Ultrasonic Imaging in Hot Liquid Sodium Using a Plate-Type Ultrasonic Waveguide Sensor

This paper reports the first set of results from ultrasonic measurements for determining the imaging capability of a plate-type ultrasonic waveguide sensor in \(200\,^{\circ }\) C liquid sodium. This 10-m long plate-type waveguide sensor has been developed for viewing objects in opaque liquid sodium coolant for the applications in a sodium-cooled fast reactor (a next generation nuclear reactor). Various imaging capabilities of the waveguide sensor have already been demonstrated in water including ultrasonic beam steering, high resolution C-scan, and so on. However, water and liquid sodium have different acoustic properties and, more importantly, different wetting characteristics with stainless steel—the material for the waveguide sensor. For applications of the developed waveguide sensor in a real reactor environment, this research performs a set of necessary ultrasonic measurements in liquid sodium. The end section of the waveguide sensor which radiates an ultrasonic beam into the liquid sodium is coated with thin beryllium and nickel layers which can significantly improve the ultrasonic beam quality and wetting property of the stainless steel. A liquid sodium facility that consists of a glove box system, a sodium test tank, and an argon purification system has been built. The resolution and beam property are determined from ultrasonic C-scan experiments; a signal-to-noise ratio of over 10 dB and the resulting detection of a 1 mm wide slit can be achieved. The inherent issues associated with wetting of the waveguide sensor in liquid sodium are discussed based on the ultrasonic imaging results.