Optical fibre void fraction determination for liquid metal cooled fast neutron reactors

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    The use of several optical fibre sensor tip designs is demonstrated for fluid discrimination in multiphase flows. These probes are made from standard silica fibres with their plane end shaped into a desired geometry using various surface treatments.
    Refractive-index contrast between phases and principles of total internal reflection at the sensor tip are used to detect interfaces in multiphase fluids. Such probes have quasi-binary outputs: their use is demonstrated in distinguishing gas bubbles from lead-bismuth eutectic (LBE) in gas-liquid metal two-phase flows and the results are compared with those obtained from simple 90° cleaved fibres. Sensor tip response quality is demonstrated by comparison of signal profiles obtained in a laboratory-scale reactor set-up.
    To progress in the optical fibre phase detection technique, a first requirement is fulfilled by manufacturing reproducible and characterized sensors. A second objective, investigated in this thesis, is to outline a methodology to perform the signal analysis. A signal processing approach, based on optical probe responses during probeinterface interactions, is presented, and its objectiveness is demonstrated.
    When used with monofibre sensors, it provides local void fractions and bubble arrival frequencies. The performance of these measurements is evaluated in various argon-LBE two-phase flow conditions for the different probe tip geometries. Cleaved (wedge) end optical fibres are employed over a wide range
    of practical operating conditions in the full-scale HEavy LIquid metal
    Oxygen control System 3 reactor (HELIOS3) at SCK•CEN. After checking
    for sources of error associated with the rise and fall times of the
    measured signals, gas void fraction and bubble count profiles are
    obtained by processing the time-series data with the developed algorithm.
    All experiments are executed with an argon-LBE system.
    The results suggest that the optical probe can successfully and readily
    determine the local void fraction inside the reactor vessel. This reveals the technique’s potential usefulness as an important research and control tool.
    Original languageEnglish
    QualificationMaster of Science
    Awarding Institution
    • BNEN - Belgian Nuclear Higher Education Network
    • Bartosiewicz, Yann, Supervisor, External person
    • Rosseel, Kris, Supervisor
    Date of Award31 Aug 2017
    StatePublished - 31 Aug 2017

    ASJC Scopus subject areas

    • Nuclear Energy and Engineering
    • Process Chemistry and Technology

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