Dissertations / Theses on the topic 'Neutron generators'

Neutron activation analysis (NAA) has been applied to furnace matte and converter matte samples with the objective of studying the natural variation in the elemental composition of the samples, with a view to characterize the samples for their source of origin. The experimental work was carried out at iThemba LABS national laboratory near Cape Town, South Africa. A new NAA facility was designed and built for this purpose, and fully characterized, featuring a 14 MeV neutron generator. Gamma-ray spectra were measured using an HPGe detector. A number of isotopes were identified in the measured spectra and the elemental concentrations calculated. Radiometric spectral measurements were also made of the samples, without prior irradiation, and the spectra analysed for isotopic variation. Consequences for sample identification via these techniques are discussed.

This thesis describes the measurement technique of fast-neutron tomography for assessing spatial distributions of steam and water in two-phase flows. This so-called void distribution is of importance both for safe operation and for efficient use of the fuel in light water reactors, which compose the majority of the world’s commercial nuclear reactors. The technique is aimed for usage at thermal-hydraulic test loops, where heated two-phase flows are being investigated under reactor-relevant conditions. By deploying portable neutron generators in transmission tomography, the technique becomes applicable to stationary objects, such as thermal-hydraulic test loops. Fast neutrons have the advantage of high transmission through metallic structures while simultaneously being relatively sensitive to the water/void content. However, there are also challenges, such as the relatively low yield of commercially available fast-neutron generators, the tendency of fast neutrons to scatter in the interactions with materials and the relatively low efficiency encountered in fast-neutron detection. The thesis describes the design of a prototype instrument, FANTOM, which has been assembled and demonstrated. The main design parameters have been optimized to achieve maximal signal count rate in the detector elements, while simultaneously reaching an image unsharpness of ≤0.5 mm. Radiographic projections recorded with the assembled instrument are presented, and the performance parameters of FANTOM are deduced. Furthermore, tomographic reconstruction methods for axially symmetric objects, which is relevant for some test loops, have been developed and demonstrated on measured data from three test objects. The attenuation distribution was reconstructed with a radial resolution of 0.5 mm and an RMS error of 0.02 cm-1, based on data recorded using an effective measurement time of 3.5 hours per object. For a thermal-hydraulic test loop, this can give a useful indication of the flow mode, but further development is desired to improve the precision of the measurements. Instrument upgrades are foreseen by introducing a more powerful neutron generator and by adding detector elements, speeding up the data collection by several orders of magnitude and allowing for higher precision data. The requirements and performance of an instrument for assessment of arbitrary non-symmetric test loops is discussed, based on simulations.

<p> Neutrons produced deuterium Z-pinch plasmas are widely acknowledged to be a consequence of highly accelerated deuterons undergoing nuclear fusion with relatively stationary deuterons. The acceleration is thought to occur in intense fields created in the MHD instabilities that punctuate the plasma column. Interestingly, the energies of the accelerated ions exceed the applied voltage across the electrode gap. We use the 1 MA Zebra pulsed-power generator at the Nevada Terawatt Facility (NTF) to explore this poorly understood fast neutron production mechanism by creating deuterium Z-pinches in three distinct types of target loads. The loads are a cylindrical shell of deuterium gas, the far less explored deuterided palladium wire arrays, and a deuterium-carbon ablated laser plume target, which is unique to the NTF. </p><p> The pinch dynamics vary considerably in these three targets and provide the opportunity to explore the ion acceleration mechanism. We infer the characteristics of the accelerating fields from a wide range of diagnostic data including the neutron yield, energy spectrum and angular distribution, and the properties of the matching electron beams that are accelerated in the same field, and the energetic X-rays they produce on stopping. The plasma and the instabilities were recorded on several high-speed imaging diagnostics along with time-integrated soft (&lt;10 keV) X-ray pinhole images. The three load types produced total neutron yields in the 10⁸&ndash;10¹⁰ n/pulse range. The synchronization we observe between the ion and electron beams and the development of instabilities leads us to conrm the acceleration hypothesis. We also present the characteristics of the fields and ion beams in these varied pinches.</p>

<p>The development of a deuterium-deuterium/ tritium-deuterium (D-D/ D-T) pulsed neutron generator based on the principle of the Plasma Immersion Ion Implantation (PI3) technique is presented, in terms of investigating development of a compact system to generate an ultra short burst of mono-energetic neutrons (of order 1010 per second) during a short period of time (&lt<br>20&mu<br>s) at repetition rates up to 1 kHz. The system will facilitate neutron detection techniques, such as neutron back-scattering, neutron radiography and time-of-flight activation analysis.</p> <p><br /> Aspects addressed in developing the system includes (a) characterizing the neutron spectra generated as a function of the target configuration/ design to ensure a sustained intense neutron flux for long periods of time, (b) the system was also characterised as a function of power supply operating conditions such as voltage, current, gas pressure and plasma density.</p>

This is a feasibility study of a new measurement technique for spent nuclear fuel. The technique combines gamma emission tomography with neutron activation analysis. The idea is to measure high-energy characteristic gamma from short-lived fission products and thereby verify the fissile material content in spent nuclear fuel assemblies. Simulations using MCNP were done to estimate the expected detector count rate for these characteristic gammas. The predicted count rate was too slow for the proposed technique to be of practical use. However, several improvements that could increase the count rate of the technique are suggested for further investigation of the prospects of this new technique.

