The restart of the world’s largest nuclear power plant was suspended Thursday only hours after it resumed for the first time since the 2011 Fukushima nuclear disaster.

The restart of the No. 6 reactor at the Kashiwazaki-Kariwa plant in north-central Japan was suspended due a glitch related to control rods, which are essential to safely starting up and shutting down reactors, according to its operator, Tokyo Electric Power Company Holdings.

TEPCO said there was no safety issue from the glitch and it was checking the situation. It was not known when the restart process would resume.

The restart at the Kashiwazaki-Kariwa plant was being watched closely since TEPCO also runs the Fukushima Daiichi plant that was ruined in the 2011 quake and tsunami and since resource-poor Japan is accelerating atomic power use to meet soaring electricity needs.

All seven reactors at Kashiwazaki-Kariwa have been dormant since a year after the meltdowns of reactors at the Fukushima plant contaminated the surrounding land with radioactive fallout so severe that some areas are still unlivable.

TEPCO is working on the cleanup at the Fukushima site that’s estimated to cost 22 trillion yen ($139 billion). It’s also trying to recover from the damage to its reputation after government and independent investigations blamed the Fukushima disaster on TEPCO’s bad safety culture and criticized it for collusion with safety authorities.

Fourteen other nuclear reactors have restarted across Japan since 2011, but the Kashiwazaki-Kariwa plant, about 220 kilometers (135 miles) northwest of Tokyo, is the first TEPCO-run unit to resume production.

A restart of the No. 6 reactor could generate an additional 1.35 million kilowatts of electricity, enough to power more than 1 million households in the capital region.

The Kashiwazaki-Kariwa plant’s combined output capacity of 8 million kilowatts makes it the world’s largest, though TEPCO plans to resume only two of the seven reactors in coming years.