Damage from the huge March 11, 2011, earthquake, and not just the ensuing tsunami, could not be ruled out as a cause of the accident, the panel added, a finding with serious potential implications as Japan seeks to bring idled reactors on line.
The panel criticised the response of Fukushima Daiichi plant operator Tokyo Electric Power Co, regulators and then Prime Minister Naoto Kan, who quit last year after criticism of his handling of a natural disaster that became a man-made crisis.
"The ... Fukushima Nuclear Power Plant accident was the result of collusion between the government, the regulators and Tepco, and the lack of governance by said parties," the panel said in an English summary of a 641-page Japanese document.
The report - issued hours after a reactor began supplying electricity to the grid for the first time in two months - put an official imprimatur on criticism of the cosy ties that have bound a powerful nexus of interests known as the "nuclear village".
