A Simple Kinetic Model of Zircaloy Zr(Fe,Cr){sub 2} Precipitate Amorphization During Neutron Irradiation

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At neutron flux levels typical for Zircaloy fuel cladding in commercial power reactors, there is insufficient thermal energy below about 600 K to maintain long-range order in hexagonal close packed (hcp) Zr(Fe,Cr){sub 2} precipitates, and these Laves-phase intermetallics gradually become amorphous. The transformation is homogeneous with no change in composition at low temperatures, but above 500 K an amorphous zone containing only 10 at% Fe grows inward from the periphery as Fe moves outward to the adjacent alloy matrix. The shrinking central cores of Zr(Fe,Cr){sub 2} precipitates in Zircaloy-4 remain crystalline, while in Zircaloy-2 these precipitates quickly undergo partial transformation ... continued below

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19 p.

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Taylor, D.F.; Peters, H.R. & Yang, W.J.S. July 1, 1999.

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At neutron flux levels typical for Zircaloy fuel cladding in commercial power reactors, there is insufficient thermal energy below about 600 K to maintain long-range order in hexagonal close packed (hcp) Zr(Fe,Cr){sub 2} precipitates, and these Laves-phase intermetallics gradually become amorphous. The transformation is homogeneous with no change in composition at low temperatures, but above 500 K an amorphous zone containing only 10 at% Fe grows inward from the periphery as Fe moves outward to the adjacent alloy matrix. The shrinking central cores of Zr(Fe,Cr){sub 2} precipitates in Zircaloy-4 remain crystalline, while in Zircaloy-2 these precipitates quickly undergo partial transformation and the low-Fe amorphous front advances into a random mixture of amorphous and crystalline regions, each with the original composition. Above 600 K, the Zr(Fe,Cr){sub 2} precipitates tend to retain both their hcp structure and original chemical composition. These observations suggest that a dynamic competition between kinetic excitation to an amorphous state and thermal recrystallization makes some fraction of the Fe atoms available for flux-assisted diffusion to the alloy matrix by displacing them from hcp lattice positions into metastable, probably interstitial, sites. With one set of kinetic constants, a simple analytic representation of these processes accurately predicts precipitate amorphization as a function of neutron flux, temperature, and time for either Zircaloy-2 or -4. By implication, over the composition range of interest, hcp Zr(Fe,Cr){sub 2} is most stable thermodynamically with about 33 at% Fe, typical of Zircaloy-2, but amorphous Zr(Fe,Cr){sub 2} has the smallest activation energy for recrystallization with the slightly higher Fe content typical of Zircaloy-4.

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19 p.

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INIS; OSTI as DE00754944

Medium: P; Size: 19 pages

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  • 9th Environmental Degradation Conference, Newport Beach, CA (US), 08/01/1999--08/05/1999

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  • Report No.: KAPL-P-000319
  • Report No.: K99115
  • Grant Number: AC12-76SN00052
  • Office of Scientific & Technical Information Report Number: 754944
  • Archival Resource Key: ark:/67531/metadc710013

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  • July 1, 1999

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  • Sept. 12, 2015, 6:31 a.m.

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  • April 7, 2017, 4:31 p.m.

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Taylor, D.F.; Peters, H.R. & Yang, W.J.S. A Simple Kinetic Model of Zircaloy Zr(Fe,Cr){sub 2} Precipitate Amorphization During Neutron Irradiation, article, July 1, 1999; United States. (digital.library.unt.edu/ark:/67531/metadc710013/: accessed October 17, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.