Acoustic coupling of ultrasonic transducers for in-service inspection of sodium fast reactors

Research studies are currently being conducted to understand the phenomena governing the acoustic coupling of ultrasonic transducers immersed in liquid sodium in relation to the development of a Generation IV sodium-cooled fast reactors (SFR). The gas surface fraction at a solid/liquid interface determines the amount of acoustic energy that can be transmitted through this interface. This is not a linear law and only a small amount of gas is sufficient to significantly reduce the transmission coefficient. An ultrasonic experiment using liquid sodium at a temperature ranging between its melting point and 500°C was conducted. The acoustic coupling between liquid sodium and 316L austenitic steel was measured during the first temperature rise of the system which occurs when the wetting process is underway.