TOKYO — Japan admitted yesterday that it was unprepared for a severe nuclear accident like the tsunami-caused Fukushima disaster, and said damage to the reactors and radiation leakage were worse than it previously thought.
In a report being submitted to the UN nuclear agency, the government also acknowledged reactor design flaws and a need for greater independence for the country’s nuclear regulators.
The report said the nuclear fuel in three reactors probably melted through the inner containment vessels, not just the core, after the March 11 earthquake and 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.
The 750-page report, compiled by Japan’s nuclear emergency task force, factors in a preliminary evaluation by a team from the International Atomic Energy Agency and was to be submitted to the agency as requested.
“In light of the lessons learned from the accident, Japan has recognized that a fundamental revision of its nuclear safety preparedness and response is inevitable,’’ the report said. It also recommended a national debate on nuclear power. The report said the flaws in basic reactor design included the venting system for the containment vessels and the location of spent-fuel cooling pools high in the buildings, which resulted in leaks of radioactive water that hampered repair.