b'Nuclear Science User Facilities High Fluence Irradiation Testing of Fiber Optic Material TransmissionDr. Thomas E. BlueThe Ohio State UniversityBlue.1@osu.eduT his work leveraged a recentlyand 688C (based on dilatometry, completed irradiation ofusing passive SiC temperature moni-capsules assembled andtors) (Figure 1). These temperatures inserted into the High Flux Isotopeare higher than those of previous Reactor (HFIR) in FY 2017. NSUFwork. Results show that RIA may be funding allowed for post-irradiationapproaching saturation for the range measurements by Dr. Petrie of theof photon energies that were tested contents of the rabbit capsules.and that the hydroxyl content has a Each capsule contained 12 fiber- significant impact on RIA when the optic-material slab specimens, splitirradiation temperature is increased equally between: 1) low-OH fusedto 688C. For 1550 nm operation, silica, 2) high-OH fused silica, andhowever, the observed increase in RIA 3) single crystal-sapphire materials.does not preclude interference-based The nominal sample dimensionsmeasurements of fiber temperature. A were 16 mm long5 mm wide model was developed for predicting 0.85 mm thick. The rabbit capsulesradiation-induced compaction, and were irradiated for approximatelythe resulting impact on signal drift one 24 day HFIR cycle. Each capsuleand RIA for Bragg grating sensors as was designed to achieve a uniquea function of neutron fluence and temperature that is typical oftemperature. The data were well fit by light-water reactors or some high- a simple model. The sapphire samples temperature advanced reactors. showed significant RIA that increased The pre- and post-irradiation transmis- with increasing temperature. However, sion and density measurements werethe samples may have suffered from made at Oak Ridge National Labora- diffusion of impurities from the tory (ORNL) at the Low Activationsurrounding capsule materials at high Materials Development and Analysistemperatures. Additional character-(LAMDA) Facility. Optical transmissionization is being planned to confirm was measured through the samplewhether impurities were introduced.thickness, using a broadband optical- Conclusiontransmission system, which allowed forThe primary concern for imple-the measurement of radiation-inducedmenting a-SiO 2fiber-optic sensors in attenuation (RIA) in the specimensa nuclear environment is the RIA of over a wavelength range from approxi- the light signal due to the formation mately 2001700 nm. of radiation-induced color centers. In Results addition, Bragg-grating sensors drift Measurements of RIA and radiation- under irradiation due to radiation-induced dimensional changes wereinduced compaction of the a-SiO 2made in a-SiO 2samples that werestructure. Our work provides new data subjected to high-dose neutronregarding RIA and radiation-induced irradiation at temperatures of 95, 298,compaction of a-SiO 2samples irradi-76'