Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Silizium-basierte Lichtemitter: auf dem Weg zur Silizium-Photonik ?
Helm, M.;
Silizium ist zwar die Basis für nahezu die gesamte Mikroelektronik, die Integration mit optischer Funktionalität ist jedoch nur eingeschränkt möglich, da Silizium als indirekter Halbleiter ein schlechter Lichtemitter ist. Andere optoelektronische Komponenten, wie Dektektoren, Modulatoren oder Wellenleiter können aus Silizium hergestellt werden, ein Siliziumlaser hat sich bisher aber allen Realisierungsversuchen widersetzt. In den letzten Jahren hat es jedoch rasante Fortschritte bei der Effizienz Silizium-basierter Lichtemitter gegeben, sogar optischer Gewinn (gain) wurde berichtet. Ich möchte diese Entwicklung zusammenfassen und dann unsere Unterschungen an Bor-implantierten Si pn Dioden und an mit seltenen Erd-Ionen implantierte MOS-Strukturen präsentieren, deren Effizienzen schon nahe zum anwendungsrelevanten Bereich kommen.
Keywords: Silicon light emitter, microcavity, rare earth
  • Lecture (others)
    Physikalisches Kolloquium, 17.01.2005, Kaiserslautern, Deutschland

Publ.-Id: 7063 - Permalink

Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung
Reuther, H.;
Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung
  • Lecture (Conference)
    Mößbauerkolloquium Dresden 2004, 30.09.-01.10.2004, Dresden-Rossendorf, Deutschland

Publ.-Id: 7062 - Permalink

Mechanisms of target poisoning during magnetron sputtering as investigated by real-time in situ analysis and collisional computer simulation
Güttler, D.; Abendroth, B.; Grötzschel, R.; Depla, D.; Möller, W.;
The evolution of reactive gas uptake at the target surface has been investigated by real-time in situ diagnostics during magnetron sputtering. Using a planar circular dc magnetron for reactive sputter deposition of TiN from a Ti target in an argon/nitrogen gas mixture, the target uptake of nitrogen was determined at varying gas flows of nitrogen using the 14N(d,)12C nuclear reaction, directly demonstrating the target "poisoning" effect. The expected hysteresis behavior at increasing/decreasing nitrogen gas flow is confirmed. Within the precision of the measurement, the nitrogen content remains unaltered after switching off the magnetron, indicating the absence of a significant mobile fraction of nitrogen in the target. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen. This is quantitatively reproduced by TRIDYN collisional computer simulations.
Keywords: reactive magnetron sputtering nra dc magnetron
  • Applied Physics Letters 85(2004)25, 6134-3163

Publ.-Id: 7061 - Permalink

An approach to cyclic plasticity and deformation-induced structure changes of electrodeposited nickel
Thiele, E.; Klemm, R.; Hollang, L.; Schell, N.; Natter, H.; Hempelmann, R.;
Bulk nickel samples, produced by electrodeposition, resulting in different initial structure properties, were experimentally studied by X-ray diffraction, as well as by scanning and transmission electron microscopy. Attempts are made to correlate the mechanical behaviour during cyclic plastic deformation with the response of the microstructure. A special effort is made to examine the influence of grain size and internal stresses on the deformation processes.
Keywords: Electrodeposition; Submicro-crystalline nickel; Cyclic plastic deformation; Grain structure; Internal stresses

Publ.-Id: 7060 - Permalink

The potential of external IBA and LA-ICP-MS for obsidian elemental characterization
Bugoi, R.; Constantinescu, B.; Neelmeijer, C.; Constantin, F.;
Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission–Proton Induced Gamma-ray Emission–Rutherford Back-Scattering (PIXE-PIGE-RBS) have been performed on several obsidian fragments with archaeological significance at the Rossendorf tandem accelerator using a 3.85 MeV proton beam. A comparison was made between these external IBA results and the ones previously obtained on the same obsidian samples using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS). The purpose of the study was to assess the potentiality of external IBA for provenance studies on archaeological obsidian, especially as a non-destructive alternative to the LA-ICP-MS method. As an example, the source attribution of an archaeological obsidian fragment from Transylvania to Tokay Mountains/Slovakian range flow is discussed.
Keywords: Obsidian, IBA, PIXE, PIGE, LA-ICP-MS, Provenance

