Effects of beryllium coating layer on performance of the ultrasonic waveguide sensor

Under-sodium viewing is one of the critical technical issues and requirements for the in-service inspection of the sodium-cooled fast reactor (SFR) that is currently under development. The waveguide sensor that uses leaky A0 mode Lamb waves has shown its potential for high-resolution viewing/scanning of the reactor core and in-vessel structures. However, a few problems arise under a liquid sodium environment due to high sound speed in liquid sodium and dispersion in the long waveguide plate, which simultaneously deteriorate the reconstructed C-scan images. This paper proposes coating the surface of the waveguide sensor plate with a thin layer of material that has a very high ultrasonic wave velocity. It is shown that this coating layer can largely reduce the size (width) and radiation angle of the acoustic beam from the waveguide sensor. This paper precisely analyzes the effects of coating parameters on the beam quality. The proposed idea is validated through ultrasonic experiments in which the radiation beam profiles and group velocities in waveguide sensors with different surface treatments are measured and compared.

► The ultrasonic waveguide sensor coated with a beryllium (Be) has been developed.
► The idea of controlling the guided waves velocity by Be coating is proposed.
► The Be coating increases the velocity of A0 mode in ultrasonic waveguide sensor.
► The Be coating decreases the dispersion effect in ultrasonic waveguide sensor.
► The Be coated ultrasonic waveguide sensor can be applied to under-sodium viewing.