The nuclear design of fusion devices such as ITER (International Thermonuclear Experimental Reactor), which is an experimental fusion reactor based on the &amp;quot;tokamak&amp;quot; concept, rely on the results of neutron physical calculations. These depend on the knowledge of the neutron and photon flux spectra which is particularly important because it permits to anticipate the possible answers of the whole structure to phenomena such as nuclear heating, tritium breeding, atomic displacements, radiation shielding, power generation and material activation. The flux spectra can be calculated with transport codes, but validating measurements are also required. An important constituent of structural materials and divertor areas of fusion reactors is tungsten. This thesis deals with the measurement of the neutron fluence and neutron energy spectrum in a tungsten assembly by means of multiple foil neutron activation technique. In order to check and qualify the experimental tools and the codes to be used in the tungsten benchmark experiment, test measurements in the D-T and D-D neutron fields of the neutron generator at Technische Universität Dresden were performed. The characteristics of the D-D and D-T reactions, used to produce monoenergetic neutrons, together with the selection of activation reactions suitable for fusion applications and details of the activation measurements are presented. Corrections related to the neutron irradiation process and those to the sample counting process are discussed, too. The neutron fluence and its energy distribution in a tungsten benchmark, irradiated at the Frascati Neutron Generator with 14 MeV neutrons produced by the T(d, n)4He reaction, are then derived from the measurements of the neutron induced &amp;amp;#947;-ray activity in the foils using the STAYNL unfolding code, based on the linear least-square-errors method, together with the IRDF-90.2 (International Reactor Dosimetry File) cross section library. The differences between the neutron flux spectra measured by means of neutron foil activation and the neutron flux spectra obtained in the same assembly, making use of an NE213 liquid-scintillation spectrometer were studied. The comparison of measured neutron spectra with the spectra calculated with the MCNP-4B (Monte Carlo neutron and photon transport) code, which allows a crucial test of the evaluated nuclear data used in fusion reactor design, is discussed, too. In conclusion, this thesis shows the applicability of the neutron foil activation technique for the measurement of neutron flux spectra inside a thick tungsten assembly irradiated with 14 MeV from a D-T generator<br>Die Konstruktion von Fusionsreaktoren wie ITER (International Thermonuclear Experimental Reactor), der ein experimenteller Fusionsreaktor ist und auf dem &amp;quot;Tokamak&amp;quot;-Konzept beruht, basiert unter neutronenphysikalischen Gesichtspunkten auf den Ergebnissen von umfangreichen Simulationsrechnungen. Diese setzen die Kenntnis der Spektren des Neutronen- und Photonenflusses voraus die besonders wichtig ist, weil sie, die möglichen Antworten der ganzen Struktur auf physikalische Prozesse vorauszuberechnen erlaubt wie z.B.: Heizen durch nukleare Prozesse, Tritium-Brüten, Atomverschiebung, Abschirmung von Strahlung, Leistungserzeugung und Materialaktivierung. Die Flußspektren können mittels Transportcodes berechnet werden, aber es werden auch Messungen zu ihrer Bestätigung benötigt. Ein wichtiger Bestandteil des Strukturmaterials und der Divertor-Flächen der Fusionsreaktoren ist Wolfram. Diese Dissertation behandelt die Messungen der Neutronspektren und ?fluenz in einer Wolfram-Anordnung mittels der Multifolien-Neutronenaktivierungstechnik. Um die anzuwendenden experimentellen Geräte und die Codes, die im Wolfram-Benchmark-Experiment eingesetzt werden, zu überprüfen und zu bestimmen, wurden Testmessungen in den D-T und D-D Neutronenfeldern des Neutronengenerator der Technischen Universität Dresden durchgeführt. Die Eigenschaften der D-T und D-D Reaktionen, die für die Erzeugung von monoenergetischen Neutronen verwendet werden, sowie die Auswahl der Aktivierungsreaktionen, die für Fusionsanwendungen geeignet sind und die Aktivierungsmessung werden detailliert vorgestellt. Korrekturen, die sich auf den Neutronen-Bestrahlungsprozess und auf den Probenzählungsprozess beziehen, werden ebenfalls besprochen. Die Neutronenfluenz und ihre Energieverteilung in einem Wolfram-Benchmark, bestrahlt am Frascati Neutronen Generator mit 14 MeV-Neutronen aus der T(d, n)4He Reaktion, werden aus den Messungen der &amp;amp;#947;-Strahlenaktivität, die von Neutronen in den Folien induziert ist, durch den STAYNL Entfaltungscode, der auf der Methode der kleinsten Fehlerquadrate basiert, zusammen mit der IRDF-90.2 Wirkungsquerschnitt-Bibliothek abgeleitet. Die Unterschiede zwischen den Neutronenflußspektren, die mit Hilfe der Multifolien-Neutronenaktivierung ermittelt wurden, und den Neutronenflußspektren, gemessen im selben Aufbau mit einem NE-213 Flüssigszintillator, wurden untersucht. Die gemessenen Neutronenspektren werden den aus MCNP-4B Rechnungen (Monte Carlo neutron and photon transport) ermittelten Spektren gegenüber gestellt. Der Vergleich stellt einen wichtigen Test der evaluierten Kerndaten für Fusionsreaktorkonzepte dar. Zusammenfassend zeigt diese Arbeit die Anwendbarkeit der Multifolien-Neutronenaktivierungstechnik bei Messungen der Neutronenflussspektren innerhalb eines massiven Wolframblocks bei Bestrahlung mit schnellen Neutronen aus D-T Generatoren

