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Eingeladener Vortrag
- nein (1102)
Experimental and numerical analyses of spent nuclear fuel behavior under transport conditions
(2019)
Packages for the transport of spent nuclear fuel shall meet the International Atomic Energy Agency regulations to ensure safety under different transport conditions. The physical state of the spent fuel and the fuel rod cladding as well as the geometric configuration of fuel assemblies are important inputs for the evaluation of the package capabilities under these conditions. The mechanical behavior of spent fuel assemblies shall be analyzed with regard to the assumptions which are used in the containment and criticality safety analysis. The package as a mechanical system is characterized by a complex set of interactions, e. g. between the fuel rods within the assembly as well as between the fuel assemblies, the basket, and the cask containment. This complexity makes it difficult to assume appropriate mechanical loads for the spent fuel inside the package. Another challenge is the assumption of material properties which represent the variation of the fuel rods regarding cladding material, burn-up and the operation history sufficiently. The objective of this paper is to give an overview about the current approaches and research for the evaluation of spent fuel behavior within the package design approval procedure. In this context, analytical, numerical and experimental results are discussed. The presented work is achieved within a collaboration of BAM with national and international partners.
In the last years, the Process Analytical Technology (PAT) research field has become of great importance due to its connection with the industrial world. This industry related research, along with the evolutionary progress that technology has seen lately, has allowed that key analytical techniques in an industrial environment have undergone a radical development. One of these techniques has been the near-infrared spectroscopy (NIRS). This technique, currently common in "online" industrial analysis, has seen a remarkable revolution, especially since the introduction of the microelectromechanical systems technology (MEMS) in the spectroscopy field. Nowadays it is possible to find compact spectrometers no bigger than a wristwatch in the market. Although there is an unavoidable question: can these compact spectrometers actually compete against the traditional spectrometers?
In this project different calibration parameters of two compact NIR spectrometers ("Spectral Engines Oy NIR-One Sensor NM2.0", with 1550 to 1950 nm range; and "NeoSpectra Si-ware", with 1300 to 2550 nm range) were evaluated, and the obtained results were compared with a reference spectrometer ("Bruker Optik GmbH Matrix-F", with 15000 to 4000 cm–1 range). In order to obtain the different calibration parameters, a sequence of quality performance tests were conducted. The results obtained after the different experiments carried out with both compact spectrometers prove that their performance is more than acceptable for routine analysis.
Afterward, model samples of different microplastics in soil at different known concentration were analyzed with all three spectrometers. Chemometric models capable to identify and classify microplastics in soil were established. For this analysis five of the most used plastics worldwide were used: polyethylene (PE), polyethylene terephthalate (PET), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC). After the Principal component analysis (PCA), it can be seen that only the NIR-One NM2.0 is capable to differentiate all types of microplastics in soil at concentrations of 1–2 %, while the NeoSpectra Si-ware is unable to identify the PET sample.
Engineering Modelling
(2019)
This chapter presents the most commonly used approach to analyse the
thermo-mechanical behaviour of concrete structures subjected to high temperatures as in the case of fire loading. Prescriptions of the Eurocode are detailed for the thermal as well as the mechanical analysis. Finally, recommendations from two national (Austrian and German) guidelines give some improvements for Underground infrastructure.
Advanced Modelling
(2019)
Halomonas elongata is a halophilic γ-proteobacterium that synthesizes and accumulates the compatible solute ectoine to cope with osmotic stress in saline environments. Ectoine possesses protecting properties and stabilizes proteins as well as whole cells against stresses like ionizing radiation and cytotoxins. These properties make ectoine a highly demanded ingredient in cosmetics and pharmaceuticals. To date H. elongata is the industrial Producer strain of ectoine, but several metabolic factors for optimum ectoine production remain to be explored.
