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Inconel alloys are commonly used as structural materials in nuclear reactors. One of these alloys, the Inconel X-750, is a γ’ Ni3(Al, Ti) strengthened superalloy extensively used in the cores of reactors, such as spacers in CANada Deuterium Uranium (CANDU) fuel channels. Prior to their application in commercial reactors, accelerated irradiation tests had been conducted in liquid metal fast reactors. Results did not indicate any problem stemming from significant fast neutron irradiation. However, recently it has been found that the ex-service CANDU Inconel X-750 spacers became severely brittle after a lengthy exposure to reactor environment. The underlying mechanism remains unclear and thus forms the focus of this current investigation, predominantly through transmission electron microscopy (TEM). This dissertation unfolds with the literature review in Chapter 2, followed by presentation of novel techniques in Chapter 3 on the preparation of TEM samples from small reactor components, namely the spacers. Chapter 4 presents TEM characterizations of ex-service spacers removed from the reactors. To simulate neutron irradiation over wide temperature range in an effort to understand the damage mechanisms, heavy ion irradiations were conducted and reported in Chapter 5 and 6. Irradiations are found to significantly alter the stability of the primary strengthening phase γ’, a systematic experimental study of which is presented in Chapter 7. To fully understand the effects of transmutation produced helium on irradiation induced cavity and dislocation microstructures, TEM in-situ heavy ion irradiations with hot/cold pre-injected helium were conducted and reported in Chapter 8 and 9. Helium was found to play an important role in the irradiation-induced instability of γ’ in nickel-based superalloys, the discussion of which is presented in Chapter 10. As one of the most important defect structures induced from irradiation, the stacking-fault-tetrahedra, were dynamically observed and are described in a journal manuscript in Appendix A. In addition to broadening current understanding of material degradation mechanism for in-service CANDU spacer, this study also provides comprehensive information on irradiation damage in nickel based superalloys, irradiation induced lattice defects and phase instability in face centered cubic alloys, as well as helium’s effects on cavity formation, dislocation evolution, and phase transformation. / Thesis (Ph.D, Mechanical and Materials Engineering) -- Queen's University, 2013-09-06 15:21:02.334

Despite decades of theoretical and experimental investigation, the fundamental interactions between nucleons remains poorly understood. While the strong interaction is responsible for binding quarks into nucleons, and nucleons into nuclei, there is no consistent description of these processes. At the low energies where nucleon binding occurs, the interactions are in principle calculable from quantum chromodynamics, but the required non-perturbative calculations are not possible. Instead, different models have been created to describe different phenomena. These models require experimental input to constrain them. As the expected weak interaction effects are not seen in the strangeness-conserving systems as have been seen in other systems, it is believed that the strong interaction interferes with the weak interaction. Therefore by measuring parity-violating observables that occur due to the weak interaction, information can be gained about the strong interaction. The NPDGamma and n3He experiments are two complementary experiments that measured a parity violating observables in a few nucleon system. They ran on the Fundamental Neutron Physics Beamline at the Spallation Neutron Source. The NPDGamma experiment measured the parity violating directional asymmetry in the gamma ray's emission direction after polarized cold neutron capture on a liquid parahydrogen target using an array of 48 CsI detectors. The n3He experiment measured the parity violating directional asymmetry in the proton emission direction after polarized cold neutron capture on a gaseous $^{3}$He target. The capture occurs inside an ionization chamber that measures the proton emission direction. Both experiments have completed data taking with data analysis in an advanced state. These experiments should be able to be used with a number of already existing experimental results to constrain the models. I designed and assembled a pair of $^{3}$He ionization chambers that were used as beam monitors during the experiments. Using the lessons learned from the beam monitors, I then designed and assembled the ionization chamber that is the combined target and detector for the n3He experiment. The monitors and target chamber were examined to determine their charge collection properties and linearity after installation. One of the monitors was calibrated to determine the neutron flux from the output current. / February 2017

Recently, attention has been drawn to the viability of using S-CO(2) as a working fluid in modern reactor designs. Near the critical point, CO2 has a rapid rise in density allowing a significant reduction in the compressor work of a closed Brayton Cycle. Therefore, 45% efficiency can be achieved at much more moderate temperatures than is optimal for the helium Brayton cycles. An additional benefit of the S-CO2 system is its universal applicability as an indirect secondary Power Conversion System (PCS) coupled to most GEN-IV concept reactors, as well as fusion reactors. The United States DOE's GNEP is now focusing on the liquid Na cooled primary as an alternative to conventional Rankine steam cycles. This primary would also benefit from being coupled to an S-CO2 PCS. Despite current progress on designing the S-CO2 PCS, little work has focused on the principal supporting systems required. Many of the required auxiliary systems are similar to those used in other nuclear or fossil-fired units; others have specialized requirements when CO2 is used as the working fluid, and are therefore given attention in this thesis. Auxiliary systems analyzed within this thesis are restricted to those specific to using CO2 as the working fluid. Particular systems discussed include Coolant Make-up and Storage, Coolant Purification, and Coolant Leak Detection. / Contract number: N62271-97-G-0026. / US Navy (USN) author

