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Lazarte A.I.,Autoridad Regulatoria Nuclear | Ferreri J.C.,Institute Tecnologia
Annals of Nuclear Energy | Year: 2014

In the analysis of the nuclear safety of complex nuclear systems, almost one-dimensional system thermal-hydraulics codes will be used perhaps for a couple of decades from now. Computational Fluid Dynamics (CFD) tools are accepted at present to be a support of such analyses and they are used coupled to systems codes or as separate analysis tools for isolated components with boundary conditions obtained from systems codes. The restricted acceptance of "pure" CFD codes is due to many reasons but two of them are relevant, namely (a) the apparent lack of CFD grade experimental data and (b) the need for a complete verification and validation (V&V) and the uncertainty quantification for the codes currently available. There is plenty of experimental data related to integral test facilities (ITFs) that constitute macroscopic systems behavior information and a consolidated data base for such purposes. Despite of this, additional verification cases may be added to the above mentioned consolidated data. In the present paper, flow oscillations in parallel channel configurations with system codes are studied in diverse configurations. Different models, calculation options and, in particular, in-phase or out-of-phase oscillations were studied, both in heated and cooled parallel channels. The emphasis is on the effects of concentrated irreversible pressure losses coefficients at the inlet and at the outlet of the channels. In the case of cooled steam generator channels, the results of the Semiscale Integral Test Facility operating in natural circulation conditions are revisited. The results presented in this paper, show how a validation case lead to find a not still reported (in the Authors knowledge) verification case. The problem is related to twin-parallel-boiling and condensing, inverted U-tubes channels and connected through common plena. This is, of course, a problem that deserved many tens of papers in the last four decades. Flow splitting without reversal was computationally found and to explain this behavior a theoretical model limited in scope was developed that was a posteriori verified using a particular systems code (RELAP5) commonly applied to perform safety analyses of nuclear power plants. The rationale followed, the theoretical analysis performed and the confirmatory computational results found are summarized in this paper. © 2014 Elsevier Ltd. All rights reserved. Source

Limandri S.P.,Bariloche Atomic Center | Fadanelli R.C.,Federal University of Rio Grande do Sul | Behar M.,Federal University of Rio Grande do Sul | Nagamine L.C.C.M.,University of Sao Paulo | And 8 more authors.
European Physical Journal D | Year: 2014

Stopping cross sections of TiO2 films were measured for H and He ions in the energy intervals 200-1500 keV and 250-3000 keV, respectively, using the Rutherford backscattering technique. Theoretical calculations were performed by means of two versions of the dielectric formalism and a non-linear model. Good agreement is found between the present experimental data and the theoretical results at intermediate and high energies, and also with the very limited experimental information available in the literature. © 2014 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg. Source

Aguiar J.C.,Autoridad Regulatoria Nuclear | Mitnik D.,University of Buenos Aires | Mitnik D.,CONICET | Di Rocco H.O.,CONICET
Journal of Physics and Chemistry of Solids | Year: 2015

Here we propose a semi-empirical approach to describe with good accuracy the electron momentum densities and Compton profiles for a wide range of pure crystalline metals. In the present approach, we use an experimental Compton profile to fit an analytical expression for the momentum densities of the valence electrons. This expression is similar to a Fermi-Dirac distribution function with two parameters, one of which coincides with the ground state kinetic energy of the free-electron gas and the other resembles the electron-electron interaction energy. In the proposed scheme conduction electrons are neither completely free nor completely bound to the atomic nucleus. This procedure allows us to include correlation effects. We tested the approach for all metals with Z=3-50 and showed the results for three representative elements: Li, Be and Al from high-resolution experiments. © 2015 Elsevier Ltd. All rights reserved. Source

Aguiar J.C.,Autoridad Regulatoria Nuclear | Aguiar J.C.,National University of Central Buenos Aires | Di Rocco H.O.,National University of Central Buenos Aires | Di Rocco H.O.,CONICET | And 2 more authors.
Journal of Physics and Chemistry of Solids | Year: 2013

Experimental analysis of isotropic Compton profiles for beryllium, aluminum and titanium was performed to assess the radial core wavefunctions and pseudo-orbitals for valence electrons generated using a generalized gradient approximation based on norm-conserving pseudo-potential calculations. Compton profiles for the different core and valence electron shells are presented in tabulated electron momentum transfer values from q=0 to 9 a.u. Derivatives of the Compton profiles were also calculated to identify the Fermi momenta. Comparison of our results to previous experimental and theoretical calculations shows acceptable agreement in most cases. Our findings indicate that the Compton profiles for Be, Al and Ti are reasonably well described within the generalized gradient approximation. © 2013 Elsevier Ltd. Source

Aguiar J.C.,Autoridad Regulatoria Nuclear | Di Rocco H.O.,CONICET
Journal of Quantitative Spectroscopy and Radiative Transfer | Year: 2014

We check the consistency of the known energy levels of the p2, p3 and p4 isoelectronic sequences tabulated at the NIST Atomic Spectroscopy Database. We used a screening parameter formulation using the Slater integrals arising from the jj-coupling relativistic expressions for the matrix elements. The general conclusion is that the use of the screening parameters is very adequate to check the consistency of level values along their isoelectronic sequences, more suitable than comparison of Slater integrals or other criteria, such as the widely used difference between theoretical and observed values. © 2014 Elsevier Ltd. Source

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