Tohoku Electric Power Company has received initial regulatory approval to resume operation of unit 2 at its Onagawa plant in Japan's Miyagi Prefecture. 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 Nuclear Regulation Authority (NRA) in December 2013 for a safety assessment of Onagawa 2 to verify countermeasures taken at the plant meet new safety standards. Tohoku expects to spend JPY340 billion (USD 3.1 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.
Today the NRA approved a draft screening document that concludes the plant will meet revised safety standards, introduced in January 2013. Tohoku will still need to obtain the approval of local authorities before it will be able to restart Onagawa 2.
"We believe that the understanding of the local community is the most important factor in restarting operations," Tohoku said in a statement. "We will continue to make efforts to gain the understanding of as many people as possible by accumulating various initiatives such as facility tours where visitors can actually see safety measures at the power plant."
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 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. Tohoku has already said it will decommission unit 1 at the plant, but has yet to decide on whether to apply for the restart of unit 3.
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."
Prior to the accident, Japan's nuclear generating capacity had provided around 30% of the country's electricity, but within 14 months of the accident Japan's nuclear generation had been brought to a standstill pending regulatory change. A total of nine units (all pressurised water reactors) have restarted since 2015, while 17 reactors are in the process of gaining approval to restart.