MENA Newswire, TOKYO: Tokyo Electric Power Company Holdings Inc. began shutting down the No. 6 reactor at the Kashiwazaki-Kariwa nuclear power plant on Thursday, a day after restarting the unit for the first time since Japan’s 2011 Fukushima Daiichi disaster.
The operator said the shutdown followed an alarm that sounded during early-morning start-up work as staff withdrew control rods, equipment used to control the nuclear fission reaction. Plant officials said the reactor remained stable and that there was no immediate safety threat while the company investigates the cause.
The restart on Wednesday night was a milestone for TEPCO, which has not brought a reactor back online since the Fukushima accident, when a massive earthquake and tsunami triggered meltdowns and forced widespread evacuations. The company has faced prolonged scrutiny over safety management and crisis response since 2011.
Kashiwazaki-Kariwa, located on the Sea of Japan coast in Niigata Prefecture, is the world’s largest nuclear power station by output capacity, with seven reactors on site. All units have been offline for years, with the last of the plant’s reactors going dormant in 2012, leaving the station unable to generate electricity despite its large installed capacity.
Operational setback during start-up
The No. 6 reactor, which has an output of about 1.35 million kilowatts, had been expected to supply electricity to the grid once it progressed through required operating stages. The interruption came after the unit’s return to operation was already delayed earlier in the week by a separate alarm issue identified during pre-start checks.
TEPCO said a safety alarm failed to activate as designed during preparations for the planned restart date, prompting the company to postpone the start-up while it checked and corrected the equipment. After the issue was addressed, the company proceeded with the restart, only to encounter the new alarm event during control-rod handling.
According to plant officials, the alarm was triggered when 52 of 205 control rods were withdrawn as part of start-up procedures, leading operators to take steps to shut the unit down. The company said it will conduct inspections and confirm the status of related equipment before deciding on the next steps for resuming operations.
Focus on Japan’s nuclear restart standards
The repeated alarms at a high-profile plant underscore the operational and public-confidence challenges that surround Japan’s nuclear restarts nearly 15 years after Fukushima. Japan introduced stricter regulatory standards after the 2011 accident, and utilities must meet upgraded safety requirements and obtain approvals before reactors can return to service.
Kashiwazaki-Kariwa has been closely watched because of its size, its location in a seismically active country, and the fact that it is run by the company that operated Fukushima Daiichi. The plant has also been the subject of extensive safety reviews and local attention over evacuation planning and emergency preparedness.
The No. 6 reactor was positioned as the lead unit for restarting the site, with TEPCO seeking to return the station to operation step by step. Thursday’s shutdown means the unit will remain offline while the operator determines what triggered the alarm and verifies that start-up systems are functioning as intended.