Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt. The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.

Advancements in material science and manufacturing techniques are enabling the use of lightweight metal alloys and polymer composites in several combinations and shapes for producing more efficient and lightweight structures for automotive applications without compromising strength, stiffness and/or durability. When evaluating the strength of the structure, the joints are of importance. For multi-material structures adhesives are often the best type of joints. However, traditional finite element methods using stress criteria cannot accurately predict the failure of these adhesive joints under static loading. In this thesis work a strength and fatigue model, formulated using energy release rate theory, is implemented in a post processing tool. Given a finite element model of an adhesive joint and a list of boundary elements and nodes this tool calculates the energy release rates in mode I and mode II, and if the fracture toughness of the adhesive is known, a prescribed mixed-mode failure index is calculated. To evaluate its predictions joint strength results are correlated to experiments. Specimens with combined shear and normal load forms the underlying experimental setup with change in strain rate and adhesive thickness as varying parameters. Methods for implementing the model for a car body structure with multiple adhesive joints is investigated, the tool proves to be scalable, however, the required finite element setup at the adhesive boundaries may not be present in a car body model and thus further work needs to carried out to accommodate irregularities like non-matching mesh in the car body finite element model. This model may be used for assessing the strength and durability of a car body structure comprising different materials joined together using adhesives.

Ziel des BMWi-Fördervorhabens 1501393 ist es, durch den Einsatz von Untersuchungsmethoden auf der nm-Skala einen Beitrag zur Aufklärung von Flusseffekten und von Late-Blooming-Effekten in bestrahlten RDB-Stählen zu leisten. Zur Untersuchung dieser Effekte wurde auf RDB-Stähle deutscher Reaktoren aus zwei bei der AREVA GmbH abgeschlossenen Vorhaben zurückgegriffen. Die Auswahl der Grundwerkstoffe und Schweißgüter erfolgte so, dass sich optimale Voraussetzungen für das Erreichen des Gesamtziels des Vorhabens ergeben. Die ausgewählten Untersuchungsmethoden umfassen mit der Neutronenkleinwinkelstreuung, der Atomsondentomographie und der Positronen-annihilationsspektroskopie solche Techniken, die die nm-skaligen bestrahlungsinduzierten Defekt-Fremdatom-Cluster bestmöglich und in komplementärer Weise zu detektieren und zu charakterisieren gestatten. Es wurde ein Flusseffekt auf die Größe der bestrahlungsinduzierten Fremdatomcluster, jedoch nicht auf den Volumenanteil und die mechanischen Eigenschaften gefunden. In einem Cu-armen RDB-Schweißgut wurde ein Late-Blooming-Effekt nachgewiesen, der sich in einem steilen Anstieg des Clustervolumenanteils und der Übergangstemperaturverschiebung nach einer Phase schwacher oder fehlender Zunahme niederschlägt. The BMWi project 1501393 aimed at contributing to the clarification of flux effects and late blooming effects in irradiated RPV steels by means of experimental techniques of sensitivity at the nm scale. The investigation of these effects was focussed on RPV steels, both base metal and weld of German reactors selected according to the objectives of the present project from two previous projects performed at AREVA GmbH. The complementary techniques of small-angle neutron scattering, atom probe tomography and positron annihilation spectroscopy were applied to detect and characterize the irradiation-induced nm-scale defect-solute clusters. A flux effect on the size of the irradiation-induced clusters but no flux effect on both cluster volume fraction and mechanical properties was found. For a low-Cu RPV weld, a late blooming effect was observed, which results in a steep slope of both cluster volume fraction and transition temperature shift after an initial stage of small or no change.

