Magnetostrictive Ultrasonic Waveguide Transducer for In-Pile Thermometry

Real-time and reliable temperature measurement on nuclear fuels is crucial for the safe operation of existing pressurized-water reactors and future advanced nuclear reactors. Magnetostrictive materials deform when subjected to a magnetic field or exhibit magnetization variation when stressed. Based on these properties, this study prototyped an ultrasonic thermometer (UT) consisting of a magnetostrictive waveguide, a dc coil providing appropriate magnetic biasing, and an ac coil generating an acoustic impulse and detecting the resulting acoustic echoes. By tracking the time of flight between the excitation pulse and the echoes, the UT can potentially detect nuclear fuel cladding temperature from a long distance. In this study, magnetostrictive iron–gallium alloys, or Galfenol, were selected as the waveguide due to their large magnetostriction, superior temperature survivability, excellent radiation resilience, and high mechanical robustness. A multiphysics finite-element model considering electrical, magnetic, and mechanical dynamics in the magnetostrictive UT was then developed. The model exhibited an error of 0.24% in time-of-flight simulation and, therefore, enabled computer-aided design and guided signal processing. Between room temperature and 120 <inline-formula><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula>C, the new Galfenol-based UT exhibits a linear sensitivity of 162.8<inline-formula><tex-math notation="LaTeX">$\times 10{^{-6}} {^\circ }$</tex-math></inline-formula>C<inline-formula><tex-math notation="LaTeX">$^{-1}$</tex-math></inline-formula>, which is 51.7% higher than a previous magnetostrictive UT based on iron–cobalt–vanadium alloys.