Hokuriku Electric Power Co. temporarily shut down a reactor Tuesday at the Shigahara Nuclear Power Plant in Shiga, Ishikawa Prefecture, after abnormal vibrations were discovered in a cooling pipe.
There were no radioactive leaks, company officials said.
Workers conducting a regular inspection of the No. 1 reactor detected a change in the pipes' vibration patterns and decided at 10:30 a.m. to manually shut down the reactor.
The vibrations previously had a width of 0.33 mm but were found to be fluctuating between 0.32 mm and 0.345 mm. Although the figures were below the warning level of 0.38 mm, workers decided to shut down the 540,000-kilowatt reactor anyway.
The inspection began Jan. 14 and was expected to be completed early this month.