Convection in a layer of fluid with a free surface due to a combination of thermocapillary stresses and buoyancy is a classic problem of fluid mechanics. It has attracted increasing attentions recently due to its relevance for two-phase cooling. Many of the modern thermal management technologies exploit the large latent heats associated with phase change at the interface of volatile liquids, allowing compact devices to handle very high heat fluxes. To enhance phase change, such cooling devices usually employ a sealed cavity from which almost all noncondensable gases, such as air, have been evacuated. Heating one end of the cavity, and cooling the other, establishes a horizontal temperature gradient that drives the flow of the coolant. Although such flows have been studied extensively at atmospheric conditions, our fundamental understanding of the heat and mass transport for volatile fluids at reduced pressures remains limited. A comprehensive and quantitative numerical model of two-phase buoyancy-thermocapillary convection of confined volatile fluids subject to a horizontal temperature gradient has been developed, implemented, and validated against experiments as a part of this thesis research. Unlike previous simplified models used in the field, this new model incorporates a complete description of the momentum, mass, and heat transport in both the liquid and the gas phase, as well as phase change across the entire liquid-gas interface. Numerical simulations were used to improve our fundamental understanding of the importance of various physical effects (buoyancy, thermocapillary stresses, wetting properties of the liquid, etc.) on confined two-phase flows. In particular, the effect of noncondensables (air) was investigated by varying their average concentration from that corresponding to ambient conditions to zero, in which case the gas phase becomes a pure vapor. It was found that the composition of the gas phase has a crucial impact on heat and mass transport as well as on the flow stability. A simplified theoretical description of the flow and its stability was developed and used to explain many features of the numerical solutions and experimental observations that were not well understood previously. In particular, an analytical solution for the base return flow in the liquid layer was extended to the gas phase, justifying the previous ad-hoc assumption of the linear interfacial temperature profile. Linear stability analysis of this two-layer solution was also performed. It was found that as the concentration of noncondensables decreases, the instability responsible for the emergence of a convective pattern is delayed, which is mainly due to the enhancement of phase change. Finally, a simplified transport model was developed for heat pipes with wicks or microchannels that gives a closed-form analytical prediction for the heat transfer coefficient and the optimal size of the pores of the wick (or the width of the microchannels).

This work scrutinises, evaluates and systematises the modern exchange rate theories. Its aim is to familiarise the reader with the concepts of expectation, Purchasing Power Parity and Interest Rate Parity, which together form the basis of the following analysis of monetary and portfolio theories of the exchange rate determination. Then, it provides a comparison of the various approaches to these theoretical frameworks with regard to their respective authors. The paper is concluded by an evaluative description of the conditions under which such theories could be applied.

<p>Thorium dioxide (ThO₂) and metallic uranium (alpha-U) represent important alternative nuclear fuels. Investigating the behavior of defects introduced into these materials in an irradiation environment is critical for understanding microstructure evolution and property changes. The objective of this dissertation is to investigate the clustering of point defects in ThO₂ and alpha-U under irradiation, into voids and prismatic dislocation loops as a function of irradiation dose rate and temperature. To achieve this, we have developed a mean-field cluster dynamics (CD) model based on reaction rate theory to predict the evolution of self-interstitial atom (SIA) and vacancy loops in neutron-irradiated alpha-U. Detailed atomistic simulations have been carried out using molecular dynamics (MD) to study the configuration of such loops and compute their energetics, which are essential parameters of the CD model. Bond-boost hyper-MD simulations have been performed to compute the diffusivity of uranium SIA and vacancies, which govern the kinetics of the clustering phenomenon. Another CD model has been demonstrated for proton-irradiated ThO₂, considering the clustering of Th and O SIA and vacancies into SIA loops and voids, respectively, with varying sizes and stoichiometry. The compositions of all SIA loops and voids dictated by crystallography of ThO₂ in its fluorite structure have been presented in their respective cluster composition space (CCS). The CD model solves the density evolution of off-stoichiometric loops and voids, with irradiation, in their respective CCS. MD simulations have been performed to compute the energetics of different clusters in their CCS, as parameters of the CD model. Temperature-accelerated MD simulations have been performed to compute the diffusivity of Th and O point defects, that dictates the kinetics of defect clustering on irradiation. In alpha-U, the CD predictions show an accumulation of small sized vacancy loops and the growth of SIA loops with irradiation dose, which closely fits the reported size distribution of loops in neutron-irradiated alpha-U by Hudson and coworkers. The CD predicted density of defect clusters in proton-irradiated ThO₂, shows the evolution of near-stoichiometric SIA loops in their CCS. The size distribution of SIA loops at high irradiation doses closely corresponds to the transmission electron microscopy (TEM) observations reported in the literature. Also, the CD model did not predict the growth of voids and vacancy clusters, which is consistent with findings in literature. The model was further used to predict the density of sub-nanometric defect clusters and point defects, on low-dose irradiation, that significantly impairs the thermal conductivity of ThO₂. An extensive TEM and CD investigation has also been carried out to study the growth and coarsening of SIA loop and voids during post-irradiation isochronal annealing of ThO₂ at high temperatures.</p>