STP1132: Effects Of LiOH on Pretransition Zirconium Oxide Films

    Cox, B
    Centre for Nuclear Engineering, University of Toronto, Toronto, Ontario

    Wong, Y-M
    Centre for Nuclear Engineering, University of Toronto, Toronto, Ontario

    Pages: 20    Published: Jan 1991


    Abstract

    At short times and intermediate LiOH concentrations (pH 10–13) the pretransition oxidation kinetics of the Zircaloys appear to be identical with those in neutral water. Nevertheless, in pH12 LiOH the time to transition is reduced and post-transition rates are increased over those in water. In a search for evidence for precursors of these effects, oxide films were formed on Zircaloy specimens in 573 K water and pH10-14.5 LiOH solutions (0.7 to 2.1 × 104 ppm Li) for times from 1–70 days and were examined subsequently by optical and electron microscopy (EM), Fourier-transform infrared (FTIR) interferometry, impedance spectroscopy, and polarization in a fused nitrate/nitrite melt at 573 K. A more limited range of measurements was performed on specimens of fuel cladding that had been oxidized in pH 7 and 12 LiOH solutions (70 ppm Li) at 633 K for other studies.

    Results showed that all specimens corroded in LiOH solutions, even at low concentrations, exhibited enhanced electronic conductivity in the oxide; this resulted in enhanced oxidation in the fused salt medium, even when no such effect was visible in aqueous solutions (from the weight gains). FTIR interferometry and impedance spectroscopy showed that some oxide films formed in pH12 LiOH were significantly thicker than in water (when no difference in their weight was evident), while in other tests the oxide in pH12 LiOH was thinner than in pH7. This dichotomy can be explained by a loss of oxide by dissolution if in some instances it reprecipitates on the surface as a porous layer, whereas in other circumstances it reprecipitates on the autoclave walls.

    Keywords:

    Zircaloy, corrosion, LiOH, oxide, dissolution


    Paper ID: STP25533S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP25533S


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