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Ítem Acceso Abierto Phase Transformations in Ag48Zn5oAu2 and Ag48Zn5oCu2 Alloys(North Holland Publishing Company, 1982) Granovsky, Marta Susana; Resta Levi, Max; Arias, DeliaThe order-disorder phase transformation temperatures for Ag48Zn50Au2 and Ag48Zn50Cu2 alloys have been determined using resistivity techniques and the ordering energies of the closest neighbors of the AuZn and AgCu pairs calculated. Investigation of the kinetics of the β′ → ζ0 phase transformation using resistivity, metallographic, microanalytical, and x-ray techniques showed a two-phase field in both alloys, corresponding to the β + ζ0 phases.Ítem Acceso Abierto Simulation of the thermomechanical effects originated on a fuel pin with a creacked pellet by different power ramp velocities, using a two dimensional finite element model(North Holland Publishing Company, 1982) Basombrío, Fernando G.Thermomechanical effects originated on a fuel pin with a cracked pellet by different power ramp velocities has been studied. To such purpose, the response of a simplified two dimensional finite element model including viscoelastic properties on the pellet and elastoplastic properties on the clad was investigated, under the influence of various ramps with durations ranging from 0 s (instantaneous ramp) to 200 s (slow ramp).The importance of both, the viscoelastic relaxation effects and their interaction with the plastic behaviour of the clad was put in evidence. It has been observed, that the mechanical response of this fuel pin model strongly depends on the ramp's duration.Ítem Acceso Abierto Welding Structures in Gas Tungsten Arc-Welded Zircaloy-4(North Holland Publishing Company, 1982) Perez, Teresa Estela; Saggese, María EugeniaMicrostructures were obtained by the gas tungsten arc welding of tubes to end caps in Zircaloy-4 fuel elements and analyzed metallographically. This article characterizes the structures and the relationships between the operative variables and structural elements and properties. The final joint properties are shown to be greatly influenced by the different structural elements, including microstructure, porosity, and inclusions. The secondary structure found after welding is Widmanstätten, varying from a parallel-plate to a basketweave pattern. Welding thermal cycles are inherently inhomogeneous, affecting both plate width and β primary grain.Ítem Acceso Abierto Point-defect diffusion in a strained crystal(American Physical Society, 1982) Tomé, Carlos N.; Ceccatto, Hermenegildo Alejandro; Savino, Eduardo JoséThe diffusion equations for interstitials and vacancies in the field of an edge dislocation are numerically solved within a theoretical model that takes into account the full lattice and defect symmetry in the migration jump. The defect concentration is calculated within two different approximations: In one, only the defect drift contribution to the diffusion is considered, while in the other, the drift and gradient terms are included as well as a constant defect generation rate. In this second approximation the steady-state concentration is calculated. The influence on the solutions of an external uniaxial stress with different orientations with respect to the dislocation is studied. Numerical results for the dislocation sink strength are obtained for vacancies and interstitials in Cu. These are compared with previous approximations in the literature. The relevance of the results to the establishing of a radiation creep mechanism is discussed.Ítem Acceso Abierto Influence of a CuS04 treatment on atmospheric steel rust formation. A Mössbauer spectroscopy study(National Association of Corrosion Engineers, 1982) Saragovi de badler, Celia; Maier, Irene Ana; Labenski de Kanter, FelisaMössbauer spectroscopy has been used to analyze the rust layers formed on a weathering steel and a 1010 steel exposed for 10-1/2 months to an urban-industrial atmosphere. No significant difference was found comparing the rusts of both steels: they were composed by γ-FeOOH, superparamagnetic α-FeOOH, and an amorphous or gel-like compound. γ-FeOOH is more abundant in the internal rust layers, whereas the amount of α-FeOOH and the amorphous compound Increase in the external rusts. Part of the samples received an Initial copper deposit by immersion of the steel plates in a CuS04 bath. Mössbauer spectroscopy analysis showed that the amorphous substance was no longer present In the rusts of those specimens; that is, the rusts of both steels were formed only by γ-FeOOH and α -FeOOH.