STP633

    Zircaloy Cladding Behavior During Irradiation Tests Under Power-Cooling-Mismatch Conditions

    Published: Jan 1977


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    Abstract

    The behavior of Zircaloy-clad fuel rods for light water reactors under off-normal operating conditions is being studied in the Power Burst Facility. Fuel rods from three irradiation experiments conducted under power-cooling-mismatch conditions have been examined destructively in remote handling facilities. The postirradiation examinations of these pressurized water reactor-type rods have included visual and photographic examination, physical dimensioning, and metallography.

    The examinations have revealed the collapse of the Zircaloy cladding onto the fuel pellets and into the gaps between pellets (waisting) of these fuel rods. In some cases, severe oxidation on the external surface of the cladding from Zircaloy-steam reaction and on the internal surface from Zircaloy-uranium dioxide (Zr-UO2) reaction caused embrittlement of the cladding which resulted in cladding cracking and fuel rod fracture.

    Cladding temperatures were estimated from the microstructures using a correlation between temperature, time, and the combined thickness of the zirconium dioxide (ZrO2) and oxygen-stabilized alpha layers. Using this method, cladding temperatures up to 1640 K have been estimated on the fuel rods tested.

    Cladding collapse occurred at temperatures estimated to be in the range of 1020 to 1170 K. The reactor coolant system pressure was 14.5 to 15.2 MPa and the rods were prepressurized to pressures within the range 2.6 to 3.8 MPa.

    Keywords:

    zirconium, cladding, oxidation, embrittlement, collapse, irradiation, zirconium alloys


    Author Information:

    Hobbins, RR
    Supervisor, Fuel Materials Section, Materials Technology Branch, senior metallurgist, Materials Technology Branch, and senior project engineer, Thermal Fuels Behavior Experiment Support Branch, Aerojet Nuclear Company, Idaho Falls, Idaho

    Smolik, GR
    Supervisor, Fuel Materials Section, Materials Technology Branch, senior metallurgist, Materials Technology Branch, and senior project engineer, Thermal Fuels Behavior Experiment Support Branch, Aerojet Nuclear Company, Idaho Falls, Idaho

    Gibson, GW
    Supervisor, Fuel Materials Section, Materials Technology Branch, senior metallurgist, Materials Technology Branch, and senior project engineer, Thermal Fuels Behavior Experiment Support Branch, Aerojet Nuclear Company, Idaho Falls, Idaho


    Paper ID: STP35572S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP35572S


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