In this work, we used up to date Metabolic engineering approaches following the ‘Push, Pull, Block – strategy’ to examine targets that contribute to ectoine synthesis. Firstly, the basics of glucose catabolism were inspected to PUSH and enhance carbon flow towards ectoine synthesis. Secondly, lysine biosynthesis was targeted to BLOCK a pathway that is competing for precursors with ectoine synthesis. Thirdly, the mechanosensitive (MS) channels of H. elongata have been examined as possible excretion routes for ectoine. An overexpression of the ectoine excretion channels potentially could PULL out product at the end of ectoine synthesis and increase overall ectoine flux. For the interrogation of central metabolic pathways, we established the new molecular tool CRISPR-mediated interference (CRISPRi) for targeted modulation of gene expression.
PUSH Glucose catabolism through the Entner-Doudoroff (ED) and Emden-Meyerhof-Parnas (EMP) pathway was targeted with CRISPRi and examined on gene expression level for ist response to changing salinity and different carbon sources. Changing salinity did not influence gene expression levels of glucose catabolism but the carbon source glucose triggered glycolysis through the (ED) pathway. When gene expression of the ED pathway was downregulated with CRISPRi, the growth rates remained constant. The observations indicate a metabolic overflow mechanism for glycolysis, in which fluxes are constantly high - even at lower salinity when no resources are demanded for ectoine synthesis. The further analysis of glucose to product conversion rates will advise optimum conditions for future industrial cultivation processes.
BLOCK Lysine biosynthesis was downregulated with CRISPRi, which led to a significant increase in ectoine production. Hence, the blockage of lysine biosynthesis would be a valuable strategy for the optimization of the industrial producer strain in future studies.
PULL MS channels and ectoine regulation are inevitably connected in osmoadaptation. Therefore, ectoine excretion, growth performance and gene expression levels of the MS channels were monitored in steady state conditions and in response to osmotic shock in the wildtype strain and in a MS channel deletion mutant. We observed that the MS channels were essential for the survival of osmotic shock but surprisingly their presence reduced cell growth under high salinity. The MS channels were only partially responsible for ectoine excretion.
Thus, alternative ectoine excretion channels must exist and remain to be explored.
Most knowledge about the structure, function, and evolution of early compound eyes is based on investigations in trilobites. However, these studies dealt mainly with the cuticular lenses and little was known about internal anatomy. Only recently some data on crystalline cones and retinula cells were reported for a Cambrian trilobite species. Here, we describe internal eye structures of two other trilobite genera. The Ordovician Asaphus sp. reveals preserved crystalline cones situated underneath the cuticular lenses. The same is true for the Devonian species Archegonus (Waribole) warsteinensis, which in addition shows the fine structure of the rhabdom in the retinula cells. These results suggest that an apposition eye with a crystalline cone is ancestral for Trilobita. The overall similarity of trilobite eyes to those of myriapods, crustaceans, and hexapods corroborates views of a phylogenetic position of trilobites in the stem lineage of Mandibulata.
Although concrete itself is not a combustible material, concrete mixtures with high density, such has high-performance concretes (HPCs), are susceptible to significant damage during fires due to explosive spalling. Past research has shown that the inclusion ofpolymer fibres in high density concrete can significantly mitigate this fire damage. The exact mechanisms causing this increased spalling resistance are not yet fully understood, but it is thought that the fibres facilitate moisture transport during fire exposure, which in turn contributes to relief of internal stresses in the spalling-susceptible region. In this study, X-ray Computed Tomography (CT) was applied to observe the interaction between polymer fibres and cracking during thermal exposure. For this purpose, two concrete samples containing different polymer fibre types were subjected to incremental application of a defined thermal exposure. CT images were acquired before and after each thermal exposure and powerful image processing tools were used to segment the various material components. This enabled a detailed analysis of crack formation and propagation as well as the visualization and quantification of polymer fibre characteristics within the concrete. The results demonstrated that the orientation of both fibres and cracks in polymerfibre reinforced concrete tend to be anisotropic. The results also indicated that crack geometry characteristics may be correlated with fibre orientation, with cracks tending to run parallel to fibre beds. Clear quantitative relationships were also observed between heating and increasing cracking levels, expressed in terms of both crack surface area and crack volume.
