Piezoelectric Surface Acoustic Device Behavior in Nuclear Reactor Environment

Piezoelectric devices have wide sensing applications from cable fault detection to coated devices for chemical sensitivity, and their purposes continue to expand. This study investigates the application of surface acoustic wave (SAW) devices in nuclear reactors to monitor behavior during temperature and neutron flux transients. Three devices, lithium niobate, bulk aluminum nitride, and thin-film aluminum nitride on sapphire were tested at The Ohio State University Nuclear Reactor Laboratory. Devices were subject to neutron flux up to 1.9x10¹² n/cm²s, and temperatures up to 500^oC. Resonant frequency was continually monitored and revealed a frequency decrease in response to both temperature and neutron flux, indicating reduction in acoustic wave velocity due primarily to softening of elastic constants. Response mechanisms including exponential saturation of defects, and a lumped parameter combined-effects mechanism were fitted to experiment data to characterize defect absorption and production as well as surface heat flux and lumped heat capacity. Utilizing a resistance temperature detector (RTD) adjacent to the SAW pattern revealed the device response to neutron flux was in fact an indirect response due to temperature change caused by absorption of gamma rays.