Tokyo Electric Power (TEPCO) said on Thursday it would shut down the No.6 reactor at the Kashiwazaki-Kariwa nuclear power station in Japan, just a day after the unit was brought back online for the first time in about 14 years.
The decision followed the detection of a malfunction early on Thursday, when an alarm was triggered during work to withdraw control rods from the reactor.
TEPCO said it would suspend operations to investigate the cause of the problem, after replacing electrical components in the control rod operation and monitoring panel failed to resolve the issue.
Takeyuki Inagaki, superintendent of the Kashiwazaki-Kariwa station, said a thorough technical investigation was necessary before operations could resume.
The utility added that the duration of the probe and the schedule for restarting the reactor remain unclear.
TEPCO had restarted the No.6 unit on Wednesday evening, marking the company’s first nuclear reactor restart since the Fukushima disaster in 2011.
The restart had already been delayed by a day due to a separate alarm malfunction, which TEPCO said had been resolved at the time.
Kashiwazaki-Kariwa, located in Niigata prefecture, is the world’s largest nuclear power plant by capacity and is central to TEPCO’s energy plans.
The latest setback highlights ongoing operational challenges facing Japan’s nuclear sector more than a decade after Fukushima.
Shares in TEPCO fell 3.5% on Thursday, underperforming Japan’s Nikkei index, which rose 1.7%.