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Ítem Acceso Abierto Finite element analysis of local overheating within plutonium enriched U02 fuel rods caused by Pu02 islands(North-Holland Publishing Company, 1980) Sánchez Sarmiento, G.Within natural UO2 fuel elements enriched with plutonium, this last material should form Pu02 solid solutions inside the UO2 pellets, in a wide range of concentrations. If the solutions are obtained by mechanical mixing o f the oxides, Pu02 islands are formed in the U02 matrix. These islands may be the source o f several problems in the fuel behavior, the most important being the overheating o f the matrix in the neighbourhood o f the particles. It is caused by the large fission cross section of plutonium compared with that of uranium.Ítem Acceso Abierto Study of intrinsic point defects in Tantalum after plastic deformation at liquid helium temperatures(Elsevier Sequoia S. A., 1980) Peretti Hollemoert, Hernán A.; Mondino, Manuel Ángel; Seeger, AlfredAn apparatus permitting extensive plastic deformation o f wires o f high melting point b.c.c. metals at liquid helium temperatures is described. The recovery o f the electrical resistivity of pure and oxygen-doped tantalum deformed at liquid helium temperatures was measured up to 540 K. In this temperature interval, only one major recovery stage superimposed on a continuous background recovery and located between 240 and 300 K was found. It is controlled by the long-range migration of an intrinsic point defect with a migration enthalpy o f 0.70 ± 0.03 eV. The results are discussed in the context of high temperature and irradiation data, and it is concluded that the defect migrating in this “stage III" is a self-interstitial configuration.Ítem Acceso Abierto Numerical simulation of the transient temperature distribution inside a close-packed array of cylindrical tubes during heating and cooling under high vacuum(North-Holland Publishing Company, 1980) Pissanetzky, SergioThe metallurgical processing of zircaloy for reactor fuel pin cladding requires the annealing of loads, each consisting of an array of tubes in a high-vacuum furnace. A knowledge of the transient temperature distribution in the load during the heating and cooling periods is of interest for the design o f the furnace, the design of each load on account of the final yield of the furnace, and the metallurgical control of the process. A general mathematical model was devised, and is presented here, for the numerical simulation of heat transfer by radiation and conduction.Ítem Acceso Abierto Hacia la producción nacional de Zircaloy 4(Editorial Ciencia Nueva, 1978) Leyt, ArnoldoEn la fabricación de elementos combustibles que se emplean en las centrales nucleares argentinas se utilizan como insumos más importantes: el óxido de uranio y las vainas y componentes estructurales de Zircaloy 4 (una aleación de base circonio Zr). Las partes en Zircaloy constituyen un 25 % del costo de la Central Atucha y un 16 % en el caso de la Central Embalse Río III. De estas partes en Zircaloy, el ítem más importante lo constituyen las vainas, por su relevancia económica. La fabricación de vainas involucra una cadena de procesos metalúrgicos como se aprecia en el siguiente esquema simplificado: mineral, esponja, fusión, forja, extrusión, trex, laminación, terminación, vaina.Ítem Acceso Abierto Theoretical fuel element modelling at CNEA(North-Holland Publishing Company, 1980) Harriague, Santiago; Savino, Eduardo José; Coroli, G.; Basombrío, Fernando Guillermo; Sánchez Sarmiento, G.Computer codes and theoretical developments aiming to model nuclear reactor fuel elements at CNEA are reviewed. The codes PELT, VAINA and BACO for the overall fuel behaviour, as well as the finite clement systems ELASTEF, PLASTEF and CTR are described. The influence on the BACO code predictions of including a fuel cracking model is discussed. Also, some examples of the calculated fuel cladding contact pressure are shown for different situations. Applications of the finite element systems to calculate the stress concentration at the skids of the Central Nuclear Atucha fuel rods and to predict local thermal effects of PuO2 particles in a UO2 fuel are discussed.