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Menezes M.A.B.C.,Brazilian Nuclear Technology Development Center (CDTN) | Jacimovic R.,Jozef Stefan Institute
Applied Radiation and Isotopes | Year: 2011

It is possible to apply the k0-method using a simplified equation for concentration calculations using Excel spreadsheet, using comparators without making corrections. The objective of this study was to confirm that the k0-standardization method is more efficient and accurate than this "k0-comparator" procedure, applying suitable software that takes into account several corrections. The reference material GBW07401 soil was analyzed in this study. Relative Bias and u-score tests were used in order to evaluate the overall results. © 2011 Elsevier Ltd. Source


Navarro M.A.,Brazilian Nuclear Technology Development Center (CDTN) | Santos A.A.C.,Federal University of Minas Gerais
Progress in Nuclear Energy | Year: 2011

The fuel assemblies of the Pressurized Water Reactors (PWR) are constituted of rod bundles arranged in a regular square configuration by spacer grids placed along its length. The presence of the spacer grids promote two antagonist effects on the core: a desirable increase of the local heat transfer downstream the grids and an adverse increase of the pressure drop due to the constriction on the coolant flow area. Most spacer grids are designed with mixing vanes which cause a cross and swirl flow between and within the subchannels, enhancing even more the heat transfer performance in the grid vicinity. The improvement of the heat transfer increases the departure from the nucleate boiling ratio, allowing higher operating power in the reactor. Due to these important thermal and fluid dynamic features, experimental and theoretical investigations have been carried out in the past years for the development of spacer grid design. More recently, the Computational Fluid Dynamics (CFD) using three dimensional Reynolds Averaged Navier Stokes (RANS) analysis has been used efficiently for this purpose. Many computational works have been performed, but the appropriate numerical procedure for the flow in rod bundle simulations is not yet a consensus. This work presents results of flow simulations performed with the commercial code CFX 11.0 in a PWR 5 × 5 rod bundle segment with a split vane spacer grid. The geometrical configuration and flow conditions used in the experimental studies performed by Karoutas et al. were assumed in the simulations. To make the simulation possible with a limited computational capacity and acceptable mesh refinement, the computational domain was divided in 7 sub-domains. The sub-domains were simulated sequentially applying the outlet results of a previous sub-domain as inlet condition for the next. In this study the k-ε turbulence model was used. The simulations were also compared with those performed by Karoutas et al. in half a subchannel and In et al. in one subchannel computational domains. Comparison between numerical and experimental results of lateral and axial velocities along of the rod bundle show good agreement for all evaluated heights downstream the spacer grid. The present numerical procedure shows better predictions than Karoutas et al. model especially further from the spacer grid where the peripheral subchannels have more influence in the average flow. © 2011 Elsevier Ltd. All rights reserved. Source


Mesquita A.Z.,Brazilian Nuclear Technology Development Center (CDTN) | Gomes do Prado Souza R.M.,Brazilian Nuclear Technology Development Center (CDTN)
Progress in Nuclear Energy | Year: 2010

The on-line monitoring of several new process variables of the IPR-R1 TRIGA Reactor of the Nuclear Technology Development Center - CDTN became possible after the data acquisition and processing system implementation and the installation of one instrumented fuel rod in the reactor core. Several neutronics and thermo-hydraulics parameters are now registered, such as the operation power, the reactivity insertion in the core, the control rod position, the fuel and the water temperatures, and so on. Since the inherently safe operation of a reactor is dependent on the reactivity control, it is essential to have information on this parameter over many different temperature ranges. The fuel elements have been designed to provide a significant negative prompt temperature coefficient that allows safe reactor operation. The developed monitoring system gives the reactivity worth of the control rods, when the rod considered is inserted into the core or withdrawn from it, and also the loss of reactivity during the reactor operation. This paper describes the methodology and the results found with the on-line monitoring of the reactivity behavior of the IPR-R1 TRIGA Reactor. © 2009 Elsevier Ltd. All rights reserved. Source


Abreu R.D.,Brazilian Nuclear Technology Development Center (CDTN) | Morais C.A.,Brazilian Nuclear Technology Development Center (CDTN)
Minerals Engineering | Year: 2014

The present work describes a study of the separation of rare earth elements (REE) from heavy REE concentrate through solvent extraction. Seven extractants were investigated: three organophosphorus acids (DEHPA, IONQUEST ®801 and CYANEX®272), a mixture of DEHPA/TOPO (neutral ester) and three amines (ALAMINE®336, ALIQUAT ®336 and PRIMENE®JM-T). The organophosphorus extractants were investigated in hydrochloric and sulphuric media whereas the amines performance was assessed in a sulphuric medium. The variables investigated were: concentration of the extractant agent, aqueous phase acidity, aqueous/organic volumetric ratio, contact time, stripping agent concentration (hydrochloric acid solution) and the selective stripping step. In the extraction step, the best separation factors for the adjacent elements were obtained with DEHPA and IONQUEST 801. For 1.0 mol L-1 DEHPA in an initial acidity of 0.3 mol L-1 H+, the separation factor was 2.5 Tb/Dy, 2.1 Dy/Ho, 1.9 Ho/Er, 2.0 Ho/Y and 1.1 Y/Er; for 1 mol L-1 IONQUEST 801 in 0.3 mol L-1 of H+ it was 2.7 Tb/Dy, 2.4 Dy/Ho, 2.1 Ho/Er, 2.1 Ho/Y e 1.5 Y/Er. The study concluded that for the extractants investigated, IONQUEST 801 is the most indicated for the separation of heavy REE because it has lower affinity with the REE compared to the affinity of DEPHA/REE, which makes the strip of the REE from Ionquest 801 easier than from DEHPA. Moreover, the number of stages necessary for the stripping of the REE from IONQUEST 801 is much lower than that observed when DEPHA is employed. © 2014 Elsevier Ltd. All rights reserved. Source


Resende L.V.,Brazilian Nuclear Technology Development Center (CDTN) | Morais C.A.,Brazilian Nuclear Technology Development Center (CDTN)
Minerals Engineering | Year: 2010

This paper describes the study of the coating powder leaching from computer monitors scraps with the view to obtain a liquor which can be treated by hydrometallurgical techniques to purify the metals studied. The technological development observed in recent years has stimulated the application of rare earth (RE) elements. TV tubes and computer monitors present as coating a powder containing some rare earth elements, mainly europium and yttrium. The recovery of the RE elements from electronics scraps is extremely important as the economic and environmental issues are concerned. The results of this study indicated the technical viability of the recovery of the metals. After the leaching process optimization, the europium and yttrium recovery was over 97% and a liquor containing 16.5 g/L Y, 0.55 g/L Eu, 59.0 g/L Zn, 0.20 g/L Fe, 131 g/LSO42 -, 0.20 g/L Ca and 2.50 g/L Al was obtained. © 2010 Elsevier Ltd. All rights reserved. Source

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