The Belle II detector is designed to collect data from the high luminosity electron-positron (e$^+$e$^-$) collisions of the SuperKEKB collider. It will explore the flavour sector of particle physics through precision measurements. The backgrounds of particles induced by the electron and positron beams will be much higher than in any previous \epem collider. It is important that these backgrounds be well understood in order to ensure appropriate measures are taken to protect the Belle II detector and minimize the impact of the backgrounds. In February 2016 electron and positron beams were circulated through the two 3 km vacuum pipe rings without being brought into collision during `Phase I' of SuperKEKB commissioning. Beam backgrounds were measured using Belle II's commissioning detector, BEAST II. BEAST II is composed of several small subdetectors, including helium-3 thermal neutron detectors. The BEAST II thermal neutron detector system and results from its Phase I running are presented in this dissertation. The Phase I experiment studies beam-gas interactions, where beam particles collide with residual gas atoms in the beampipes, and beam-beam interactions, where beam particles interact with each other. Simulations of these two types of backgrounds were performed using the Strategic Accelerator Design (SAD) and GEometry And Tracking (GEANT4) software packages. A method to account for the composition of the gas in the beampipes was developed in order to correctly analyse the beam-gas component of the background. It was also determined that the thermal neutron rates in the data on the positron beam were 2.18$^{+0.44}_{-0.42}$ times higher than the simulation of beam-gas interactions and 2.15$^{+0.34}_{-0.33}$ times higher for beam-beam interactions. The data on the electron beam were 1.32$^{+0.56}_{-0.36}$ times higher for beam-gas interactions and 1.91$^{+0.54}_{-0.48}$ time higher for beam-beam interactions. The impact of these studies on Belle II is discussed. / Graduate / samdejong86@gmail.com

Le palladium est couramment utilisé pour le stockage du tritium, isotope radioactif de l’hydrogène, car il forme un tritiure réversible, à basse pression d’équilibre. La décroissance du tritium en hélium-3 provoque un vieillissement du tritiure, caractérisé notamment par l’apparition de bulles d’hélium-3, qui est étudié ici. De précédents travaux de modélisation du vieillissement avaient abouti à la création de deux modèles traitant, d’une part, de la germination des bulles d’hélium-3 (utilisation d’un automate cellulaire) et, d’autre part, de la croissance des bulles (mécanique des milieux continus). Ces modèles étaient fonctionnels, mais leur utilisation était limitée par le manque de données expérimentales d’entrée et de recalage. Ce travail de thèse a donc consisté à acquérir les données expérimentales les plus pertinentes pour améliorer la modélisation du vieillissement du tritiure de palladium. La première partie de ce travail a consisté à estimer les propriétés mécaniques du tritiure de palladium (limite d’élasticité, contrainte maximale, loi de comportement…), déduites de celles de l’hydrure et du deutérure de palladium, mesurées à l’aide d’essais de traction in situ. En seconde partie, la caractérisation du vieillissement a été entreprise, focalisée sur des observations de bulles dans le tritiure de palladium par microscopie électronique en transmission, des mesures de pression à l’intérieur des bulles par résonance magnétique nucléaire et des mesures de gonflement macroscopique du matériau par pycnométrie. Ces travaux ont conduit à des avancées significatives quant à la compréhension du vieillissement et ont permis d’améliorer considérablement sa modélisation. / Palladium is commonly used for the storage of tritium (the hydrogen radioactive isotope), since it forms a low-equilibrium-pressure and reversible tritide. Tritium decay into helium-3 is responsible for the ageing of the tritide, leading to the apparition of helium-3 bubbles for instance. Both experimental and theoretical aspects of this phenomenon are studied here.Previous works on ageing modelling led to two main models, dealing with:- Helium-3 bubbles nucleation (using a cellular automaton),- Bubbles growth (using continuum mechanics).These models were quite efficient, but their use was limited by the lack of input data and fitting experimental parameters.To get through these limitations, this work has consisted in studying the most relevant experimental data to improve the modelling of the palladium tritide ageing.The first part of this work was focused on the assessment of the mechanical properties of the palladium tritide (yield strength, ultimate strength, mechanical behaviour…). They were deduced from the in situ tensile tests performed on palladium hydride and deuteride.In the second part, ageing characterization was undertaken, mainly focusing on:- Bubbles observations in palladium tritide using transmission electron microscopy,- Internal bubble pressure measurements using nuclear magnetic resonance,- Macroscopic swelling measurements using pycnometry.The present work has led to significant progress in ageing understanding and has brought very valuable improvements to the modelling of such a phenomenon.

