STP1423

    Role of Microchemistry and Microstructure on Variability in Corrosion and Deuterium Uptake of Zr-2.5Nb Pressure Tube Material

    Published: Jan 2002


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    Abstract

    Understanding the reasons for variability in D uptake in Canadian Deuterium Uranium (CANDU) reactor Zr-2.5Nb pressure tubes (PT)s will lead to improved surveillance and predictive strategies. Results from out-reactor aqueous exposures that suggest PT performance should be predictable based on offcut characteristics and may lead to the development of techniques to identify PTs with highest D uptake rates. The range of out-reactor corrosion and D uptake rates in Zr-2.5Nb coupons from different PT offcuts is similar to that found in test/power reactors. Out-reactor post-transition corrosion and D uptake rates at 310 and 360°C are found to be strongly correlated and decrease with increasing concentrations of Fe and Cr in the alloy. In the Bruce 3 reactor, PTs with higher D uptake show ‘curly’ α-β microstructures with a large number of basal planes (in the α-Zr grains), and β-Zr grains, oriented towards the radial direction of the tube. Since oxidized β-Zr regions are found to be associated with lateral cracking, the presence of a higher frequency of β-Zr grains aligned normal to the surface in these curly microstructures may result in increased routes for D uptake in this material. Oxide structure is also found to be dependent on the α-Zr orientation that results in different relative proportions of [001] growth versus general columnar oxide grains. Improved corrosion and D uptake performance is also found in Zr-2.5Nb material that is prefilmed (400°C for ≥24 h), β-quenched in the billet stage and in material from the back of the extrusion.

    Keywords:

    hydrogen uptake, corrosion, electron microscopy, characterization, Zr-2.5Nb alloy microstructure, oxide microstructure


    Author Information:

    Warr, BD
    Principal Engineer, Fuel Channels, Generation Plant Technologies, Kinectrics Inc., Toronto, Ontario

    Perovic, V
    Senior Scientist, Generation Plant Technologies, Kinectrics, Inc., Toronto, Ontario

    Lin, YP
    Senior Scientist, Generation Plant Technologies, Kinectrics, Inc., Toronto, Ontario

    Wallace, AC
    Senior Design Engineer, Bruce Power, 700 University, Toronto, Ontario


    Paper ID: STP11395S

    Committee/Subcommittee: B10.02

    DOI: 10.1520/STP11395S


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