Restart Halted at World’s Largest Nuclear Plant as Kashiwazaki-Kariwa Reactor Shuts Down After Technical Glitch

BY EMMANUEL OGBONNA

A reactor at the world’s largest nuclear power station has been shut down again just hours after restarting for the first time since the 2011 Fukushima nuclear disaster, highlighting the persistent technical and public confidence challenges facing Japan’s nuclear revival.

The No. 6 reactor at the Kashiwazaki-Kariwa nuclear plant in north-central Japan resumed operations late Wednesday, marking its first reactivation in 14 years. The restart process began as plant workers gradually withdrew neutron-absorbing control rods from the reactor core, a critical step toward initiating and stabilizing nuclear fission.

However, Tokyo Electric Power Company Holdings, the plant’s operator, said Thursday that the process was suspended after a malfunction involving the control rods was detected only hours into the restart. Control rods are a central safety component of nuclear reactors, used to regulate the nuclear reaction and to safely start up or shut down a unit.

TEPCO said the glitch did not pose a safety risk and emphasized that no abnormal radiation levels or other hazards were detected. Even so, the company decided to halt the restart and later moved to place the reactor back into a full shutdown to allow for a more comprehensive inspection. The utility said it was still assessing the cause of the malfunction and could not immediately say how long the reactor would remain offline.

The restart of Kashiwazaki-Kariwa’s No. 6 reactor has been closely watched both inside Japan and internationally. The plant, located about 220 kilometers northwest of Tokyo, is the largest nuclear power facility in the world, with a total capacity of roughly 8 million kilowatts across seven reactors. All of its units have remained idle since shortly after the Fukushima Daiichi disaster, when a powerful earthquake and tsunami triggered meltdowns that contaminated large areas of northeastern Japan.

TEPCO’s role as the operator of both Kashiwazaki-Kariwa and the crippled Fukushima Daiichi plant has added to scrutiny of the restart. Government and independent investigations into the Fukushima disaster concluded that it was not simply a natural catastrophe but was worsened by poor safety practices, weak oversight, and close ties between the utility and regulators. Those findings severely damaged TEPCO’s reputation and led to sweeping reforms in Japan’s nuclear regulatory framework.

Japan, which has few domestic energy resources, is now accelerating efforts to bring nuclear power back online as electricity demand rises and the government seeks to reduce reliance on imported fossil fuels while meeting climate targets. Since 2011, 14 nuclear reactors at other utilities have restarted under stricter safety standards, but Kashiwazaki-Kariwa is the first TEPCO-operated facility to attempt a return to operation.

If fully restarted, the No. 6 reactor alone could generate about 1.35 million kilowatts of electricity, enough to supply more than one million households in the greater Tokyo area. TEPCO has said it ultimately plans to bring two of the plant’s seven reactors back online in the coming years, rather than restoring the entire complex at once.

The utility is simultaneously managing the long-term cleanup at Fukushima Daiichi, a project expected to cost around 22 trillion yen, or roughly $139 billion, and to last for decades. That effort includes the removal of melted fuel debris and the decommissioning of damaged reactors, all under intense public and international scrutiny.

The latest setback at Kashiwazaki-Kariwa underscores the technical complexity of restarting reactors that have been dormant for more than a decade and the narrow margin for error facing Japan’s nuclear industry. While TEPCO insists the malfunction posed no danger, the incident is likely to fuel continued debate over safety, preparedness, and public trust as the country cautiously moves toward expanding its use of atomic energy once again.