Japan’s Tohoku Electric Power Company has restarted the 825 MWe boiling water reactors (BWR) at unit 2 of the Onagawa NPP in Miyagi Prefecture. The reactor has been offline since November 2010 and will become Japan’s 13th reactor and first BWR to be restarted since all NPPs were closed down in the wake of the 2011 Fukushima Daiichi accident.
Tohoku has completed safety measures to meet the more stringent rules adopted after the Fukushima disaster. These include building a seawall 29 metres above sea level and 800 metres in length. It is designed to withstand a tsunami of up to 23.1 metres. The reactor also has a venting system with filters to reduce pressure inside the primary containment vessel while minimising the leakage of radioactive materials. The plant was also reinforced to ensure it could withstand major earthquakes. The total estimated cost of the safety measures, including planned anti-terrorism facilities for the plant, is JPY710bn ($4.5bn).
Once the reactor is in operation, a daily report will be issued, and any problems will be disclosed appropriately according to the level of importance. Tohoku Electric President Kojiro Higuchi said: “There is no end to safety measures. We want to restart the reactors so that they can be trusted by the local community.”
The restart is expected to boost Tohoku Electric’s profit by JPY13bn for the financial year ending March 2025, as a result of spending less on fossil fuels, a company spokesperson said. At a press conference following a Cabinet meeting, Japan’s Economy, Trade & Industry Minister Yoji Muto said it is extremely important to restart the NPPs in eastern Japan to meet the expected increase in electricity demand and other factors.
Tohoku applied to the Nuclear Regulation Authority (NRA) in December 2013 for a safety assessment of Onagawa 2 to ensure the reactor complied with the more stringent safety standards introduced after Fukushima. In November 2019, NRA approved a draft screening document stating that the plant would meet the revised safety standards following upgrades. In February 2020, NRA approved the final screening report, clearing the way for the unit to restart after more than a decade of construction work to secure safety.
The Onagawa plant was the closest NPP to the epicentre of the earthquake and tsunami in March 2011 but avoided the core meltdowns that occurred at Fukushima. Although earthquake destroyed four of the plant’s five external power lines, the remaining line provided sufficient power for the three BWRs to be brought to cold shutdown. The plant was relatively unaffected by the tsunami as it is built on an elevated embankment more than 14 metres above sea level. However, the earthquake caused the ground to sink by a metre and the plant was struck by tsunami waves around 13 metres high flooding the basement floors of unit 2. The reactor coolant pumps were broken, and more than 1,000 cracks were found in the unit 2 reactor building. Tohoku Electric has since decided to decommission unit 1 and is now in the process of seeking clearance to restart unit 3.
A group of residents in Ishinomaki filed a lawsuit in 2021 seeking to stop the plant from restarting, citing the inadequacy of the emergency evacuation plan. The Sendai District Court dismissed the claim in May 2023, and the plaintiffs appealed. Around 30 protestors gathered near the plant ahead of the restart. Two civic groups, issued a joint statement opposing the resumption, saying concerns over the evacuation plan have not been addressed.
