Development of Remote Robot Welding System for On-site Maintenance of Reactor Internals

Preventative maintenance of nuclear power plants has been promoted in recent years. It is difficult and dangerous for a welder to weld the reactor internal component materials, because the welding operation continues for many hours with radiation at an extremely high level. Therefore, a portable remote controlled welding robot system has been developed in order to reduce welder's exposure to radiation. The new welding robot system comprises two robots each having a 6-axis multi-joint manipulator, a controller, a TIG welding power source and a monitor CRT. The welding head on the robot is provided with a small welding torch designed for the narrow sections encountered in the welding of riser braces. Also this robot system has two visual sensing systems using CCD cameras for welding condition control and shape measurement. Visual sensing system for shape measurement comprises a CCD camera. Root gap width before welding and bead width after welding can be 3 dimensionally measured by stereo vision method. Therefore, in another visual sensing system for welding condition control molten pool size of root pass can be observed directly from back side by CCD camera attached. Welding current can be controlled during welding by size of molten pool measured according to the fuzzy rule in order to ensure penetration. This welding robot system actually applied to replace jet pumps on nuclear on-site maintenance and the work was completed satisfactorily.