In this paper we report on the characterization by X-ray computed tomography of calcium phosphate (CaP) and polycaprolactone (PCL) coatings on Ti-6Al-4V alloy scaffolds used as a material for medical implants. The cylindrical scaffold has greater porosity of the inner part than the external part, thus, mimicking trabecular and cortical bone, respectively. The prismatic scaffolds have uniform porosity. Surface of the scaffolds was modified with calcium phosphate (CaP) and polycaprolactone (PCL) by dip-coating to improve biocompatibility and mechanical properties. Computed tomography performed with X-ray and synchrotron radiation revealed the defects of structure and morphology of CaP and PCL coatings showing small platelet-like and spider-web-like structures, respectively.
The risk analysis of road tunnels faces a growing complexity in fire scenarios, e.g. caused by new energy carriers. Essentially, such complex scenarios involve many interactions between the tunnel users, the fire source and the safety measures. One example is the alarm of tunnel users either initiated by the perception of smoke or by the fire alarm system. To consider these interactions for the quantification of consequences, e.g. fatalities, risk analysis requires a complex model. However, the complex model can compute in practice only few discrete scenarios due to its high computational cost, whereas risk analysis generally needs the consequences of a high number of random scenarios. Metamodels can solve this contradiction. They are able to approximate the consequences of many random scenarios with low computational cost based on the consequences of few discrete scenarios computed with the complex model. The efficiency of metamodels depends on the required number of these discrete scenarios. In this sense, this dissertation proposes an efficient metamodel within an innovative methodology for risk analysis of road tunnels to allow to consider an increased complexity of scenarios. This metamodel applies the following methods or models: the projection array-based design method specifies the experimental design for the discrete scenarios; the combination of the fire model FDS and the microscopic evacuation model FDS+Evac constitutes the complex model; and moving least squares produces the response surface model. The response surface model approximates the consequences of the random scenarios and therewith introduces an uncertainty, called metamodel uncertainty, which is quantified with the prediction interval method. Additionally, stochastic individual characteristics of tunnel users in discrete scenarios computed with FDS+Evac attribute evacuation uncertainties to the consequences. An original development in this dissertation, the ’direct approach’, directly transfers the evacuation uncertainties of the discrete scenarios to any random scenario. The evaluation of the metamodel in this dissertation shows following results. Firstly, the response surface model sufficiently represents the consequences of the complex model. Secondly, the metamodel uncertainty is also essential for this representation, but the prediction interval method reveals a drawback in the risk analysis. Potential approaches to deal with this drawback are discussed. Finally, the direct approach reproduces the evacuation uncertainty of the complex model which then clearly affects the consequences of random scenarios. Therefore, the consideration of the evacuation uncertainty plays an important role for the risk analysis. Furthermore, the projection array-based design method was adapted in this dissertation with two approaches, namely the combination of the experimental designs for FDS and FDS+Evac as well as their sequential refinement. Both approaches contribute to the efficiency of the metamodel. These results lead to following conclusions. Firstly, the metamodel efficiently integrates the consequences of discrete scenarios into risk analysis and thus allows to consider an increased complexity. Secondly, the metamodel is an advancement for risk analysis not only for road tunnelsbutalsomoregeneralinfiresafetyengineering. Forthesetworeasons,themetamodel might be interesting for other methodologies for risk analysis. In addition, the metamodel is generic and is therefore widely applicable on other issues beside from risk analysis, e.g. to assess the safety of structures related to time-consuming experiments depending on multiple variables.
