Although optical fibers have been used in the telecommunications industry for decades, the extreme temperature and radiation environments of next generation nuclear reactors has recently led to the exploration of optical fibers for advanced instrumentation and control. Optical fibers appear to be well suited for high temperature nuclear applications because they are immune to electromagnetic interference, can withstand harsh environments, and are capable of performing distributed sensing. Previous work with optical fibers has focused on the transmission of light. This thesis presents an alternative interferometric technique that measures the Rayleigh backscatter as a function of position using Luna Technologies’ Optical Backscatter Reflectometer (OBR). The OBR has the capability to perform distributed temperature and strain sensing. However, this work investigated the optical backscattered signal as a function of position when the Corning SMF-28e+ single-mode optical fiber was exposed to high temperatures and radiation environments.
The work has created a large set of OBR data that was analyzed to characterize single-mode fiber interrogated by the OBR at high temperatures and in radiation environments by monitoring the average fiber Amplitude (dB). Three experiments were performed: a 100 hour thermal-only experiment up to 1000°C, a 73 hour gamma irradiation experiment in the cobalt-60 irradiator at The Ohio State University Nuclear Reactor Laboratory up to 400°C, and a 450 hour reactor irradiation experiment at The Ohio State University Research Reactor up to 1000°C. This work has proven that optical amplitude measurements can be performed with the OBR at high temperatures in radiation environments. A temporary temperature effect was seen where the average fiber Amplitude (dB) increased with increasing temperature and decreased with decreasing temperature. Slight permanent damage was seen in the thermal-only and reactor irradiation experiments as a decrease in average fiber Amplitude (dB) due to high temperatures. The maximum decrease in average fiber Amplitude (dB) for the thermal-only and reactor irradiation experiments was less than 1 dB and 6 dB, respectively. Even at high temperatures in a reactor irradiation environment, light propagates to the heated and irradiated region of the test fiber and is scattered back with a large enough fraction to measure a signal that is distinguishable from the noise floor.
As a next step, the experimental data acquired in these experiments will be analyzed with Luna Technologies’ distributed sensing software to extract temperature information to determine if the OBR can function as a distributed sensor at high temperatures in radiation environments.