Ultrasonic NDE in a reactor core

We have irradiated bulk single crystal piezoelectric AlN operating as an ultrasonic transducer up to a fast and thermal neutron fluence of 1.85×10¹⁸ n/cm² and 5.8×10¹⁸ n/cm² respectively along with a gamma dose of 26.8 MGy. Our primary interest was in the radiation effects on the piezoelectric performance of the AlN crystal. Ideally standard procedures for extracting material properties from the impedance spectra would have been applied. However, this procedure was anticipated to be very error prone due the effects of radiation on passive components, such as electrodes and cabling. As a result the transducer was coupled to an aluminum cylinder and operated in pulse echo mode throughout the irradiation. In addition to the pulse echo testing impedance data were obtained. Although, material parameters such as d33 could not be measured in-situ during irradiation with our procedure, our work is the only publication, to the author´s knowledge, showing the operation of an ultrasonic transducer in a reactor core. Further, the piezoelectric coefficient was measured prior to irradiation and found to be 5.5 pC/N which is unchanged from as-grown samples, and in fact higher than the measured d33 for many as-grown samples. Further proof of the viability of utilizing ultrasonic transducers in a reactor core is provided by means of successful time of flight (TOF) measurements throughout the irradiation. The TOF data was used to measure the gamma heating of an aluminum cylinder. The heating due to short lived isotopes in the Al was also detected via TOF.