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Languages : en
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Microstructural evolution in Zircaloy-2 and -4 spent-fuel cladding specimens after approx. 3 years of irradiation in commercial power reactors has been investigated by TEM and HVEM. Two kinds of precipitates induced by the fast-neutron irradiation in the reactors have been identified, i.e., Zr3O and cubic-ZrO2 particles approximately 2 to 10 nm in size. By means of a weak-beam dark-field ''2-1/2D-microscopy'' technique, the bulk nature of the precipitates and the surficial nature of artifact oxide and hydride phases could be discerned. The Zr(Fe/sub x/, Cr/sub 1-x/)2 and Zr2(Fe/sub x/, Ni/sub 1-x/) intermetallic precipitates normally present in the as-fabricated material virtually dissolved in the spent-fuel cladding specimens after a fast-neutron fluence of approx. 4 x 1021 ncm−2 in the power reactors. The observed radiation-induced phase transformations are compared with predictions based on the currently available understanding of the alloy characteristics. 29 refs.
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Languages : en
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Microstructural evolution in Zircaloy-2 and -4 spent-fuel cladding specimens after approx. 3 years of irradiation in commercial power reactors has been investigated by TEM and HVEM. Two kinds of precipitates induced by the fast-neutron irradiation in the reactors have been identified, i.e., Zr3O and cubic-ZrO2 particles approximately 2 to 10 nm in size. By means of a weak-beam dark-field ''2-1/2D-microscopy'' technique, the bulk nature of the precipitates and the surficial nature of artifact oxide and hydride phases could be discerned. The Zr(Fe/sub x/, Cr/sub 1-x/)2 and Zr2(Fe/sub x/, Ni/sub 1-x/) intermetallic precipitates normally present in the as-fabricated material virtually dissolved in the spent-fuel cladding specimens after a fast-neutron fluence of approx. 4 x 1021 ncm−2 in the power reactors. The observed radiation-induced phase transformations are compared with predictions based on the currently available understanding of the alloy characteristics. 29 refs.
Author: HM. Chung
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ISBN:
Category : Brittle failure
Languages : en
Pages : 24
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Microstructural evolution in Zircaloy-2 and -4 spent-fuel cladding specimens after three years of irradiation in commercial power reactors has been investigated by transmission and high-voltage electron microscopies. Two kinds of precipitates induced by the fastneutron irradiation in the reactors have been identified, that is, Zr3O and cubic-ZrO2 particles approximately 2 to 10 nm in size. By means of specimen tilting and dark-field stereomicroscopy, the bulk nature of the cubic-ZrO2 particles has been shown. The Zr(Fex,Cr1-x)2 and Zr2(Fex,Ni1-x) intermetallic precipitates normally present in the as-fabricated material virtually dissolved in the spent-fuel cladding specimens after a fast-neutron fluence of ~4 x 1021 n/cm2 in the power reactors. The observed radiation-induced phase transformations are discussed in relation with the currently available understanding of the alloy characteristics.
Author: WJS Yang
Publisher:
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Category : Amorphous transformation
Languages : en
Pages : 15
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Zircaloy-4, a zirconium base alloy used extensively as cladding and core structural material in water cooled nuclear reactors, was examined by transmission electron microscopy after neutron irradiation and postirradiation annealing. Phase instabilities found during irradiation include the amorphous transformation and the dissolution of intermetallic precipitate Zr(Fe,Cr)2 in the ?-recrystallized matrix and the dissolution of the metastable precipitate Zr4(Fe,Cr) in the ?-quenched matrix. The alloy is driven toward a single phase solid solution during the irradiation. The presence of fast diffusion iron species in the matrix due to the precipitate dissolution may have caused the irradiation growth breakaway phenomenon. The microstructural evolution during irradiation consists of ̄c dislocation development and grain boundary migration. The presence of ̄c dislocations indicates permanent strain in the matrix. The postirradiation annealing at 833 K does not anneal out the ̄c dislocations. The ̄c dislocation is postulated to have developed due to the intergranular constraints under the continuous growth in the breakaway region.
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Languages : en
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[Sup 40]Ar and [sup 209]Bi ion irradiations of Zr[sub 3]Fe were performed at 35--725 K using 15-1500 keV ions. Results are presented on role of deposited-energy density on nature of the damaged regions in individual cascades produced by ion bombardment of Zr[sub 3]Fe. Comparison is also made between irradiation-induced amorphization of Zr[sub 3]Fe during electron irradiation and under ion bombardments. Dependence of damage production on incident electron energy in Zr[sub 3]Fe was also determined. Preliminary results are also discussed for amorphization of ZrFe[sub 2], Zr(Cr, Fe)[sub 2] and ZrCr[sub 2] by electron irradiation. Results of a recent investigation on amorphization of Zr(Cr, Fe)[sub 2] and Zr[sub 2](Ni, Fe) precipitates in Zircaloy-4 are discussed in context of previous experimental results of neutron and electron irradiations and likely amorphization mechanisms are proposed.
Author: B. A. Cheadle
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Category :
Languages : en
Pages : 0
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Author: Arthur Moses Thompson Motta
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ISBN:
Category :
Languages : en
Pages : 170
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Author: Gerry D. Moan
Publisher: ASTM International
ISBN: 0803128959
Category : Nuclear fuel claddings
Languages : en
Pages : 891
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Annotation The 41 papers of this proceedings volume were first presented at the 13th symposium on Zirconium in the Nuclear Industry held in Annecy, France in June of 2001. Many of the papers are devoted to material related issues, corrosion and hydriding behavior, in-reactor studies, and the behavior and properties of Zr alloys used in storing spent fuel. Some papers report on studies of second phase particles, irradiation creep and growth, and material performance during loss of coolant and reactivity initiated accidents. Annotation copyrighted by Book News, Inc., Portland, OR.
Author: LL. Harris
Publisher:
ISBN:
Category : Amorphous transformation
Languages : en
Pages : 15
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A variety of forms of irradiation have been observed to induce an amorphous phase: heavy ion, proton, and electron. More recently neutron irradiation has been observed to induce an amorphous transformation in Laves precipitates found in Zircaloy and austenitic steel. Up to this point, only conjectures have been made about the irradiation conditions necessary to achieve the amorphous transformation and about the characteristics of a material susceptible to the amorphous transformation. From these conjectures, a theory to explain the amorphous transformation is developed, and its application illustrated by simulation with a computer model. The amorphous transformation of the Zr(Fe, Cr)2 phase in Zircaloy induced by neutron irradiation is used as the example in the model. The theory proposes that during irradiation the free energy of the crystalline state increases beyond that of the amorphous state, and thus in efforts to minimize the free energy of the system the amorphous transformation occurs. The factors that contribute to this increase in free energy include the defect formation energies and the energies of mixing that arise as the lattice is disordered. The later contribution is found to be significant. It is this factor that makes the amorphous transformation possible at defect concentrations lower than required for transformation when defect generation alone is considered.
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Category : Power resources
Languages : en
Pages : 544
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Author: M. Griffiths
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Category :
Languages : en
Pages : 0
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