STP681

    Analysis of Irradiation Growth and Multiaxial Deformation Behavior of Nuclear Fuel Cladding

    Published: Jan 1979


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    Abstract

    Postirradiation analysis of the multiaxial strain behavior of nuclear fuel cladding requires a comprehensive evaluation of the various mechanisms contributing to the total observed principal strains. Measurements are usually taken for diametral change, which accrues as a result of irradiation-enhanced multiaxial creep, and of changes in axial length, which is predominantly caused by irradiation-induced growth. In this context, it is important to note that under multiaxial loading, the generalized strain vector produced by creep deformation is not coincident with the hoop direction of the cladding except under special conditions and, similarly, that the expected direction of the irradiation growth component derived from texture considerations is not coincident with the axial direction of the tubing. Rather, both mechanisms usually produce component strains in each of the principal directions of the cladding. It is generally observed, in fact, that the total strain vector determined from postirradiation measurements is well displayed from that which would be predicted for either creep deformation or the irradiation growth mechanism and is obviously the resultant strain produced by the combined effects of irradiation growth and multiaxial creep deformation.

    Thus, it becomes important in efforts to model and predict this behavior from baseline laboratory test results and material anisotropy constants to appropriately separate the strain components that result from irradiation growth from those produced by multiaxial creep behavior. This paper describes a procedure that leads to an expected direction of the creep vector based on multiaxial flow equations for an anisotropic material and a predicted irradiation growth vector based on crystallographic texture analyses and stress-free irradiation growth data. The observations discussed here support the hypothesis that irradiation growth is essentially stress independent in Zircaloy and suggest that anisotropic multiaxial strain ratios due to creep or plastic deformation are unaffected by the presence of a neutron flux.

    The mechanistic aspects of irradiation growth are discussed, particularly as they relate to cold-worked material, and the ideas of Northwood are extended to hypothetically account for observed variations in irradiation damage rate and loss of ductility in materials having varying degrees of cold work and recrystallization.

    Keywords:

    Zircaloy, irradiation growth, multiaxial deformation, creep, anisotropy, fuel rod cladding, strain ratios


    Author Information:

    Clevinger, GS
    Group supervisor, senior engineer, and senior research engineer, Nuclear Metallurgy, The Babcock and Wilcox Company, Lynchburg Research Center, Lynchburg, Va.

    Adams, BL
    Group supervisor, senior engineer, and senior research engineer, Nuclear Metallurgy, The Babcock and Wilcox Company, Lynchburg Research Center, Lynchburg, Va.

    Murty, KL
    Group supervisor, senior engineer, and senior research engineer, Nuclear Metallurgy, The Babcock and Wilcox Company, Lynchburg Research Center, Lynchburg, Va.


    Paper ID: STP36680S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP36680S


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