An alarm sounds and Tepco suspends restart at Kashiwazaki-Kariwa

A September survey asked 12,000 residents if they believed the conditions for restarting operations were already in place — 37% responded positively and 60% negatively.

By Francis Tang, 23 Jan 26, https://www.japantimes.co.jp/news/2026/01/23/japan/science-health/kashiwazaki-kariwa-alarm/

One day after Tokyo Electric Power Company Holdings (Tepco) restarted the world’s largest nuclear power plant, what was meant to mark a turning point in Japan’s long-stalled nuclear revival became an object lesson in just how fragile that effort remains.

At stake is Japan’s decadelong attempt to reduce imported energy dependency, which increased following the 2011 disaster at the Fukushima No. 1 nuclear power plant, and restore trust lost during the meltdown and in the 15 years since.

On Wednesday night, Tepco restarted reactor No. 6 at the Kashiwazaki-Kariwa nuclear power plant — the company’s first restart since all of its reactors were shut down in the aftermath of Fukushima.

Hours later, an alarm sounded for one rod inside the reactor, and the removal of control rods was suspended. About 16 hours later, Tepco announced that it would carry out a “planned temporary shutdown,” taking the reactor back offline to allow a full probe into the cause of the alarm to proceed.

“We are not assuming that the investigation and related work will be wrapped up in one day or two, but at this point, we cannot say at all how many days it will take,” plant manager Takeyuki Inagaki told a news conference on Thursday night.

Control rod insertion began at 11:56 p.m. on Thursday, and the reactor was formally shut down early Friday morning, according to the company.

“For now, our priority is to move forward with the cause investigation,” Inagaki said.

The company said that the alarm came from a control panel for a motor that drives the control rod, indicating a problem in the control panel. A separate alarm indicated a problem with an inverter.

Tepco added that the alarms indicate with light and sound.

Control rods regulate the nuclear reaction inside a nuclear power reactor. They are pulled out to start fission and reinserted to slow and stop it.

Located 120 kilometers northwest of Tokyo, Kashiwazaki-Kariwa is the world’s largest nuclear power plant, with seven reactors. It is one of the three nuclear power plants owned by Tepco, with the other two located in Fukushima.

After the March 2011 earthquake and subsequent tsunami triggered triple meltdowns at the Fukushima No. 1 plant, all nuclear plants in Japan were shut down. While some owned by other operators have since resumed operation after meeting stricter safety standards, Tepco has not been able to restart any of its reactors until this week.

Two prerequisites come into play when the government greenlights the restart of a nuclear plant: that it meets the post-Fukushima regulation standards set by the Nuclear Regulation Authority, and that it gains the “understanding” of local communities.

The local community in Niigata Prefecture, where Kashiwazaki-Kariwa is located, has mixed views on the plant’s restart. A September survey asked 12,000 residents if they believed the conditions for restarting operations were already in place — 37% responded positively and 60% negatively.

In 2017, Kashiwazaki-Kariwa units No. 6 and No. 7 passed Nuclear Regulation Authority reviews required for restart, but the subsequent discovery of inadequate antiterrorism measures in 2021 led to an effective withdrawal of approval through 2023.

Tepco was initially set to restart the reactor on Tuesday, but postponed the restart after a problem — which was separate from Thursday’s — was identified in one of the control rod alarms during testing.

An alarm that was designed to notify of unintended control rod removals did not go off when one of the rods was pulled out, the company said on Saturday. The process to address this delayed the restart by a day.

The government has positioned its restart as central to Japan’s energy strategy, which includes a goal of achieving 30% to 40% energy self-sufficiency by fiscal 2040, and having nuclear power generating roughly 20% of the country’s power, up from 8.5% in fiscal 2023

Prime Minister Sanae Takaichi is also keen on energy security.

During her campaign for the ruling Liberal Democratic Party’s presidency last year, she vowed to achieve “100% self-sufficiency” in energy, and said in her first policy speech as prime minister that her government would aim for the quick implementation of next-generation reactors and fusion power.

In the aftermath of the Fukushima disaster, Japan’s rate of self-sufficiency on energy dropped from 20.2% in fiscal 2010 to 6.5% in fiscal 2012. While it rebounded to above 10% in recent years, data center and semiconductor needs are expected to lead to a surge in electricity demand.

Kashiwazaki-Kariwa’s restart is “extremely important” in resolving vulnerabilities in eastern Japan’s power supply, containing electricity prices and developing decarbonized power sources, Economy, Trade and Industry Minister Ryosei Akazawa said on Friday, calling the restart a “highly significant step.”

“Under guidance of the Nuclear Regulation Authority, Tepco should continue to respond with the highest priority placed on safety and with a strong sense of vigilance. It should first and foremost work to identify the cause and resolve the issue, and provide careful and easy-to-understand explanations to local communities and the public,” he added.