A narrow, attic-like space lies directly below the No. 5 reactor at the Fukushima No. 1 nuclear power plant, showing the difficult route a robotic arm must take to collect samples of melted fuel debris in a sister reactor. 

The robotic arm is 22 meters long, weighs 4.6 tons and has 18 articulatable joints.

It has been developed to retrieve samples from the No. 2 reactor of Tokyo Electric Power Co.’s Fukushima No. 1 plant—which was crippled when the 2011 Great East Japan Earthquake and tsunami triggered a nuclear disaster at the facility.

To this day, an estimated 880 tons of melted fuel debris remain in the No. 1 through No. 3 reactors, and recovering this material is considered the most challenging phase in the long decommissioning process.

After more than six years of development using taxpayer money and undergoing numerous setbacks, the robotic arm may go on its first real debris retrieval mission later this fiscal year—or face being scrapped.

“The latest attempt may prove a failure since numerous trials have produced no successful outcomes so far,” said a nuclear industry insider. “The robot arm might be left to gather dust without ever being used.”

News reporters were given a tour in January of the crippled power plant’s No. 5 reactor, which is the same model and reportedly has the same dimensions as the No. 2 reactor, to see the route the arm must take if it is to succeed.

THE MISSION

To reach the debris, the arm will have to be navigated—by remote control—through the same narrow route at the No. 2 reactor that the reporters traversed at its twin.

The first step will be to carefully insert the arm, which is 40 centimeters tall, through an opening with an inner diameter of just 55 cm.

Once inside the 1.5-meter-tall space directly under the reactor, the approximately 4-meter-long tip of the arm will be slowly rotated and lowered to reach the fuel debris at the bottom of the containment vessel.

“Adjusting the joints’ angles is particularly difficult,” said a TEPCO public relations representative. “Even a single error can cause the device to hit its surroundings.”

TRIAL AND ERROR

The robotic arm has been under development since fall 2018 by Mitsubishi Heavy Industries Ltd. and a British company from the nuclear power industry. As much as 7.8 billion yen ($53.1 million) in taxpayers’ money has been invested in the arm and related projects.

However, the project has faced numerous setbacks.

The government and TEPCO initially planned to debut the arm in a debris retrieval test in 2021, but the device was unable to move with the necessary precision, causing delays.

When the first retrieval test was finally undertaken in November 2024, a simpler device with a solid track record in past applications was used instead. The same device was used in the second retrieval test earlier this month—while revisions on the robotic arm continued.

Because the arm’s weight is supported at its base, the device tends to bend and move unsteadily when extended.

“They are working hard to carry out this difficult procedure under particularly challenging conditions,” said Hajimu Yamana, president of the Nuclear Damage Compensation and Decommissioning Facilitation Corp. (NDF), which serves as an adviser on the decommissioning work.

As the arm’s development dragged on for more than half a decade, new problems arose in and after August 2024.

Disconnection of motor cables that had deteriorated over time was detected, as was a failure in the arm’s obstacle removal mechanism.

In December that year, the robotic arm came into contact with a model of the containment vessel during a test. However, it later safely passed through the opening without encountering any obstructions after its operators fine-tuned the insertion point.

“New issues arise each time a test is conducted,” lamented Yusuke Nakagawa, a TEPCO group manager involved in the project. “We just have to address them one by one again and again.”

TEPCO began dismantling part of the robotic arm in February to examine the deteriorated cable. The inspection is expected to take three to four months, and the arm will likely undergo additional operational tests after that.

THE FUTURE

For now, TEPCO plans to put the robotic arm to practical use at the site in the latter half of fiscal 2025.

“The final decision (on whether to actually use the arm on site) will be made after taking into account the results of the envisioned operational tests,” said Akira Ono, president of TEPCO’s Fukushima Daiichi Decontamination and Decommissioning Engineering Co.

The future of the robotic arm is still unclear given that its official introduction has already been delayed four times.

Officials involved are expressing a growing sense of alarm.

Toyoshi Fuketa, an ex-chairman of the Nuclear Regulation Authority, calls for reviewing the current plan.

“Never changing a plan once it has been decided upon, even if it does not work properly, is a bad habit of Japan,” he noted. “People should have the courage to back down at times (by giving up on the robotic arm).”