Japan Underestimated Tsunami Hazard for Nuclear Sites

VIENNA, Austria, June 1, 2011 (ENS) – Japan had underestimated potential tsunami hazards to its nuclear power plants before the March 11 earthquake and tsunami that damaged the Fukushima Daiichi facility, experts from the UN’s International Atomic Energy Agency said today.

The team of international nuclear safety experts from 12 countries said in a draft report summary delivered to Japanese authorities today, that “the tsunami hazard for several sites was underestimated.”

IAEA said the team held extensive discussions with officials from the Japanese nuclear-related agencies and visited three nuclear power plant sites, including the plant at Fukushima Daiichi.

The expert team from 12 countries assembled by the IAEA visits the Fukushima Daiichi nuclear power plant. (Photo courtesy IAEA)

The visits gave the team a first-hand appreciation of the scale of devastation wreaked by the earthquake and tsunami on 11 March and of the extraordinary efforts Japanese workers have been applying ever since to stabilize the situation.

“Our entire team was humbled by the enormous damage inflicted by the tsunami on Japan. We are also profoundly impressed by the dedication of Japanese workers working to resolve this unprecedented nuclear accident,” said team leader Mike Weightman, the United Kingdom’s chief inspector of nuclear installations.

The team includes experts with experience across a range of nuclear specialties from: Argentina, China, France, Hungary, India, Indonesia, Russia, South Korea, Spain, Turkey, United Kingdom, and the United States.

Created by an agreement of the IAEA and the Government of Japan, the team sought to identify lessons learned from the accident that can help improve nuclear safety around the world.

UK nuclear expert Mike Weightman (Photo courtesy IAEA)

“I appreciate the high level of cooperation and access that our team has received from Japan, as the devastating natural events and subsequent accident at TEPCO’s Fukushima Daiichi have provided a unique opportunity for learning,” Weightman said. “It is of fundamental importance for all with responsibility for nuclear safety across the world to seek to learn from this unique event.”

The Great East Japan Earthquake on March 11, a magnitude 9 earthquake, generated a series of large tsunami waves that struck the east coast of Japan, the highest being 38.9 meters (127.6 feet) at Aneyoshi, Miyako Prefecture.

As well as other industries, several nuclear power facilities were affected by the severe ground motions and large multiple tsunami waves: Tokai, Higashi Dori, Onagawa, and Tokyo Electric Power Co.’s Fukushima Daiichi and Daini power plants.

The operational units at these facilities were successfully shut down by the automatic systems installed as part of the design of the nuclear power plants to detect earthquakes. However, the large tsunami waves affected all these facilities to varying degrees, with the most serious consequences occurring at TEPCO’s Fukushima Daiichi.

Tsunami waters rush into the radioactive waste disposal building at TEPCO’s Fukushima Daiichi nuclear power plant, March 11, 2011 (Photo courtesy TEPCO)

These tsunami waves overwhelmed the defenses of the Fukushima Daiichi facility, which were only designed to withstand tsunami waves of a maximum of 5.7 meters (18.7 feet) high. The larger waves that impacted this facility on that day were estimated to be larger than 14 meters (45.9 feet) high, according to the team’s draft report summary.

In its draft report, the team offered a set of preliminary conclusions and identified lessons learned in three broad areas: external hazards, severe accident management and emergency preparedness.

The experts found that “Japan’s response to the nuclear accident has been exemplary, particularly illustrated by the dedicated, determined and expert staff working under exceptional circumstances.”

“Japan’s long-term response, including the evacuation of the area around stricken reactors, has been impressive and well organized. A suitable and timely follow-up programme on public and worker exposures and health monitoring would be beneficial,” according the the experts’ report.

“The tsunami hazard for several sites was underestimated,” the report states. “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.”

“Nuclear regulatory systems should address extreme events adequately, including their periodic review, and should ensure that regulatory independence and clarity of roles are preserved,” the report states.

The experts said that the Japanese accident demonstrates the value of “hardened on-site Emergency Response Centres with adequate provisions for handling all necessary emergency roles, including communications.”

The team’s final report will be delivered to the Ministerial Conference on Nuclear Safety at IAEA headquarters in Vienna from June 20 to 24.

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