72-foot robot arm tackles Fukushima nuclear debris 13 years after disaster

The boom-style arm is engineered to enter the reactor vessel through an isolation valve and retrieve samples for surface analysis.

Ameya Paleja

Representational stock image for nuclear reactor.

Artush/iStock

Tokyo Electric Power Company (TEPCO), which runs the Fukushima Dai-ichi nuclear plant, has introduced a massive robot to retrieve the first fuel sample from a reactor. This comes 13 years after a devastating earthquake and tsunami triggered a meltdown and radioactive leak at the site. The robotic device features an extended 72-foot arm and weighs 4.6 tons.

On March 11, 2011, a magnitude 9.0 earthquake struck East Japan, and a tsunami cut off power at the Fukushima-Daiichi nuclear power station, leading to a meltdown of the reactors. Estimates suggest that 880 tons of highly radioactive nuclear fuel remain under the three reactor buildings at the site.

The substance, termed “fuel debris” by TEPCO, is a radioactive blend created when intense heat caused fuel rods and internal reactor components to melt and fuse. After cooling, this material solidified. TEPCO theorizes that this amalgam, likely containing uranium, zirconium, and various other elements, resides within the reactors’ primary containment vessels (PCVs). However, the precise composition and characteristics of this debris remain uncertain, requiring further analysis.

TEPCO has begun the decommissioning of the nuclear power plant, a process expected to take decades. This effort involves using multiple robots for various tasks, from surveying the buildings to measuring radiation levels. However, until now, TEPCO did not have a robot capable of retrieving a sample of the fuel.

After years of planning and analysis, TEPCO has identified an isolation valve in the PCV as a site where they could source a sample. However, they needed a specialized robot to carry out the task.

Working with Mitsubishi Heavy Industries, the International Research Institute for Nuclear Decommissioning, and Veolia Nuclear Solutions, a UK-based company offering a range of solutions for the nuclear industry, TEPCO has engineered a robotic arm capable of entering the PCV and grabbing a sample of the fuel.

Built using stainless steel and aluminum, the robot has a boom-style arm and can move along 18 degrees of freedom.

The robot’s arm comprises four main elements: a mobile carriage designed to navigate through openings, foldable arm segments that can extend as needed, telescoping sections equipped with cameras, and a specialized gripper for sample collection. This gripper features small, precise pincers capable of plucking tiny amounts of debris from the floor of the primary containment vessel (PCV).

TEPCO intends to utilize the robotic arm in Unit 2 of the facility, which remained relatively intact during the disaster. This unit is believed to contain approximately 237 tons of nuclear fuel. The arm is designed for precision, capable of extracting a minute sample of just three grams while minimizing disturbance to the surrounding area.

The debris would be transferred to a container and returned to the surface for initial testing, followed by an extensive analysis at the Japan Atomic Energy Agency.

Following approval from Japan’s Nuclear Regulation Authority, the robot made an attempt last month to retrieve debris from the site, successfully bringing some to the surface. However, two of its cameras malfunctioned during the operation, likely caused by radiation penetrating the semiconductor components.

An analysis report on the debris is still awaited, reported IEEE Spectrum.

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Ameya Paleja Ameya is a science writer based in Hyderabad, India. A Molecular Biologist at heart, he traded the micropipette to write about science during the pandemic and does not want to go back. He likes to write about genetics, microbes, technology, and public policy.

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