The UN atomic agency said on Friday that Japan’s Onagawa nuclear power plant, despite having been closest to the epicenter of the earthquake and tsunami that struck the country last year, was in surprisingly good shape.
The structural elements of the plant were “remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake,” the International Atomic Energy Agency (IAEA) said in an initial report.
The Onagawa plant recorded temblors — “among the strongest of any plant affected by the earthquake” — that exceeded its design capacity and the basement of one of its reactor buildings flooded, but the plant maintained its cooling capacity, its reactors shut down without damage to their cores and there were no signs of major damage to crucial safety systems, the Vienna-based IAEA said.
The Fukushima Dai-ichi plant, 120km to the south, was not so lucky, suffering multiple reactor meltdowns and releasing radioactivity into the environment in the world’s worst nuclear accident in 25 years.
The IAEA report followed a two-week trip by 19 international experts that will be followed by further visits at Onagawa and reviews of other Japanese nuclear plants.
Findings will be added to an IAEA database being compiled by its International Seismic Safety Center (ISSC) that was part of the watchdog’s “action plan” on nuclear safety drawn up in the wake of the Fukushima disaster.
“The data we are collecting will make an important contribution to improving safety,” mission head Sujit Samaddar said. “Information in the database will allow IAEA member states to measure the performance of their nuclear power plants in the face of external hazards.”
In contrast, the magnitude 9.0 earthquake on March 11 last year knocked out a power line at the Fukushima Dai-ichi plant and generated a large tsunami that flooded its emergency generators, destroying the plant’s cooling systems. Catastrophic meltdowns occurred in three reactors, releasing radiation that has tainted the surrounding environment.
The plant has since stabilized, but more than 100,000 people still can’t go home due to radiation fears, while work to decommission the plant will take about 40 years. It was the world’s worst atomic accident since Chernobyl.
The Onagawa plant was about 70km from the quake’s epicenter, while Fukushima Dai-ichi was nearly 180km from the epicenter.
The tsunami was more than 13m high at both nuclear plants. Fukushima Dai-ichi’s seawall was built to withstand a tsunami of up 5.7m. Onagawa’s seawall was nearly 14m high and survived the tsunami. It has since been extended to nearly 17m above sea level.
Investigations by the government, the parliament and private groups have found that Tokyo Electric Power Co (TEPCO) underestimated the earthquake and tsunami risks faced by its plant at Fukushima despite a history of quakes in the region. The investigations have also criticized TEPCO and government regulators, which have developed cozy relationships, for ignoring safety standards and recommendations, including those by IAEA and other groups.
The IAEA visit from July 30 to Wednesday this week was its first to the Onagawa plant since the disaster. The group inspected the plant and interviewed dozens of workers and officials to assess how its structure, systems and components responded to the quake and its violent shakings.