Tohoku Electric Power on Monday morning halted operations at the No. 2 reactor at its Onagawa nuclear power plant in northeastern Japan following a problem that occurred when a measuring instrument was delivered into the reactor, the company said.
The power supplier halted the reactor in Miyagi Prefecture at 8:36 a.m. to allow it to investigate the cause of the problem.
The Onagawa No. 2 reactor was brought back online only on Oct. 29 for the first time in about 13 years, and the turbine was started on Friday. It is a boiling water reactor, the same type as Tokyo Electric Power Company Holdings' Fukushima No. 1 plant, the site of a triple meltdown in March 2011. The Onagawa reactor was expected to start commercial operations on Dec. 25.
On Sunday morning, Tohoku Electric found that it was unable to electrically move the auxiliary instrument for the neutron detector, which monitors the reactor's internal conditions. The instrument was recovered manually.
Tohoku Electric found no problems with the reactor, suspecting that there are some problems with the instrument or a device that moves it.
No radioactive material has leaked out, the company said on Sunday.
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