STP939

    Influence of the Initial Material Condition on the Deformation Behavior of Zircaloy Cladding Tubes in the High-α-Phase Region

    Published: Jan 1987


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    Abstract

    The influence of the initial material condition on the deformation behavior of Zircaloy cladding tubes at 600 and 800°C is systematically investigated by closed end creep rupture tests and transient burst tests in air. At 800°C the strain rate of the cladding tube diameter can be described by the Norton creep equation ˙ε = n exp(− Q/RT) with a constant structure parameter A, stress exponent n, and activity energy Q. The structure parameter A depends on the normalized initial stress σ0/G(T) (σ0 = initial stress; G(T) = temperature-dependent shear modulus) and the initial material condition of the cladding characterized by the yield stress at 400°C and the degree of cold work during the final rocking step.

    At 600°C nonstationary creep behavior is reported for the as-cold-worked and partly recrystallized material condition. The Norton creep equation can be maintained with the same constants n and Q if a time-dependent structure parameter is assumed. As a result, the structure parameter A(t) can be written as a function of (1) the “extended normalized annealing time” K(ϕ, t, T), which describes the influence of cold work ϕ, annealing time t, and temperature T on the degree of recrystallization, and (2) the creep deformation represented by the normalized true tangential stress σ(t)/G(T) of the cladding tube sample: A(t)AminAmaxA(t)=a[σ(t)G(T)K(ϕ,t,T)]b where Amin, Amax = empirical minimum and maximum values of A, respectively, and a, b = empirical constants, depending on the degree of cold work.

    The analytical treatment is extended to temperature transient processes by using in Eq 1 an effective temperature instead of the actual temperature. The empirical equation (1) together with the Norton creep equation enable the description of the strain rate history of a Zircaloy cladding tube in the temperature range between 600 and 800°C and the dependency on the initial material condition.

    Keywords:

    Zircaloy-4, cladding tube, fuel rod, pressurized water reactor, deformation behavior, high temperature, creep rupture test, transient burst test, material condition, yield strength, degree of cold work, influence


    Author Information:

    Ortlieb, E
    Kraftwerk Union AG, Erlangen,

    Cheliotis, G
    Kraftwerk Union AG, Erlangen,

    Weidinger, HG
    Kraftwerk Union AG, Erlangen,


    Paper ID: STP28142S

    Committee/Subcommittee: B10.05

    DOI: 10.1520/STP28142S


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