The simulation of the structural response for impact scenarios strongly requires an accurate simulation of both the impact event as well as the subsequent wave propagation. The numerical modeling of the impact event is intrinsically ill-posed due to the instantaneous changes of velocities in the contact area, leading to unbounded accelerations for decreasing time steps which causes oscillations in the contact stresses. These oscillations then propagate into the bulk material. Using a rate dependent material model, like concrete, they might lead to significant errors and a wrong prediction of the structural response. A regularization is thus required to avoid oscillations in the contact stresses. Another issue is related to the numerical computation of the contact conditions. In impact simulations, the nonlinear contact computation needs to be evaluated in every time step. A segmentation technique of the contact area is accurate but time consuming and may result in a bottleneck for the simulation and implementation, especially for 3D problems. The modeling of the subsequent wave propagation requires small time steps, which is primarily due to accuracy reasons. Implicit schemes are thus not affordable. Explicit time integration schemes are efficient only for diagonal mass matrices, as in this case no solution of a linear system is required. In this work, a coupled finite element - Non-Uniform Rational B-Spline (FE-NURBS) approach is applied to impact problems. The coupled approach uses an intermediate NURBS layer to compute the contact forces between the contacting bodies discretized by FEs. The advantages of a smooth isogeometric contact formulation are used to compute the contact forces. A segmentation of the contact area is avoided and an efficient element-based integration is used. The impact event is regularized using a mesh dependent nonlinear penalty approach. The penalty function is a polynomial which ensures a smooth transition between the noncontact and the contact state during the impact. For finer meshes, the penalty regularization becomes stiffer while still avoiding artificial oscillations in the contact stresses. Efficient higher order space and time discretizations are used to model the wave propagation. Explicit time integration is combined with higher order spectral element spatial discretization.
The full-notch creep test (FNCT) is a common method to evaluate the environmental stress cracking (ESC) behavior of high-density polyethylene (PE-HD) container materials . The test procedure as specified in ISO 16770 provides a comparative measure of the resistance against ESC using the time to failure of specimens mechanically loaded in a well-defined liquid environment. Since the craze-crack damage mechanism underlying the ESC process is associated with brittle failure, the occurrence of globally brittle fracture surfaces is a prerequisite to consider an FNCT measurement as representative for ESC . Therefore, an optical evaluation of FNCT fracture surfaces concerning their brittleness is essential. Due to the experimental setup, an inevitable increase of the true mechanical stress and the associated appearance of small ductile parts on fracture surfaces is induced in any case. Hence, an FNCT experiment is considered as 'valid', if the corresponding fracture surface is predominantly brittle . Based on laser scanning microscopy (LSM) height data of FNCT fracture surfaces , a universal and easy-to-use phenomenological criterion was developed to assess the validity of distinct FNCT experiments. This criterion is supposed to facilitate a quick evaluation of FNCT results in practical routine testing.
During their lifetime, polymer components subjected to mechanical loads and environmental influences show a loss of their mechanical properties required for their specific applications. In this respect, the craze-crack damage mechanism slow crack growth (SCG) is relevant for PE-HD components used in high-performance applications such as pipes and containers for the storage and transport of dangerous goods. SCG is considered to be the major failure mechanism in polyolefins and it typically occurs suddenly and unexpectedly. Due to the fields of application, SCG is a safety relevant issue. To test for the resistance of PE-HD pipe and container materials against SCG, the full-notch creep test (FNCT) is widely applied in Europe. In this study, SCG phenomena in PE-HD are investigated in detail based on an improved FNCT, especially including the consideration of the influence of environmental liquids effecting the damage mechanism. Using an enhanced fracture surface and a crack propagation analysis with imaging techniques such as light microscopy (LM), laser scanning microscopy (LSM), X-ray computed tomography (CT-scan) and scanning electron microscopy (SEM), detailed data concerning SCG are obtained.
The combined application of FNCT and such imaging techniques is explicitly advantageous and recommended to gain important information on damage occurring to PE-HD induced by mechanical stress and the influence of environmental liquids, which is essential within the Fourth Industry Revolution.
The separation of two closely spaced defects in fields of Thermographic NDE is very challenging. The diffusive nature of thermal waves leads to a fundamental limitation in spatial resolution. Therefore, super resolution image reconstruction can be used. A new concerted ansatz based on spatially structured heating and joint sparsity of the signal ensemble allows for an improved reconstruction of closely spaced defects. This new technique has been studied using a 1D laser array with randomly chosen illumination pattern.