Publ.-Id: 7059 - Permalink

Structure modifications in silicon irradiated by ultra-short pulses of XUV free electron laser
Pełka, J. B.; Andrejczuk, A.; Reniewicz, H.; Schell, N.; Krzywinski, J.; Sobierajski, R.; Wawroa, A.; Zytkiewicz, Z. R.; Klinger, D.; Juha, L.;
Structural modifications of solid Si (0 0 1) targets exposed to the XUV TESLA free lectron laser radiation were studied. The samples were irradiated with the photon energy centered at 14 eV, in short pulses of only 80 fs and of peak power up to 1 GW. The FEL beam was focused on sample surfaces to microspots of size 10–100m. The energy density in the spots varied from below the ablation threshold up to far above this threshold. The structural modifications induced with the irradiation were studied by AFM, Nomarski contrast microscopy and by X-ray diffraction methods. A variety of morphological structures created in the damaged areas was found. The maps of the X-ray diffracted intensity distribution recorded around chosen spots on the Si surface made it possible to probe the damage distribution range around the spots. The observed features are related to the FEL irradiation fluencies applied.
Keywords: Semiconductors; Laser processing; XUV free electron laser; Material modification; Ablation; Silicon
  • Journal of Alloys and Compounds (2004)382, 264-270

Publ.-Id: 7058 - Permalink

X-ray fluorescence and ion beam analysis of iridescent Art Nouveau glass - authenticity and technology
Jembrih-Simbürger, D.; Neelmeijer, C.; Mäder, M.; Schreiner, M.;
EDXRF analysis with subsequent multivariate data analysis proves useful for the determination of the authenticity of iridescent glass artifacts. Thus, clusters of the glass groups investigated were formed which can be associated with the glass manufacturers. By means of ion beam analysis with the external proton beam the producing technology of iridescent glass objects of the Art Nouveau glass manufacturer Loetz/Austria with so-called Papillon pattern was characterised in a non-destructive way. Due to the simultaneous application of PIXE and RBS the glass structure including a sequence of glass layers covered with a SnO2-layer of approximately 50 nm thickness on the surface could be described.
Keywords: X-ray fluorescence analysis, Ion beam analysis, Iridescent layers, Art Nouveau glass, Tiffany, Loetz

Publ.-Id: 7057 - Permalink

Experimental Investigations on Bubble Turbulent Diffusion in a Vertical Large Diameter Pipe and in a Rectangular Bubble Column by means of Different Measurement Techniques
Manera, A.; Zaruba, A.;
The dispersion of bubbles in a vertical two-phase flow is studied experimentally by means of wire-mesh sensors and high-speed video camera. The first technique is applied to a 200 mm pipe with flow patterns ranging from bubbly to slug/churn flow. The latter technique is instead applied to a rectangular bubble columns at low void-fractions. The experimental results are compared with numerical investigations.
Keywords: turbulent dispersion, two-phase flow
  • Lecture (Conference)
    Multi-phase Flow: Simulation, Experiment and Applications, ANSYS-CFX / FZR workshop, 28.-30.06.2004, Dresden, Germany

Publ.-Id: 7056 - Permalink

Experiments and CFX-5 calculation of the stratified flow in a horizontal channel (Part 2: Measurements)
Vallee, C.; Sühnel, T.;
For the investigation of air/water stratified flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows under atmospheric pressure, especially the slug behaviour.
Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. Further, an interface capture technique was developed and possible applications (e.g. plot of the time dependent water level in a cross-section, recognition of the slug position) presented.
Keywords: Horizontal two-phase flow, Slug flow, High-speed video observations, Image processing
  • Lecture (Conference)
    Joint FZR & ANSYS Multiphase Flow Workshop: Simulation, Experiment and Applications, 28.-30.06.2004, Dresden, Germany

