Nuclear decommissioning robots take on dangerous work at Fukushima Daiichi

Robots are helping engineers tackle the complex cleanup of Japan’s Fukushima Daiichi Nuclear Power Station by inspecting damaged reactors and surveying radioactive deposits.

Hitachi has developed specialized robotic systems that can operate in confined spaces, underwater environments, and high-radiation areas, reducing the need for workers to enter hazardous locations.

One system, PMORPH, is a shape-changing crawler designed to inspect the reactor’s primary containment vessel and assess conditions inside.

Another, HUMALT, uses flexible robotic arms to perform tasks in high-radiation environments, with potential applications in nuclear fuel debris retrieval.

Recent reports suggest that more than 53,000 Fukushima cleanup workers have exceeded an annual radiation exposure of 5 millisieverts since 2011, with 17 occupational illnesses recognized.

Probe radioactive reactors

PMORPH passes through a pipe approximately 10 centimeters in diameter in an I-shaped configuration before transforming into a U-shape inside the vessel.

The first PMORPH unit entered the Unit 1 containment vessel in April 2015, using a camera, thermometer, and radiation dosimeter to examine conditions outside the reactor pedestal. A second version, deployed in March 2017, used a winch-lowered sensor unit to investigate submerged deposits and measure radiation levels on the basement floor.

To examine these deposits more closely, Hitachi developed six types of underwater remotely operated vehicles (ROVs). They create three-dimensional maps of deposit surfaces, measure deposit thickness and radiation levels, prevent cable entanglement, and collect physical samples. During an investigation from February 2022 to March 2023, the vehicles gathered information needed to develop a method for recovering deposits inside the Unit 1 containment vessel.

Hitachi has also developed the Telescopic Active Scope Camera (TASC) to access bent pipes and help remove contaminated water. At Unit 1, highly contaminated water inside a heat exchanger has raised radiation levels nearby.

TASC uses short cilia covering a hose to propel itself through vibrations generated by a motor. Wheels at its tip control its direction, while an inner hose carries water out. An active scope camera allows operators to monitor conditions at the tip as the device navigates the piping.

Tackle nuclear decommissioning

Another system, HUMALT, is a flexible robotic arm designed for high-radiation environments and potential fuel debris retrieval operations.

Instead of placing radiation-sensitive electronic components throughout its body, it uses multiple cylinder-type water-hydraulic actuators to move its arm. Its joints combine bending and rotational movements, enabling controlled manipulation while reducing the likelihood of damage from contact with surrounding structures.

The system uses water as its hydraulic fluid, limiting environmental impact if a line is damaged. Operators control it remotely through hose lines connected to a pump unit and control panel. A predecessor equipped with two flexible arms was deployed in Fukushima Daiichi’s Unit 3 turbine building in 2019 to remove obstacles.

Radiation remains a major challenge for these machines. Hitachi uses radiation-resistant sensors, shielding, and designs that separate sensitive electronics from robot bodies. Components may also need replacement when they approach their accumulated radiation-dose limits.

The company is developing automation for repetitive operations, such as rubble removal in areas with comparatively low radiation levels. For more complex tasks, operators continue to rely on remote control. Hitachi is also developing systems that use external stereo cameras to estimate the three-dimensional positions of robots, their surroundings, and their articulated arms when sensors cannot be mounted directly on the machines.

Hitachi plans to combine these robotic platforms with artificial intelligence, sensor data, workers’ expertise, and digital twin technologies. The goal is to let robots assess their surroundings and perform instructed tasks with greater autonomy, while people supervise operations and make decisions when needed.

By combining specialized hardware with remote operation and AI-assisted control, these systems could improve worker safety and help engineers tackle the complex, long-term process of nuclear decommissioning.