushima nuclear emergency - week three
• Interactive: Efforts to contain the nuclear accident
The radioactive core in a reactor at the crippled Fukushima nuclear power plant appears to have melted through the bottom of its containment vessel and on to a concrete floor, experts say, raising fears of a major release of radiation at the site.
The warning follows an analysis by a leading US expert of radiation levels at the plant. Readings from reactor two at the site have been made public by the Japanese authorities and Tepco, the utility that operates it.
Richard Lahey, who was head of safety research for boiling-water reactors at General Electric when the company installed the units at Fukushima, told the Guardian workers at the site appeared to have "lost the race" to save the reactor, but said there was no danger of a Chernobyl-style catastrophe.
Read more at www.guardian.co.uk
Workers have been pumping water into three reactors at the stricken plant in a desperate bid to keep the fuel rods from melting down, but the fuel is at least partially exposed in all the reactors.