STP458: The Significance of Irradiation-Induced Creep on Reactor Performance of a Zircaloy-2 Pressure Tube

    Watkins, B.
    Research Manager and Section Leader, United Kingdom Atomic Energy Authority, Reactor Materials Laboratory, Culcheth, Warrington, Lancashire

    Wood, D. S.
    Research Manager and Section Leader, United Kingdom Atomic Energy Authority, Reactor Materials Laboratory, Culcheth, Warrington, Lancashire

    Pages: 15    Published: Jan 1969


    Abstract

    Zircaloy-2 has been used for pressure tubes in water reactors which operate in the temperature range 250 to 300 C. Irradiation enhances the creep rate under these conditions to such an extent that design must be based on creep rupture.

    Insufficient data are available to allow a Larson-Miller extrapolation of the in-reactor creep-rupture strength, and in its place a limiting creep-strain criterion is proposed. The use of a strain limit in design of pressure tubes is discussed and both tubular and uniaxial creep-rupture data are presented. These show that the time to reach 2 or 3 percent strain is only about half the time to failure. Irradiation creep-rupture data are presented which indicate that irradiation substantially increases the strain at which tertiary creep commences and it is suggested that irradiation increases the rupture ductility.

    Assuming that the in-reactor creep rate does not decrease with increase of testing time the anticipated creep strain under design conditions is of the order of 2 percent. This is well within the limit which could lead to operational restriction and the time to reach 2 percent strain is about half the time to reach failure in out-of-reactor creep-rupture tests. Thus even with this pessimistic approach there is no risk of a creep-rupture failure under design conditions.

    Keywords:

    Zircaloy-2, stress rupture, ductility, low-deformation creep, effects of irradiation


    Paper ID: STP43830S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP43830S


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