Results 1 - 10 of 7806
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[en] Ellipsometric measurements on the wavelength and temperature dependence of the complex refractive index, n-ik, of Zircaloy 2 and 4; the refractive index n and the extinction coefficient k are reported. These were found to range from 1.135 to i1.523 at 0.3131 μm wavelength to 4.846 to i7.345 at 3.39 μm. These values are close to those reported in the literature for zirconium. The similarity in values is not unexpected because Zircaloy is approximately 98% zirconium. In the same wavelength range the complex refractive index of Zircaloy oxide was also determined. n varies from 2.3 at 0.3131 μm to about 2.0 at 3.39 μm. These results are also similar to literature values for zirconium oxide. Unlike zirconium oxide the extinction coefficient of Zircaloy oxide was found to be between 0.1 and 0.3, dependent on both temperature and thickness in addition to exhibiting wavelength dispersion. This behavior of the extinction coefficient is undoubtedly related to the structure of the oxide as influenced by temperature and oxide thickness. This and other aspects of oxide formation and behavior can be examined in situ by ellipsometry, which is one of the unique features of the technique. Oxide kinetics could be monitored in real time in a variety of vapor or liquid ambients, as long as the ambient medium allows penetration of the measuring light beam to the surface under study. It should be possible to measure thicker films if the measuring wavelength is increased. However, the greatest benefits will probably be derived from in situ studies in real time. Such measurements should reveal useful information on the time-temperature dependence of oxide growth from initial onset of oxidation
[en] The influence of tensile specimen geometry on the deformation behavior of flat Zircaloy-4 tensile specimens has been examined for gauge length-to-width ratios that range from 1:1 to 4:1. Specimen geometry has only minor effect on the values of the yield stress, tensile strength, apparent uniform strain at maximum load, and strain-hardening exponent. However, in all geometries but the 4:1 configuration, diffuse necking occurs before maximum load. As result, strain distributions at maximum load are uniform only in the 4:1 geometry. The elongation to failure is also affected by specimen geometry with the shorter gauge sections exhibiting much higher total elongation values, due in large part to the concomitant specimen necking behavior
[en] Oxide nodules form on Zircaloy nuclear components under irradiation. Similar nodules were observed on Zircaloy coupons in cold rolled or extended conditions after autoclave treatments at 475 and 5000C in steam at 1500 to 1700 psi. Stages of nodular corrosion in the autoclave were nodule nucleation, growth, coalescence, propagation to accelerated uniform corrosion, and complete specimen oxidation. Observations on BWR fuel rods suggest that a similar progressive attack has occurred; however, in no case has the in-reactor attack progressed to the stage of complete fuel rod failure. Recent autoclave tests confirmed the nodular character of the attack on cold-worked materials. Alpha anneals (up to 7900C) did not consistently suppress the nodular attack. However, alpha + beta (8400C) and beta (1010 and 10400C) anneals did suppress the attack if followed by a fast cool. The efficacy of the anneals applied similarly to Zircaloy-2 and Zircaloy-4. Stresses associated with U-bend specimens and heavy (86 percent) cold work did not enhance the nodular attack before stress relief occurred. The nodular attack on reactor components appears to depend on nuclear flux, and develops in oxygenated reactor coolants, principally in the vicinity of fuel rod spacers. Experience with irradiated specimens in reactor loops suggests that uniform concentrations of dissolved oxygen alone do not initiate nodular attack. Localized water chemistry associated with flow disturbances or, in some cases, dissimilar metals in fuel spacers, may be factors in the nodular attack in-reactor
[en] A summary is presented about the theoretical and experimental results obtained at present in thermofluency under radiation in zirconium alloys. The phenomenon of thermofluency is presented in a general form, underlining the thermofluency at high temperature because this phenomenon is similar to the thermofluency under radiation, which ocurrs in zirconium alloys into the operating reactor. (author)
[en] A procedure for producing a uniformly thick continuous oxide layer on the surface of Zircaloy-2 and Zircaloy-4 has been developed. This coating is hard and wear resistant; it has good electrical and thermal insulating properties, and good corrosion resistance in water. Methods of calculating the oxide thickness and the dimensional changes due to oxidation are also provided. (author)
