Tokyo Electric Power Company (TEPCO) suspended the restart of the Kashiwazaki-Kariwa nuclear power plant in Japan’s Niigata Prefecture just hours after operations began late Wednesday. The company confirmed Thursday that the reactor remains stable and poses no radioactive risk. The restart followed final approval from Japan’s nuclear regulator, marking the first TEPCO-operated plant to resume since the 2011 Fukushima disaster.

TEPCO spokesperson Takashi Kobayashi said an alarm in the monitoring system triggered the precautionary shutdown, and the cause is under investigation. Earlier in the week, the restart had already been delayed due to a technical fault that TEPCO claims has since been resolved. Only one of the plant’s seven reactors was being restarted.

Local opposition remains strong, with about 60 percent of Niigata residents reportedly against the restart. Seven civic groups recently submitted a petition with around 40,000 signatures to TEPCO and regulators, citing earthquake risks and past damage to the facility. Japan is seeking to reduce energy imports and achieve carbon neutrality by 2050 through renewed use of nuclear power.