TOKYO: Japan on Feb. 9 restarted a reactor at the Kashiwazaki-Kariwa nuclear power station in Niigata Prefecture, bringing the country back to production at the world’s largest nuclear plant by capacity after a late-January shutdown tied to a monitoring alarm. The operator, Tokyo Electric Power Company Holdings, said it resumed operations at Unit 6 following checks and adjustments to the system that triggered the earlier halt.
Kashiwazaki-Kariwa sits on the Sea of Japan coast in the cities of Kashiwazaki and Kariwa, about 220 kilometers northwest of Tokyo. The site has seven reactors with total capacity of about 8.2 gigawatts. Unit 6, a 1,360-megawatt reactor, is one of the plant’s largest units and the first reactor TEPCO has restarted since the 2011 Fukushima Daiichi nuclear disaster.
The restart came after a stop-start sequence that began in January. TEPCO initially planned to bring Unit 6 online on Jan. 20, but delayed the work after a problem was found in a control-rod related test. The reactor was restarted on Jan. 21, then placed into cold shutdown in the early hours of Jan. 22 after an alarm sounded during work to withdraw control rods needed to begin the fission process.
TEPCO said its investigation found no equipment abnormalities and focused on the alarm’s settings and how the system detected slight changes in electrical current. The utility said it adjusted settings to avoid a repeat of the January alarm and confirmed control rod systems could be monitored by other protection and alarm functions at the plant. The company restarted the unit on Feb. 9 and said it would proceed in stages under regulatory oversight.
Restart follows alarm shutdown
Kashiwazaki-Kariwa has been a central site in TEPCO’s nuclear restart efforts because of its scale and because the company has not operated a reactor since Fukushima. The plant has been offline for more than a decade, and its return has required meeting post-2011 safety requirements and restoring operational approvals. Japan’s Nuclear Regulation Authority lifted an effective operational ban on the facility in late 2023 that had been imposed after security lapses at the station.
Local and regional approvals have also been a key step before restart work could move ahead. Niigata Governor Hideyo Hanazumi approved a partial restart in November 2025, and the Niigata prefectural assembly later backed that decision, clearing a major political hurdle for Unit 6 and the adjacent Unit 7 to advance restart preparations. TEPCO has said it has spent more than 1 trillion yen on safety measures at Kashiwazaki-Kariwa.
Regulatory path and local approvals
The restart adds to Japan’s broader return to nuclear power since Fukushima, when the country’s reactors were shut down as safety rules were tightened and licensing reviews were overhauled. Multiple reactors have since returned to operation after meeting the updated standards, while others remain in various stages of review, upgrades, or decommissioning plans. Kashiwazaki-Kariwa, with its large generating capacity, is among the biggest potential contributors to nuclear output once fully operating.
TEPCO said it will gradually raise Unit 6’s operating parameters and begin power generation and transmission after additional checks, followed by inspections and a final review process with the regulator before commercial operation. The company said its work schedule includes staged testing and inspections during February and a final check in March as part of the transition from restart to routine electricity production. – By Content Syndication Services.