This paper presents the results after applying super resolution algorithms, such as the iterative joint sparsity (IJOSP) algorithm, to our processed measurement data. Different data processing techniques before applying the IJOSP algorithm as well as the influence of regularization parameters in the data processing techniques are discussed. Moreover, the degradation of super resolution reconstruction goodness by the choice of experimental parameters such as laser line width or number of measurements is shown.
The application of the super resolution results in a spatial resolution enhancement of approximately a factor of four which leads to a better separation of two closely spaced defects.
Bei Störfallauswirkungsbetrachtungen an Biogasanlagen muss das Versagen der Folien- oder Membranabdeckung des Fermenters untersucht werden. Hierbei sind insbesondere Risse in derselben hinsichtlich des austretenden Massenstromes an Biogas zu bewerten, ebenso wie der durch eine Zündung resultierende Flammenstrahl. Zurzeit existieren für Folien- oder Membranabdeckungen jedoch keine Erkenntnisse zu realistischen Ausflussziffern für die Massenstromberechnung. Im Leitfaden KAS-32 wird für Störfallauswirkungsbetrachtungen für die Berechnung des austretenden Massenstromes eine Ausflussziffer von 1 und eine „Leckfläche“ von 0,6 m2 vorgegeben. Die Anwendbarkeit verfügbarer Modelle zur Berechnung des Flammenstrahls ist bisher ebenso ungeklärt. Um diese Fragestellungen zu untersuchen, wurden in der BAM Versuche zur Bestimmung der Ausflussziffer, sowie der Zündung des austretenden Gases an einem 80 m3 Sack zur Speicherung von Biogas durchgeführt, der aus demselben Material besteht wie die in Biogasanlagen verwendeten Folien- und Membranabdeckungen.
Bei Störfallauswirkungsbetrachtungen an Biogasanlagen muss das Versagen der Membranabdeckung des Fermenters untersucht werden.
Hierbei sind insbesondere Risse in derselben hinsichtlich des austretenden Massenstromes an Biogas zu bewerten, ebenso wie der durch eine Zündung resultierende Flammenstrahl. Zurzeit existieren für Membranabdeckungen jedoch keine Erkenntnisse zu realistischen Ausflussziffern für die Massenstromberechnung. Im Leitfaden KAS-32 wird für Störfallauswirkungsbetrachtungen für die Berechnung des austretenden Massenstromes eine Ausflussziffer von 1 und eine „Leckfläche" von 0,6 m2 vorgegeben. Die Anwendbarkeit verfügbarer Modelle zur Berechnung des Flammenstrahls ist bisher ebenso ungeklärt. Um diese Fragestellungen zu untersuchen, wurden in der BAM Versuche zur Bestimmung der Ausflussziffer, sowie der Zündung des austretenden Gases an einem 80 m3 Sack zur Speicherung von Biogas durchgeführt, der aus demselben Material besteht wie die in Biogasanlagen verwendeten Membranabdeckungen.
