The decommissioning of the Fukushima Daiichi Nuclear Power Plant presents significant challenges, particularly in the inspection of areas that are inaccessible to human workers owing to high radiation levels and structural hazards. To address this, we developed a teleoperated robotic system capable of conducting internal inspections in environments like that found in the primary containment vessel. The effectiveness of the system was evaluated based on its performance at the “9th Decommissioning Creative Robotics Competition.” The system employs a dual-robot configuration comprising a parent robot and smaller child robot. The parent robot utilizes a sub-track system and full-surface crawler mechanism to ensure stable traversal over obstacles. To inspect locations that are accessed using large staircases, the parent robot deploys a crawler-equipped child robot connected by a tether for power, communication, and retrieval. This mechanism allows the child robot to descend for inspection and then be retrieved by the parent robot, enabling effective exploration of otherwise inaccessible areas. The experimental results demonstrated that the proposed system could successfully navigate through the X-1 penetration and conduct inspections beneath a staircase with a 65° incline. The robot successfully completed all of the mission objectives, although it did not return to its starting point within the competition time limit. This study developed a robust and cost-effective dual-robot system that provides a practical solution for versatile remote inspections in hazardous environments. The proposed system will contribute to the advancement of decommissioning efforts by offering a reliable method for accessing and investigating high-risk areas. Future work will focus on enhancing the system reliability and adaptability for deployment in real-world nuclear decommissioning operations.

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