Characterization of Sodium Compatible Ultrasonic Transducers Using Ultrasonic C-Scan Imaging

Ultrasonic technique is useful for viewing the internals of sodium cooled fast reactors. Ultrasonic transducer is the key element to carry out ultrasonic viewing and inspection. Sodium compatible high temperature ultrasonic transducers are being developed for this application. Lead zirconate titanate (PZT) crystal is used as active element. Nickel (Ni) face plate is used to facilitate sodium wetting at low temperatures. Bonding of the PZT crystal to the nickel faceplate is carried out by soldering/diffusion bonding techniques. Bond quality is important as it influences the performance of the transducer. Ascertaining the bond quality would help in fabricating high quality transducers. We have used under water ultrasonic C-scan imaging technique to assess the bond quality. In order to develop the technique, studies have been performed on a few transducers using reference defects introduced at the interface. Bond quality of the diffusion bonded high temperature transducers has been checked before and after exposure to high temperatures and the results are discussed in this paper.