Investigations

Three investigations into the accident showed the man-made nature of the catastrophe and its roots in regulatory capture associated with a "network of corruption, collusion, and nepotism." A New York Times report found that the Japanese nuclear regulatory system consistently sided with, and promoted, the nuclear industry based on the concept of amakudari ('descent from heaven'), in which senior regulators accepted high paying jobs at companies they once oversaw.

In August 2011, several top energy officials were fired from their jobs by the Japanese government; affected positions included the Vice-minister for Economy, Trade and Industry; the head of the Nuclear and Industrial Safety Agency, and the head of the Agency for Natural Resources and Energy.

In 2016 three former TEPCO executives, chairman Tsunehisa Katsumata and two vice presidents, were indicted for negligence resulting in death and injury. The three pleaded not guilty, and in September 2019, the court agreed.

NAIIC

The Fukushima Nuclear Accident Independent Investigation Commission (NAIIC) was the first independent investigation commission by the National Diet in the 66-year history of Japan's constitutional government.

The accident "cannot be regarded as a natural disaster," the NAIIC panel's chairman, Tokyo University professor emeritus Kiyoshi Kurokawa, wrote in the inquiry report. "It was a profoundly man-made accident – that could and should have been foreseen and prevented. And its effects could have been mitigated by a more effective human response." "Governments, regulatory authorities and Tokyo Electric Power [TEPCO] lacked a sense of responsibility to protect people's lives and society," the Commission said. "They effectively betrayed the nation's right to be safe from nuclear accidents. He stated that the accident was "made in Japan", since it was a manifestation of certain cultural traits, saying:

“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.”

The Commission recognized that the affected residents were still struggling and facing grave concerns, including the "health effects of radiation exposure, displacement, the dissolution of families, disruption of their lives and lifestyles and the contamination of vast areas of the environment".

ICANPS

The purpose of the Investigation Committee on the Accident at the Fukushima Nuclear Power Stations (ICANPS) was to identify the accident's causes and propose policies designed to minimize the damage and prevent the recurrence of similar incidents. The 10 member, government-appointed panel included scholars, journalists, lawyers, and engineers. It was supported by public prosecutors and government experts and released its final 448-page investigation report on 23 July 2012.

The panel's report faulted an inadequate legal system for nuclear crisis management, a crisis-command disarray caused by the government and TEPCO, and possible excess meddling on the part of Prime Minister Naoto Kan's office in the crisis' early stage. The panel concluded that a culture of complacency about nuclear safety and poor crisis management led to the nuclear accident.