The historic 2011 Fukushima nuclear disaster, after more than 900 hours of hearings and 1,100 interviews with officials, was after all deemed an implanted bomb just waiting when to literally explode.

In a 641-page report released by the Fukushima Nuclear Accident Independent Investigation Commission, it found that Tokyo Electric Power Co. (TEPCO), operator of the Fukushima Daiichi Nuclear Power Plant, "intentionally postponed putting safety measures in place" even when it had been advised way back in 2006 that a large scale tsunami could possibly lead to a power outage at the plant, if not totally destroy it.

The 2011 Fukushima nuclear disaster discharged radiation and forced some 150,000 individuals from their homes, of which most will no longer be able to return.

The Fukushima nuclear accident "cannot be regarded as a natural disaster," Kiyoshi Kurokawa, Tokyo University professor emeritus and panel chairman of the commission, wrote in the report released in Tokyo on Thursday. "It was a profoundly manmade disaster - that could and should have been foreseen and prevented. And its effects could have been mitigated by a more effective human response."

Japan's Fukushima nuclear crisis was a preventable disaster, but a "collusion" among the government, regulators and the plant operator effectively sealed its fate.

The report said the nuclear regulators and TEPCO knew the risk of reactor-core damage from the loss of seawater pumps, but both the Nuclear and Industrial Safety Agency and plant operator TEPCO kept postponing putting safety measures so as to escape the need to shut down the reactor.

"We found evidence the regulatory agencies would explicitly ask about the operators' intentions whenever a new regulation was to be implemented," the commission wrote. "From TEPCO's perspective, new regulations would have interfered with plant operations and weakened their stance in potential lawsuits."

"This was a disaster 'Made in Japan," Mr Kurokawa said in the report's introduction. "Its fundamental causes are to be found in the ingrained conventions of Japanese culture: our reflexive obedience; our reluctance to question authority; our devotion to 'sticking with the program,' our groupism, and our insularity."

"There were many opportunities for taking preventive measures before March 11. The accident occurred because Tepco did not take these measures," and regulators, unfortunately, just went along, the report said.

The report's release coincided on the same day a nuclear reactor went back online in western Japan, the first time since the Fukushima accident in March 2011.

"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 report is one of three panels looking into the Fukushima 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.

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