Axial offset anomaly (AOA) in pressurized water reactors (PWR) refers to deviation of the measured neutron flux in the top half of the core from the predicted values. Among other difficulties, AOA reduces the shutdown margin, and may force the plant to reduce power output. AOA is believed to be caused by three related phenomena occurring in the core while operating at full power: sub-cooled nucleate boiling concentrated mainly in the upper half of the core, corrosion product deposition on the cladding surface (crud), and the deposition of boron within the porous crud layer in regions of vigorous sub-cooled boiling. This study replicates the conditions within the PWR primary coolant; specifically, the temperature, pressure, peak surface heat flux, coolant velocity and water chemistry are simulated in order to produce prototypical crud on an electrically heated Zircaloy-4 test element. At the conclusion of each test run, the heated Zircaloy-4 test element is rapidly isolated from the coolant in order to trap any soluble boron species that may be present in the crud layer. The results of this investigation indicate that prototypical crud with significant boron deposition can be produced. The deposited boron compound has been determined to be lithium tetraborate (Li2B4O7). Comparative experiments have been run to determine the effect of coolant pH, concentration and type of additives, and duration of exposure on the thickness of the crud deposit. The data obtained in this investigation can be used to validate mechanistic models for crud deposition and AOA in pressurized water reactors.

Size and Shape Controlled Synthesis and Superparamagnetic Properties of Spinel Ferrites Nanocrystals Qing Song 216 pages Directed by Dr. Z. John Zhang The correlationship between magnetic properties and magnetic couplings is established through the investigations of various cubic spinel ferrite nanocrystals. The results of this thesis contribute to the knowledge of size and shape controlled synthesis of various spinel ferrites and core shell architectured nanocrystals as well as the nanomagnetism in spinel ferrites by systematically investigating the effects of spin orbital coupling, magnetocrystalline anisotropy, exchange coupling, shape and surface anisotropy upon superparamagnetic properties of spinel ferrite nanocrystals. A general synthetic method is developed for size and shape control of metal oxide nanocrystals. The size and shape dependent superparamagnetic properties are discussed. The relationship between spin orbital coupling and magnetocrystalline anisotropy is studied comparatively on variable sizes of spherical CoFe2O4 and Fe3O4 nanocrystals. It also addresses the effect of exchange coupling between magnetic hard phase and soft phase upon magnetic properties in core shell structured spinel ferrite nanocrystals. The role of anisotropic shapes of nanocrystals upon self assembled orientation ordered superstructures are investigated. The effect of thermal stability of molecular precursors upon size controlled synthesis of MnFe2O4 nanocrystals and the size dependent superparamagnetic properties are described.

Luminescence measurements have been applied to three different structures namely, sulphate, fluorides and YAG. In all cases the RE doping suppresses the intrinsic emission and results in intense luminescence characteristic of the RE dopant. Additionally, in double doped samples, or contaminated ones, the TL data show that each dopant defines a glow peak, which is displaced in temperature relative to the others. Examples of this were discussed for CaS04:Ce,Mn; YAG:Nd,Tb,Cr,Mn; BaF2:Ho,Ce and BaF2:Tm,Ce. The data are discussed in terms of an energy transfer model between different parts of extended defect complexes which encompass the RE ion and the lattice defects. Calcium sulphate doped with Dy define a TL peak near 200°C suitable for radiation measurements, but when co-doped with Ag the TL peak move to higher temperatures with minor effects on the peak sensitivity. In Ce,Mn double doped samples, the peak temperatures differ by -7°C between the Ce and Mn sites. The TL glow curves from alkaline earth fluorides are complex and contain several overlapping peaks. Curve fitting show that the peak maxima below room temperature are insensitive to the RE dopant. Additionally the host material has a modest effect on the peak positions. Above room temperature each dopant provides a TL curve specific to the added RE ion and do not show common peaks. Concentration has many effects on the resultant glow curve, and even at the lowest concentration used here (0.01%) there is evidence of cluster formation. Samples with high RE content show low values of the frequency factor consistent with the energy transfer model in that the emission from RE-RE cluster dominates over the emission from direct charge recombination within the defect complex. The effect of concentration and the TL mechanism operating below room temperature are also discussed. Luminescence signals from the near surface of YAG:Nd (via CL) were contrasted with those from the bulk material via RL. Results indicate that the outer few micron layers differ significantly in luminescence response from the bulk crystal. The differences were ascribed to result from solvents that enter the YAG lattice during the growth stage or subsequently from cleaning treatments via the dislocations caused by cutting and polishing. Additionally, the growth stage may include gases from the residual air in the growth furnace trapped into the YAG lattice. In each case there is a discontinuity in luminescence intensity and/or emission wavelengths at temperatures which mach the phase transitions of the contaminants. At the transition temperature there will be a sudden pressure change and this will induce surface expansion or bulk compression. The differences between the two cases were detected by the alternatives of CL and RL excitation, where the Nd or Er lines have moved in opposite directions. The detection of such low concentrations of solvents/trapped gases by luminescence is extremely difficult due to experimental limitations. Hence their role in luminescence generation is normally ignored.

