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

Abstract

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 asmore » 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.« less

Authors:
; ;
Publication Date:
Research Org.:
Knolls Atomic Power Lab., Niskayuna, NY (US)
Sponsoring Org.:
US Department of Energy (US)
OSTI Identifier:
754944
Report Number(s):
KAPL-P-000319; K99115
TRN: US0003549
DOE Contract Number:  
AC12-76SN00052
Resource Type:
Conference
Resource Relation:
Conference: 9th Environmental Degradation Conference, Newport Beach, CA (US), 08/01/1999--08/05/1999; Other Information: PBD: 1 Jul 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 22 GENERAL STUDIES OF NUCLEAR REACTORS; PHYSICAL RADIATION EFFECTS; FUEL CANS; ZIRCALOY 2; ZIRCALOY 4; MATHEMATICAL MODELS; MICROSTRUCTURE; NUCLEAR POWER PLANTS; CRYSTAL-PHASE TRANSFORMATIONS; RECRYSTALLIZATION; AMORPHOUS STATE; LAVES PHASES; ZIRCALOY; LAVES PHASE; NEUTRON FLUX; AMORPHOUS ZONE; IRON DEPLETION

Citation Formats

Taylor, D F, Peters, H R, and Yang, W J.S. A Simple Kinetic Model of Zircaloy Zr(Fe,Cr){sub 2} Precipitate Amorphization During Neutron Irradiation. United States: N. p., 1999. Web.
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. United States.
Taylor, D F, Peters, H R, and Yang, W J.S. Thu . "A Simple Kinetic Model of Zircaloy Zr(Fe,Cr){sub 2} Precipitate Amorphization During Neutron Irradiation". United States. https://www.osti.gov/servlets/purl/754944.
@article{osti_754944,
title = {A Simple Kinetic Model of Zircaloy Zr(Fe,Cr){sub 2} Precipitate Amorphization During Neutron Irradiation},
author = {Taylor, D F and Peters, H R and Yang, W J.S.},
abstractNote = {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.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {1999},
month = {7}
}

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