En plongée, lors d’une décompression, une partie des gaz dissous dans l’organisme est éliminée sous formede bulles qui peuvent être à l’origine d’accidents parfois sévères. Des modèles mathématiques permettentde déterminer des procédures de décompression par paliers fiables mais ne s’appliquent que pour certainesconfigurations de plongée (profondeur, durée, gaz respirés). Une extrapolation de ces modèles à denouveaux types d’exposition comme la plongée profonde aux mélanges est actuellement hasardeuse. Onsuppose ici qu’une modélisation biophysique des mécanismes de la décompression doit apporter dessolutions préventives plus sures, même pour des expositions moins explorées combinant azote et hélium.Deux modèles ont été élaborés pour la prévention des accidents articulaires et neurologiques, formesd’accident les plus fréquentes. Ils ont été corrélés à partir de bases de données et d’analyses de risqueexistantes. Tous deux permettent de représenter l’apparition de symptômes tardifs. Pour l’accidentarticulaire, on montre 1/ l’impact de la diffusion intra-tissulaire (entre un tendon et son voisinage) de gazinerte sur la dynamique d’amplification de la phase gazeuse générée 2/ une augmentation quantifiable durisque d’accident avec le volume de gaz généré 3/ une faible efficacité des paliers 4/ une efficacité modéréede la respiration d’oxygène pur aux paliers proches de la surface. Pour les accidents neurologiques, lemodèle global proposé permet d’estimer le volume instantané des microbulles formées dans les tissus(muscles et graisses) et transférées (via le système lymphatique par ex) dans le sang veineux de retour. Lasurcharge du filtre pulmonaire par les bulles est supposée être un événement précurseur dans la genèse del’accident. La méthode de corrélation du modèle, originale, utilise notamment des campagnes d’écoutes debulles circulantes par système Doppler après plongées, dont une dédiée à cette thèse. Il ressort de cesinvestigations que I/ le risque d’accident peut être relié au volume des bulles transféré dans le sang sur unepériode donnée II/ l’introduction de paliers profonds ne diminue pas le risque III/ la respiration d’oxygènepur aux paliers est très efficace pour réduire ce risque. Un deuxième modèle neurologique dédié à laprévention des accidents médullaires se produisant rapidement après la décompression et à la déterminationdes premiers paliers requis est aussi proposé. L’ensemble de ces trois modélisations offre des perspectivesde prévention intéressantes. / During a scuba diving decompression, a part of the gas that is dissolved in the body is eliminated throughbubbles that can generate potentially severe forms of decompression sickness (DCS). Known mathematicalmodels allow the determination of safe decompression procedures by stages but can only be applied for alimited range of diving configurations (pressure, duration, breathing gas). An extrapolation of these modelsto new expositions such as deep/short dives using mixtures is currently hazardous. In the presented work itis deemed that a biophysical modeling of the decompression mechanisms can produce safer preventivesolutions even for less explored expositions combining nitrogen and helium. Two models have beendeveloped for the prevention of articular and neurological DCS, which are the most frequent forms ofinjury. Existing database and risk analyses have been used to correlate the models. Both predict potentialdelays for the occurrence of DCS symptoms after a decompression. For the articular model it is shown that1/ the intratissular diffusion of inert gases between a target tendon and its neighborhood impacts theamplification dynamics of the generated gas phase 2/ the more the generated gas volume, the bigger theDCS risk 3/ stages of short and moderate durations have a low efficiency 4/ the efficiency of pure oxygenbreathing in order to reduce the risk during the shallow stages is moderated. For neurological DCS, theproposed global model allows estimation of the instantaneous volume of microbubbles that are formed intissues (muscles and adipose tissues) and that are transferred via the lymphatic system for instance in thevenous blood. The overload of the pulmonary filter by bubbles is assumed to be a primary event in the DCSpathogenesis. The original model correlation method uses in particular the recording of circulating bubblessignals through Doppler detections campaigns. One of these campaigns is dedicated to the presented thesiswork. The analysis leads to the following conclusions: I/ the DCS risk is linked to the total bubbles volumethat is transferred into the blood over a given period II/ the introduction of deep stages does not decreasethe risk III/ the breathing of pure oxygen during the shallow stages is very efficient in reducing this risk. Asecond neurological model is proposed: it is dedicated to the prevention of spinal cord DCS forms whichoccur early after the decompression and to the determination of the first required stops. The threedeveloped models give interesting prevention perspectives.

