STP1023

    Influence of the Manufacturing Process on the Corrosion Resistance of Zircaloy-4 Cladding

    Published: Jan 1989


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    Abstract

    A study of a wide range of thermomechanical processing parameters for the manufacture of fuel clad tubing revealed that the corrosion resistance in 673 and 698 K steam varied little within the variations expected to occur in current commercial processing. Long exposure to 673 K steam was used as the test most likely to relate to in-reactor performance with the time to departure from the usual multiple rate transition behavior believed to be the significant measure of performance. The parametric study commenced with the beta heat treatment before extrusion where time at temperature and cooling rate were varied. No changes were made in the extrusion process, but several combinations of anneals during the cold reduction sequences were applied to produce a set of 23 variants. Corrosion tests on the extruded and tube reduced tube hollows without an anneal showed an adverse effect on corrosion resistance of the very high quench rates on the outer surface of the billet. Data from the test series made it possible to estimate that a cooling rate of about 20 to 40 K/s produced a minimum in the weight gain in a 673 K corrosion test. The adverse effect of the high cooling rates illustrated on the outer surface of unannealed tube reduced extrusion (TREX) specimens is eliminated by the subsequent heat treatments and is not seen on either annealed TREX or the tubing made from it. The annealing parameter provided a good measure of corrosion behavior only for identical final tube heat treatments. The difference between unannealed, stress relieved, and recrystallized tubing is not predicted by application of this annealing parameter alone. Increasing the annealing parameter from 2.3 × 10-18to29 × 10-18h improved the corrosion resistance of unannealed cold-worked tubes but did not affect the stress relieved or recrystallized tube specimens. In the same manner, unannealed cold-worked tubes display an effect of quenching conditions when stress relieved tubes did not. A series of tests with various amounts of metal removed from the outer surface of the heat treated tubes showed that the corrosion resistance was largely constant through the tube wall in the 673 K steam test, again showing that the effect of cooling rate at the billet stage was removed by subsequent heat treatment. The test series confirmed the observation in earlier work that a cumulative annealing parameter greater than 10-18 h is sufficient to provide uniformly good corrosion resistance in Zircaloy-4.

    Keywords:

    corrosion, Zircaloy-4, heat treatment, tubes, quenching, anneal parameter


    Author Information:

    Schemel, JJ
    Vice-president, Research and Engineering, Sandvik Special Metals Corp., Kennewick, WA

    Charquet, D
    Assistant vice-president and research engineer, CEZUS Research, Ugine,

    Wadier, J-F
    Assistant vice-president and research engineer, CEZUS Research, Ugine,


    Paper ID: STP18862S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP18862S


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