Tokyo Electric Power Company said workers were conducting a test at the Number 6 reactor unit of the Kashiwazaki-Kariwa nuclear power plant in Niigata Prefecture on January 17 when an alarm system failed to work properly.

The alarm did not sound when the workers were withdrawing control rods from the reactor, ahead of its restart scheduled for January 20.

TEPCO said an examination showed that there was a problem with the alarm setting, and the alarm rang properly after the setting was corrected.

The company is checking to see if the alarm sounds correctly for all control rods and will postpone the restart for the time being.

This would be the first time TEPCO resumes operation at any of its nuclear power stations since the 2011 Fukushima disaster.