Ultrasonic Thermometry for In-Pile Temperature Detection

The Idaho National Laboratory (INL) recently initiated an effort to evaluate the viability of using ultrasonic thermometry technology as an improved in-pile sensor for detecting temperature during irradiation testing. Ultrasonic Thermometers (UTs) work on the principle that the speed at which sound travels through a material (acoustic velocity) is dependant on the temperature of the material. By introducing an acoustic pulse to the sensor and measuring the time delay of echoes, temperature may be derived. UTs offer several advantages over other temperature sensors. UTs can be made very small, as the sensor consists only of a small diameter rod which may or may not require a sheath. Measurements may be made near the melting point of the sensor material, as no electrical insulation is required; and shunting effects are avoided. Most attractive, however, is the ability to introduce acoustic discontinuities to the sensor, as this enables temperature measurements at several points along the sensor length (allowing temperature profiling with a single sensor). Although UTs have been successfully deployed in several applications, several problems have limited their success. This paper summarizes the capabilities of UTs, their prior applications, and the proposed project to develop an optimized UT probe. As described in this paper, options to resolve issues identified with prior UT use are under evaluation in this INL feasibility study. Once most promising options are demonstrated, an optimized prototype UT design will be developed and evaluated.