Microstructural aspects of zircaloy nodular corrosion in steam

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Zircaloy-2 becomes susceptible to nodular corrosion in high-temperature, high-pressure steam when the total solute concentration of the {beta}-stabilizing alloying elements Fe, Ni and Cr in the {alpha}-zirconium matrix falls below a critical value C{sub c} that is characteristic of the test conditions. C{sub c} for typical commercial Zircaloy-2 in a 24hr/510 C/10.4MPa steam-test is the precipitate-free a-matrix concentration in equilibrium with solute-saturated {beta} phase at about 840 C, the corresponding critical temperature T{sub c}.Thus, immunity to nodular corrosion is a metastable condition for {alpha}-Zircaloy that requires fast cooling from above T{sub c} to achieve adequate solute concentration throughout the matrix. ... continued below

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45 p.

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Taylor, D.F. July 1, 1999.

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Description

Zircaloy-2 becomes susceptible to nodular corrosion in high-temperature, high-pressure steam when the total solute concentration of the {beta}-stabilizing alloying elements Fe, Ni and Cr in the {alpha}-zirconium matrix falls below a critical value C{sub c} that is characteristic of the test conditions. C{sub c} for typical commercial Zircaloy-2 in a 24hr/510 C/10.4MPa steam-test is the precipitate-free a-matrix concentration in equilibrium with solute-saturated {beta} phase at about 840 C, the corresponding critical temperature T{sub c}.Thus, immunity to nodular corrosion is a metastable condition for {alpha}-Zircaloy that requires fast cooling from above T{sub c} to achieve adequate solute concentration throughout the matrix. Annealing Zircaloy at any temperature below T{sub c} for a sufficiently long time makes it susceptible to nodular corrosion. In the ({alpha}+{chi}) phase field, where {chi} collectively designates the Fe-, Cr-, and Ni-containing precipitate phases, lowering the solute concentration to less than C{sub c} by Ostwald ripening can require many hundreds of hours. Above about 825 C, the temperature of the ({alpha}+{chi})/({alpha}+{beta}+{chi}) transus, solute-saturated {beta} phase surrounds each precipitate and a strong inverse activity gradient promotes equilibration with the much lower solute concentration in the {alpha} matrix. Sensitization to nodular corrosion occurs most rapidly at about 835 C between the ({alpha}+{chi})/({alpha}+{beta}+{chi}) transus and T{sub c}. Annealing Zircaloy at temperatures above T{sub c} for a sufficiently long time will raise the solute concentration above C{sub c} and, with rapid cooling, heal any degree of susceptibility. Annealing within the protective coarsening window between T{sub c} and about 850 C, the temperature of the ({alpha}+{beta}+{chi})/({alpha}+{beta}) transus, achieves rapid precipitate growth in a matrix immune to nodular corrosion.

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45 p.

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INIS; OSTI as DE00754941

Medium: P; Size: 45 pages

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  • Other Information: PBD: 1 Jul 1999

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  • Report No.: KAPL-P-000317
  • Report No.: K99108
  • Grant Number: AC12-76SN00052
  • DOI: 10.2172/754941 | External Link
  • Office of Scientific & Technical Information Report Number: 754941
  • Archival Resource Key: ark:/67531/metadc711826

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • July 1, 1999

Added to The UNT Digital Library

  • Sept. 12, 2015, 6:31 a.m.

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  • April 12, 2017, 6:47 p.m.

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Taylor, D.F. Microstructural aspects of zircaloy nodular corrosion in steam, report, July 1, 1999; United States. (digital.library.unt.edu/ark:/67531/metadc711826/: accessed November 21, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.