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More than a decade after the 2011 Fukushima nuclear disaster, much of the areas remained unexplored. Some of the doors to rooms in the facility had not been opened since the disaster, and officials had little idea what was on the other side.

But in 2022, decommissioning crews began using Spot®, the quadruped robot from ���˶���, to collect data, shoot video, measure radiation dose, and gather debris samples for radiation testing. Although officials were already using other tracked and wheeled robots, the superior mobility and the automated arm of Spot proved to be “game changers,” says Brad Bonn, head of nuclear programs for Spot.

“When you’re dealing with an accident like this, very frequently you’ll have areas that robots have a difficult time navigating,” Bonn explains. “For instance, stairs are enormously challenging for a lot of robots. When you add in the debris from an accident, it makes traveling through these areas very difficult, and if the dose rate is high enough, human beings simply cannot enter. So robots are critical, and the ability to have a robot with almost no limits with regards to mobility is really significant.” 

Koji Watanabe, Deputy Manager of 2nd Mechanical Equipment Group of the Decommissioning Division of Nuclear Power Plant of Tokyo Power Technology (TPT) notes that the effort requires robots that can not only navigate difficult terrain, but can also carry substantial weight, open and close doors, and collect analysis samples. “A robot with excellent mobility—one that can move freely inside the building and is easy to communicate with—was required for this project,” Watanabe says. “Spot was exactly what we needed.” 

A Daunting Challenge

On March 11, 2011, a powerful earthquake and subsequent tsunami hit the Tohoku region of Japan, killing 15,900 people, impacting many people, and resulting in more than $200 billion in damages. When waves up to about 50 feet tall hit the Fukushima Daiichi plant, they destroyed the diesel generators that were needed to power coolant-circulating pumps, resulting in three nuclear meltdowns, three hydrogen explosions, and widespread radioactive contamination at the site. 

Despite an intensive cleanup program, full decommissioning of the plant is expected to take several decades. Human exploration of the site is not only dangerous, but also extremely slow, given the precautions that people must take in areas with high levels of radiation. Workers must don large amounts of cumbersome personal protective equipment and observe strict limits on how much time they can spend in radioactive areas. And then, some areas are designated as “LD50” (or even worse), meaning that a 30-day exposure would be lethal for half of the population. Those areas, of course, cannot be entered by people at all. 

A robot with excellent mobility—one that can move freely inside the building and is easy to communicate with—was required for this project. Spot was exactly what we needed.

Koji Watanabe, Deputy Manager of 2nd Mechanical Equipment Group of the Decommissioning Division of Nuclear Power Plant of Tokyo Power Technology (TPT)

Robots are needed to identify which areas can be entered by people, explore those areas that cannot, and help speed up exploration of areas where PPE requirements and exposure limits bring cleanup efforts to a near standstill. Drones are not always ideal because their rotor blades can kick up dust and debris, potentially spreading contaminated materials. And robots that rely on tracks or wheels are typically unable to solve what Bonn calls the “dirty laundry” problem. 

“If you throw a hamper of clothes all over the floor, a tracked or a wheeled robot will effectively be completely unable to move,” he says. “There are areas at Fukushima that are full of different types of debris. Other robots can’t move around the site, because it’s essentially covered in dirty laundry.” 

Spot’s ‘Sense of Mission’

Spot was brought on board at Fukushima Daiichi to help investigate the disaster, simulate necessary data for future decommissioning operations, and create a decommissioning archive. The robot was outfitted with the necessary equipment to shoot videos, measure radiation levels, obtain point cloud data, and collect samples for radioactivity analysis. 

First, though, ���˶��� teams had to test Spot to make sure the robot would be able to stand up to high levels of radiation. Just as nuclear radiation can cause mutations in the cellular structure of humans, it can interfere with electronic systems—jumbling data in logical circuits, for instance, or simply causing physical damage to circuitry. To make sure Spot could withstand radiation exposure, ���˶��� . The results were important, because while the decommissioning team could have outfitted Spot with lead protection, this would have added weight and placed limits on the amount of additional equipment that the robot would be able to carry. 

