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    Implications of Embrittlement During the Life of a Zirconium Pressure Tube Reactor


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    The existing evidence on the effect of hydrogen and irradiation on the mechanical properties of Zircaloy-2 has been reviewed, and it has been shown that the only change of importance to pressure tube technology is that of the resulting embrittlement. In order to assess how much embrittlement can be tolerated it is necessary to determine the influence of this embrittlement on the failure stress of tubes containing defects. A number of such tests have been mounted on unirradiated 5-in.diameter tubes typical of those used in the SGHW reactor, and these have shown that even with 400 ppm of hydrogen, defects several inches long can be tolerated under SGHW conditions. Study of the effect of irradiation necessitates developing a correlation between practical small specimen tests and actual size tube tests. Preliminary results indicate that measurements of the crack opening displacement provides such a correlation, and further work is in hand on this. In the meantime, the results available from irradiation of notch impact specimens to doses of up to 1021 n/cm2 in DFR suggest that the embrittlement effect saturates at relatively low doses. Interpretation of these results suggests that, even with the maximum effect of irradiation and 400 ppm H2 the critical defect size for failure under SGHW operating conditions is several inches long. The occurrence of such major defects is extremely improbable: the use of the limit approach based upon the quantitative interpretation of the overpressure further strengthens the improbability of such an occurrence. On this basis it is argued that the SGHW pressure tubes will be able to withstand high irradiation doses and large amounts of hydrogen without fear of failure.


    zirconium alloys, pressure vessels, embrittlement, nuclear reactors, hydrogen, irradiation, mechanical properties, tensile properties, radiation effects, metals, tubes, cracks

    Author Information:

    Nichols, R. W.
    Deputy head of laboratory and research manager, Culcheth, Nr., Warrington, Lancashire

    Watkins, B.
    Deputy head of laboratory and research manager, Culcheth, Nr., Warrington, Lancashire

    Committee/Subcommittee: E10.07

    DOI: 10.1520/STP41330S