"There in fact were various opinions (about the plant's safety) before the accident, but no well-thought-out preparations were made," Kan said in an interview with The Yomiuri Shimbun. "In that sense, the nuclear accident should be considered a manmade disaster."
Kan said two watchdogs -- the Economy, Trade and Industry Ministry's Nuclear and Industrial Safety Agency and the Cabinet Office's Nuclear Safety Commission -- did not foresee the possibility that all power sources could be lost at the plant.
Thus, he said, neither could effectively respond after a March 11 earthquake and tsunami knocked out the plant's cooling systems. Kan resigned last June.
"That accident was beyond our expectations, so there were no preparations to cope with it properly," Kan said. "It had been assumed there was no possibility the plant's power sources would be lost, so it was only natural that we were one step behind as the crisis unfolded."
He expressed frustrations with the response from Tokyo Electric Power Co., the plant's owner.
Kan said TEPCO didn't follow his instructions to vent vapor from the nuclear reactor containers.
And he said staff at an off-site emergency-response center near the plant -- designed to function as a front-line communications center in a crisis -- vacated soon after the accident.
"As a result, arrangements that had been assumed in accident simulations hardly worked at all," said Kan, who resigned last month.
He also apologized to the tens of thousands of people unable to return to their homes because of radiation.