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California<br>This paper presents a new approach for the effective generation of translator scripts that can be used to automate the translation of data display configurations from one vendor format to another. Our approach uses the IDEF5 ontology description method to capture the ontology of each vendor format and provides simple rules for performing mappings. In addition, the method includes the specification of mappings between a language-specific ontology and its corresponding syntax specification, that is, either an eXtensible Markup Language (XML) Schema or Document Type Description (DTD). Finally, we provide an algorithm for automatically generating eXtensible Stylesheet Language Transformation (XSLT) scripts that transform XML documents from one language to another. The method is implemented in a graphical tool called the Data Display Translator Generator (DDTG) that supports both inter-language (ontology-to-ontology) and intra-language (syntax-to-ontology) mappings and generates the XSLT scripts. The tool renders the XML Schema or DTD as trees, provides intuitive, user-friendly interfaces for performing the mappings, and provides a report of completed mappings. It also generates data type conversion code when both the source and target syntaxes are XML Schema-based. Our approach has the advantage of performing language mappings at an abstract, ontology level, and facilitates the mapping of tool ontologies to a common domain ontology (in our case, Data Display Markup Language or DDML), thereby eliminating the O(n^2) mapping problem that involves a number of data formats in the same domain.

Consistent international efforts have been made over the past few decades to move the world towards an environmentally sustainable society. Wind energy conversion systems (WECSs) are one of the largest contributors within this movement. Furthermore amongst existing wind turbine power generation technologies, the doubly fed induction generator (DFIG) has been distinctively popular for its lower capital costs especially in higher power applications. In order to study the integration of this type of generator into the grid, a laboratory based DFIG test rig was developed where its complete design process is presented in this dissertation. Mathematical modelling of related system components were thoroughly investigated so as to facilitate controller design based on the internal model control (IMC) methodology. In addition, a complete soft grid synchronisation procedure for the DFIG was investigated. It was found that the application of active damping within the IMC control law resulted in reduced stator current transients during synchronisation. Control voltage excitation for the DFIG rotor circuit was achieved by the implementation of two voltage source converters (VSC’s) connected in a back-to-back configuration via a common DC-link. The rotorside converter (RSC) was responsible for regulating the machine speed whereas the grid-side converter (GSC) was responsible for regulating the DC-link voltage. In addition, these converters provided decoupled and bidirectional power flow control which enabled the DFIG to operate at sub synchronous and super synchronous speeds. A three-level VSC was chosen for the GSC control, where a resource conservative modulation algorithm that eliminates DC-link neutral voltage unbalance was implemented. The DFIG system design was simulated, and the results were verified through experimental tests performed on a 1.5kW wound rotor induction machine (WRIM). A detailed description of the laboratory setup of the DFIG is presented, and various practical limitations are discussed. It was found that the performance of the developed DFIG test rig correlated well with results of the simulations. Stable operation was achieved for various system test conditions, which indicated the system’s robustness to serve as a practical platform for future DFIG related research.

Uno dei principali protagonisti della caccia alla Materia Oscura è il Progetto XENON presso i LNGS, con l'obiettivo di rivelare le WIMP. Forti dell'esperienza proveniente dalle precedenti fasi del Progetto, l'attuale esperimento XENON1T è il primo che contiene circa 3.2 t di xenon liquido, di cui circa 2 t costituiscono la massa attiva della TPC a doppia fase. E questa è la prima TPC con massa attiva superiore a 1 t e con il più basso livello di fondo tra tutti gli esperimenti di questo tipo. Nel 2017, con un tempo di esposizione di soli 34.2 giorni, XENON1T ha ottenuto uno dei miglior limiti di esclusione per la sezione d'urto di interazione WIMP-nucleo non dipendente dallo spin. Nella prima parte del presente lavoro di tesi, verifico la possibilità che il neutron generator (NG), una sorgente di neutroni per la calibrazione della risposta del rivelatore ai rinculi nucleari (NR), possa essere una sorgente di fondo per il rivelatore essendo posizionato vicino alla TPC. Dalla stima del rate di eventi in presenza o meno del NG, nessuna differenza è stata osservata per gli eventi da rinculo elettronico (ER) a bassa energia. Successivamente alla valutazione dell'attività di U238 e Th232 nei materiali del NG, è possibile stimare il fondo indotto da neutroni radiogenici atteso dal NG: poiché risulta essere due ordini di grandezza inferiore a quanto atteso dai materiali di costruzione del rivelatore, può essere considerato un contributo trascurabile. Nella parte finale della tesi si presentano tutte le possibili sorgenti di fondo per eventi ER nel rivelatore di XENON1T e la simulazione, con il programma GEANT4, di tale fondo. In particolare, è esaminata e discussa la nuova implementazione della simulazione per il doppio decadimento beta dell'isotopo Xe136. Lo stato dell'arte del confronto delle simulazioni Monte Carlo con i dati reali è mostrato alla fine del lavoro di tesi: i risultati preliminari evidenziano una buona conoscenza del fondo dell'ER nel rivelatore XENON1T.

