Japan’s Tohoku Electric Power confirmed that unit 2 at the Onagawa NPP in Miyagi Prefecture has been taken offline to inspect and replace a faulty valve. The operator noticed rising water levels in a drainage sump. It estimated that around 0.2 tonnes of water has been leaking each hour from a valve in the feedwater heater since early July.
While the leaked water contains a trace amount of radioactive material, Tohoku Electric stated that all leaked water has been collected inside the facility. No abnormal radiation levels have been detected in the surrounding environment.
The process of cooling the reactor, inspecting the valve, and replacing the faulty components is expected to take approximately 10 days before the unit can be restarted.
Onagawa 2 unit was the first nuclear reactor to resume operations in eastern Japan following the catastrophic 2011 earthquake and tsunami. The reactor was briefly shut down in November 2024, just days after restarting, because of equipment problems. It resumed operations later that month following repairs.
