LAROB: Laser-Guided Underwater Mobile Robot for Reactor Vessel Inspection

In a nuclear power plant, there are several cylindrical vessels such as a reactor vessel and pressurizer. The vessels are usually constructed by welding large rolled plates or nozzle pipes together. To ensure the integrity of the vessel, their welds should be periodically inspected using sensors such as ultrasonic transducers or visual cameras. To inspect these welds effectively, we developed an underwater mobile robot, which is guided by a laser pointer. The robotic system was devised to reduce the inspection time and schedule during mandatory code inspections compared to a conventional inspection machine with a large structure. The system mainly consists of an underwater mobile robot, a laser positioning unit, and a main control station. The underwater mobile robot is guided by a laser positioning unit with a precise resolution of 0.05°. The mobile robot moves on the reactor vessel wall with four magnetic wheels. This paper presents the design and implementation of the underwater mobile robot. The laser guidance control of the mobile robot is also described along with the experimental results. The system was integrated with the main control station, and tested in the reactor vessel of a Korean nuclear power plant. After many improvements in its design and engineering, the system is expected to dramatically reduce the critical path of the reactor vessel inspection, if the system is used practically.