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IAEA Expert Team Concludes Mission to Onagawa NPP

Tokyo, Japan

An IAEA team of international experts today delivered its initial report at the end of a two-week mission to gather information about the effects of the Great East Japan Earthquake on the Onagawa Nuclear Power Station (NPS), saying the plant was "remarkably undamaged".

Findings from the visual investigation will be added to an IAEA data base being compiled by its International Seismic Safety Centre (ISSC) to provide knowledge for Member States about the impact of external hazards on nuclear power plants.

The ISSC data bank makes an important contribution to the IAEA's Action Plan on Nuclear Safety, which was unanimously endorsed by the Agency's Member States following last year's nuclear accident at Fukushima Daiichi NPS.

Onagawa, facing the Pacific Ocean on Japan's north-east coast, was the nuclear power plant closest to the epicentre of the 11 March 2011 magnitude 9.0 earthquake that struck Japan and resulted in a devastating tsunami.

The plant experienced very high levels of ground shaking - among the strongest of any plant affected by the earthquake - and some flooding from the tsunami that followed, but was able to shut down safely.

In its draft report the team said that "the structural elements of the NPS were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake".

The mission's objective was to observe how structures, systems and components with significance to the safety of the plant responded to the earthquake and heavy shaking. At the damaged Fukushima Daiichi NPS, nearly 120 km south of Onagawa NPS, the effects of the earthquake, tsunami and hydrogen explosions make it impossible to single out the impact of external hazards on safety-related parts of the power station.

The Government of Japan and the IAEA therefore agreed to deploy a mission to the three-unit Onagawa NPS. The team's 19 members from six countries, including IAEA staff, held discussions with the operators of the Onagawa power station, and reviewed logbooks and repair reports documented after the earthquake.

Presenting information collected by the team to the Japanese Government, the mission recommended that follow-up missions be conducted at Onagawa and reviews be conducted at other nuclear power plants in Japan that have experienced varying magnitudes of earthquakes.

"The data we are collecting will make an important contribution to improving safety," said Sujit Samaddar, mission leader and Head of the IAEA's ISSC. "Information in the database will allow IAEA Member States to measure the performance of their nuclear power plants in the face of external hazards. We are also seeking such data from Member States of the IAEA other than Japan."

"This is an initial step in a much longer process. The level of cooperation and frank sharing of information that we received from the staff at Onagawa NPS and its owners, the Tohoku Electric Power Company, sets a very good example," Samaddar said.

General information about the IAEA Action Plan on Nuclear Safety can be found on the IAEA Website.

Last update: 16 Feb 2018

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