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Role of Microchemistry and Microstructure on Variability in Corrosion and Deuterium Uptake of Zr-2.5Nb Pressure Tube Material Pages: 26 Published: Jan 2002
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View License Agreement 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. | ||
