Development of ultrasonic thermometry for high-temperature high-resolution temperature profiling applications in LMFBR safety research

Ultrasonic thermometry was developed as a high temperature profiling diagnostic for use in the Liquid Metal Fast Breeder Reactor (LMFBR) Debris Coolability Program at Sandia National Laboratories. These instruments were used successfully in the DC series experiments and the D10 experiment. Temperatures approaching 3000 C with spatial resolution of 10 mm and indicated temperature gradients of 700 C/cm were measured. Instruments were operated in molten sodium, molten steel, and molten UO2 environments. Up to 14 measurement zones on a single instrument in molten sodium were used with 12 mm and 15 mm spatial resolution. Hermetically sealed units operating at elevated temperatures were used. Post-test examination revealed very little systematic calibration drifts (less than 10 C) with random drifts occuring with less than 40 C standard deviation in a 10 to 12 mm measured zone. The stability of the system varies from +/- 1 C to +/- 15 C depending on the sensor design constraints for a particular application. Doped tungsten sensors were developed to permit operation of total measurement zone length of 30 cm at temperatures above 2500 C.