STP458: Embrittlement of Zircaloy-2 Pressure Tubes

    Watkins, B.
    United Kingdom Atomic Energy Authority, Reactor Materials Laboratory, Wigshaw Lane, Culcheth, Warrington, Lancashire

    Cowan, A.
    United Kingdom Atomic Energy Authority, Reactor Materials Laboratory, Wigshaw Lane, Culcheth, Warrington, Lancashire

    Parry, G. W.
    Westinghouse Electric Corporation, Atomic Power Division, Pittsburgh, Pa.

    Pickles, B. W.
    United Kingdom Atomic Energy Authority, Reactor Materials Laboratory, Wigshaw Lane, Culcheth, Warrington, Lancashire

    Pages: 19    Published: Jan 1969


    Abstract

    Previous work on hydrogen absorption has been extended to cover the effect of radial hydrides and greater hydrogen concentrations, and the effect of neutron irradiation on Zircaloy-2 pressure tubes. Specimens with radial hydrides were produced by modification of tube-manufacturing route and by hydriding under pressure in lithiated water. Both series of tests showed that the effect of the hydrides was marked at 20 C but was small at 300 C. Thus, at design condition, the critical crack length is of the order of 3 to 4 in. Critical crack-length tests on irradiated tubes show that, up to doses of 1021 n/cm2 (>1 MeV), there is no decrease in critical crack length on irradiation.

    Results from small specimens and tube behavior have been correlated. This has permitted assessing the effect of a large number of material variables (for example, H2 content, hydride orientation, neutron dose, etc.). For example, the effect of irradiation up to doses of 2 × 1021 n/cm2 (Ni) has been assessed on the basis of both tension and notched specimens. These show that the effect on impact specimens saturates at 1020 n/cm2 but there is a progressive but small increase in tensile strength over the range of neutron dose examined.

    This work shows that the critical crack length of through-thickness defects under reactor-design conditions is of the order of 3 to 4 in. Leakage can be expected to occur when the through-thickness crack is of the order of 0.5 in. and failure due to instability is not, therefore, considered feasible.

    Keywords:

    Zircaloy-2, irradiation effects, hydrogen embrittlement, fracture mechanics


    Paper ID: STP43825S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP43825S


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