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Evaluation of Optical Fiber Sensors in High Temperature and Nuclear Reactor Environments

Wilson, Brandon Augustus

Abstract Details

2017, Doctor of Philosophy, Ohio State University, Nuclear Engineering.
The Department of Energy and Idaho National Laboratory are restarting the TREAT reactor and are interested in updating the reactor’s instrumentation regarding the analysis of the test fuel. Optical fibers’ ability to make distributed temperature measurements coupled with its small footprint makes optical fiber a viable candidate to monitor fuel performance in the TREAT reactor. In addition to TREAT reactor, the U.S. Department of Energy and nuclear reactor companies like TerraPower have shown interest in using distributed optically based instrumentation for nuclear instrumentation in Next-gen reactors. The performance and evaluation of optical fiber based instrumentation in high temperature and radiation environments is the main goal of this work. A feasibility study to determine the viability of extending this technology to the nuclear field was made. In addition to the performance testing of commercial optical fiber based instrumentation, I was able to modify and innovate various aspects of the optical fiber based instrumentation, so that it could survive the high temperature and radiation environments of a Next-Gen reactor. Distributed temperature sensing using optical fiber based methods in silica optical fibers was found to have a temperature limit of around 700 C. Above the 700 C mark, various effects, from annealing of the glass to environmental effects from the atmosphere, start to cause sensing failure in the fiber. This temperature limit can be extended to 1000 C if the silica optical fiber is placed in an inert environment with a micro capillary tube or high temperature coating to support it mechanically. Distributed temperature sensing with commercial optical fibers was also tested in a reactor environment and was found to incur a sensing failure after a neutron fluence of around 1018 n/cm2. Radiation hardness can be added to the distributed sensing ability of optical fibers by placing Bragg gratings into the fiber. The high reflective signature off of the Bragg gratings in the fiber allows the distributed temperature sensing to continue to provide accurate measurements, even when the noise floor from radiation damage is increased in the fiber. Femtosecond Bragg gratings have the most potential for long term use in a nuclear reactor, since they were shown to survive long periods of high temperature and radiation fluences without much degradation. Sapphire fiber was also analyzed in this work for its suitability as optical instrumentation in Next-Gen reactors. Sapphire fiber has a temperature limit of 1300 C for light transmission in the fiber. Above 1300 C, aluminum oxyhydroxide forms on the surface of the fiber, causing massive light attenuation in the fiber. An inert atmosphere can extend the temperature range of sapphire optical fibers and sapphire instrumentation above 1300 C. Distributed temperature sensing with sapphire fiber was also achieved in this work by creating an internal reflective cladding using, high energy ion implantation in the fiber. This internal reflective cladding creates a graded index in the sapphire fiber creating a near single mode fiber. The sapphire cladded fiber has tremendous promise and should be further researched in the future.
Thomas Blue (Advisor)
Raymond Cao (Committee Member)
Marat Khafizov (Committee Member)

Recommended Citations

Citations

  • Wilson, B. A. (2017). Evaluation of Optical Fiber Sensors in High Temperature and Nuclear Reactor Environments [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483626659096251

    APA Style (7th edition)

  • Wilson, Brandon. Evaluation of Optical Fiber Sensors in High Temperature and Nuclear Reactor Environments. 2017. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1483626659096251.

    MLA Style (8th edition)

  • Wilson, Brandon. "Evaluation of Optical Fiber Sensors in High Temperature and Nuclear Reactor Environments." Doctoral dissertation, Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1483626659096251

    Chicago Manual of Style (17th edition)