La thèse s’inscrit dans le cadre industriel de la détection de la réaction entre l’eau et le sodium dans un générateur de vapeur d’un réacteur à neutrons rapides à caloporteur sodium. Plus précisément, il s’agit de détecter une micro-fuite d’eau dans le sodium (débit &lt; 1 g/s) en moins de 10 secondes à partir des signaux vibratoires mesurés sur la virole externe du générateur de vapeur. Le bruit de fond très important de l’installation en fonctionnement risque de mettre en défaut la détection basée sur un dépassement de seuil de l’énergie vibratoire. Nous nous intéressons dans cette thèse à la technique de la formation de voies qui permet d’augmenter le rapport signal à bruit et de détecter et de localiser une source acoustique à l’intérieur du système à partir de signaux vibratoires mesurés par une antenne de capteurs accéléromètres placés sur la coque cylindrique (i.e. virole du générateur de vapeur). Une étude numérique a d’abord été réalisée. Des modèles numériques sont développés afin de simuler les signaux mesurés (virtuellement) par les accéléromètres de l’antenne linéaire considérée. Les performances de la formation de voies sont alors étudiées suivant différents paramètres (i.e. position source, amortissement, fréquence, type de bruit de fond, etc.). Le premier modèle consiste en une plaque plane infinie en contact avec un fluide lourd et excitée par un monopole acoustique situé dans ce fluide. L’analyse des déplacements transverses de la plaque nous permet d’établir un critère sur l’échantillonnage spatial du champ vibratoire par l’antenne. Un second modèle, plus représentatif de la virole du générateur de vapeur, est ensuite proposé. Une coque cylindrique élastique infinie, remplie par un fluide lourd est considérée. Le caractère « fini » de ce système dans les directions radiales et circonférentielles fait apparaitre un comportement modal. Son impact sur la formation de voies est étudié. La méthode est finalement testée expérimentalement. Des mesures sont réalisées sur une maquette composée d’un cylindre en acier rempli d’eau, placé dans un circuit hydraulique dont on maitrise le débit. La source acoustique est générée à partir d’un hydrophone. On étudie alors le gain d’antenne pour différents débits et niveaux d’excitation de la source<br>This thesis deals with a new method to detect a sodium-water reaction in a steam generator of a fast sodium-cooled nuclear reactor. More precisely, the objective is to detect a micro-leak of water (flow &lt; 1 g/s) in less than 10 seconds by measuring the external shell vibrations of the component. The strong background noise in operation makes impossible the use of a detection system based on a threshold overrun. A beamforming method applied to vibrations measured by a linear array of accelerometers is developed in this thesis to increase the signal-to-noise ratio and to detect and locate the leak in the steam generator. A numerical study is first realized. Two models are developed in order to simulate the signals measured by the accelerometers of the array. The performances of the beamforming are then studied in function of several parameters, such as the source location and frequency, the damping factor, the background noise considered. The first model consists in an infinite plate in contact with a heavy fluid, excited by an acoustic monopole located in this fluid. Analyzing the transverse displacements in the wavenumber domain is useful to establish a criterion to sample correctly the vibration field of the plate. A second model, more representative of the system is also proposed. In this model, an elastic infinite cylindrical shell, filled with a heavy fluid is considered. The finite dimensions in the radial and circumferential directions lead to a modal behavior of the system which impacts the beamforming. Finally, the method is tested on an experimental mock-up which consists in a cylindrical pipe made in stainless steel and filled with water connected to hydraulic circuit. The water flow speed can be controlled by varying the speed of the pump. The acoustic source is generated by a hydrophone. The performances of the beamforming are studied for different water flow speeds and different amplitude and frequencies of the source

FPGAs are frequently used in network systems to provide the performance and flexibility that is required of modern computer networks while allowing network vendors to bring products to market quickly. Like all electronic devices, FPGAs are vulnerable to ionizing radiation which can cause applications operating on an FPGA to fail. These low-level failures can have a wide range of negative effects on the performance of a network system. As computer networks play a larger role in modern society, it becomes increasingly important that these soft errors are addressed in the design of network systems.This work presents a framework for testing the soft-error reliability of FPGA-based networking systems. The framework consists of the NetFPGA development board, a custom traffic generator, and a custom high-speed JTAG configuration device. The NetFPGA development board is versatile and can be used to implement a wide range of network applications. The traffic generator is used to exercise the network system on the NetFPGA and to determine the health of that system. The JTAG configuration device is used to manage reliability experiments, to perform fault injection into the FPGA, and to monitor the NetFPGA during radiation tests.This thesis includes soft-error reliability tests that were performed on an Ethernet switch network system. Using both fault injection and accelerate radiation testing, the soft error sensitivity of the Ethernet switch was measured. The Ethernet switch design was then mitigated using triple module redundancy and duplication with compare. These mitigated designs were also tested and compared against the baseline design. Radiation testing shows that TMR provides a 5.05x improvement in reliability over the baseline design. DWC provides a 5.22x improvement in detectability over the baseline design without reducing the reliability of the system.

