Safety analysis of neutron flux optimization in irradiation channels at the NUR research reactor

Prior to core reloading, planned power upgrading, or as a part of required analyses of past events, accurate safety evaluations should be carried out. Generally speaking, the content of a safety report has to be modified whenever a new type or design of fuel is to be used in a reactor core. As the existing plants have well established licensing procedures, including well founded analysis methods, the application of new analysis methods has to be thoroughly evaluated, with specific emphasis on their capability of producing results beneficial to reactor operation. The detailed study presented here was carried out so as to insure that the allowed operational safety limits of the NUR research reactor are not exceeded under any circumstances

3D simulation of incompressible Poiseuille flow through 180° curved duct of square cross-section under effect of thermal buoyancy

CITATION: Mokeddem, M., et al. 2019. 3D Simulation of Incompressible Poiseuille Flow through 180° Curved Duct of Square Cross-section under Effect of Thermal Buoyancy. Periodica Polytechnica Mechanical Engineering, 63(4):257–269. doi:10.3311/PPme.12773The original publication is available at https://pp.bme.hu/me/indexIn this paper, three-dimensional numerical simulations are carried out to investigate and analyze the gradual effects of thermal buoyancy strength on laminar flow of an incompressible viscous fluid and heat transfer rate inside a 180° curved channel of square cross-section. The governing equations of continuity, momentum and energy balance are obtained and solved numerically using finite volume method. The effect of Dean number, De, and Richardson number, Ri, on dimensionless velocity profiles and Nusselt number are examined for the conditions: De = 125 to 150, Ri = 0 to 2 at Pr = 1. The mean results are illustrated in terms of streamline and isotherm contours to interpret the flow behaviors and its effect on heat transfer rate. Dimensionless velocity profiles and the local Nusselt number at the angle 0° and 90° are presented and discussed. Also, the average Nusselt number on surfaces of curved duct is computed. The obtained results showed that by adding thermal buoyancy to computed domain, some early Dean vortices are observed at the angle 0° and new sort are observed at 90°. Furthermore, increase in Dean number increases the heat transfer rate. In other hand, increase in Richardson number decreases the average Nusselt number of 180° curved duct.https://pp.bme.hu/me/article/view/12773Publisher’s versio

Delineation of arteries with atherosclerosis in dynamic three-dimensional PET images

L'athérosclérose est à l'origine d'une grande proportion de maladies cardio-vasculaires (MCV) qui sont les principales causes de mortalité dans le monde. L'athérosclérose est un processus inflammatoire qui affecte les vaisseaux sanguins périphériques, touchant principalement la paroi interne des artères et formant des plaques. La plaque vulnérable peut se détacher et obstruer des vaisseaux sanguins. Plusieurs facteurs sont connus pour contribuer à l'athérosclérose: hypercholestérolémie, régime riche en gras saturé, hyperglycémie, hypertension, obésité, vieillissement, sédentarité, tabagisme et pollution de l'air. En clinique, l’inflammation des plaques est habituellement diagnostiquée par le C-reactive protein (CRP), une substance produite par le foie en réponse à une inflammation, ce qui la rend moins spécifique à l’inflammation artérielle. L'imagerie moléculaire par la tomographie d'émission par positrons (TEP) couplée à la tomodensitométrie (TDM) a été rapportée comme la plus sensible et la plus spécifique à détecter la formation et le métabolisme des plaques de même que leur localisation absolue dans les sections des artères. Nous avons utilisé des mesures TEP/TDM de sujets en bonne santé et de sujets avec des complications vasculaires. Ces sujets volontaires, hommes et femmes, étaient âgés entre 65 ans et 85 ans. Notons que même chez les sujets en bonne santé, plusieurs sections des artères de l’aorte, des iliaques et des fémorales contiennent des calcifications. Les images des artères en TEP sont d’abord segmentées, afin de les jumeler aux images de TDM d’où l’on repère les calcifications. Plusieurs approches de segmentation ont été essayées et nous avons retenu l’approche par la propagation d’affinité (PA). L’application de la méthode PA a permis de bien délimiter les artères sur les images TEP en comparaison à d’autres techniques usuelles. La délimitation des artères nous a aussi permis de corriger leur intensité pour l’effet du volume partiel, un phénomène physique inhérent à la TEP. Nous avons aussi conçu une mire à utiliser avec l’imagerie TEP/TDM pour effectuer les calculs des coefficients de récupération pour corriger l’effet du volume partiel en fonction de la position des artères par rapport au centre du scanner.Abstract : Atherosclerosis is responsible for a large proportion of cardiovascular diseases (CVD), which are the leading causes of death in the world. Atherosclerosis is an inflammatory process affecting the peripheral blood vessels, mainly the inner lining of the arteries and forming plaques. The vulnerable plaque can detach and obstruct small blood vessels in the brain or in the heart causing complications. Several factors are known to contribute to atherosclerosis: hypercholesterolemia, high saturated fat diet, hyperglycemia, hypertension, obesity, aging, sedentary lifestyle, smoking and air pollution. Clinically, plaque inflammation is usually diagnosed by CRP, a substance produced by the liver in response to inflammation, which makes it less specific to arterial inflammation. Positron emission tomography (PET) and computed tomography (CT) have been reported to be the most sensitive and specific in detecting plaque formation and metabolism as well as their absolute localization in artery sections. We used PET/CT images of healthy subjects and subjects with vascular complications. These volunteers, men and women, were between 65 and 85 years old. Note that even in healthy subjects, several sections of the arteries of the aorta, iliac and femoral contain calcifications. The images of PET arteries were first segmented in order to pair them with CT images from which the calcifications were identified. Several segmentation approaches have been tried and we have retained the approach by affinity propagation (AP). The application of the AP method has made it possible to delimit the arteries on the PET images in comparison with other usual techniques. The delineation of arteries has also allowed us to correct their intensity for the partial volume effect, a physical phenomenon inherent to PET imaging. We also designed a phantom to be used with PET/CT imaging to perform recovery coefficient calculations to correct the effect of partial volume, based on the position of the arteries relative to the center of the scanner

