DESIGN OF HIGH-TEMPERATURE ULTRASONIC LINEAR ARRAYS FOR UNDER-SODIUM VIEWING

摘要

This paper summarizes the design process for high-temperature ultrasonic phased array transducers for imaging in liquid sodium at temperatures up to 260°C. The project is funded by the USDOE Generation IV Reactor Program and includes collaboration with the Japanese Atomic Energy Agency. The transducer system is being designed to be able to provide images inside a sodium-cooled fast reactor, to support operation and maintenance activities, potentially including location of loose or damaged parts during service outages. Considerations in the design process include array dimensions and spacing, frequency, diffraction effects, ultrasonic beam properties, coupling to sodium, backing materials, and protection from the corrosive sodium environment. Array parameters were evaluated using simulation software. The prototype transducer array is being designed for 8 to 16 rectangular lead niobate (K-81) or bismuth titanate (K-15) 3MHz piezoelectric elements. The theoretically ideal spacing is λ/2 (wavelength in sodium), but a spacing of λ is acceptable and has practical advantages. A nickel or nickel alloy faceplate serves as the sodium wetting surface. The scan angle of the focused ultrasonic beam is ±30°. The imaging spatial resolution is < 15 mm. The array is designed to be operated using a commercial phased-array control system and it is planned that array testing will be performed in room temperature water, hot oil (260°C), and molten sodium (260°C).