La graine constitue le point de départ du cycle d’une plante et abrite une diversité de micro-organismes qui peuvent impacter négativement ou positivement la fitness de la plante. De plus, la graine permet la dispersion et la survie des agents phytopathogènes entre deux cycles de culture de la plante hôte. Dans ce contexte, l’objectif de ce travail était de : (i) décrypter les processus écologiques impliqués dans l’acquisition du microbiote des graines, (ii) analyser sa réponse à l’invasion par des agents phytopathogènes et(iii) suivre sa dynamique durant la germination de la graine et l’émergence de la plantule. Premièrement, nous avons analysé la structure du microbiote de graines de radis(Raphanus sativus) produites dans un même site sur trois générations successives. Ces analyses ont révélé une faible héritabilité du microbiote des graines avec peu de taxons dominants transmis d’une génération à l’autre. Ceci pourrait être expliqué par l’importance des processus neutres dans l’assemblage du microbiote des graines.Ensuite, nous avons étudié la réponse de ce microbiote à une invasion par Xanthomonas campestris pv. campestris(Xcc) et Alternaria brassicicola (Ab), deux agents phytopathogènes transmis par les graines. La transmission de Xcc aux graines n’impacte pas la composition globale du microbiote. En revanche, la transmission d’Ab modifie la structure des communautés fongiques. Ces différences de réponse sont probablement dues aux compétitions pour l’espace et les nutriments entre l’agent phytopathogène et les autres membres du microbiote. Finalement, la composition et la structure du microbiote des graines germées et des plantules ont révélé une transmission de la majorité des taxons associés à la graine y compris Xcc etAb. Globalement, les résultats de ce travail de thèse permettront à terme d’élaborer des stratégies de biocontrôle basées sur la modulation du microbiote des graines<br>Seed represents the initial step of the plant life cycle and harbors diverse microorganisms that can have detrimental or beneficial impacts on plant fitness. Moreover, seed represents an important means of pathogen dispersion and survival during intercrop periods. For those reasons, the aims of this work were to (i) unveil the ecological processes involved in the acquisition of the seedmicrobiota, (ii) to analyze its response against plant pathogens invasion and (iii) to monitor its dynamics during the first plant developmental stages, namely germination and emergence. First, we assessed the structure of the radish seed microbiota (Raphanus sativus) in the same experimental site across three successive plant generations. These analyses revealed a low heritability of the seed microbiota with few dominant taxa transmitted across generations. Neutral-based processes seem to be important in assembly of the seed microbiota. Second, we monitored the response of the seed microbiota to invasions by Xanthomonas campestris pv. campestris (Xcc) and Alternaria brassicicola (Ab), two seed-transmitted pathogens. While Xcc seed transmission do not change the composition of microbial communities, Ab transmission modified the structure of seed-associated fungal communities. This differences in response could be partly explained by competition for space and nutrients between the pathogenic agents and the members of the seed microbiota. Finally, composition and structure of microbial communities associated to germinating seed and seedling revealed transmission of most seed-borne microorganisms including Xcc and Ab from seed to seedling. Altogether, the results of this thesis could be helpful for designing future biocontrol strategies based on seed microbiota modulation

One obstacle preventing more engineers from using finite element analysis (FEA) is the difficulty of transferring data between steps in the modeling process. A Fortran computer program, Rosetta.BYU, has been developed to open data paths between finite element preprocessors (mesh generators) and finite element analysis programs, using a custom data structure. It accepts neutral data files, Version 2.0 IGES data files, and Movie.BYU files for input/output. An application of Rosetta is described. A general workstation manager program, Davinci.BYU, is reviewed that provides a support layer between the engineer and the operating system, organizes software and data files, and facilitates on-line documentation and demonstrations. Requirements of a good user interface are discussed and supporting software, Squire.BYU, is described. An application of this software in an industrial setting is described.

