TEPCO Restarts Nuclear Reactor After Determining Cause Of Alarm Trouble

TOKYO, Feb 9 (Bernama-Kyodo) -- Tokyo Electric Power Company Holdings Inc. restarted a reactor at its seven-unit nuclear power plant in Niigata Prefecture, northwest of Tokyo, on Monday after determining the cause of an alarm that halted the facility last month, Kyodo news agency reported.

An alarm sounded during control rod withdrawal from the No. 6 reactor at the Kashiwazaki-Kariwa plant in the early hours of Jan. 22, about five hours after the utility brought its first nuclear unit back online since the 2011 Fukushima disaster.

The alarm signalled abnormalities in an inverter that controls the speed of a motor that moves the control rods, prompting the utility to shut down the reactor the following day and investigate the problem further.

According to the investigation, the inverter itself was not broken, but the alarm was set to be too sensitive in detecting changes in electric current.

Since abnormalities in control rods can be detected by other alarm systems, TEPCO decided to adjust the inverter's settings so it would not be triggered by such changes.

TEPCO said the No. 6 reactor has 205 control rods and that it plans to withdraw all of them later Monday, when the reactor is expected to reach criticality, a controlled self-sustaining nuclear fission chain reaction.

The company will then start up the turbine and conduct power generation and transmission on a trial basis from Sunday, as well as facility checkups by halting the reactor again, and move to commercial operations on March 18 if no problems are detected when output is increased to near full capacity, the company said.

-- BERNAMA-KYODO