Officials in Japan were "astonishingly unprepared" for the events that led to the Fukushima nuclear disaster, a damning report has concluded.
Investigators highlighted a catalogue of human errors before and after the earthquake and tsunami which killed thousands of people, devastated the Japanese economy and threatened the future of the nuclear industry.
In particular, they attacked the myth of "absolute safety" promoted by supporters of nuclear power.
The independent report, published in the Bulletin of the Atomic Scientists, criticised the building of multiple nuclear reactor units so close together, and the failure to take the risk of a deadly tsunami seriously.
The nine-magnitude earthquake on March 11 last year triggered a 14-metre tsunami which wiped out coastal towns, shut roads, severed communications and claimed thousands of lives.
It also cut off all electricity to the Fukushima Daiichi nuclear power station, setting the stage for a major nuclear accident.
A cascade of events followed, including meltdowns of reactor cores, explosions and the release of radioactive material.
After the disaster the Rebuild Japan Initiative Foundation set up an independent panel to review the actions and responses of the Japanese government, nuclear plant owners the Tokyo Electric Power Company (Tepco) and regulatory agencies.
Almost 300 people involved in the accident were interviewed, including Japan's prime minister at the time, Naoto Kan.
The report, written by foundation chairman Yoichi Funabashi and investigation panel director Kay Kitazawa, said the tsunami could and should have been anticipated.
Earlier research on a tsunami that occurred in 869 AD demonstrated the risk of high waves after an earthquake. But even though Tepco's own nuclear energy division understood the danger, the company dismissed it as "academic".
Regulatory authorities encouraged the company to incorporate new findings about tsunami risk into its safety plans but did not make the measures mandatory.
The folly of building a collection of nuclear reactor units in one place was also highlighted.
It meant the nuclear power station's director, Masao Yoshida, had to cope simultaneously with core meltdowns at three reactors and exposed fuel pools at four units.
Major systemic failure was built on a raft of small individual problems, said the report.
For instance, when on-site workers referred to the severe accident manual, the answers they were looking for were not there. A lack of training had also led to the condition of the emergency cooling system being misjudged.
Tepco was said to bear the primary responsibility for incompetent handling of the disaster's aftermath. The organisation failed to make rapid decisions and lost the government's trust, it was claimed.
Confusion about the roles of public and private institutions also contributed to the poor response.
Questioning why preparations were so inadequate, the report said: "One factor was a twisted myth - a belief in the 'absolute safety' of nuclear power.
"This myth has been propagated by interest groups seeking to gain broad acceptance for nuclear power."
The safety myth had been nurtured for decades, partly to overcome strong anti-nuclear feelings linked to the dropping of atomic bombs on Hiroshima and Nagasaki at the end of the Second World War, said the report.
Japanese government regulators including the Nuclear and Industrial Safety Agency (Nisa) and the Nuclear Safety Commission (NSC) were criticised for their lack of leadership.
In particular, a system designed to help governments decide when to evacuate in the event of a radioactive leak was not used.
The report told how secret plans were drawn up for what to do under six increasingly drastic scenarios.
In the most extreme case, some 30 million residents could have been evacuated from the Tokyo metropolitan area.
The authors concluded: "It's clear from our investigation of the Fukushima Daiichi accident that even in the technologically advanced country of Japan, the government and the plant operator, Tokyo Electric Power Company, were astonishingly unprepared, at almost all levels, for the complex nuclear disaster that started with an earthquake and a tsunami. And this grave oversight will affect the Japanese people for decades.
"Ultimately, the final outcome of studies of Fukushima Daiichi should be an intense effort to build up the resilience of the country, its organisations and its people, so future disaster can be averted or responded to effectively."
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