Les travaux de thèse s’inscrivent dans les problématiques des travaux de recherche de l’équipe thématique : Maitrise des Energies Renouvelables et systèmes de Stockage (MERS) du laboratoire GREAH-EA3220. Ils englobent le dimensionnement des éléments constitutifs du système et la gestion optimale de l’énergie électrique pour un système hybride (Diesel à vitesse variable, Eolien, PV et Batteries) dédié aux sites isolés. Les sources de production d'énergie alimentent des charges par le biais de convertisseurs multi-niveaux d’électronique de puissance. Le groupe électrogène comportant un moteur diesel à vitesse variable est considéré comme la principale source d’énergie utilisée pour contrôler la tension continue du point de couplage. Ce type de groupe électrogène est choisi pour optimiser la consommation du carburant. Il est sollicité pour délivrer une puissance électrique compatible avec le régime du moteur qui supporte mal les variations fréquentes et rapides. Les sources d’énergie renouvelables dont on cherche à augmenter la part d’énergie pour satisfaire la demande sont pilotées de manière à extraire instantanément le maximum de puissances disponible par les ressources (ensoleillement, vent). Celles-ci imposent ainsi leurs dynamiques et leurs intermittences au point de couplage. Le pack des batteries sert à compenser les fluctuations rapides de l’énergie provenant des sources d’énergie renouvelables par rapport à une évolution plus lente prise en charge par le groupe électrogène. La gestion des interactions au sein du système électrique hybride résultant est assurée au moyen de convertisseurs statiques multi-niveaux (AC / DC, DC / DC et DC / AC). Une approche de gestion d’énergie électrique fondée sur la répartition fréquentielle des perturbations induites au point de couplage par les sources renouvelables. Une plateforme expérimentale à échelle réduite (1/22) a été développée pour valider expérimentalement les approches théoriques et les simulations. Les résultats de simulations obtenus dans l’environnement logiciel Matlab/Simulink/SimPowerSystems et ceux issus du dispositif expérimental réalisé et piloté par dSPACE-1104 prouvent l’adéquation des méthodes de contrôle proposées<br>The thesis works are part of the research work of the thematic team: Mastery of Renewable Energies and Storage Systems (MERS) of the GREAH-EA3220 laboratory. They include the dimensioning of the constituent elements of the system and the optimal management of electrical energy for a hybrid system (Variable speed Diesel, Wind, PV and Batteries) dedicated to isolated sites. Power sources supply loads through multi-level converters of power electronics. The generator set with a variable speed diesel engine is considered to be the main source of energy used to control the DC voltage at the coupling point. This type of generator is chosen to optimize fuel consumption. It is used to deliver an electrical power compatible with the engine speed which does not tolerate frequent and rapid variations. Renewable energy sources whose share of energy is sought to meet demand are managed so as to instantly extract the maximum power available from resources (sunshine, wind). These thus impose their dynamics and their intermittences at the coupling point. The battery pack is used to compensate for rapid fluctuations in energy from renewable energy sources compared to a slower evolution supported by the generator. Interactions within the resulting hybrid electrical system are managed by means of multi-level static converters (AC / DC, DC / DC and DC / AC). An electrical energy management approach based on the frequency distribution of disturbances induced at the coupling point by renewable sources. An experimental platform on a reduced scale (1/22) has been developed to experimentally validate theoretical approaches and simulations. The results of simulations obtained in the Matlab / Simulink / SimPowerSystems software environment and those from the experimental device produced and piloted by dSPACE-1104 prove the adequacy of the proposed control methods

The main focus of this thesis is on the power electronic converter system challenges associated with the grid integration of variable-renewable-energy (VRE) sources like wave, marine current, tidal, wind, solar etc. Wave energy conversion with grid integration is used as the key reference, considering its high energy potential to support the future clean energy requirements and due the availability of a test facility at Uppsala University. The emphasis is on the DC-link power conditioning and grid coupling of direct driven wave energy converters (DDWECs). The DDWEC reflects the random nature of its input energy to its output voltage wave shape. Thereby, it demands for intelligent power conversion techniques to facilitate the grid connection. One option is to improve and adapt an already existing, simple and reliable multilevel power converter technology, using smart control strategies. The proposed WECs to grid interconnection system consists of uncontrolled three-phase rectifiers, three-level boost converter(TLBC) or three-level buck-boost converter (TLBBC) and a three-level neutral point clamped (TLNPC) inverter. A new method for pulse delay control for the active balancing of DC-link capacitor voltages by using TLBC/TLBBC is presented. Duty-ratio and pulse delay control methods are combined for obtaining better voltage regulation at the DC-link and for achieving higher controllability range. The classic voltage balancing problem of the NPC inverter input, is solved efficiently using the above technique. A synchronous current compensator is used for the NPC inverter based grid coupling. Various results from both simulation and hardware testing show that the required power conditioning and power flow control can be obtained from the proposed multilevel multistage converter system. The entire control strategies are implemented in Xilinx Virtex 5 FPGA, inside National Instruments’ CompactRIO system using LabVIEW. A contour based dead-time harmonic analysis method for TLNPC and the possibilities of having various interconnection strategies of WEC-rectifier units to complement the power converter efforts for stabilizing the DC-link, are also presented. An advanced future AC2AC direct power converter system based on Modular multilevel converter (MMC) structure developed at Siemens AG is presented briefly to demonstrate the future trends in this area.

