Under sodium viewing (USV) using ultrasonic pulse-echo techniques offers the potential for the inspection of generation IV, liquid sodium-cooled fast reactors (SFRs) at the hot stand-by temperature (260C). However, the harsh environment effects on the transducer reduce the ultrasonic signal strength which also limits the probability of detection (POD) of the defects.

Current work presents a unified modeling and measurement-based methodology to analyze the high temperature effects on the transducer components. Resonance analysis-based characterization has shown that the conventional d33 piezoelectric parameter is not a sufficient condition to estimate resonance characteristics of high temperature ultrasonic transducers. A full piezoelectric material matrix needs to be utilized in order to estimate high temperature performance. In seeking materials, BiScO3-PbTiO3 (Bismuth Scandium oxide-lead titanate) is demonstrated to be the piezoelectric material that could potentially be used for hot stand-by mode (260C) inspection of SFRs.

However, a high temperature ultrasonic transducer is also a multi-layer system where the interaction of multiple acoustic layers is equally important as the temperature dependence of a single piezoelectric layer. A 3-layer problem was studied which demonstrated the thermal cycling effect on the interfaces, evident from the echo amplitudes and bandwidth of the frequency response up to 260C. A unique bi-modal resonance phenomenon was also found in the transducer due to interaction of the multiple acoustic layers.

Utilizing these insights, design, development and high temperature evaluation of several prototypes was performed in surrogate fluids. This resulted in an air-backed transducer using BS-PT piezoelectric material, nickel faceplate, and liquid acoustic coupling with silicone oil. The transducer demonstrated the ability for imaging regions of different thickness within the specimen, critical for USV capabilities in SFRs.

Current work also developed a cost effective, novel temperature compensated transfer function approach to predict POD at high temperature using room temperature experimental data. Such a model-assisted POD approach quantified effect of temperature dependence of PZT-5A material on POD near 200C. This approach could be extended for other high temperature transducer materials using a physics based-model and room temperature experimental data to estimate high temperature POD.