Ítem Acceso Abierto Plan de investigaciones neutrónicas en combustibles nucleares(Editorial Ciencia Nueva, 1978) Lolich, José V.; Abbate, Máximo JulioEl problema actual más importante de la física de reactores de potencia, es el referente al uso de uranio enriquecido y /o plutonio en sistemas de uranio natural. Esto es debido a que en sistemas físicos enriquecidos de esta forma se presenta una doble heterogeneidad (entre combustible y moderador; y entre combustible de distinta composición), una fuerte absorción de neutrones en el uranio enriquecido y /o plutonio, y una absorción “no 1/v" en el plutonio.Ítem Acceso Abierto Recristallisation secondaire et recristallisation apres ecrouissage critique de l'uranium de haute purete(Elsevier, 1963) Ambrosis De Libanati, Nelly; Calais, Daniel; Lacombe, PaulOn a observé sur de l'uranium de haute pureté (d'origine électrolytique) la croissance de gros grains soit par recristallisation secondaire consécutive à un écrouissage par laminage élevé et recuit prolongé en haut de la phase α, soit par écrouissage critique et recuit appliqué à une texture de recristallisation primaire. Seul l'uranium de haute pureté donne naissance à ces deux types de croissance de gros grains. Ces deux méthodes de croissance fournissent donc un critère qualitatif très sûr de la pureté de l'uranium. La recristallisation secondaire donne naissance à des cristaux de plus petite dimension que la croissance après écrouissage critique, car il subsiste toujours, quelle que soit la durée et la température du recuit, des restes de la texture à grains fins de recristallisation primaire. Par écrouissage critique au contraire, il est possible d'obtenir de très gros grains très parfaits (de 1 à 3 cm2 de surface) avec disparition complète de la texture de recristallisation primaire. Les orientations cristallines d'un très grand nombre de grains formés par les deux méthodes de croissance ont été déterminées par diagramme de Laue en retour. Les cristaux de recristallisation secondaire possèdent une texture beaucoup plus prononcée que celle développée par la croissance de cristaux par écrouissage critique. Cependant dans les deux cas, il est remarquable que l'axe de tous les cristaux semble jouer un rôle essentiel dans la croissance puisqu'il est toujours sensiblement orienté parallèlement à la direction de laminage. C'est seulement dans le cas où l'écrouissage appliqué à la texture de recristallisation primaire dépasse nettement le taux d'écrouissage critique que l'on observe la croissance par recuit ultérieur de cristaux ayant des orientations très diverses. On a tenté d'expliquer ces deux modes de croissance par recristallisation secondaire ou par écrouissage critique en reliant les textures de déformation obtenues par écrouissage élevé par laminage aux textures soit de recristallisation secondaire, soit de recristallisation après écrouissage critique.Ítem Acceso Abierto Sous-structures de solidification de l´aluminium 99,99 %: leur étude par les couches épitaxíques d'oxyde et par les figures de corrosion(1959) Biloni, Heraldo; de Destaillats, L. H.Aprés la solidification d’un métal on peut observer divers aspects de sa structure, liés á la ségrégation des impuretés. On a pu identifier deux sortes de sous-structures de ségrégation: la sous-structure de Smialowski ou sous-structure striée et la sous-structure dendritique. La premiére a été mise en évidence par Smialowski au cours de ses travaux sur le Zn, le Cu et le Pb. Déjá dans ces travaux l’auteur indique que l´apparition de la sous-structure est due á la ségrégation d´impuretés.Ítem Acceso Abierto Perméation électrochimique d’hydrogène dans un acier ferritique Influence des oxydes superficiels(1986) Collet Lacoste, Juan RamónEn este trabajo hemos tratado de demostrar que este aumento del flujo es consecuencia de los cambios producidos en la superficie y que, en este caso concreto, se debe a la formación y posterior eliminación de óxidos.