TOKYO - Tokyo Electric Power Company (TEPCO) on Thursday decided to shut down a reactor at the Kashiwazaki-Kariwa nuclear power plant after an alarm went off during the withdrawal of control rods, only a day after the unit was restarted for the first time in about 14 years.

Earlier in the day, TEPCO suspended control rod withdrawal operations at the just-restarted reactor No 6 of the plant in Niigata Prefecture after the alarm was triggered at 00:28 am local time as a third batch of control rods was being withdrawn.

The utility said it suspected a malfunction in the control rod operating system and replaced electronic components in the device, but the problem persisted.

TEPCO said there was no external radiation leak following the glitch, adding it would stop the reactor to investigate the cause of the malfunction.

The No 6 reactor at the seven-unit complex was reactivated shortly after 7 pm local time on Wednesday, marking the first operated by TEPCO to go back online since the 2011 Fukushima nuclear disaster. The reboot came a day later than initially planned, after a control-rod alarm also sounded during a final pre-startup test.