Nuclear Science User Facilities 72 tested material. Observed online signal changes were deemed to have been caused by thermal and mechanical effects within the transducers. ULTRA2 Based on the results of the ULTRA irradiation test, a follow-on irra- diation (ULTRA2) was selected for funding by NSUF.This test included INL-developed UTs and fiber-optic sensors provided by the French Atomic and Alternative Energy Commission (CEA) and by the University of Pittsburgh (only the UTs will be discussed here).Three UTs were included in the ULTRA2 irradiation test.Two of the experi- mental UTs use Inconel 606 wire as the sensing element; one had a single measurement zone, and the other had three zones.The third UT had a single zone and used commer- cially pure titanium wire as the sensing element. Spatial constraints of the MIT test capsule restricted the length of these UTs. As such, the UTs could not be directly calibrated without damaging the transducers. Performance was determined by examining the trends in measured delay times against temperatures measured by included thermocouples. Each of the three UTs included in this test experienced failures of the driver coil before the completion of the test.This is likely due to a material change in a ceramic cement used to fill the transducer housing that was made between the original ULTRA experiment and ULTRA2. The new cement likely lost cohe- sion, allowing the coil wire to move during temperature transients and during refueling operations. All UTs survived for between ~5000 and 7000 hours and produced reason- able signals over that time. Figure 4 shows the normalized delay time and thermocouple (TC) temperature of the single segment Inconel sensor.The data during initial reactor start-up were unus- able, possibly due to a mechanical Figure 4. Single-segment Inconel sensor results Figure 5. Multi-segment Inconel sensor results. Figure 6. Single-segment titanium results.