Cette thèse vise à élaborer de nouvelles stratégies de commande basées sur la commande prédictive pour le système de génération d’énergie éolienne. La topologie des systèmes de production éolienne basées sur le Générateur Asynchrone à Double Alimentation (GADA) qui convient à des plateformes de génération dans la gamme de puissance de 1.5 à 6 MW est abordée. Du point de vue technologique, le convertisseur à trois niveaux et clampé par le neutre (3L-NPC) est considéré comme une bonne solution pour une puissance élevée en raison de ses avantages: capacité à réduire la distorsion harmonique de la tension de sortie et du courant, et augmentation de la capacité du convertisseur grâce à une tension réduite appliquée à chaque semi-conducteur de puissance. Une description détaillée de la commande prédictive à ensemble de commande fini (FCS-MPC) avec un horizon de prédiction de deux pas est présentée pour deux boucles de régulation: celle liée au convertisseur connecté au réseau et celle du convertisseur connecté au GADA. Le principe de la commande repose sur l’utilisation d’un modèle de prédiction permettant de prédire le comportement du système pour chaque état de commutation du convertisseur. La minimisation d’une fonction de coût appropriée prédéfinie permet d’obtenir la commutation optimale à appliquer au convertisseur. La thèse étudie premièrement les problèmes liées à la compensation du temps de calcul de la commande et au choix et aux pondérations de la fonction de coût. Ensuite, le problème de stabilité de la commande FCS-MPC est abordé en considérant une fonction de Lyapunov dans la minimisation de la fonction de coût. Finalement, une étude sur la compensation des effets des temps morts du convertisseur est présentée<br>This thesis aims to elaborate new control strategies based on Model Predictive control for wind energy generation system. We addressed the topology of doubly fed induction generator (DFIG) based wind generation systems which is suitable for generation platform power in the range in 1.5-6 MW. Furthermore, from the technological point of view, the three-level neutral-point clamped (3L-NPC) inverter configuration is considered a good solution for high power due to its advantages: capability to reduce the harmonic distortion of the output voltage and current, and increase the capacity of the converter thanks to a decreased voltage applied to each power semiconductor.In this thesis, we presented a detailed description of finite control set model predictive control (FCS-MPC) with two step horizon for two control schemes: grid and DFIG connected 3L-NPC inverter. The principle of the proposed control scheme is to use system model to predict the behaviour of the system for every switching states of the inverter. Then, the optimal switching state that minimizes an appropriate predefined cost function is selected and applied directly to the inverter.The study of issues such as delay compensation, computational burden and selection of weighting factor are also addressed in this thesis. In addition, the stability problem of FCS-MPC is solved by considering the control Lyapunov function in the design procedure. The latter study is focused on the compensation of dead-time effect of power converter

This thesis focused on creating a model of a small hydropower plant model (SHPP) and a part of the electricity network in the simulation software "PSCAD" (basing on real sources). The model will be specified on the basis of the data obtained from the measurements to correspond with the real equipment.

Non-stoichiometric strontium iron oxide is described by an abbreviated formula SrFeOx (2.5 ≤ x ≤ 3.0) exhibits a variety of interesting physical and chemical properties over a broad range of temperatures and in different gaseous environments. The oxide contains a mixture of iron in the trivalent and the rare tetravalent state. The material at elevated temperature is a mixed oxygen conductor and it, or its derivatives,can have practical applications in oxygen conducting devices such as pressure driven oxygen generators, partial oxidation reactors in electrodes for solid oxide fuel cells (SOFC). ¶ This thesis examines the behaviour of the material at ambient and elevated temperatures using a broad spectrum of solid state experimental techniques such as: x-ray and neutron powder diffraction,thermogravimetric and calorimetric methods,scanning electron microscopy and Mossbauer spectroscopy. Changes in the oxide were induced using conventional thermal treatment in various atmospheres as well as mechanical energy (ball milling). The first experimental chapter examines the formation of the ferrite from a mixture of reactants.It describes the chemical reactions and phase transitions that lead to the formation of the oxide. Ball milling of the reactants prior to annealing was found to eliminate transient phases from the reaction route and to increase the kinetics of the reaction at lower temperatures. Examination of the thermodynamics of iron oxide (hematite) used for the reactions led to a new route of synthesis of the ferrite frommagnetite and strontium carbonate.This chapter also explores the possibility of synthesis of the material at room temperature using ball milling. ¶ The ferrite strongly interacts with the gas phase so its behaviour was studied under different pressures of oxygen and in carbon dioxide.The changes in ferrite composition have an equilibrium character and depend on temperature and oxygen concentration in the atmosphere. Variations of the oxygen content x were described as a function of temperature and oxygen partial pressure, the results were used to plot an equilibrium composition diagram. The heat of oxidation was also measured as a function of temperature and oxygen partial pressure. ¶ Interaction of the ferrite with carbon dioxide below a critical temperature causes decomposition of the material to strontium carbonate and SrFe12O19 . The critical temperature depends on the partial pressure of CO2 and above the critical temperature the carbonate and SrFe12O19 are converted back into the ferrite.The resulting SrFe12O19 is very resistant towards carbonation and the thermal carbonation reaction does not lead to a complete decomposition of SrFeOx to hematite and strontium carbonate. ¶ The thermally induced oxidation and carbonation reactions cease at room temperature due to sluggish kinetics however,they can be carried out at ambient temperature using ball milling.The reaction routes for these processes are different from the thermal routes.The mechanical oxidation induces two or more concurrent reactions which lead to samples containing two or more phases. The mechanical carbonation on the other hand produces an unknown metastable iron carbonate and leads a complete decomposition of the ferrite to strontiumcarbonate and hematite. ¶ Thermally and mechanically oxidized samples were studied using Mossbauer spectroscopy. The author proposes a new interpretation of the Sr4Fe4O11 (x=2.75) and Sr8Fe8O23 (x=2.875)spectra.The interpretation is based on the chemistry of the compounds and provides a simpler explanation of the observed absorption lines.The Mossbauer results froma range of compositions revealed the roomtemperature phase behaviour of the ferrite also examined using x-ray diffraction. ¶ The high-temperature crystal structure of the ferrite was examined using neutron powder diffraction.The measurements were done at temperatures up to 1273K in argon and air atmospheres.The former atmosphere protects Sr2Fe2O5 (x=2.5) against oxidation and the measurements in air allowed variation of the composition of the oxide in the range 2.56 ≤ x ≤ 2.81. Sr2Fe2O5 is an antiferromagnet and undergoes phase transitions to the paramagnetic state at 692K and from the orthorhombic to the cubic structure around 1140K.The oxidized formof the ferrite also undergoes a transition to the high-temperature cubic form.The author proposes a new structural model for the cubic phase based on a unit cell with the Fm3c symmetry. The new model allows a description of the high-temperature cubic form of the ferrite as a solid solution of the composition end members.The results were used to draw a phase diagramfor the SrFeOx system. ¶ The last chapter summarizes the findings and suggests directions for further research.

