The Nuclear Regulation Authority (NRA) today formally accepted a report concluding unit 2 of Tohoku Electric Power Company's Onagawa plant in Miyagi Prefecture meets revised safety standards. The plant was the closest nuclear power plant to the epicentre of the earthquake and tsunami of 11 March 2011, but sustained far less damage than expected.
Tokohu's Onagawa plant (Image: Kurihalant Co Ltd)
The utility applied to the NRA in December 2013 for a safety assessment of Onagawa 2 to verify countermeasures applied at the plant meet new safety standards. Tohoku expects to spend about JPY340 billion (USD3.1 billion) on these, which include seismic reinforcement of the unit and construction of a 29-metre high and 800m long sea wall to protect the plant from tsunamis. Work on them is expected to be completed by March 2021. The company has already decided to decommission unit 1 of the plant and is considering applying to restart unit 3.
In late November, the NRA approved a draft screening document that concluded the upgraded plant will meet revised safety standards, introduced in January 2013. Today the NRA approved the final screening report, clearing the way for the unit to resume operation.
"Today's permission is based on the judgement that the basic policy and basic design for safety measures at unit 2 of the Onagawa nuclear power plant conform to the new regulatory standards," said Tohoku President Hiroya Harada. "I think we have reached a major milestone."
The utility is still required to obtain the approval of local authorities before it will be able to restart Onagawa 2. "We believe that the understanding of the local people is of paramount importance," said Harada. He noted the company has launched various initiatives - including plant tours and the dissemination of information - to gain the confidence of local residents.
The March 2011 earthquake knocked out four of the Onagawa plant's five external power lines, but the remaining line provided sufficient power for its three boiling water reactors (BWRs) to be brought to cold shutdown. Onagawa 1 briefly suffered a fire in the non-nuclear turbine building. The plant was largely unaffected by the tsunami as it sits on an elevated embankment more than 14m above sea level, but the basement floors of unit 2 were flooded.
A mission from the International Atomic Energy Agency in August 2012 concluded, "The structural elements of the nuclear power station were remarkably undamaged given the magnitude of ground motion experienced and the duration and size of this great earthquake."
Onagawa 2 will become the first Japanese BWR - the same type as used at the damaged Fukushima Daiichi plant - to be restarted. BWRs at Tokyo Electric Power Company's Kashiwazaki-Kariwa plant in Niigata Prefecture and unit 2 of Japan Atomic Power Company's Tokai plant in Ibaraki Prefecture have already received NRA approval to restart, but have yet to obtain local consent.