Tokyo: The operator of the Onagawa nuclear power station in Miyagi Prefecture, northeastern Japan, said that it will halt the facility's No. 2 reactor after radioactive steam was detected within its turbine building.

Tohoku Electric Power Co. on Friday said a small amount of radioactive steam was found in the reactor unit's turbine building at around 5:10 p.m. local time, 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 on Friday night.

The No. 2 reactor at the plant had previously been taken offline for a regular inspection and was only brought back online on Monday, with commercial operations scheduled to resume on June 9.

Earlier on May 8 morning, a reactor at a nuclear power plant in Fukui Prefecture, central Japan, was halted following a steam leak near the unit's high-pressure turbine, local media reported.

The leak was detected at around 4:10 a.m. local time at the No. 3 reactor of the Mihama nuclear power plant, Kyodo News reported.

The reactor was manually shut down about 15 minutes later. Kansai Electric Power Co., the plant's operator, said the steam did not contain radioactive material and there was no impact on the external environment.

The No.3 reactor at the Mihama nuclear power plant began operation in 1976. It was temporarily taken offline following the 2011 Fukushima nuclear disaster and resumed operation in 2021. 

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

Tohoku Electric Power Company said that the Onagawa No. 2 reactor had restarted power generation. After an adjustment operation to check for any abnormalities while gradually increasing output, the reactor will be temporarily halted for equipment checks.

The 825,000-kilowatt reactor, if operated at about 70 per cent of its capacity for one year, is estimated to generate electricity equivalent to the power consumption of 1.62 million households, according to Tohoku Electric.

The three reactors at the Onagawa plant are of the same boiling water type as those at Tokyo Electric Power Company's Fukushima Daiichi nuclear plant, where the country's worst nuclear accident was triggered by the massive earthquake and tsunami on March 11, 2011.