Modeling and understanding the doses around the neutron generator provides insightful data in regard to radiation safety and protection precautions. Published data can be used to predict doses, but realistic data for the Nuclear Engineering Teaching Laboratory’s Thermo MP 320 Neutron Generator helps health physicists more accurately predict dose rates and protect experimenters against exposure. The goal was to create a model inclusive of the entire setup and room where the neutron generator is housed. Monte Carlo N-Particle (MCNP) Code reigns as the preferred method for modeling radiation transport and was utilized to model the transport of neutrons within the current configuration of the 14 MeV neutron generator facility. This model took into account all shielding materials and their respective dimensions and locations within the concrete room. By utilizing tallies and tally modifiers, the model predicts dose rates that can be used with experimental factors such as irradiation time and flux to predict a dose in millirem. Validation experiments were performed in the current setup using Landauer Luxel®+ with Neutrak dosimeters placed in strategic locations to record the neutron dose vi received as well as a Ludlum Model 42-41 PRESCILA neutron probe to predict dose rates. The dosimeters and PRESCILA measurement locations matched the positions of the point detector tallies in MCNP. After laboratory analysis, a comparison was performed between the model output and the dosimeter and PRESCILA values to successfully validate the accuracy of the model.<br>text

<p>Excess sodium (Na) intake is directly related to hypertension and an increased risk of developing many chronic diseases, but there is currently no method to directly quantify Na retained in the body. Because of this, the locations of Na storage and its exchange mechanisms are not well known. This information is critical for understanding the impact of increased Na intake in modern diets. In order to non-invasively quantify Na in bone and soft tissue, a compact deuterium-deuterium (DD) neutron generator-based <i>in vivo</i> neutron activation analysis (IVNAA) system was developed. MCNP was used to design a custom irradiation assembly to maximize Na activation in hand bone while minimizing dose. In order to test the system, live pigs were used. Two 100% efficient high purity germanium (HPGe) detectors collected Na-24 counts over 24 hours post irradiation. From the pig studies, a two-compartment model of exchange was developed to quantify Na in bone and in soft tissue. The right legs of four live pigs, two on a low Na diet and two on a high Na diet, both for 14 days, were irradiated inside the customized irradiation cave for 10 minutes (45 mSv dose to the leg) and then measured with the HPGe detectors. The spectra were analyzed to obtain the net Na counts at different time points. Analysis shows exponential decrease of Na in the leg during the first one hour of measurement, while the change was minimal at the second hour, and the counts were stabilized at the second and third 2 hour measurements, taken 7 and 21 hours post irradiation. Bone Na and soft tissue Na concentrations were calculated using calibration lines created with bone and soft tissue equivalent Na phantoms as well as the parameters obtained from the two-compartment model. The results show that the difference in bone and soft tissue Na between the pigs on high vs low Na diets was significant. With these results, we conclude that DD neutron generator-based IVNAA can be used to accurately quantify Na in bone and soft tissue <i>in vivo </i>and the system is a potential valuable tool for nutrition studies.</p>

The use of fission product yield data is pervasive among nuclear calculations, particularly in the realm of nuclear forensics and active interrogation for special nuclear material. The capital source of fission product yield data is the work of T.R. England and B.F. Rider, of Los Alamos National Laboratory, in the early 1990s. Though their work was certainly substantial, a great deal of data was generated computationally, in lieu of done empirically—particularly with low-yield, short-lived progeny. Due to this, relative uncertainties in the measurements can be as high as 64%, and vary wildly from database to database (oft times not even within one standard deviation of one another). The purpose of this work is to build a pneumatic system capable of cyclic irradiation coupled to a D-T neutron source, in order to cumulate proper counting statistics, by which one can backcalculate independent and cumulative fission yields. Beyond the design and control parameters of the pneumatic system, a precise flux characterization of the facility is presented, and finally, proof-of-concept is demonstrated by causing 14 MeV neutron-induced fission and identifying every observed fission product photopeak.<br>text