b'2019 | ANNUAL REPORTto irradiation while the remaining fiber was heat-treated at 1000C. The thermal annealing of the clad optical fiber may have a significant effect on transmission in the fiber, due to the creation of nanovoids [2]. The FBGs inscribed in the silica fibers showed no significant noise or signal drift over five days of irradiation, indicating that the Type II gratings themselves perform well under irradiation.ConclusionThis work showed that temperature sensing using FBGs in sapphire optical fiber is possible given that at least one FBG in two of the three sapphire fibers survived and gave reliable readings up to a total neutron fluence of approximately 2.51018 n/cm2. There is still a need to reduce the modal volume and the intrinsic attenuation in the sapphire fibers. However, if these challengesreactor applications.can be overcome, the high melting temperature of sapphire (2000C)Referencesmakes sapphire optical-fiber sensors[1.] Brandon A. Wilson and Thomas a potential candidate for monitoringE. Blue, Creation of an Internal of centerline temperatures duringCladding in Sapphire Optical irradiation testing of advanced fuelsFiber Using the 6Li(n,)3H, IEEE for high-temperature Sensors Journal, vol. 17, no. 22, pp. 7433-7439, Nov. 15, 2017.[2.] B. A. Wilson, S. Rana, H. Subbara-man, N. Kandadai and T. E. Blue, Figure 1. Experiment installed in the central irradiation facility of The Ohio State University Research Reactor. 69'