Ítem Acceso Abierto Ciclo de combustible nuclear. Participación industrial(1982) Aráoz, CarlosEl tema combustible fue el factor determinante en la elección del tipo de reactores para el plan núcleo eléctrico argentino, ha estado y está muy ligado con la situación del mercado internacional y con aspectos de política energética. Las decisiones tomadas hace ya más de una década para asegurar una generación de energía nuclear sobre bases indenpendientes, se llevan a cabo: En sus aspectos tecnológicos, teniendo en cuenta la capacidad local y las inversiones que realiza CNEA en este campo. En sus aspectos industriales y comerciales, con el aporte de la industria nacional a fin de que dichas decisiones sean también económicamente convenientes.Ítem Acceso Abierto Suministro nacional de combustibles nucleares. Posibilidad de una tecnología independiente(1982) Cirimello, Roberto OmarHoy nadie duda de la necesidad de fuentes alternativas de energía primaria, si se mantiene la tendencia de la sociedad moderna hacia una sociedad industrial avanzada. El consumo creciente de energía, en sus diversas formar y usos, agotará rápidamente los recursos de combustibles fósiles los cuales, prácticamente, desaparecerán a mediados del próximo siglo. La energía solar y la fusión, actualmente en etapas preliminares de desarrollo, no estarán disponibles para comenzar a ser usadas en forma masiva y económica hasta la misma época.Ítem Acceso Abierto On the measurement of Young's modulus of tubes by propagation of longitudinal waves(North Holland Publishing Company, 1983) Povolo, Francisco; Bolmaro, R. E.The equation that describes the propagation of elastic waves has been solved numerically for longitudinal vibrations of tubes and the results are used to calculate Young's modulus for Zircaloy-4 fuel sheathings. The values are compared with the results obtained by using the approximate equations proposed in the literature. The differences observed are less than 0.5% for the fundamental frequency. For the harmonics, however, the numerical solution leads to resonant frequencies that are within 1% of the experimental values and the approximate equations give errors higher than 10%.Ítem Acceso Abierto Some aspects of thermal fatigue in stainless steel(Elsevier, 1986) Iorio, Antonio Francisco; Crespi, Juan CarlosThis paper is concerned with the analysis of failures in the moderator circuit branch piping of the ATUCHA-1 pressurized heavy water reactor (PHWR), which is made of austenitic steel to DIN 1·4550 specification (similar to AISI 347). These failures are considered to result from thermal fatigue processes induced by fluctuations in a zone where stratified temperature layers occurred, the fluctuations being associated with variations in moderator flow.The first section evaluates the possibility of cracking due to thermal fatigue phenomena and concludes that under service conditions a crack may initiate and grow through 7 mm thickness of the branch pipe. In laboratory thermal fatigue tests that simulated the thermomechanical conditions for such a component, the number of cycles required to initiate a thermal fatigue crack in a notched modified standard fatigue specimen was about 103. This value may be used to give a conservative prediction of the number of thermal cycles for crack initiation in actual branch pipes, including those subject to the cold plug condition which is produced in some emergency shut-down and valve testing situations.It was also demonstrated that beyond a crack depth of 7 mm stress corrosion cracking is the main process in further crack propagation. The relevance of this prediction is confirmed by microfractographic observations, since the brittle nature of the fracture surfaces under service conditions appears very different from the transgranular ductile striations found in both thermal and mechanical fatigue test specimens as a result of interacting environmental effects.Ítem Acceso Abierto Transferencia de tecnología y fabricación en la Argentina de elementos combustibles nucleares para la Central Nuclear Atucha. Experiencia desde planta piloto a fábrica industrial(1983) Erramuspe, Hugo Juan; Sametband, Moisés José; Bisogni, Edgardo Ángel; Biondo, Carlos Domingo; Koll, José HelmutDada la importancia que la energía tiene en el desarrollo industrial y económico, la implementación de una política apropiada, realista y coherente, implica el logro del mayor grado de autonomía posible en tal vital sector. Este ha sido uno de los motivos fundamentales de la decisión argentina de adoptar la línea de uranio natural y agua pesada para la generación de energía nucleoeléctrica, pues ello asegura la posibilidad del dominio del ciclo de combustible, entendido como el conjunto de operaciones industriales sucesivas, a las que se someten los materiales fisionables para su aprovechamiento en un reactor nuclear.