Mitsubishi Develops Underwater Robot for Nuclear Inspections

Mitsubishi Heavy Industries has unveiled a cutting-edge underwater navigation robot designed for non-destructive inspections of nuclear reactor vessels in Japan. Announced on October 10, 2025, the innovation aims to enhance safety and efficiency in high-radiation environments, as detailed by the Japan Society of Maintenology.

The newly developed unit, named the A-UT Machine, is engineered to operate underwater, performing detailed weld-line inspections using its advanced manipulator arm. Measuring 1.8 metres in length, 1 metre in width, and 0.9 metres in height, the robot weighs 400 kilograms, although it becomes weightless when submerged. Its mobility is facilitated by a combination of thrusters and wheels, allowing it to traverse along wall surfaces effectively.

The manipulator arm of the A-UT Machine boasts a design with seven axes, enabling it to carry a load of up to 10 kilograms with positioning precision of ±0.1 millimetres. “The manipulator features a tool changer at the tip, allowing for easy swapping of inspection tools,” the developers noted, highlighting the unit’s versatility in various inspection scenarios.

Operational Capabilities and Efficiency

Designed for depths of up to 20 metres, the robot’s real-time positioning is tracked via a target mounted on the unit, employing triangulation to ensure accurate orientation. The developers emphasized that the simultaneous operation of two A-UT Machines significantly reduces inspection time, enhancing efficiency in critical maintenance tasks.

Control of the robot is managed remotely through a desktop computer and joystick, simplifying operations for technicians. Since its introduction, the system has been utilized in pressurised water reactor (PWR) plants across Japan since 1995, with a total of 46 deployments recorded to date.

The A-UT Machine has received recognition as the #1 Maintenance Heritage by the Japan Society of Maintenology. The society characterizes Maintenance Heritage as a “historic heritage related to maintenance technology also constituting a cultural heritage of humankind,” underscoring the significance of this technological advancement.

As nuclear safety remains a paramount concern, the deployment of such innovative technologies as the A-UT Machine represents a proactive step toward ensuring the integrity of critical infrastructure while safeguarding human operators from hazardous environments.