Nuclear Irradiation and Characterization of Langasite SAWR Sensors up to 800 ^∘C

For next-generation advanced nuclear reactors, there is a significant need for new sensor materials and sensor technologies that are capable of withstanding in-core high gamma radiation (e.g., >10 Gy/s), neutron flux levels [ $\gt 10^{{12}}$ n/(cm $^{{2}} \cdot $ s)], and high operating temperatures ( $\gt 700~^{\circ }$ C). In this work, langasite (LGS)-based surface acoustic wave resonator (SAWR) sensor devices were designed, fabricated, and tested in a research grade test reactor and demonstrated the ability to quantify total neutron flux by monitoring the SAWR frequency responses calibrated against the reactor's total neutron flux when exposed to reactor powers of 100, 300, and 461 kW [or 0.42, 1.3, and $2.0\times 10^{{12}}$ n/(cm $^{{2}} \cdot $ s)] at temperatures up to $800~^{\circ }$ C and at a maximum gamma dose rate of 21 Gy/s. The effects of gamma heating on SAWR sensor frequency responses were accounted for by using instrumented control of an in situ furnace, where the sensor devices were loaded during irradiation. The controlled furnace allowed for the SAWR devices to be kept at a fixed temperature when exposed to different reactor powers/neutron flux levels. Using this approach, the measured variations in sensor frequency responses were then primarily attributed to neutron flux induced material softening of the SAWR devices. For irradiation measurements acquired at $800~^{\circ }$ C, the LGS SAWR sensors produced linear shifts in frequency response as a function of reactor power at a rate of approximately 3 kHz/100 kW.