Die Additive Fertigung (AM) wird eingesetzt, um komplexe Bauteile für die Luftfahrt-, Medizin- und Automobilindustrie kostengünstig und zeitsparend herzustellen. Der Einsatz von AM in der Industrie erfordert eine strenge Qualitätskontrolle der hergestellten Teile, um die geforderten Normen erfüllen zu können. Aus diesem Grund spielen die Prozessüberwachung und die Anwendung von Methoden der zerstörungsfreien Prüfung eine große Rolle, was im Fokus unserer aktuellen Forschung steht. In dieser Arbeit benutzen wir Röntgenrückstreuung, welche lediglich einen einseitigen Zugang zum Objekt benötigt, um innenliegende, künstlich hergestellte Defekte in additiv gefertigten Stufenkeilen aus Polyamid 12 (PA 12, Laser Sintering) sowie Acrylnitril-Butadien-Styrol (ABS, Fused Layer Modeling) zu untersuchen. Dafür wurde ein von der Firma AS&E (Boston, USA) konstruierter Prototyp verwendet, der ursprünglich für den Sicherheitsbereich entwickelt wurde. Die Messung der Rückstreuung basiert auf der Flying-Spot Technik mit einem stark kollimierten Nadelstrahl, erzeugt von einem rotierenden Kollimator, wobei großflächige Detektoren die rückgestreute Strahlung sammeln. Da die Anforderungen an die räumliche Auflösung sowie die Kontrastempfindlichkeit in der zerstörungsfreien Prüfung (ZfP) über denen im Sicherheitsbereich liegen, ist eine Optimierung des Prototyps notwendig, um eine Bildqualität zu erreichen, wie sie in der ZfP gefordert ist. Darüber hinaus wurden klassische Durchstrahlungsprüfungen durchgeführt, um die Fähigkeit des Rückstreusystems bei der Defekterkennung in den untersuchten Objekten einschließlich innenliegender Defekte vergleichen und bewerten zu können. Die nachweisbaren Poren und Lufteinschlüsse sind in den Durchstrahlungsaufnahmen, besonders bei den PA 12 Proben, kleiner als in den mittels Rückstreuung erzeugten Bildern. Daher ist eine weitere Optimierung des AS&E- Prototypen notwendig und zusätzliche Untersuchungen sind erforderlich, um die ZfP-Anforderungen zu erfüllen und die Anwendungsgrenzen dieses Geräts zu ermitteln. Jedoch zeigen Vergleichsmessungen mit gedruckten Leichtmetallen (Al), dass die Rückstreutechnik eine vielversprechende Methode zur in-situ Qualitätssicherung mehrerer cm großer Bauteile mit inneren Defekten ab ca. 400 μm Größe ist.
Alkali and alkaline earth chlorides are discussed as heat storage media and are characterized by their low price and high availability. Disadvantages are a high corrosion rate and formation of Cr6+ ions in the melt, as observed in various binary chlorine salt melts. In our work the system NaCl-KCl-MgCl2 is considered. The storage capacity in this salt system is between 2 and 3 MWh per 10 t salt, depending on composition, melting temperature and working temperature. At the same time the system offers a eutectic line, which allows a high variance of the composition and possibly different corrosion rates can be observed. Corrosion tests in melts were carried out and the corrosion layers investigated. The tests with chloride melts on 12% Cr steel show an inner corrosion zone of up to 40 µm depth after 96 hours. The corrosion mechanisms and potential solutions are discussed.
Fatigue safety verification of existing bridges that uses ‘‘re-calculation’’ based on codes, usually results in insufficient fatigue safety, triggering invasive interventions. Instead of “re-calculation”, Structural Health Monitoring (SHM) should be used for the assessment of the existing bridges. Monitoring systems provide data that can reduce uncertainties associated with the fatigue loading process and the structural resistance. The objective of this paper is to quantify the value of the SHM system implemented in a 60-years-old road viaduct to investigate its fatigue safety, through modeling of the fundamental decisions of performing monitoring in conjunction with its expected utility. The quantification of the conditional value of information is based on the decision tree analysis that considers the structural reliability, various decision scenarios as well as the cost-benefit assessments. This leads to a quantitative decision basis for the owner about how much time and money can be saved while the viaduct fulfills its function reliably and respects the safety requirements. The originality of this paper stands in the application of the value of information theory to an existing viaduct considering the fatigue failure of the system based on the monitoring data and the cost-benefit of monitoring method.
Sicherheitskonzepte werden für die verschiedenen Szenarien für Lithiumakkus benötigt: Vor allem für den Bereich der Lagerung gibt es im Moment nur wenige Vorgaben. Im Vortrag werden verschiedene Brandschutzkonzepte vorgestellt. Für die Lagerung werden Empfehlungen ausgesprochen, die teilweise an die Vorgaben der Transportvorschriften anknüpfen.