Japan acknowledged Tuesday that it was unprepared for a severe nuclear accident like the tsunami-generated Fukushima disaster and said damage to the reactors and radiation leakage were worse than it previously thought.
In a report being submitted to the United Nations' nuclear watchdog agency, the government also acknowledged reactor design inadequacies and a need for greater independence for the country's nuclear regulators.
The report says the nuclear fuel in three reactors probably melted through the inner containment vessels, not just the core, after the March 11 earthquake, and the tsunami knocked out the Fukushima Daiichi nuclear plant's power and cooling systems. Fuel in the Unit 1 reactor started melting hours earlier than previously estimated.