Japan Restarts Reactor at World’s Largest Nuclear Plant

Japan has restarted a nuclear reactor at the Kashiwazaki-Kariwa plant, the largest nuclear power station in the world, nearly 15 years after the Fukushima disaster brought the country’s nuclear industry to a halt.

Reactor No.6 at the site in Niigata prefecture was switched back on Wednesday after inspections were completed. The switch on was delayed by a day due to an alarm malfunction, which operator Tokyo Electric Power Company (TEPCO) said had been resolved. The reactor is expected to begin commercial operations by the end of February, boosting electricity supply to the Tokyo region.

The restart marks the first time TEPCO has brought a reactor back online since the 2011 Fukushima Daiichi meltdown, which followed a massive earthquake and tsunami and shattered public trust in nuclear power. All 54 of Japan’s reactors were shut down in the aftermath.

Filippo Pedretti, a nuclear and thermal power analyst at Japan NRG, called the move “a major turning point” for the government. “It signals the end of the post-Fukushima nuclear stalemate and reaffirms the importance of the atom for a stable power supply,” he said. “If even TEPCO, the utility involved in the Fukushima Daiichi disaster, can restart its most important plant, other facilities can follow.”

Only one of Kashiwazaki-Kariwa’s seven reactors is being restarted for now. While the plant can generate 8.2 gigawatts when fully operational, the next reactor is not expected to come online until around 2030, and others may never be restarted.

Japan has now brought 15 of its 33 operable reactors back into service since 2015. Nuclear power currently supplies about 8.5% of the country’s electricity, far below pre-Fukushima levels. The government now wants it to reach around 20% by 2040 as it looks to cut emissions, reduce reliance on imported fossil fuels and meet rising demand from data centres and semiconductor factories.

Chief Cabinet Secretary Minoru Kihara said the restart was crucial for energy stability. “The importance of restarting reactor (No. 6) is increasing from the perspective of controlling electricity supply and demand, electricity tariffs and securing decarbonized power sources,” he said.

Prime Minister Sanae Takaichi has gone further, pushing not only for reactor restarts but also for new-generation reactors and small modular reactors, backed by a new public funding scheme.

Still, the move has reignited safety concerns. Kashiwazaki-Kariwa sits near active seismic fault lines and was damaged by a strong earthquake in 2007. Earlier this month, nearly 40,000 people signed a petition opposing the restart. “We can’t remove the fear of being hit by another unforeseen earthquake,” the petition said. “Making many people anxious and fearful so as to send electricity to Tokyo … is intolerable.”

TEPCO President Tomoaki Kobayakawa acknowledged those fears, saying safety was “an ongoing process, which means operators involved in nuclear power must never be arrogant or overconfident”.

The restart comes as Japan’s nuclear sector grapples with fresh scandals. Regulators recently halted a review to restart reactors at Chubu Electric’s Hamaoka plant after the company was found to have falsified seismic data. Japan’s Nuclear Regulation Authority has warned it may tighten scrutiny across the industry.

Beyond safety, cost is another challenge. New post-Fukushima standards have made nuclear power far more expensive to run, raising questions about whether the government will subsidise operators or pass costs on to consumers — a sensitive issue as households struggle with rising bills.

Public opinion remains split. While opposition to nuclear power surged after Fukushima, more recent polls suggest over half of Japanese now support its use if safety can be guaranteed. Protests, however, continue, and fears were reignited in 2023 when treated radioactive water from Fukushima was released into the sea.

As Japan restarts its nuclear engines, the Kashiwazaki-Kariwa reactor has become a critical test — not just of energy policy, but of whether public trust can be rebuilt.