Japan’s Tohoku Electric Power Co has unit 2 at its Onagawa NPP in Miyagi Prefecture for inspection, following the detection of a trace of radioactive steam. The reactor 825 MWe boiling water reactor had been restarted a few days before following a scheduled maintenance outage.
The shutdown took place after a patrolling worker confirmed that the steam was leaking out from a sump collecting wastewater from equipment in the basement of the reactor’s turbine building. The steam did not stop even after the valve connected to the sump was retightened.
The level of radioactivity in the water accumulated on the surrounding floor was about one-thousandth of the government’s reporting threshold.
Tohoku Electric said a small amount of radioactive steam was found in the reactor unit’s turbine building, adding no radioactive materials had leaked into the environment and that the halt was for inspection purposes. The company also dismissed any link between the incident and a 6.4-magnitude earthquake that struck northeastern Japan the previous night.
The Onagawa nuclear plant had resumed power generation for the first time since the Fukushima nuclear disaster in March 2011 in November 2024.
Earlier in May, unit 3 at Kansai Electric’s Mihama NPP in Fukui Prefecture, was halted following a steam leak near the unit’s high-pressure turbine. The reactor was manually shut down although Kansai Electric said the steam did not contain radioactive material and there was no impact on the external environment.