[en] In an effort to understand observed differences in high temperature steam corrosion resistance, high frequency (> 500 Hz) a-c impedance measurements have been used to monitor the permeability of oxidation films formed on Zircaloy-2 and Zircaloy-4 samples exposed to high temperature steam. Differences in oxidation resistance are related to differences in oxidation film permeability and ultimately to film characteristics. When these results are added to the existing data base established for zirconium alloy oxidation films using the high frequency impedance technique, improved understanding of the role of bulk corrodent access to the metal-oxide interface during oxidation becomes possible. In addition, differences in film character resulting from differences in oxidation environment become apparent upon review of the existing data base. Such differences may have practical application in selecting material preconditioning procedures and suggest explanations for some oxide film memory effects reported in the literature
[en] The fuel element with circular cross-section for BWR and PWR consists of a core surrounded by a compound jacket container where there is a gap between the core and jacket during operation in the reactor. The core consists of U, Pu, Th compounds and mixtures of these. The compound jacket consists of zircaloy 2 or 4. In order to for example prevent the corrosion of the compound jacket, its inner surface has a metal barrier with smaller neutron absorbers than the jacket material in the form of a zirconium sponge. The zirconium of this metal barrier has impurities of various elements in the order of magnitude of 1000 to 5000 ppm. The oxygen content is in the range of 200 to 1200 ppm and the thickness of the metal barrier is 1-30% of the thickness of the jacket. (DG)
[de]Das BE mit kreisfoermigem Querschnitt fuer SWR oder DWR besteht aus einem Kern, den ein Verbundmantelbehaelter umgibt, wobei ein Spalt zwischen Kern und Mantel waehrend des Einsatzes im Reaktor vorhanden ist. Der Kern besteht aus Verbindungen des U, Pu, Th und Mischungen davon. Der Verbundmantel besteht aus Zirkaloy-2 oder - 4. Um z.B. ein Korrodieren des Verbundmantels zu verhindern, ist dessen Innenflaeche mit einer Metallsperre mit geringerer Neutronenabsorption als das Mantelmaterial in Form eines Zirkoniumschwammes versehen. Das Zirkonium dieser Metallsperre enthaelt Verunreinigungen von verschiedenen Elementen in der Groessenordnung von 1000 bis 5000 ppm. Der Sauerstoffgehalt liegt im Bereich von 200 bis 1200 ppm und die Dicke der Metallsperre betraegt 1-30% der Dicke des Mantels. (DG).
[en] A body composed of a zirconium alloy is afforded enhanced corrosion resistance to a high pressure and high temperature steam environment by an integral surface region of β-quenched zirconium formed in situ by laser beam scanning and afforded good mechanical and structural properties by a bulk region whose metallurgical structure is selected to optimize these mechanical properties. (author)
[en] A new approach based on a stability analysis of a uniformly growing oxide film was applied to estimate the effect of alloying additives on the susceptibility of zirconium alloys to nodular corrosion. The analytical results agree with available experimental data on effect of Fe and Ni on resistance of Zircaloy-2 and Zircaloy-4 to the growth of nodular oxide.
[en] Channel-control-blade interference has been a challenging issue over the past eight years for operating boiling water reactors plants where ∼2-year cycles are normal and Zircaloy-2 is the standard channel material. The primary reason for this was the unaccounted channel distortion caused by differential hydrogen across the channel that resulted from shadow corrosion on the blade side (known as shadow corrosion-induced bow). Zircaloy-2 is particularly susceptible to this distortion mechanism because it has a high hydrogen pickup fraction that increases with exposure. GNF developed a two-stage strategy to mitigate channel distortion. The first was to optimize the performance of Zircaloy-2 by developing a cell friction methodology that accounted for all known distortion mechanisms: the fluence-gradient bow, the elastic and creep bulge, and now the shadow corrosion-induced bow. This has allowed GNF to better manage the use of Zircaloy-2, which in some cases has required rechanneling during refueling outages. The second stage is to implement alternative channel materials that are inherently more resistant to channel distortion. The first part of this second stage is the reintroduction of Zircaloy-4, which is effectively resistant to shadow corrosion-induced bow and has similar irradiation growth and creep performance to Zircaloy-2. The one disadvantage of Zircaloy-4 is that it has less corrosion resistance than Zircaloy-2. However, based on the extensive experience with Zircaloy-4 channels both in the U.S. and Japan (and the processing improvements made to specifically enhance corrosion resistance), the corrosion performance of Zircaloy-4 is shown to be adequate for channel applications