Wedoany.com Report-Nov 4, 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 reactor in Miyagi Prefecture was halted at 8:36 a.m. to allow the company to investigate the problem.

No radioactive material has leaked out, the company said on Sunday.

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 company is investigating the cause of the problem, focusing on potential issues with the instrument itself and the equipment that delivers the instrument into and out of the reactor.

After the reactor is brought to a cold shutdown, the company will look into the cause of the malfunction. The duration of the investigation has not yet been decided.

The Onagawa No. 2 reactor was brought back online only on Tuesday for the first time in about 13 years. It is a boiling water reactor, the same type as Tokyo Electric Power Company Holdings' disaster-crippled Fukushima No. 1 plant, and the Onagawa reactor was expected to start commercial operations on Dec. 25.