A new report by the OECD’s Nuclear Energy Agency (NEA) – ‘Five years after the Fukushima-Daiichi accident: nuclear safety improvements and lessons learnt’ – says experience during the accident "highlighted the need to reconsider approaches to information sharing and assessment, both domestically and internationally". Nuclear regulators internationally should "continue improving" their communication strategies, despite progress made since the March 2011 accident, it notes.

It recommends closer involvement with the general public and other stakeholders in decision-making, which is "appropriate and advisable to enhance the credibility, legitimacy, sustainability and final quality of regulatory and off-site emergency management decisions".

The NEA’s report is a follow-up to one published in 2013 (‘OECD/NEA nuclear safety response and lessons learnt’), which concluded that, in the aftermath of Fukushima-Daiichi, "nuclear power plants in NEA member countries were safe".

NEA director-general William Magwood said in the report that "much work is still before us to address new lessons, including how to effectively deal with more complex issues such as the human aspects of nuclear safety reflected in safety culture, training and organisational factors".

A separate report published last year by the International Atomic Energy Agency (IAEA) said a major factor that contributed to the Fukushima-Daiichi accident "was the widespread assumption in Japan that its NPPS were so safe that an accident of this magnitude was simply unthinkable". IAEA director-general Yukiya Amano, said then: "This assumption was accepted by nuclear plant operators and was not challenged by regulators or by the government."

A 2012 report by Japan’s government said there had been a lack of regulatory independence in Japan at the time of the accident and collusion between regulators and operators. The independent Nuclear Regulation Authority was established in September 2012 to meet the need for clear separation of regulation from promotion. The report identified other contributory factors such as a flawed safety culture, organisational failures and weaknesses, weak emergency preparedness and response, and poor onsite and offsite disaster handling.

Accident analyses are continuing in Japan. A third-party investigative panel is being set up by Tokyo Electric Power Co (Tepco) to look at why the company failed to find its own manual containing criteria for judging nuclear reactor core meltdowns until nearly five years after the onset of the Fukushima nuclear disaster, and Investigate whether the document was covered up.

The discovery of the manual earlier in February, highlighted the lack of a crisis mentality among Tepco employees, as well as the utility’s fear of a negative reaction from the government, which was excessively nervous about the phrase, "reactor core meltdowns", according to Japanese press reports.

Akio Takahashi, president of the Japan Atomic Industrial Forum (JAIF), who was in charge of responding to the Fukushima accident as a then Tepco fellow, declined to mention the manual issue. "I don’t know whether there was a judgment that meltdowns had occurred," he told a JAIF regular news conference on 25 February. However, there are records that Tepco employees held teleconference discussions on the company’s response to the accident on the assumption that meltdowns had occurred.

The manual on countermeasures against nuclear disasters, which was compiled in 2003, defines a meltdown as a situation in which over 5% of the core of a reactor has been damaged. If the utility had followed the manual, it should have assessed the damage was a meltdown three days after the accident, when the reactors’ sensors were restored. Engineers learned at that time that fuel in unit 1 was 55% damaged, and 30% damaged in unit 3, NHK reported. Yet it was more than two months later that the company acknowledged the meltdowns.

Tsuneo Futami, a specially appointed professor at the Tokyo Institute of Technology who served as head of the Fukushima plant from 1997 to 2000, said, "I guess employees failed to share the manual because they were under the impression that meltdowns would never take place, and forgot its existence." Tepco’s report on its investigation into the disaster, released in 2012, makes no mention of the manual.