Ítem Acceso Abierto Complejo Fabril Córdoba(1983) Comisión Nacional de Energía Atómica. Dirección de Suministros NuclearesEl Complejo Fabril Córdoba (CFC ) se ubica en Alta Córdoba, en la ciudad homónima ( calle Rodríguez Peña N9 3200), en un predio de 65.000 metros cuadrados, el que cuenta con diversas instalaciones, que cubren unos 10.000 metros cuadrados. El Complejo dispone de dos líneas de obtención de dióxido de uranio (U02):1. La Planta de Producción de U02, totalmente integrada, con un sector de purificación nuclear por TBP (tributil fosfato), desarrollado y construido por la CNEA y un horno de reducción a U02 e instalaciones vinculadas, provistas por REAKTOR BRENNELE MENT UNION GmbH de Alemania. 2. La Línea Nacional AUTC UO2 , con un sector de purificación nuclear, el que utiliza solventes aminados, proceso patentado por CNEA, y hornos de reducción, de fabricación nacional, los que se encuentran en etapa de optimización.Ítem Acceso Abierto Creep of stress-relieved Zry-4 at 673 K(North Holland Publishing Company, 1983) Povolo, FranciscoCreep data, at 673 K, up to times of about 400 h and stresses between 120 and 242 MPa, in flat specimens of Zry-4 stress-relieved for 1 h at 813 K, are presented. The creep curves, when viewed in a log σ−log ge diagram, show a scaling behaviour leading to a master curve similar to the one obtained in 64% cold-worked material. The data are interpreted in terms of a constitutive equation based on a creep model involving jog-drag and cell-formation, and the apparent activation energy was found to be independent of stress with a value close to the one found in the cold-worked material.Ítem Acceso Abierto Apparent activation energy for creep controlled by jog-drag and cell-formation(North Holland Publishing Company, 1983) Povolo, Francisco; Marzocca, A. J.The expression for the apparent activation energy for creep controlled by jog-drag and cell-formation is given in terms of the parameters of the physical model. It is shown that, in general, this energy does not coincide with that for self-diffusion. The results are applied to actual experimental data obtained in stress-relieved Zircaloy-4 at 673 K.Ítem Acceso Abierto Fabricación a nivel industrial de pastillas de UO2 para los elementos combustibles de la Central Nuclear Atucha I(1982) Dyment, Isaac G.; Noguera Rojas, FranciscoCon la construcción de la primera Central Nuclear argentina, ATUCHA I (CNA), surge la inquietud de fabricar, en el país los elementos combustibles nucleares para abastecerla en el futuro y en el marco de una política de autoabastecimiento en el suministro de los mismos. Los primeros pasos hacia esa meta, se realizaron en el procesamiento del óxido de uranio para transformarlo en pastillas o núcleos combustibles de alta densidad.Ítem Acceso Abierto High-temperature internal friction in polycrystalline Zirconium and Zircaloy-4(North Holland Publishing Company, 1983) Povolo, Francisco; Molinas, B. J.The data on the high-temperature internal friction of zirconium and zirconium alloys are reviewed and new results on zirconium and Zircaloy-4, measured at low and at intermediate frequencies, are presented. It is shown that the damping spectrum of pure zirconium, for annealed polycrystals, shows a peak probably related to relaxation of grain or subgrain boundaries. The data on Zircaloy-4 show two peaks: one near the grain-boundary peak in the pure metal and another one at a higher temperature. Possible mechanisms for these peaks are discussed. Finally, the high-temperature internal friction background of zirconium and zirconium alloys is analyzed and, for Zircaloy-4, the apparent activation enthalpy is found to be related to the grain size.