Onagawa Nuclear Power Station Shuts Down Reactor for Inspection After Radioactive Steam Detected

Onagawa Nuclear Power Station Update

Tokyo, May 16: The operator of the Onagawa nuclear facility, located in Miyagi Prefecture in northeastern Japan, announced the shutdown of its No. 2 reactor following the detection of radioactive steam within the turbine building.

Tohoku Electric Power Co. reported on Friday that a minor quantity of radioactive steam was identified in the turbine building of the reactor unit around 5:10 p.m. local time. The company assured that no radioactive substances had escaped into the surrounding environment and that the reactor's halt was solely for inspection purposes.

Furthermore, the company clarified that there was no connection between this incident and a 6.4-magnitude earthquake that occurred in northeastern Japan later that evening.

The No. 2 reactor had recently undergone a routine inspection and was only reactivated on Monday, with plans for commercial operations to resume on June 9.

Earlier, on the morning of May 8, another reactor at a nuclear facility in Fukui Prefecture was also shut down due to a steam leak near its high-pressure turbine, as reported by local media.

This leak was detected at approximately 4:10 a.m. local time at the No. 3 reactor of the Mihama nuclear power plant, according to Kyodo News. The reactor was manually shut down about 15 minutes later, with Kansai Electric Power Co. confirming that the steam did not contain radioactive materials and posed no risk to the external environment.

The No. 3 reactor at Mihama began operations in 1976 and was temporarily taken offline after the Fukushima nuclear disaster in 2011, resuming operations in 2021.

In November 2024, the Onagawa nuclear plant's reactor had restarted power generation for the first time since the Fukushima disaster in March 2011.

Tohoku Electric Power Company indicated that the Onagawa No. 2 reactor had resumed power generation. Following a gradual increase in output to check for any irregularities, the reactor will be temporarily halted for equipment inspections.

The reactor, with a capacity of 825,000 kilowatts, is projected to generate enough electricity to power approximately 1.62 million households if operated at about 70% capacity for a year, according to Tohoku Electric.

Notably, the three reactors at the Onagawa facility are of the same boiling water design as those at Tokyo Electric Power Company's Fukushima Daiichi nuclear plant, which was the site of Japan's most severe nuclear accident triggered by a massive earthquake and tsunami on March 11, 2011.