British News Agency

According to The Guardian, Japan’s Kashiwazaki-Kariwa plant—the world’s largest nuclear power station—halted operations just one day after being restarted. Operator Tokyo Electric Power Company (Tepco) said operations were suspended following an alarm from the monitoring system during startup.

The facility in Niigata Prefecture had been shut down after the 2011 Fukushima disaster. Restart efforts began on Wednesday after receiving final approval from the nuclear regulator.

Plant chief Takeyuki Inagaki told a press conference that the problem would not be resolved within one or two days and that the timeframe is currently unknown. Spokesperson Takashi Kobayashi told AFP that, as it became clear the issue would take time, control rods were reinserted in a planned manner and the reactor is stable, with no radioactive impact on the environment.

Kashiwazaki-Kariwa is considered the world’s largest nuclear power plant by potential capacity. However, only one of its seven reactors has been restarted. The plant was taken offline following the massive earthquake and tsunami in 2011, after Japan decided to halt nuclear power.