Ítem Acceso Abierto Metallurgy at the Argentine Atomic Energy Commission(1963) Sabato, Jorge AlbertoArgentina is a country full of paradoxes. In saying that it is not suggested that Argentina is richer in paradoxes than other countries, but merely that it has its full quota! Relatively speaking, the country is practically empty, the population being 21,500,000 in an area of more than 4,000,000 square kilometres. In spite of this, land is more expensive in Buenos Aires than in London. The national economy is in very bad shape; unemployment is rising, the foreign debt is of the order of 3,000 million U.S. dollars, and civil servants have not received their salaries for the last two months.Ítem Acceso Abierto Ordering in ternary Beta phase Cu Zn alloys(Pergamon Press Inc., 1977) Rapacioli, Ricardo; Ahlers, ManfredA large number of Beta phase noble metal alloys show long range order below a critical ordering temperature. The contribution of order to the stability of the phases has been analyzed by the Bragg – Williams - Gorski (BWG) model. In this model it is assumed that the internal energy can be described in terms of chemical interchange energies.Ítem Acceso Abierto Homogenization of primary microsegregation(ASM Publications, 1971) Fainstein, Daniel; Biloni, Heraldo; Bolling, G. F.The homogenization kinetics of a segregated binary alloy have been studied using electron probe microanalysis after annealing for various times at several temperatures. The concentration and number of microsegregation nodes are quantitatively examined in detail and compared with the evolution of the whole solidification substructure revealed by X-ray images and metallography. The comparison leads to the conclusion that nodes are representative of all solidification substructure and can be taken as a characteristic. The combined study also shows that nodes dissolve in two stages, starting preferentially along cell walls and continuing later in a more uniform fashion. However, a single activation energy near that for bulk diffusion is obtained for the whole process, showing that the homogenization is a collective process and volume diffusion limited.Ítem Acceso Abierto Estructura de laminación en caliente de aluminio y cobre(1986) Pochettino, Alberto; Cuyás, J. C.; Gónzalez, A. C.Las propiedades de los materiales deformados en caliente cambian por efecto de procesos que se desarrollan durante o inmediatamente después de la deformación. La velocidad de formación de las dislocaciones depende en mayor medida de la velocidad de deformación y de la tensión efectiva que del grado de deformación. Mediante laminación fueron deformadas muestras de aluminio comercialmente puro y cobre "tough pitch" a distintas velocidades de deformación y temperaturas. Las muestras fueron templadas inmediatamente a la salida de los cilindros laminadores y las estructuras obtenidas fueron estudiadas mediante el empleo de la microscopía óptica y electrónica de transmisión. El aluminio en ningún caso presentó evidencias de recristalización, pero sí recuperación dinámica y/o estática y coalescencia de subgranos en las muestras laminadas a 450° C y velocidad de deformación de 13 s-1 y 26 s-1. En cambio el cobre a 725° C y velocidad de deformación de 13 s-1 sufriría un proceso de recristalizadón dinámica.Ítem Acceso Abierto On vacancy condensation and the origin of dislocations in growth from the melt(Taylor and Francies, 1972) Fainstein, Daniel; Bolling, G. F.The formation of dislocations from condensed vacancies has boon re-examined. Conditions for transformation of vacancy clusters into dislocation loops are analysed, taking into account an entropy contribution of atoms in the dislocation coro. New evidence in the literature for a vacancy concentration beyond that of equilibrium at the advancing solid-liquid interface is used to calculate an excess vacancy concentration trapped in the solid as a function of freezing velocity. This excess leads to an estimation of the nuoleation frequency of loops and supports the condensation mechanism as the source for dislocations. The critical stage for dislocation formation in growing crystals is also shown to depend upon the temperatura distribution in the solid. .Results of this analysis are applied to the formation of dislocations in a general f.c.c. metal, and specifically in lead, aluminium and copper, for which experim ental inform ation is available. Striation formation is discussed for these metals; it is concluded that the original mechanism proposed b y Teghtsoonian and Chalmers (1951) and extended by Frank (1956) cannot be discarded.