Mitsubishi Unveils Underwater Robot for Nuclear Reactor Inspections

Mitsubishi Heavy Industries has introduced a specialized underwater navigation robot designed for non-destructive inspections of nuclear reactor vessels in Japan. This development, announced on October 10, 2025, marks a significant advancement in safety technology for the nation’s nuclear plants, particularly in high-radiation environments.

The robot, named the A-UT Machine, features advanced capabilities for inspecting weld lines within reactor vessels. According to the Japan Society of Maintenology, this unit measures 1.8 metres in length, one metre in width, and stands at a height of 0.9 metres. Weighing 400 kilograms in air, its weight effectively becomes negligible when submerged.

Designed for mobility, the A-UT Machine employs both thrusters and wheels, allowing it to navigate along wall surfaces. The robot is equipped with a seven-axis manipulator arm that can handle loads of up to 10 kilograms with a remarkable positioning accuracy of ±0.1 millimetres. The manipulator arm further enhances versatility through a tool changer, enabling the seamless swapping of inspection tools.

Operational Depths and Real-Time Tracking

The A-UT Machine can operate at depths of up to 20 metres, making it suitable for various reactor conditions. Its position is tracked in real time via a target mounted on the robot, utilizing triangulation methods to ensure accurate orientation. This feature is particularly beneficial for conducting thorough inspections.

Mitsubishi’s developers highlight that operating two units simultaneously can significantly reduce the time required for inspections. The control system is designed for remote operation, utilizing a desktop computer and joystick, thus enhancing user experience and safety.

Since its introduction to pressurised water reactor (PWR) plants in Japan in 1995, the A-UT Machine has been deployed 46 times, underscoring its reliability and effectiveness. The machine has received recognition as the #1 Maintenance Heritage by the Japan Society of Maintenology, which describes Maintenance Heritage as a historic heritage related to maintenance technology that is also part of humanity’s cultural heritage.

As the demand for advanced safety measures in the nuclear industry continues to grow, Mitsubishi’s A-UT Machine represents a notable step forward in ensuring the integrity and safety of nuclear reactor operations.