"Remarkably undamaged"

August 11, 2012

IAEA: Nuke plant near Fukushima largely undamaged

http://mainichi.jp/english/english/newsselect/news/20120811p2g00m0dm040000c.html 

TOKYO (AP) -- The Japanese nuclear power plant that was closest to the epicenter of last year's earthquake suffered more ground shaking than Fukushima but was largely undamaged because it was designed with enough safety margins, nuclear inspectors said Friday.

The Onagawa plant in northern Japan recorded temblors 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 U.N. nuclear watchdog's inspectors found the Onagawa plant managed to avoid a catastrophe like Fukushima because its safety systems "successful functioned," said Sujit Samaddar, who led the 19-member International Atomic Energy Agency mission.

"With the earthquake of this magnitude, we would have expected the plant to have more damages, and that was not the case," Samaddar said. "This indicated there were significant margins in the designs."

In contrast, the 9.0-magnitude earthquake on March 11, 2011, 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.

A fisherman washes his fishing boat near the Onagawa nuclear power plant, seen at left, in Onagawa, Miyagi Prefecture, on July 31, 2012. (AP Photo/Koji Sasahara)

拡大写真

The Onagawa plant was about 70 kilometers (44 miles) from the quake's epicenter, while Fukushima Dai-ichi was nearly 180 kilometers (112 miles) from the epicenter. Onagawa is about 120 kilometers (74 miles) north of Fukushima Dai-ichi.

The tsunami was more than 13 meters (43 feet) high at both nuclear plants. Fukushima Dai-ichi's seawall was built to withstand a tsunami of up 5.7 meters (18.7 feet). Onagawa's seawall was nearly 14 meters (46 feet) high and survived the tsunami. It has since been extended to nearly 17 meters (56 feet) above sea level.

Investigations by the government, the parliament and private groups have found that Tokyo Electric Power Co. 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 July 30-Aug. 9 visit 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.

Samaddar said he hoped to make similar inspections at other plants in Japan to share information and improve safety at nuclear power across the world. No visits are scheduled yet and would only take place at Japan's invitation.

Five nuclear plants total suffered some level of damage from the earthquake and tsunami, but all but Fukushima Dai-ichi were shut down safely.

In May, the last of Japan's 50 working reactors were turned off as safety checks were carried out, but two are now back online and generating power. Despite public protests, the government is eager to restart reactors because of the ballooning cost of fuel imports to keep the power supply running.

IAEA only finds light damage at Onagawa

By KAZUAKI NAGATA

Staff writer

http://www.japantimes.co.jp/text/nn20120811a4.html

Although the Great East Japan Earthquake and tsunami wrecked the Fukushima No. 1 plant in Fukushima Prefecture, the younger Onagawa plant in neighboring in Miyagi was "remarkably undamaged" by the violent temblor and tsunami and safely shut down, experts from the International Atomic Energy Agency said Friday.

Given a quake of this magnitude, "we would have expected the plant to have more damage, and that was not the case," Sujit Samaddar, who led the 19-member team, told reporters in Tokyo, wrapping up their two-week on-site probe.

From its visual investigation, the IAEA team did not find any signs that cooling pipes or other critical equipment were damaged or caused coolant loss at the 28-year-old plant, said Samaddar, who heads the IAEA International Seismic Safety Centre.

The IAEA team arrived last month to see how the magnitude 9.0 temblor on March 11, 2011, affected the Onagawa plant, which runs three reactors on the Pacific coast about 120 km north of the 40-year-old Fukushima plant.

Whether the quake itself damaged the pipes and cooling systems at Fukushima No. 1, which was swamped by tsunami and suffered three meltdowns, has been hotly debated since a Diet-appointed investigative panel suggested that possibility over denials by Tokyo Electric Power Co.

Samaddar stressed that while his team did not find any trace of such damage, its investigation didn't cover everything in great detail. He said the team only conducted visual checks — of samples of equipment — because time was limited.

Asked what the main differences are between Tepco's Fukushima plant and Tohoku Electric Co.'s Onagawa plant, Samaddar said various factors and data need to be scrutinized and that it will take time to find an answer.

The killer earthquake registered as a weak 6 on the Japanese seismic intensity scale to 7 at Onagawa, which saw tsunami reach about 13 meters high.

Samaddar said there was minor damage from the quake, including cracks in the turbine buildings, but that none of it would have led to a nuclear calamity like Fukushima.

The team investigated structural elements of the plant and the systems safeguarding the reactors, and held interviews with some of the engineers.

The data and experience collected from the investigation will be added to the IAEA's database to improve safety at nuclear power plants worldwide.