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José de San Martín, Argentina

Sileo N.R.,U. A. Materiales GIDAT | Fuentes N.O.,Programa Nacional de Gestion de Residuos Radiactivos | Fuentes N.O.,Instituto Sabato UNSAM CNEA
Materials Research Society Symposium Proceedings | Year: 2012

Development of numerical tools for performance assessment studies of radioactive waste disposal facilities, must address the management of the wide-ranging uncertainties associated with the long-term behaviour of these complex systems. Different approaches and assumptions are made in order to identify and describe relationships between the disposal system and its environment. They take into account, among other factors, the uncertainties associated with temporal evolution of the system within a proposed scenario; the landscape changes arising from future human actions, climate and geological events and processes; the relationships between components of the disposal system and its immediate environment; the behaviour and characteristics of radionuclides within the system and their role in contributing to radiation exposure. In all cases, the different scenario-based models are typically used to determine the radiological significance of potential future discharges from waste disposal facilities. However, it is important to keep always in mind that in any specific case, the purpose of developing and/or applying a model may vary from a simple calculation (e.g. to support concept development) to detailed site-specific performance assessment in support of a disposal license application. The assumptions and modelling simplifications that are appropriate to one type of calculation may not be so easily justified in different circumstances. In order to develop the capability of modelling different long-term scenarios for a generic disposal site for low and intermediate level radioactive wastes, implementation of models of both the near-field/geosphere and biosphere were performed using general approaches for geosphere-biosphere interface, with sub-models for the whole system. © 2012 Materials Research Society. Source

Ramos P.B.,U. A. Materiales GIDAT GAEN CNEA | Fuentes N.O.,Programa Nacional de Gestion de Residuos Radiactivos | Fuentes N.O.,Instituto Sabato UNSAM CNEA | Luca V.,Programa Nacional de Gestion de Residuos Radiactivos
Materials Research Society Symposium Proceedings | Year: 2012

The pyrolysis of ion exchange resin beads that are used for the purification of water in reactor primary- and secondary-cooling circuits can result in stable and leach resistant carbonaceous products. However, free flowing beads are less desirable waste forms for disposal in sub-surface or surface repositories than monolithic masses of low porosity. We have investigated the pyrolysis of polymeric resin - cation exchange resin composites to give mechanically robust and chemically durable monolithic carbonaceous waste forms that are suitable for repository disposition. Also investigated was the dependence of product properties on various processing parameters (temperature ramp and final temperature). As a first approach, epoxy resins were used for the preparation of monoliths since such resins cure at room temperature and result in a relatively high carbon yield. Carbonaceous monolithic products were prepared at 400, 500, 600, 700 and 800°C using a temperature ramp of 2°C/min. The products were maintained at the chosen temperatures for a period of one hour. Mass losses, volume reduction, hardness and compressive strength were measured and mathematical functions are proposed to describe the measured values of these properties. The carbon monoliths were observed to be mechanically robust. © 2012 Materials Research Society. Source

Raviola L.A.,Instituto Sabato UNSAM CNEA | Rivas A.M.F.,CNEA | Carlo G.G.,CNEA
Physica D: Nonlinear Phenomena | Year: 2011

We have studied two complementary decoherence measures, purity and fidelity, for a generic diffusive noise in two different chaotic systems (the baker map and the cat map). For both quantities, we have found classical structures in quantum mechanicsthe scar functionsthat are specially stable when subjected to environmental perturbations. We show that these quantum states constructed on classical invariants are the most robust significant quantum distributions in generic dissipative maps. © 2011 Elsevier Ltd. All rights reserved. Source

Perez R.A.,Comision Nacional de la Energia Atomica | Perez R.A.,CONICET | Perez R.A.,Instituto Sabato UNSAM CNEA | Gordillo J.A.,Comision Nacional de la Energia Atomica | Lalla N.D.,CONICET
Philosophical Magazine | Year: 2013

α-spectrometry was used in order to measure the diffusion of U in bulk α-Ti in the temperature range 863-1123 K (540-850 °C). A straight Arrhenius plot was found, giving diffusion parameters Q = 297 kJ/mol and D 0 = 5 × 10-3m2/s, which are similar to the α-Ti self-diffusion ones, when measured in Ti samples with a similar impurity content than presently. This behaviour is compatible with the hypothesis of U diffusing via a vacancy-assisted mechanism in the α-Ti lattice and contrasts with older results in which the activation energy is almost a third the self-diffusion one, even lower than the vacancy formation energy. © 2013 Copyright Taylor and Francis Group, LLC. Source

Dalibon E.L.,University of Concepcion del Uruguay | Dalibon E.L.,Instituto Sabato UNSAM CNEA | Trava-Airoldi V.,National Institute for Space Research | Pereira L.A.,National Institute for Space Research | And 2 more authors.
Surface and Coatings Technology | Year: 2014

Precipitation hardening stainless steels are extensively used as a material for plastic injection dies because of their dimensional stability during hardening, impact strength and wear and corrosion resistance. Plasma surface engineering can enhance even more the working life of these components preserving them from wear and corrosion damage by means of surface modification or coatings. In this work PH stainless steel Corrax® was ion nitrided and coated with DLC in a modified PACVD duplex process. DLC films are known not only for their hardness but also for their low friction coefficient, features that improve the wear resistance of steel components. Adhesion tests were performed; wear resistance was tested in a pin on disk machine with different counterparts and in the abrasion ASTM G65 test. Nitrided samples were compared in all tests with DLC only coated samples and the duplex ones (nitriding. +. coating). The thickness of the nitrided layer was of 14. μm, and the coating, 1.8. μm. The duplex samples had the best abrasive wear resistance; their mass loss was almost negligible and within the error of the instrument. The only coated samples had a very low mass loss compared with the only aged steel, but the coating was detached.The coated samples presented a low friction coefficient, about 0.03 against alumina and the no wear loss was detected. On the other hand, only the duplex samples presented an acceptable adhesion in the Rockwell C indentation test with 600. N and the critical load was 28. N in the scratch test. © 2013 Elsevier B.V. Source

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