STP1023: Influence of Chemical Composition and Manufacturing Variables on Autoclave Corrosion of the Zircaloys

    Graham, RA
    Senior research metallurgist, manager, process analysis, and senior research metallurgist, Teledyne Wah Chang Albany, Albany, OR

    Tosdale, JP
    Senior research metallurgist, manager, process analysis, and senior research metallurgist, Teledyne Wah Chang Albany, Albany, OR

    Finden, PT
    Senior research metallurgist, manager, process analysis, and senior research metallurgist, Teledyne Wah Chang Albany, Albany, OR

    Pages: 12    Published: Jan 1989


    Abstract

    Previous investigators have reported the separate influences of chemical composition and heat treatment on the nodular and uniform corrosion of zirconium-based alloys. However, many of these compositions lie outside the allowable Zircaloy ranges required by most nuclear fuel specifications. The current study shows that the corrosion performance of the Zircaloys can be optimized by adjusting chemical compositions within current ASTM ranges, and examines the influence of composition on response to heat treatment. It is believed that this approach will yield improved corrosion performance and results in a product that can be introduced for immediate nuclear service application.

    To investigate the effect of tin, iron, chromium, and nickel on the nodular corrosion of Zircaloy-2, a special 5500-kg ingot was triple melted. The composition was intentionally varied within a controlled portion of the ASTM range along the ingot length. Specimens of the ingot with different compositions were hot worked and beta quenched at a common size. Strip specimens (0.67 mm thick) were fabricated using three process schedules spanning the annealing parameter (∑Ai = ∑ti, exp — QIRTi) range applicable to current production practice for either tubeshell or strip material. Corrosion weight gains were obtained from a 500°C static autoclave test. A statistically significant reduction in 500°C weight gain was found as (1) the percentage nickel and iron increased; (2) the percentage of tin decreased; and (3) the accumulated annealing parameter decreased.

    A “controlled composition” is defined where nickel and iron are adjusted towards the upper ASTM composition limits and tin is adjusted towards the lower limit. The 500°C weight gain of controlled composition Zircaloy-2 is basically insensitive to accumulated annealing parameter over the range of 6.2 × 10−21 h to 1.1 × 10−17 h. The effect of beta quench rate on 500°C weight gains was also determined for Zircaloy-2 controlled composition material. Weight gains varied less than 5 mg/dm2 over a range of surface cooling rates from 18 to 36°C/s.

    Analysis of the effect of beta quench rates on the uniform and nodular corrosion of Zircaloy-4 was performed. Uniform corrosion post-transition rates are not significantly affected by beta quench rate for 360, 400, and 420°C autoclave tests. During 450°C testing, unrecrystallized microstructures of Zircaloy-4 promoted retention of tight, adherent oxide layers for much longer exposures than fully recrystallized microstructures. 500°C static autoclave weight gains are inversely proportional to the logarithm of the cooling rate for Zircaloy-4.

    Keywords:

    zirconium, Zircaloy, corrosion, nodular corrosion, autoclave tests, chemical composition, beta quenching, quench rate, thermomechanical processing, annealing parameter


    Paper ID: STP18873S

    Committee/Subcommittee: B10.05

    DOI: 10.1520/STP18873S


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