Chemistry of Waterside Oxide Layers on Pressure Tubes

    Volume 5, Issue 1 (January 2008)

    ISSN: 1546-962X

    CODEN: JAIOAD

    Published Online: 18 January 2008

    Page Count: 17


    Do, T.
    Reactor Chemistry and Corrosion Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

    Saidy, M.
    Reactor Chemistry and Corrosion Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

    Hocking, W. H.
    Reactor Chemistry and Corrosion Branch, Atomic Energy of Canada Limited, Chalk River Laboratories, Chalk River, Ontario

    (Received 15 June 2007; accepted 4 December 2007)

    Abstract

    The pressure tubes that contain the fuel bundles and the primary coolant within the core of a CANDU heavy-water reactor are fabricated from a Zr-2.5Nb alloy with a complex microstructure. During reactor operation the pressure-tube interior surface is slowly oxidized by heavy water and a fraction of the deuterium that is released through this process enters the underlying alloy and can reduce its fracture toughness. Considerable variability in deuterium ingress has been observed among the pressure tubes within a single reactor as well as between different reactors. These differences are thought to be due not only to metallurgical variables, such as alloy microstructure and composition, but also to variations in the primary coolant chemistry, including pH and dissolved impurities. In the present study, a combination of surface analytical methods has been employed to characterize the microchemistry and oxidation history of the waterside oxide layers grown on two pressure tubes that were removed from different CANDU reactors. The presence of varying concentrations of iron, manganese and uranium, derived mainly from corrosion of feeder pipes and fuel failures, has been found throughout the oxide layers. An increase in the oxidation rate of one pressure tube later in life could be correlated with evidence of greater open porosity, provided by the depth distributions of impurities, extending deep within the oxide layer.


    Paper ID: JAI101292

    DOI: 10.1520/JAI101292

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    Author
    Title Chemistry of Waterside Oxide Layers on Pressure Tubes
    Symposium 15th International Symposium on Zirconium in the Nuclear Industry, 2007-06-28
    Committee B10