By Risa Maeda and Linda Sieg
TOKYO (Reuters) - Japan's Fukushima nuclear crisis was a preventable disaster resulting from "collusion" among the government, regulators and the plant operator, an expert panel said on Thursday, wrapping up an inquiry into the worst nuclear accident in 25 years.
Damage from a big earthquake on March 11 last year, and not just the ensuing tsunami, could not be ruled out as a cause of the accident, the panel said, a finding that could have serious implications as Japan seeks to bring idled reactors back on line.
The panel also pointed to problems in the response of plant operator Tokyo Electric Power Co and then Prime Minister Naoto Kan, who resigned last year after criticism of his handling of a natural disaster that developed into 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 report.
Regulators, it said, had been were reluctant to adopt global safety standards that could have helped prevent the disaster in which reactors melted down, spewing radiation and forcing about 150,000 people from their homes, many of whom will never return.
"Across the board, the Commission found ignorance and arrogance unforgivable for anyone or any organization that deals with nuclear power. We found a disregard for global trends and a disregard for public safety," the panel said.
The panel's finding that seismic damage may well have played a role could also affect the restart of reactors that were taken offline, mostly for maintenance and safety checks, in the months since Fukushima.
"We have proved that it cannot be said that there would have been no crisis without the tsunami," Katsuhiko Ishibashi, a seismologist and panel member, said in the report.
Experts have said that an active fault may lie under Kansai Electric Power Co's Ohi plant in western Japan, whose No. 3 unit began supplying electricity to the grid early on Thursday. Ohi's No. 4 unit will come on line later this month after the government approved the restarts to avoid a power shortage.
The report by the experts - one of three panels looking into the Fukushima disaster - follows a six-month investigation involving more than 900 hours of hearings and interviews with more than 1,100 people, the first such inquiry of its kind.
Many of the shocking details of the disaster, including operator Tokyo Electric Power Co's (Tepco) failure to prepare for a massive tsunami and a chaotic response by the utility and government, have already been made public.
The report pointed to numerous missed opportunities to take steps to prevent the disaster, citing lobbying by the nuclear power companies as well as a "safety myth" mindset that permeated the industry and the regulatory regime as among the reasons for the failure to be prepared.
Resource-poor Japan has for decades promoted nuclear power as safe, cheap and clean. Atomic energy supplied nearly 30 percent of electricity needs before the disaster.
"As a result of inadequate oversight, the SA (Severe Accident) countermeasures implemented in Japan were practically ineffective compared to the countermeasures in place abroad, and actions were significantly delayed as a result," it said.
Tepco came under heavy criticism in the report, including for putting cost-cutting steps ahead of safety as nuclear power became less profitable over the years. "While giving lip service to a policy of 'safety first', in actuality, safety suffered at the expense of other management priorities," the team said.
In a report on its own internal investigation issued last month, Tepco denied responsibility, saying the big "unforeseen" tsunami was to blame - though it admitted that in hindsight it was insufficiently prepared.
Tepco, struggling under huge costs for compensation, cleanup and decommissioning, was effectively nationalised last month with a 1 trillion yen injection of public funds.
The panel also said it had found no evidence to back up Kan's allegation that Tepco had planned to abandon the tsunami-ravaged plant as the crisis risked spinning out of control.
(Editing by Robert Birsel)