Mitsubishi Unveils Underwater Robot for Nuclear Reactor Inspections

Mitsubishi Heavy Industries has introduced a cutting-edge underwater navigation robot designed for non-destructive inspections of nuclear reactor vessels, particularly in high-radiation environments. This development was reported on October 10, 2025, by the Japan Society of Maintenology. The robot, named the A-UT Machine, is expected to enhance safety and efficiency in inspections at nuclear facilities across Japan.

The A-UT Machine measures 1.8 metres in length, 1 metre in width, and 0.9 metres in height, weighing 400 kilograms. When submerged, its weight effectively becomes zero, allowing for easier maneuverability. The robot employs a combination of thrusters and wheels, enabling it to traverse wall surfaces within reactor vessels.

Equipped with a seven-axis manipulator arm, the robot can perform precise weld-line inspections with a load capacity of up to 10 kilograms and positioning accuracy of ±0.1 millimetres. The arm features a tool changer at its tip, allowing for the quick interchange of inspection tools. This flexibility enables the A-UT Machine to adapt to various inspection requirements efficiently.

Advanced Navigation and Real-Time Tracking

The robot is designed to operate at depths of up to 20 metres, making it suitable for most reactor vessel environments. Its position is monitored in real time through a target mounted on the device, utilizing triangulation techniques to maintain accurate orientation. Mitsubishi developers highlighted that the simultaneous operation of two units can significantly reduce inspection time, enhancing overall productivity in maintenance tasks.

Control of the A-UT Machine is conducted remotely via a desktop computer and joystick, allowing operators to manage inspections from a safe distance. This system has been in active service at pressurized water reactor (PWR) plants in Japan since 1995, with a total of 46 deployments recorded to date.

The Japan Society of Maintenology has recognized the A-UT Machine as the “#1 Maintenance Heritage,” a designation that underscores its significance in maintenance technology and its contribution to cultural heritage. This certification reflects the robot’s role in advancing safety protocols in nuclear facilities, an area of critical importance to public safety and environmental security.

Mitsubishi’s innovation in the field of underwater robotics not only showcases technological advancement but also reinforces the commitment to maintaining safety standards within the nuclear industry. As the demand for efficient and effective inspection methods grows, the A-UT Machine stands out as a pivotal development in ensuring the integrity of nuclear reactor vessels.