Japanese officials and Tokyo Electric Power ignored the risk of an atomic accident because they believed in the "myth of nuclear safety", a government-backed report on the Fukushima crisis said Monday.
The study, compiled by a panel of scholars, journalists, lawyers and engineers, also said officials were poorly trained to deal with the crisis after the plant's reactors went into meltdown last year.
"The fundamental problem lies in the fact that utilities, including TEPCO and the government, have failed to see the danger as reality," it said, adding that "they were bound by a myth of nuclear safety and the notion that severe accidents do not happen at nuclear plants in our country."
The 450-page report is the fourth inquiry into the worst nuclear accident in a generation, which happened after the huge tsunami of March 2011 crashed into the Fukushima Daiichi nuclear power station.
Reactors went into meltdown, sending clouds of radiation over a wide area, forcing tens of thousands of people from their homes, some possibly for the rest of their lives.
A damning parliamentary study that said the disaster was "man-made" was released earlier this month, following a private report by a group of journalists and scholars.
Tokyo Electric Power, or TEPCO, the operator of the crippled plant, largely cleared itself of blame, saying the size of the earthquake and tsunami was beyond all expectations and could not have reasonably been foreseen.
The latest report said however that TEPCO and the Nuclear and Industrial Safety Agency (NISA) were ill-prepared to cope with a tsunami or severe accidents, and that the government bungled the evacuation.
"Preparedness for a large-scale complex disaster was insufficient; and they were unprepared for the release of a large amount of radioactive materials into the environment," it added.
The report also took a swipe at former Japanese premier Naoto Kan and his government, saying there was a swirl of bureaucratic confusion in the days following the natural disasters and reactor meltdowns.
Kan's bid to wrestle the crisis from incompetent nuclear officials did not help, it added.
"More harm was done (than good) as his involvement... could have confused the scene, potentially missing opportunities to make important judgments and creating opportunities for misjudgments," the report said.
TEPCO did not train employees "to think independently and to act, and lacked flexible and proactive thinking required for crisis response", the report added.
The latest report backed the government and TEPCO's findings that the plant's cooling systems were knocked out by giant waves that slammed into the plant.
Many scientists and activists have disputed this finding, suggesting it was the initial earthquake that damaged the reactors.
A parliamentary report released earlier this month charged that ingrained collusion between TEPCO, the government and regulators -- combined with a lack of any effective oversight -- led directly to crisis.
"They effectively betrayed the nation's right to be safe from nuclear accidents. Therefore, we conclude that the accident was clearly 'man-made'," said the Fukushima Nuclear Accident Independent Investigation Commission's report released on July 5.
The independent group of scholars and journalists, who reported their findings in February, said TEPCO could and should have done more.
It also said that had the company had its way, its staff would have been evacuated from the crippled plant and the catastrophe could have spiralled even further out of control.
Japan has seen a wave of anti-nuclear sentiment with weekly protests in the tens of thousands gathering in front of the prime minister's official residence, which have grown since the approved restart of two reactors.