“We bombarded it with tons of radiation to try to determine just how much the robot can absorb,” Bonn says. “The bad news is, we don’t know how much Spot can absorb. The good news is, the reason we don’t know is that we never got it to fail.” Testers initially exposed Spot to 82 years’ worth of the allowable human dose of radiation—and then later tripled that amount at another location—without any adverse effects, and the robot has not experienced any issues with radiation exposure at the Fukushima site. In fact, Spot has “lived” inside the contamination zone, ever since it arrived at Fukushima. 

Spot used a lidar device to collect point cloud data, used a mounted camera to shoot video, and collected smear samples with the Spot Arm. To facilitate communications, Spot placed mesh radios in appropriate locations around the site. 

Operators controlled the robot remotely from a safe distance, but Bonn notes that Spot’s autonomous sensing and movement capabilities came into play, even while it was being piloted by human drivers. “The robot has a great deal of intelligence and autonomy that it uses even for walking,” he says. “It plans every step that it takes, autonomously. All the driver is doing is telling it to walk in a direction, and the robot does everything else.”

The Spot Arm also opens doors mostly autonomously. (The operator shows the robot where the doorknob is and which side the hinge is on, and Spot does the rest.) While some other robotic platforms have gripper arms, these are largely operated manually, and the process of opening a door is up to 10 or 20 times faster with Spot Arm, Bonn says. “The ability for Spot to let itself into these environments and open these doors that haven’t been opened in a decade – this was something that really changed the game. You’re on limited time, you have limited battery, you have limited access to the site. It’s all about, how fast can we get this done?” 

Yoichiro Naka, CEO of Tohoku Enterprise Co. (TECO), the ���˶��� Preferred Solution Partner that is assisting with the decommissioning effort, says that Spot’s effectiveness made it feel like ���˶��� and the various project crews were part of “one team” focused on a common mission. “The ���˶��� team supported us to such an extent that we didn’t feel the time difference with Japan,” he says. “And Spot performed its mission dutifully, as if it had the same sense of mission as us.” TECO provides important in-country support and integration for Spot, working with key customers to expand their use of robotics.

“Our customers in Japan such as Mr. Watanabe (TPT) and TEPCO, among others, are extremely progressive and innovative with their implementation of robotics within their operations,” says Kyle Hulse, Partnerships Manager for ���˶���.  “The team at Tohoku Enterprise Co. has done a great job of working with our key customers in this region to ensure the continued success of their Spot robotics programs”.

The decommissioning work at Fukushima Daiichi is still ongoing, and it is easy to imagine that there will be many more situations where Spot can be used. We greatly look forward to its future activities.

Sample Transport & Investigation for Accident Analysis Project Group – Fuel Debris Retrieval Program Department, Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company Holdings (TEPCO)

Findings for the Future

Naka says that Spot’s data collection project “ended in success,” with the robot completing the planned video shooting, radiation measurement, and gathering of point cloud data and analysis samples. For instance, Spot’s investigation revealed that the windows in the operation room of one unit were broken and the room was contaminated.

“There’s a mix of things that they’re going to use this information for,” Bonn says. “One is simply determining whether humans can go into specific spaces—and if so, for how long, and what protective equipment is going to be necessary. They may come up with a strategy to put shielding up to make safer areas, but they need this information first. There’s also the matter of prioritization: deciding how to go about the decommissioning process, and what needs to happen in which order.” 

It’s not yet clear what role Spot will have on future decommissioning efforts, but Bonn says he imagines that the robot will be busy. For one, Spot may collect progress data, using lidar scans to monitor decommissioning over time. He also thinks the robot will likely use its arm to clear away small debris—essentially solving the “dirty laundry” problem and clearing the way for larger unmanned machinery to conduct more intensive cleanup work. 

“Although small, Spot can perform various movements and was found to be suitable for the Fukushima Daiichi site, so we want to actively utilize it in the future,” says Owada, Sample Transport & Investigation for Accident Analysis Project Group of Fuel Debris Retrieval Program Department of Fukushima Daiichi Nuclear Power Plant of Tokyo Electric Power Company Holdings (TEPCO). “The decommissioning work at Fukushima Daiichi is still ongoing, and it is easy to imagine that there will be many more situations where Spot can be used. We greatly look forward to its future activities.”