Ítem Acceso Abierto Evaluación de diagramas de fase de sistemas binarios: su utilización tecnológica. El caso particular del sistema circonio-niobio(1986) Bolcich, Juan Carlos; Abriata, José PabloSe discuten las condiciones requeridas para la determinación de diagramas de fase confiables de sistemas binarios, así como la posibilidad de programas de velocidades de enfriamiento y tratamientos termomecánicos, para las fases metaestables, que pueden dar lugar a múltiples microestructuras con propiedades asociadas muy variadas. Como un ejemplo de materiales de interés tecnológico se discute el sistema circonio – niobio.Ítem Acceso Abierto Mechanism of intergranular corrosion of Al-Cu alloys(Pergamon Press, 1970) Galvele, José Rodolfo; de De Micheli, S. M.The anodic behaviour of pure Al and some specially prepared Al-Cu alloys has beenstudied to check the mechanism of intergranular corrosion of aged Al-4%Cu. A clear relationship between pitting and intergranular corrosion has been found. Intergranular corrosion only occurs in the presence of certain anions, and over a narrow range of potentials. Difference in pitting potentials, rather than difference in electrode potentials, is the main factor in producing intergranular corrosion of Al-4%Cu. The conditions of heat treatment, solution composition, and potential, at which intergranular corrosion appears, have been established.Ítem Acceso Abierto El empleo actual de los materiales radiactivos(Contribuciones de Cultura S.A., 1970) Papadópulos, Celso C.Para entrar en materia soslayaremos la mayor parte de las definiciones que pueden encontrarse en los textos de Física, y nos limitaremos a recordar que los materiales radiactivos, que en estado elemental se llaman radioisótopos, se caracterizan porque los núcleos de sus átomos inestables buscan estabilidad desintegrándose, y al hacerlo emiten partículas (electrones, positrones, o partículas alfa) u ondas electromagnéticas (rayos equis, rayos gamma), que constituyen las radiaciones que nos ocupan.Ítem Acceso Abierto The temperature dependence of work-hardening in Cu3Au and Ni3Fe(Pergamon Press, 1971) Shoeck, G.; Perez, E.There is still some discussion about the nature of work hardening in super lattices. Among the mechanisms which have been proposed (1) the most widely accepted ones in alloys of the LI2 structure are the cross-slip of superdislocations (2) and the production of antiphase boundary tubes (APB tubes).Ítem Acceso Abierto Kinetics of growth of spherical GP zones: experimental verification of the vacancy pump model(Pergamon Press, 1970) Ipohorsky, Miguel; Bonfiglioli, Alberto F.The experimental verification of the “vacancy pump model” by X-ray small angle scattering is attempted on the Al-10% Zn and Al-10% Zn-0.1% Mg alloys. For the binary alloy the calculation of diffusion coefficients for the vacancy-zinc complexes and their initial number per unit volume gives values that cannot be explained by the existent data of activation energies. Without discussing the mechanism of the cyclic pump, a revision of the hypothesis that leads to the quantitative formulation of the model is suggested. For the ternary alloy, the possibility of a diffusion mechanism similar to that proposed for the binary alloy is admitted.Ítem Acceso Abierto On the reversion of G P zones in AI-10% Zn and AI-10% Zn-0.1% Mg alloys(Chapman and Hall, 1969) Ipohorsky, Miguel; Acuña, R.; Bonfiglioli, AlbertoMost of the previous studies on spherical G P zones, which characterise the pre-precipitation process in the Al-Zn alloys, were related to their formation and growth [1 5]. However, very few of them have been concerned with reversion, i.e. dissolution of the G P zones that results when the solid solution containing them is heated above a given temperature. This tem perature is determined, for a given composition of the alloy considered, by the metastable miscibility gap which seems to control the formation of such zones.