Low temperature cleavage fracture behaviour was investigated using four experimental microalloyed bainitic plate steels. The four plate samples were produced by different thermomechanical processing (TMP) schedules and had yield strengths in the range 540 - 670 MPa. Microstructures were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron back scattered diffraction (EBSD). Quantitative data was obtained for prior austenite grain (PAG) size, volume fractions of two bainite types (conventional bainite and acicular ferrite) and EBSD 15° domain size. Charpy impact tests (using two notch orientations) were carried out over a range of temperatures. Cleavage facet sizes were measured on -196°C Charpy samples. The range of TMP schedules produced variations in PAG width, type of bainite and 15° domain size. The effects of these three microstructural features on cleavage crack propagation are discussed. Results indicate that the microstructures are controlled by i) deformation below TNR and ii) accelerated cooling rate. Domain structure reflects TMP. There is no clear correlation between domain size and cleavage facet size. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-07-30 19:17:01.25

Ces travaux de thèse s'inscrivent au sein d'une démarche multi-échelles visant à améliorer lacompréhension de la fragilisation par l'irradiation de l'acier de cuve. Dans ce cadre, nous nousintéressons à la description de la mobilité des dislocations dans la ferrite, l'une des entrées clépour les codes de dynamique de dislocations (DD). Nous présentons ainsi une revuebibliographique exhaustive des différentes théories et expressions de la mobilité, à partir delaquelle nous proposons une nouvelle expression pour les dislocations vis. Cette loi, utilisablepour la première fois dans le régime de transition ductile-fragile, permet de reproduire lesprincipales observations expérimentales disponibles à ce niveau. Finalement, nous montronsles améliorations apportées au code de DD Tridis BCC 2.0, qui intègrent la nouvelle loi demobilité avec une nouvelle gestion des segments de dislocation permettant de stabiliser etaccélérer des simulations complexes avec prise en compte du glissement dévié.

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Ce travail de thèse concerne la miniaturisation et l'intégration de composants magnétiques comme les inductances utilisées dans les convertisseurs DC-DC et les circuits haute fréquence. Cette thèse a pour objectifs : - de développer une méthodologie d'étude des inductances à couches magnétiques - de montrer la faisabilité de tels composants utilisant des couches épaisses de ferrite (50 à 500µm). Le contenu de notre document s'articule ainsi autour de trois axes : la simulation, la réalisation et la caractérisation. En simulation, le logiciel HFSS, nous a permis de concevoir, de prédire le comportement du composant et d'étudier l'influence des différents entrefers et épaisseurs du matériau magnétique. La réalisation fait appel aux différentes et nombreuses étapes micro technologiques qui sont décrites en détail. Ces étapes concernent les techniques de dépôt sous vide, les procédés de photolithographie, les techniques de dépôt électrolytique, les techniques de sciage et de collage. Enfin, la caractérisation des inductances réalisées a été effectuée en basses, moyennes et hautes fréquences respectivement au LCR mètre (20Hz à 1MHz), à l'impédance mètre (40Hz à 110MHz) et à l'analyseur vectoriel de réseaux (10MHz à 67GHz)

After nearly a decade of development, human-implantable sensors for detection of muscle activity have recently been demonstrated in the literature. The implantable sensors are powered and communicate wirelessly through the skin using coupled inductor coils. The focus of the present work has been the development of a new approach to modeling the inductively coupled link by using the finite element method (FEM) to simulate a three-dimensional representation of the coils and surrounding magnetic field. The validity of the simulation is tested by comparison to analytically-developed formulas for self-inductance, ac resistance and mutual inductance of the coils. Determination of these parameters is necessary for calculation of the coupling coefficient between the coils, and to fully define the lumped circuit model of the link. This 3D FEM approach is novel and attractive because it is able to encompass physical geometric parameters and material properties that have been traditionally been a challenge to determine. In particular the contribution of a ferrite-core, and the case of non-symmetrical relative coil positioning can be evaluated. / Graduate

Bismuth ferrite (BFO) is a multiferroic material with cross-correlation between magnetic and electric orders. With no applied external fields the spin structure of BFO is anitferromagnetic and cycloidal. This ordering prevents the detection of the weak ferromagnetism known to exist in the material. The application of magnetic and electric fields of suitable strength and direction is capable of compelling the Fe3+ spins to align in a homogeneous, antiferromagnetic fashion. This report details how numerical methods were used to simulate the spin alignment of a BFO system under different fields. The results were compiled into electric field-magnetic field phase diagrams of BFO to show the divide between cycloidal and homogeneous systems. / Graduate / 0607 / 0611 / marca@uvic.ca

Thesis (Ph.D.); Submitted to Iowa State Univ., Ames, IA (US); 19 Dec 2004. / Published through the Information Bridge: DOE Scientific and Technical Information. "IS-T 2322" Yoon-Jun Kim. US Department of Energy 12/19/2004. Report is also available in paper and microfiche from NTIS.