High-Temperature Fiber Optic Sensing Development and Deployment into an Optical Fiber Based Gamma Thermometer

All dates for this event occur in the past.

Name: Joshua Jones

Abstract:
This thesis focuses on the redesign of an Optical Fiber Based Gamma Thermometer (OFBGT) for the high temperature and high radiation conditions that would be experienced in a power reactor. In support of this redesign effort, both silica and single crystal sapphire based optical fiber sensors have been developed for high temperature applications. Monte Carlo radiation transport and thermal analyses have also been performed to understand how the sensors would behave in a reactor environment. The work in this dissertation characterized the performance of SMF-28 Ultra fibers up to 1000 ℃, ~350 ℃ past their normal limit, by leveraging a new technique for post-processing of optical frequency domain reflectometry (OFDR) results. Due to the expanded temperature range, these common fibers are now able to be used in the OFBGT for applications in even the highest operating temperature reactors. For temperatures in excess of 1000 ℃, this work has also developed the internal cladding process used to make OFDR sensing possible in single crystal sapphire fibers. This work has shown that there is light that escapes the core of the fiber and propagates within the cladding. It is demonstrated that improved behavior can be achieved when this clad propagating light is addressed properly, either by suppressing it at the injection point of the fiber, or by removing it along the length of the fiber. Sapphire fibers properly set up with an internal cladding have been demonstrated capable of measuring temperatures up to 1500 ℃. The radiation modeling of the OFBGTs has found two key interrelated behaviors that must be considered. First, there are delayed gamma sources from fission and non-fission activation, which result in the OFBGT temperature difference increasing to about double its original predicted value over time. Additionally, it has been demonstrated that the specific increase due to these delayed gamma sources across the core are not equal, as delayed gamma sources are not as energetic as the prompt sources. These time and space changes in the OFBGT response are responsible for errors that are observed in the practical application of the data analytics methodology, which was devised to extract core power from an array of OFBGTs. Incorporating the lessons learned from prior development efforts with the OFBGT, as well as a detailed review of the geometry and materials used, a new design of the sensor has been devised. This new design utilizes a zirconia thermal mass, with a zircalloy outer sheath. The benefits of the design include stability in the higher power, higher temperature conditions, faster response time, better ability to handle non-uniform boundary temperature and power inputs, and a more uniform behavior across a wide range of temperatures. This new design is able to incorporate the outer sheath fiber inside the outer sheath, as well as being able to have fins or other texture to aid in cooling, when necessary. It has been shown that the sensitivity of the OFBGT designs can be tuned to specific applications by changing the gas-gap composition.

Zoom Link (or alternative) - if available
https://osu.zoom.us/j/95957035756?pwd=MWZzdzJGbnhuV0Y2cGZYakpPTDFzUT09

Committee Members
Dr. Thomas Blue
Dr. Tunc Aldemir
Dr. Marat Khafizov
 

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