Ítem Acceso Abierto 51Cr diffusion in α-Zr single crystals(North Holland Publishing Company, 1983) Balart, Silvia Noemí; Varela, N.; Hojvat de Tendler, RuthThe volume diffusion coefficients of the fast-diffusing solute 51Cr have been obtained in oriented α-Zr single crystals, in the directions parallel and perpendicular to the c axis. The dependence of these diffusion coefficients on temperature was also measured between 750°C and 848°C.Single crystals were grown by thermal cycling through the α α β transformation temperature (862°C). Diffusion coefficients were measured using the “ thin film” method. In some experiments non-Gaussian penetration profiles were obtained and this behaviour is also analyzed.The diffusion of 51Cr is faster in the c axis direction, with Q∥(153 kj/mol) < Q⊥ (163 kj/mol). The anisotropy factor . This factor, the activation energies and frequency factors are discussed in comparison with those of other solutes.Ítem Acceso Abierto Diffusion of Nb in Fe and Fe alloys(The Metals Society, 1983) Kurokawa, Susana; Ruzzante, José Evaristo; Hey, Alfredo Martín; Dyment, FannyThe diffusion coefficients of Nb have been studied in unalloyed γ Fe over the temperature range 948–1201°C and in Fe–1·5Mn, Fe–0·6Si, and Fe–1·5Mn–0·6Si alloys over the range 1081–1201°C by the direct sectioning method using the isotopes 94Nb and 95Nb. The Arrhenius curves for diffusion into pure γ Fe and γ Fe alloyed with Mn and/or Si are linear in the temperature range 1081–1201°C, and give approximately the same activation energy Q = 267·4 kJ mol−1. Below these temperatures lnD v. 1/T, where D is the volume diffusion coefficient and T the temperature, is non-linear for diffusion into γ Fe. The values of Q and D 0 (the frequency factor) obtained in pure γ Fe are more representative than the values Q = 344·5 kJ mol−1 and D 0 = 5·30 × 10−2 m2 s−1 found in the literature. It was possible to examine the influence of the substitutional alloying elements Mn and Si on the behaviour of Nb diffusion in γ Fe and the following effects were observed: the diffusivity of Nb decreases with Mn content but increases with Si content and when both Mn and Si are added the two effects appear to compensate each other.Ítem Acceso Abierto El mercado mundial de elementos combustibles nucleares y la inserción de la Argentina en el mismo(1983) Biondo, Carlos DomingoEl presente trabajo pretende mostrar el desarrollo de la industria de los elementos combustibles nucleares dentro del correspondiente mercado actual y proyectado a nivel mundial, el cual se encuentra condicionado por la situación que atraviesa el parque nucleoeléctrico correspondiente, cuya evolución sumariamente también se señala bajo el punto de vista del mercado considerado. Por medio de la función oferta/demanda del mercado de elementos combustibles, se analiza el comportamiento del mismo a través de la estructura del “Ciclo de Combustible”, que relaciona las etapas industriales correspondientes, mostrando los desbalances regionales en los recursos uraníferos existentes en el mundo, como así también aquellos factores que inciden en forma desfavorable en la ecuación económica del mencionado ciclo.Ítem Acceso Abierto Control de calidad en paredes de hormigón de gran epesor destinadas a blindaje(1983) Arcama, Julio A.; Cannistracci, Carlos A.; San Pedro, MarceloEl presente trabajo fue desarrollado, ante la necesidad de verificar el grado de homogeneidad que presentan las paredes de hormigón de gran espesor, que conforman las denominadas celdas de proceso para uso Radioquímico, actualmente en construcción en el Centro Atómico Ezeiza. Dichas paredes, además de su función estructural, fueron proyectadas para actuar como blindaje biológico, dado que estarán destinadas a confinar materiales nucleares irradiados.Ítem Acceso Abierto Desarrollo y puesta a punto, a nivel de producción industrial de las demás técnicas de fabricación y control del elemento combustible para la Central Nuclear Atucha l(1982) Biondo, Carlos DomingoCon la decisión tomada en 1968 por la República Argentina en relación a la instalación de su primera Central Nuclear (C.N.A), se planificaron programas de realizaciones correspondientes al “Ciclo de Combustible” y tendientes a posibilitar la producción nacional de elementos combustibles de potencia, basándose en una política de autoabastecimiento en dicho ciclo. Dentro de los programas planificados se encontraba el correspondiente a la fabricación y puesta en marcha, en 1976, de un Proyecto cuyo objetivo fue el desarrollo y puesta a punto de las técnicas de fabricación y control de los mismos y a un nivel de producción industrial. La implementación llevada a cabo fue realizada con miras al establecimiento de una industria eficiente y moderna, dotada de una tecnología de avanzada y compatible con la correspondiente infraestructura disponible en el país.