In-service inspection equipment and technology development for butt welds of CRDM pipe seats and through fittings

The butt weld seam between the tube seat and the penetration member of the control rod drive mechanism (CRDM) in a nuclear power plant belongs to the pressure-bearing boundary of the primary circuit in the nuclear power plant, and its reliability and safety directly affect the safe operation of the reactor. The position of the butt weld between the CRDM pipe seat and the through member is narrow in space, has poor accessibility, and poses a high risk of radiation exposure to personnel, making it difficult for conventional in-service inspection methods to carry out the inspection. This paper takes the butt weld of the pipe seat and the through piece driven by the control rod as the research object and develops an automatic ultrasonic scanning device, achieving the automatic ultrasonic scanning of the outer pipe of the butt weld of the CRDM pipe seat and the through piece in a small space.