Development of ultrasonic waveguide techniques for under-sodium viewing

An ultrasonic imaging system based on waveguide techniques was developed to provide in-service inspection of reactor core of a sodium-cooled fast reactor (SFR) and potential applications in other hostile environments. By using the ultrasonic waveguide techniques, we overcome the major technical challenge in developing an under-sodium viewing (USV) system that can withstand the high-temperature and corrosive environment. The chosen design of the prototype waveguide (WG) is a hybrid of bundle and spiraled-sheet WG. The prototypes show high detection sensitivity with minimal background noise by effectively reducing spurious echoes and mode conversions. Tests on prototype waveguide transducers were conducted in liquid sodium up to 340°C (650°F). C-scan images of the targets were successfully developed from both time-of-flight and amplitude variations of the reflected echoes. The ultrasonic waveguide imaging system demonstrates a capability of detecting defects with 1mm width and 0.5mm depth under molten sodium.