U.N. inspectors faulted Japan on Wednesday for underestimating the threat of a devastating tsunami on its crippled Fukushima Dai-ichi nuclear plant but praised its overall response to the crisis as exemplary.
The preliminary report by a team from the International Atomic Energy Agency also said the tsunami hazard was underestimated at several other nuclear facilities in Japan, and called for experts worldwide to learn from the disaster to avert future accidents.
The IAEA team of international experts from 12 countries, which spent a week in Japan conferring with officials and inspecting the plant, will submit its full report at a high-level IAEA conference in Vienna from June 20-24.
"Japan's response to the nuclear accident has been exemplary, particularly (as) illustrated by the dedicated, determined and expert staff working under exceptional conditions," the report said. It also praised the evacuation of those living near the plant as "impressive and well-organized."
The Fukushima Dai-ichi facility was crippled when a huge tsunami generated by a magnitude 9.0 earthquake hit Japan on March 11. It suffered explosions, fires and meltdowns in the days after the tsunami.
More than 80,000 people have been evacuated from its vicinity.
The report said the earthquake and tsunami were the direct cause of the power outages and communications blackouts that ensued. It said the potential size of the tsunami that hit the plant, estimated at as high as 49 feet (15 meters), was not sufficiently planned for and "overwhelmed" the plant's defenses.
"The tsunami hazard for several sites was underestimated," it said. "Nuclear plant designers and operators should appropriately evaluate and protect against the risks of all natural hazards, and should periodically update those assessments and assessment methodologies."
It did not go into further detail.
The report said Japan's crisis underscored the value of disaster-proof emergency centers onsite to protect workers and provide a safe command headquarters for the management of the response.
A crisis center was built at Fukushima Dai-ichi after an earthquake hit a different part of Japan in 2007. The center still serves as the crisis headquarters at the plant, and the IAEA report suggested it has functioned well.
Further, the report suggested that long-term efforts to monitor the health and exposure levels of workers and the public "would be beneficial."
Mike Weightman, the IAEA team leader and the United Kingdom's chief inspector of nuclear installations, said the IAEA team focused on finding lessons from the crisis that can be applied around the world.
"You can make nuclear plants safe against natural events, but you have to understand those events," Weightman said.
The team examined the technical processes more closely than political or managerial issues, which he said would likely be a topic raised at the IAEA meeting in Vienna.
He said Japanese officials offered their full cooperation, and his team was provided access to the plant and officials and answers to their questions.
"I think there are many constructive suggestions in this report," said Goshi Hosono, director of the government's nuclear crisis taskforce. "We will read it thoroughly."
TEPCO spokesman Junichi Matsumoto said the utility, which operates the facility, provided all available information to the IAEA team, including details on how it coordinated its efforts between Tokyo headquarters and workers onsite at the plant.
"We hope that the results of the IAEA investigation of what happened at the plant will be shared as a common international asset and used in a way that will contribute to nuclear safety around the world," he said.