2018 | ANNUAL REPORT 69 to operation at frequencies up to the order of 100 kHz. However, mechan- ical coupling and guided-wave-mode generation makes magnetostrictive transduction ideal for low-frequency measurements, such as ultrasonic thermometry .The irradiation behavior of magnetostrictive materials has not previously been studied in depth, leaving their appropriateness for use in irradiation tests unknown. An NSUF-funded irradiation, dubbed the ULtrasonicTRAnsducer (ULTRA) irradiation test, led by Pennsylvania State University and executed at the Massachusetts Institute ofTechnology Research Reactor allowed for long- term irradiation testing of both piezoelectric and magnetostrictive transducers and evaluation of their survival within a high-radiation environment.The magnetostrictive transducer designed for this test was based on research by Lynnworth  and Daw .The magnetostrictive transducers consist of a small driving/ sensing coil, a biasing magnet, and a magnetostrictive waveguide.The ultrasonic signal is generated when a high frequency alternating-current pulse is driven through the coil. The induced magnetic field causes magnetic domains within the material to oscillate.The domains are pre- biased by the magnet to maximize the response. Received echoes are detected through the reciprocal effect. The design of the transducers was identical to the UT shown in Figure 1, except the entire waveguide consisted of the magnetostrictive alloy being evaluated. Candidate Materials The magnetostrictive transducer materials were selected based on previous use in radiation environ- ments, amounts of neutron sensitive materials, Curie temperature, and saturation magnetostriction. Remendur Remendur has the most history of use in nuclear applications of all magnetostrictive alloys, having been used previously for short-duration thermometry applications. Remendur These technologies, which have performed successfully in out-of-pile tests, have not been well qualified in a test- reactor environment. The first in-core sensor, based on ultrasonic technologies and targeted for deployment, is the ultrasonic thermometer (UT), which can provide a temperature profile in candidate metallic and oxide fuels and would provide much-needed data for validating new fuel performance models.