STP1423: On the Embrittlement of Zircaloy-4 Under RIA-Relevant Conditions

    Daum, RS
    Assistant engineer, Argonne National Laboratory, Argonne, IL

    Majumdar, S
    senior engineer, Argonne National Laboratory, Argonne, IL

    Bates, DW
    Graduate student, U.S. Navy,

    Motta, AT
    Assistant professor, The Pennsylvania State University, University Park, PA

    Koss, DA
    professor, The Pennsylvania State University, University Park, PA

    Billone, MC
    engineer and program manager, Argonne National Laboratory, Argonne, IL

    Pages: 18    Published: Jan 2002


    Abstract

    The extended use of Zircaloy cladding in light water reactors degrades its mechanical properties by a combination of irradiation embrittlement, coolant-side oxidation, hydrogen pickup, and hydride formation. The hydrides are usually concentrated in the form of a dense layer or rim near the cooler outer surface of the cladding. Utilizing plane-strain ringstretch tests to approximate the loading path in a reactivity-initiated accident (RIA) transient, we examined the influence of a hydride rim on the fracture behavior of unirradiated Zircaloy-4 cladding at room temperature and 300°C. Failure is sensitive to hydride-rim thickness such that cladding tubes with a hydride-rim thickness >100 μm (≈700 wppm total hydrogen) exhibit brittle behavior, while those with a thickness <90 μm (≈600 wppm) remain ductile. The mechanism of failure is identified as strain-induced crack initiation within the hydride rim and failure within the uncracked ligament due to either a shear instability or damage-induced fracture. We also report some preliminary results of the uniaxial tensile behavior of low-Sn Zircaloy-4 cladding tubes in a cold-worked, stress-relieved condition in the transverse (hoop) direction at strain rates of 0.001/s and 0.2/s and temperatures of 26 to 400°C.

    Keywords:

    mechanical properties, ring stretch specimens, Zircaloy-4 cladding, hydrides, hydride rim, stress-state, fracture strain


    Paper ID: STP11412S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP11412S


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