Etude et modélisation des couches minces Cu-AL2O3 et Cu-SiO2 par la méthode du premeir principe

123 p. : ill. ; 30 cmLe travail presente dans ce memoire consiste en une etude a partir du premier principe "ab initio" du substrat du cuivre, des surfaces propres Cu(111) et Cu(001), ainsi que l'adsorption de l'foxygene sur ces structures. Les proprietes structurales et electroniques ont ete calculees a l'aide de la Theorie de la Fonctionnelle de la Densite (DFT). Les surfaces sont modelisees par la superposition de couches dپfatomes separees par un vide (modele de supercell). Les energies des liaisons de l'foxygene sur differents sites de la structure ont ete determinees et le site le plus stable a ete defini. La nature de la liaison entre les atomes Cu et O est discutee a partir de lپfanalyse de la densite de charges, son transfert, ainsi que la densite dپfetats electroniques de la structure. Nous avons egalement etudie l'finterface entre l'alumine (a-.Al2O3) et la silice (a-SiO2) sur les surfaces propres Cu(111) et Cu(001) respectivement. Les structures de bandes ont ete calculees pour les deux systemes et le transfert de charges au niveau de lپfinterface a ete etudie

Negative capacitance in Aluminum/hydrogenated amorphous silicon nitride/n type crystalline silicon structure

The dynamic admittance of Al/a-SiNx:H/n-c-Si structure as function of bias voltage (V) and frequency (ω) have been investigated in wide ranges of frequency (300 Hz–1 MHz) and bias voltage (0–9 V) respectively at room temperature. Negative capacitance (NC) behavior has been observed at forwards bias voltages. It appears from value of bias voltage which depends on the frequency. This value corresponds on the current–voltage characteristics at the beginning bias voltage of thermionic emission regime of electrical conduction. Therefore the injection of electrons at a-SiNx:H/n-c-Si interface by thermionic emission may be involved in the NC mechanism. In C−ω plot, a strong peak of NC has been observed at low-frequency, its intensity is about 110 times the geometrical capacitance. The frequency and the intensity of the NC peak show a linear variation versus a square root of bias voltage in semi logarithmic representation. The NC behavior is always accompanied with relatively high conductance “G/ω

Effect of nitrogen mole fraction on hydrogenated amorphous silicon nitride deposited by DC magnetron sputtering: transition between metallic and reactive sputtering

The hydrogenated amorphous silicon nitride thin films are deposited by DC magnetron sputtering in argon, molecular hydrogen and nitrogen plasma mixture. The films are deposited at 150 °C and at 130 W sputtering power with wide range of nitrogen mole fraction. The plasma is characterized by the target voltage measurement. The samples are characterized by the optical transmission measurements and the physicochemical structure is studied by the FTIR absorption spectroscopy. When the nitrogen mole fraction increases from 0.075 to 0.24 the target voltage decrease from 413 to 325 V and increases suddenly to 450 V when nitrogen mole fraction increases to 0.69. The decrease of target voltage may be due to the transition from metallic to reactive sputtering process and its increase can be explained by the implantation of reactive ions in the target. Sputtering rate and refractive index decrease respectively from 8.33 to 1.73 Å/sec and from 2.52 to 1.68 with nitrogen mole fraction. The value of refractive index at critical nitrogen mole fraction is about 1.8. When the nitrogen mole fraction increases the frequency related to Si-H band, on FTIR spectrum, shift from 2097 cm-1 to reach 2209 cm-1 at the critical nitrogen mole fraction. Thereafter it varies sharply to 2190 cm-1 and remains constant. A sudden change is observed on the sputtering rate, on the intensity of the band attributed to the stretching vibration of N-H and Si-H bonds. From these results we believe that the stoichiometric composition is reached at the critical nitrogen mole fraction and beyond this the deposited films are rich of nitrogen and hydrogen. This is consistent with the explanation given of the variation of the target voltage. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

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Fuel depletion calculation in MTR-LEU NUR reactor

In this article, we present the results of a few energy groups calculations for the NUR reactor fuel depletion analysis up to 45 000 MWd/tU taken as the maximum fuel burn up. The WIMSD-4 cell code has been employed as a calculation tool. In this study, we are interested in actinides such as the uranium and plutonium isotopes, as well as fission products Xe-135, Sm-149, Sm-151, Eu-155, and Gd-157. Calculation results regarding the five energy groups are in a good agreement with those obtained with only two energy groups which can, therefore, be used in all subsequent calculations. Calculation results presented in this article can be used as a microscopic data base for estimating the amount of radioactive sources randomly dispersed in the environment. They can also be used to monitor the fuel assemblies inventory at the core level