An advanced ultrasonic waveguide concept for spatially distributed monitoring of in-core temperatures

Critical process temperatures in a reactor core are conventionally measured using either resistance temperature detectors or thermocouples, both of which exhibit performance degradation at the temperature ranges of advanced reactors. Ultrasonic thermometry (UT) has long been offered as an alternative, potentially robust measurement option. With emerging interest in advanced reactors and a trend toward extracting more information from the core and the connected heat transport systems, UT is again considered a potential measurement method. Conventionally, acoustic waveguides employ simple notches at a measurement point to reflect incident waves. However, this approach results in rapid attenuation of acoustic energy as the wave crosses notches, as some fraction of its energy is reflected while the rest is transmitted. This research addresses this fundamental issue. This paper reports on the development of an ultrasonic waveguide concept that exploits the constructive interference of wave dynamics. The waveguide uses acoustic filters at the measurement zones that exhibit very high transmittance or reflectance as a function of interrogation frequency. Preliminary results will be discussed.