The operator of the Onagawa nuclear power plant in northeastern Japan shut down reactor 2 after a leak of water containing radioactive substances. The environment was not contaminated

Reactor 2 of the Onagawa nuclear power plant, in Miyagi Prefecture, northeastern Japan, was shut down on Saturday after a water leak containing small amounts of radioactive substances was identified. Operator Tohoku Electric Power announced that the water had been collected and that no abnormal radiation levels had been detected outside the plant.

The plant entered a cold shutdown state, allowing the affected components to be safely inspected and replaced. The leak was observed at the beginning of September through a safety valve in the turbine building, with the flow initially estimated at approximately 200 liters per hour. The water was transferred to a special tank and then to the radioactive waste treatment system.

The company will inspect the valve and replace the affected parts. During the shutdown, the hydrogen detector in the reactor containment will also be replaced; the gas can become explosive at high concentrations. The work and preparations for restarting are expected to take approximately ten days.

Reactor 2 had also been shut down in May following a leak of radioactive steam. It had been restarted in October 2024 after an interruption of more than 13 years, following the tightening of safety rules after the Fukushima accident.