SEOUL >> A newly released report vividly portrays the doubts confronted by the Japanese government in the first hours and days after the March 11 tsunami overran a coastal nuclear power plant, and a fear that officials might have to evacuate Tokyo.

The six-month investigation was conducted by a private policy group called the Rebuild Japan Initiative Foundation and involved 30 independent researchers, academics, lawyers and journalists.

Their report, due to be published later this week but released beforehand to several media organizations, disclosed that the government feared “a devil’s chain reaction” following the meltdown at the Fukushima Daiichi nuclear power plant, while at the same time assuring the public that all was under control.

The team is one of several that are conduction independent reviews of how the Japanese government responded to the crisis. At best, the results so far are mixed.

The administration of then-prime minister Naoto Kan as well as nuclear regulators and the Tokyo Electric Power Co., the utility that runs Fukushima, have been chided for their haphazard response to the crisis and for failing to keep the public informed of the dangers they faced.

At one point, the Rebuild Japan report claims advisers to Kan began referring to a worst case scenario that would not only force the evacuation of tens of millions of Tokyo residents, but worse, could cause widespread environmental damage across Japan. But Kan’s staff continued to assure the Japanese public and the international community that the situation was under control.

Kan reportedly ordered workers to remain at the devastated nuclear plant, struck by a wall of water after an earthquake hit northeastern Japan on the afternoon of March 11, fearing that thousands of spent fuel rods stored at a damaged reactor would melt and spew radiation following a hydrogen explosion at an adjacent reactor, the report said.

To reach its findings, the review panel interviewed more than 300 government officials and nuclear regulators — as well as Kan himself — to piece together a timeline of the tense hours following Japan’s worst-ever environmental disaster.

Kan was forced to resign in September under hard criticism that he bungled the handling of the crisis. At one point, Kan flew over the plant by helicopter on the morning of March 12; a tactic critics say slowed the response effort.

While the devastation did not prompt Tokyo’s evacuation the Fukushima meltdowns spewed radioactivity into the atmosphere, leading to the evacuation of some 80,000 nearby residents, many of whom have yet to return.

Engineers stemmed further damage by pumping seawater into the plant’s ailing reactors and spent fuel pools.

But as the nation marks the first anniversary of the disaster next month, the plant remains abandoned and officials say it may take decades to conduct a proper cleanup.

During a recent tour, plant officials told reporters that stemming the release of additional radioactivity is a day-to-day job.

“An earthquake or tsunami like the ones seen a year ago could be a source of trouble for these (cooling) systems. But we are currently reinforcing the spent fuel pool and making the sea walls higher against tsunamis,” Takeshi Takahashi, the Daiichi plant’s manager, told reporters.

Government spokesman Yukio Edano on Tuesday told reporters in Tokyo that he revealed all information in the hours after the disaster.

“I shared all information. Back then, I was not in a position where I, as someone who is not an expert, could irresponsibly speak about my own personal impressions and my sense of crisis,” he told a news conference. “I conveyed assessments and decisions of the government, government agencies and experts.”