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**Source: **STP28142S

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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 = *Aσ*^{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 *σ*^{0}/*G(T)* (*σ*^{0} = 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*^{min}, *A*^{max} = 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,*

**Committee/Subcommittee:** B10.05

**DOI:** 10.1520/STP28142S