Though the report echoes other investigations into last year's disaster at the Fukushima Dai-ichi plant, it could fuel complaints that Japan is trying to restart nuclear reactors without doing enough to avoid a repeat. Thursday's resumption of operations at a reactor in Ohi, in western Japan, already had been hotly contested.
Government officials and the utility that runs the Ohi plant announced last month that the No. 3 reactor had passed stringent safety checks and needed to be brought back online to ward off blackouts as Japan enters the high-demand summer months. The government hopes to see the restart of more of Japan's 50 working reactors as soon as possible.
"We have finally taken this first step," said Hideki Toyomatsu, vice president of Kansai Electric Power Co., which operates the plant and hopes to restart another reactor there in a few weeks. "But it is just a first step."
The reactor is the first to be restarted since last year's devastating tsunami inundated the Fukushima plant, setting off meltdowns in three reactors in the world's worst nuclear crisis since Chernobyl in 1986. All of Japan's reactors were gradually taken offline for maintenance or safety checks, and in early May the last reactor shut down, leaving the country without nuclear-generated electricity for the first time since 1970.
The report released Thursday said the Fukushima disaster was "man-made" because it should have been foreseen and avoided. It said that since at least 2006, Japan's Nuclear and Industrial Safety Agency and plant operator Tokyo Electric Power Co. — or TEPCO — knew the risk of a total power outage at Fukushima Dai-ichi in case of a major tsunami. The report accused both of "intentionally" postponing safety measures to avoid reactor stoppages.
It said that the response "betrayed the nation's right to be safe from nuclear accidents" and that collusion between the government, regulators and the utility itself had allowed lax preparation and precautions.
The 10-member panel, appointed by parliament in December, interviewed 1,167 people in hearings exceeding 900 hours. Members also inspected Fukushima Dai-ichi and the neighboring and less-damaged Dai-ni plant, as well as two others in nearby prefectures.
Its bulky final report urged parliament to monitor a new regulatory agency and supervise reforms in the crisis management system. It also urged the government to set clear disclosure rules about its relationship with nuclear operators, construct a cross-monitoring system and overhaul laws governing nuclear energy "to meet global standards of safety, public health and welfare."
Commission Chairman Kiyoshi Kurokawa told a news conference that parliament and the people must keep checking the government.
"Fukushima's nuclear crisis is not over," Kurokawa said. "The world is watching how Japan deals with it and changes."
"Parliament should continue monitoring the government's actions and share that with the people. We should keep checking," he said. "If Japan wants to regain trust, it's now or never."
The commission's report could complicate government efforts to get more reactors going. Over the past month, large demonstrations against restarts have been held each week outside the prime minister's office, reflecting deep grass-roots opposition. Before the crisis, Japan got one-third of its electricity from nuclear plants.
Experts and activists have criticized Prime Minister Yoshihiko Noda's government, saying it is putting business ahead of safety by going forward with the resumption before studying the findings and recommendations in the report.
The Ohi restart that came ahead of the commission report and a launch of the a new regulatory agency is a "red flag," said opposition lawmaker Taro Kono, a key member of a bipartisan anti-nuclear group. "It's a real bad sign."
Hiromitsu Ino, a nuclear expert at the University of Tokyo and a member of the government's safety test panel, called the Ohi reactor's resumption "outrageous," saying safety measures at the plant and emergency plans around it are still inadequate.
Some of the crucial measures designed to protect residents in case of a crisis at Ohi won't be ready immediately — a raised sea wall will be finished next year and an on-site command center by March 2016. Filtered vents, which could reduce radiation leaks to the environment, won't be ready for three more years.
"Its safety is approved only on paper," Ino said. "It hasn't factored in the commission's report, or re-evaluated anti-earthquake measures since the accident. They haven't even examined the impact of radiation on the communities."
Recent findings by seismologists about several fault lines underneath the Ohi plant and others in the area have also renewed safety concerns, prompting the government to order operators to conduct fresh examinations of faults across the country. Kansai Electric, the Ohi plant's operator, failed to submit data about the plant during a review meeting this week.
Other groups, including a private probe panel, have also issued lengthy studies detailing a serious lack of communication between the government and TEPCO, the Fukushima plant's operator, along with a failure by both to provide the public with important information on radiation leaks.
Thursday's report also raised the question of damage to the plant caused by the earthquake itself, though TEPCO, in its own internal investigation, has said it found no evidence of major quake damage.
It claims the unanticipated size of the tsunami was the primary cause, but acknowledges that its tsunami plans were too optimistic and that initial communications were problematic.
TEPCO president Naomi Hirose balked at the report for holding the company responsible for the accident.
"We have to check every single detail in the report and correct one by one if necessary," Hirose said in an interview with public broadcaster NHK.