Research on Full-Cover Fixed Ultrasonic Inspection Technology for AP1000 Control Rod

The control rod assembly is the component inserted into the fuel assembly to control the reactivity of the reactor core, so its status needs to be evaluated timely to ensure the safety of the plant operation. According to the structure and size of AP1000 control rod, the full-cover fixed ultrasonic inspection technology is studied in this paper, and the special inspection device is developed. Through the test of the mock-up flaw rod, it is known that the axial measurement accuracy of the flaw is ≤1 mm and the wall thickness measurement accuracy is <0.01 mm. The device has been successfully applied in the field overhaul of AP1000 unit, and several wear and swelling defects have been found. The application results show that the full-cover fixed ultrasonic inspection technology can visually display the defects of the control rod cladding, and give information such as the position, axial length, circumferential span and maximum wear depth of the defects.