High resolution characterisation of corrosion and hydrogen pickup of Zr cladding alloys

Jing Hu, Brian Setiadinata, Thomas Aarholt, Paul A J Bagot, M.P. Moody, S Lozano-Perez, C Grovenor, Alistair Garner, Allan Harte, Katie Moore, Philipp Frankel, Michael Preuss, Na Ni

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    Abstract

    As part of the MUZIC-2 project, several state-of-the-art high resolution analysis techniques
    are being used to study the microstructure of a range of commercial and developmental Zr
    alloys corroded under autoclave simulated PWR conditions. Samples were chosen to be
    representative of the early, pre-transition, transition and post-transition stages of the
    oxidation process. We have studied the development of the equiaxed-columnar-equiaxed
    grain structure, and observe that the columnar grains are both longer and show a stronger
    preferred texture in more corrosion-resistant alloys. Fresnel imaging revealed the existence
    of both parallel interconnected pores and some vertically interconnected pores along the
    columnar oxide grain boundaries, which become disconnected near the metal-oxide interface.
    Analytical (Scanning) Transmission Electron Microscope ((S)TEM) has been used to study
    two types of second phase particles (SPPs): β-Nb and Zr(Nb,Fe)2. The Zr(Nb,Fe)2 SPPs are
    present at a lower number density and tend to become amorphous quickly once incorporated
    into the growing oxide. Atom Probe Tomography (APT) was used to study finer Nb and Fe
    clusters in the suboxide and metal regions, Fe clusters are also found at the oxide grain
    boundaries. Electron Energy Loss Spectroscopy analysis (EELS) and automated crystal
    orientation mapping with TEM have also revealed Widmanstatten-type suboxide layers in
    some samples with compositions in different regions of either the hexagonal ZrO structure
    predicted with ab initio modelling or Zr3O2. Some of these layers are much thicker than
    observed previously in other oxidised zirconium alloys. Hydrogen pickup mechanisms have
    been studied by high resolution Secondary Ion Mass Spectrometry (NanoSIMS) analysis of
    deuterium-spiked samples, showing that at different stages of oxidation the penetration of
    deuterium occurs in quite different patterns. These observations are discussed in the context
    of current models for oxidation and hydrogen pickup in zirconium alloys.
    Original languageEnglish
    Title of host publicationProceedings of the TopFuel conference 2015
    Publication statusPublished - 1 Sept 2015

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