Cette thèse s'intéresse au comportement de l'hélium dans le verre nucléaire de type R7T7. Pour cela, quatre types de matériaux ont été utilisés dans ce travail, à savoir des verres R7T7 inactifs infusés par de l'hélium sous pression, des verres implantés par des ions 3He+, des verres dopés au curium et des verres irradiés en réacteur. L'étude de la solubilité de l'hélium par infusion dans le verre R7T7 a permis de monter que l'hélium s'insère dans le volume libre du verre et indique une valeur d'environ 1016 at. cm-3 atm.-1. La limite d'incorporation de l'hélium dans ce type de verre a été aussi déterminée ; sa valeur s'élève à environ 2×1021 at.-He cm-3.Les études de diffusion ont montré que la migration de l'hélium est contrôlée par la seule population d'hélium dissoute dans le volume libre du verre. Les données de relâchement qui ont pu être traitées par un modèle de diffusion classique, indiquent des coefficients de diffusion obéissant à la loi d'Arrhenius suivante : D = D0 exp(-Ea/kBT), avec D0 = 0,022 et 5,4×10-3 cm2 s-1 et Ea = 0,61 eV pour les verres infusés et dopés respectivement. Ces résultats traduisent un mécanisme de diffusion thermiquement activé qui n'est pas être influencé par l'endommagement du verre ni par les fortes teneurs en hélium étudiées (jusqu'à 8×1019 at. g-1).Les caractérisations des propriétés macroscopiques, structurales et microstructurales des verres irradiés en réacteur n'ont pas révélé d'impact lié à la présence d'hélium à fortes teneurs. Les modifications observées, à savoir un gonflement de 0,7%, une baisse de la dureté de 38%, une augmentation entre 8 et 34% de la ténacité et une satbilisation de la structure sous irradiation, ont été attribuées à l'endommagement balistique du verre induit par l'irradiation en réacteur. Les caractérisations microstructurales au MEB des verres implantés à fortes teneurs, dopés au curium et irradiés en réacteur ont montré une microstructure homogène exempte de bulles, de pores ou bien de fissuration.Les résultats de ce travail ont été utilisés pour développer un modèle prédictif de comportement à long terme de l'hélium dans un colis réel de verre R7T7. Le modèle considère l'historique thermique du colis, sa fracturation et son activité alpha. / The present thesis focuses on the study of helium behavior in R7T7 nuclear waste glass. Therefore, four types of materials were used in this work. These are non radioactive R7T7 glasses saturated with helium under pressure, glasses implanted with 3He+ ions, glasses doped with curium and glasses irradiated in nuclear reactor.The study of helium solubility in saturated R7T7 glass has shown that helium atoms are inserted in the glass free volume. The results yielded a solubility of about 1016 at. cm-3 atm.-1. The incorporation limit of helium in this type of glass has been determined ; its value amounted to about 2×1021 at. cm-3.Diffusion studies have shown that the helium migration is controlled by the single population dissolved in the glass free volume. An ideal diffusion model was used to simulate the helium release data. The determined diffusion coefficients fall into the following Arrhenius law : D = D0 exp(-Ea/kBT), where D0 = 0,022 and 5,4×10-3 cm2 s-1 and Ea = 0,61 eV for the helium saturated glass and the doped one respectively. Theses results reflect a thermally activated diffusion mechanism which is not influenced by the glass radiation damage and the studied helium concentrations (up to 8×1019 at. g-1).Characterizations of the macroscopic, structural and microstructural of glasses irradiated glasses did not reveal any impact associated with the presence of helium at high concentrations. The observed modifications i.e. a swelling of 0,7%, a decrease in hardness by 38%, an increase between 8 and 34%of the fracture toughness and a satbilization of the glass structure under irradiarion were attributed to the glass nuclear damage induced by the irradiation in reactor. Characterizations by SEM of R7T7 glasses implanted with helium at high concentrations, doped with curium and irradiated in nuclear reactor showed a homogeneous microstructure free of helium bubbles, pores or cracking.The results of the present work were used to develop a long term diffusion model of helium in an industrial R7T7 nuclear waste glass. The model considers the glass thermal history, its fracturing and its alpha activity.

