Tokyo Electric Power Company Holdings Inc halted the release of treated radioactive water from the Fukushima Daiichi plant on Saturday after a low-flow alarm triggered an automatic shutdown.
The company said the emergency shutoff valve on a seawater dilution pump closed after water flow dropped due to a momentary power outage affecting two power lines inside the plant. Thunderstorms were reported in the area at the time.
Radiation monitoring systems detected no abnormalities and the water pump continued functioning. TEPCO said it will resume releasing treated water once it confirms the system is safe.
The same alarm sounded on Wednesday, also halting the release. The operator replaced a valve in a tank outlet and resumed the discharge the following day.
Massive amounts of radioactive water have accumulated at the plant since the March 2011 earthquake and tsunami, as melted nuclear fuel has been cooled. The water is treated to remove most radionuclides except tritium before dilution and release into the Pacific Ocean.