Japanese radiation leak 'twice the estimated figure'

Japan has doubled its estimate for the amount of radiation leaked at the Fukushima Daiichi power plant in the days after the tsunami on 11 March. It has also admitted to being unprepared for such a severe nuclear accident.

In a report submitted to the UN nuclear agency, the government said the cores melted in three units and probably breached the inner containment vessels after the tsunami knocked out the plant's power and cooling systems. Fuel at Unit 1 started melting hours earlier than previously estimated.

The report, compiled by Japan's nuclear emergency taskforce, will be submitted to the International Atomic Energy Agency. It acknowledged a lack of independence at Japan's nuclear regulator and promised to improve the safety control system.

The report comes the day after the government's nuclear officials doubled the estimate of how much radiation leaked from the plant. The Nuclear and Industrial Safety Agency said in a report on Monday that nuclear fuel inside three reactors at the Fukushima Daiichi plant probably melted through not only the reactor cores, but also through the reactors' inner containment vessels.

The report said twice as much radiation may have been released as earlier estimated. That would be about one-sixth of the amount released at Chernobyl instead of the earlier estimate of one-tenth.