Parmi les réacteurs de génération IV, le GFR et le VHTR utilisent l'hélium comme caloporteur. Il est nécessaire de contrôler sa qualité chimique. Outre des impuretés radiochimiques et particulaires, il peut contenir H2, CO, CH4, CO2, H2O, O2 et des composés azotés, et doit être purifié en permanence. Au CEA, un pilote permet d'étudier cette purification, réalisée en trois étapes: oxydation de H2 et CO sur CuO, puis deux étapes d'adsorption. L’objectif est de fournir une analyse détaillée des deux premières étapes, en les mettant en œuvre à l'échelle du laboratoire. On montre à l’aide d’une première modélisation que la consommation du lit de CuO est totale, et en régime chimique. Les particules de CuO sont constituées de grains d'environ 200 nm de diamètre. Un deuxième modèle, défini à l'échelle de ces grains, permet de trouver des résultats en accord avec les précédents. Un facteur d'échelle lié à la géométrie entre les constantes cinétiques issues des deux types de modélisation a été mis en évidence. Une compétition entre les réactions d'oxydation du CO et de H2 a été observée. Les énergies d'activation des ces réactions sont de l'ordre de 30 kJ.mol-1. La réaction CO/CuO est favorisée. La simulation numérique du déroulement simultané des deux réactions montre qu'il faut envisager une adsorption préférentielle de CO sur le CuO. Dans le cas de l'étape d'adsorption sur tamis moléculaire de CO2 et H2O, une méthodologie similaire a été mise en œuvre. Les isothermes expérimentales obtenues sont de type Langmuir. Les courbes de percée en sortie d'adsorbeur ont montré que le comportement global du lit était correctement représenté par le modèle retenu / In GEN IV studies on future fission nuclear reactors, two concepts using helium as a coolant have been selected: GFR and VHTR. Among radioactive impurities and dusts, helium can contain H2, CO, CH4, CO2, H2O, O2, as well as nitrogenous species. To optimize the reactor functioning and lifespan, it is necessary to control the coolant chemical composition using a dedicated purification system. A pilot designed at the CEA allows studying this purification system. Its design includes three unit operations: H2 and CO oxidation on CuO, then two adsorption steps. This study aims at providing a detailed analysis of the first and second purification steps, which have both been widely studied experimentally at laboratory scale. A first modelling based on a macroscopic approach was developed to represent the behaviour of the reactor and has shown that the CuO fixed bed conversion is dependent on the chemistry (mass transfer is not an issue) and is complete. The results of the structural analysis of the solids allow considering the CuO as particles made of 200 nm diameter grains. Hence, a new model at grain scale is proposed. It is highlighted that the kinetic constants from these two models are related with a scale factor which depends on geometry. A competition between carbon monoxide and hydrogen oxidation has been shown. Activation energies are around 30 kJ.mol-1. Simulation of the simultaneous oxidations leads to consider CO preferential adsorption. A similar methodology has been applied for CO2 and H2O adsorption. The experimental isotherms showed a Langmuir type adsorption. Using this model, experimental and theoretical results agree