Publ.-Id: 7055 - Permalink

New possibilities for velocity measurements in metallic melts
Eckert, S.; Gerbeth, G.; Stefani, F.;
During last decades magnetohydrodynamic (MHD) effects have attracted growing interest because of its potential impact on numerous industrial technologies. In processes involving electrically conducting liquids, the application of an external magnetic field offers efficient opportunities for a contactless flow control and fluid handling. However, for a well-aimed optimisation of the flow structure local information about flow quantities like velocity, pressure, temperature, concentration or void fraction is necessary. In case of liquid metals the choice of a suitable measuring technique is a crucial problem, because the user is confronted with the problems of opaque fluids, high temperatures as well as a strong chemical reactivity of the fluid against many materials. Therefore, measuring techniques well-known from ordinary hydrodynamics generally fail for liquid metal applications. As a consequence, no commercial measuring systems are available for liquid metal applications.
We present a summary of our R&D activities on velocity measuring techniques for liquid metal flows. Various model experiments with various liquid melts at different temperatures have been performed to test and evaluate local sensors as well as integral methods.
A mechano-optical probe was developed which has to be positioned directly inside the liquid metal flow. The measuring principle is based on the separation of a direct mechanical interaction between flow and sensor tip and the optical acquisition and processing of the signal. The insensitivity of the system to electrical noise and external magnetic fields can be considered as an important advantage. Until now, the sensor has been tested in metallic melts up to temperatures of about 450 °C, but an extension up to 800°C should be straightforward. The ultrasound Doppler velocimetry (UDV) represents a powerful tool since it delivers a full velocity profile along the ultrasonic beam. It can operate with a direct contact to the melt, but also through a channel wall. To overcome the thermal restriction of the ultrasonic transducers an acoustic wave guide has been used. The acoustic wave guide and the piezoelectric element are combined in form of an integrated sensor. This approach allowed the first successful application of the ultrasound Doppler technique in liquid metals at temperatures above 200°C. The feasibility of this integrated sensor concept was demonstrated in experiments in metallic melts as sodium, PbBi, CuSn or aluminium.
In some applications even a coarse knowledge of the flow topology and the direction of the main eddies would be of high value. We study the possibility of velocity reconstruction in electrically conducting fluids from external measurements of induced magnetic fields. The method is based on the fact that an external magnetic field is deformed by the motion of the fluid. Applying the primary magnetic field in two different directions and measuring the related induced magnetic fields at an array of Hall probes, the three-dimensional velocity field can be reconstructed. Besides some theoretical basics, we present experimental results of a demonstration experiment.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7054 - Permalink

Magnetic field control of the mould filling process of aluminium investment casting
Eckert, S.; Galindo, V.; Gerbeth, G.; Witke, W.; Gerke-Cantow, R.; Nicolai, H.; Steinrücken, U.;
The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. Several types of filters are already in use for the purpose of inclusion filtering but velocity reduction, too.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical calculations were performed to simulate the filling process and the effect of the magnetic field. The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. 3d transient calculations using the commercial finite- element code FIDAP (FLUENT Inc.) were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented into the code via a user defined subroutine, and an additional equation for the electrical potential was solved. End effects due to the limited size of the magnet poles were taken into account. In that way, results from three-dimensional transient simulations of the filling process were obtained.
Parallel to the simulations model experiments have been performed using the low melting eutectic InGaSn. The casting unit was modelled by a plexiglas model. The ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. Such measurements delivered the basis to validate the numerical calculations. A comparison between numerical and experimental results showed an excellent agreement, allowing scaling up the simulations to the realistic aluminium casting process.
Real tests have been performed at an industrial investment caster with molten aluminium. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly shown. In a second set of experiments the amplitude of the DC field was tuned during the process. At the beginning the maximum braking force was applied, whereas the field strength was reduced with increasing fluid level in the casting unit. In this regime, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7053 - Permalink

The Thermal Hydraulic Test Facility Topflow: Overview on Experimental Capabilities and Instrumentation
Prasser, H.-M.; Beyer, M.; Carl, H.; Gregor, S.; Manera, A.; Pietruske, H.; Schütz, P.; Weiss, F.-P.;
TOPFLOW stands for Transient TwO Phase FLOW. The new thermal-fluiddynamic test facility of FZR was built for generic and applied studies of transient two phase flow phenom-ena in power and process industries. It is used as experimental basis to develop and validate three-dimensional CFD, in particular for an application to safety relevant flow simulations in the field of nuclear reactor safety. The work is carried out in a close and very fruitful coopera-tion with the code developer ANSYS-CFX. Object of the experimental studies is a gas-liquid two-phase flow. In the field of nuclear technology, the introduction of CFD is connected with high expectations concerning the quality of the predictions compared to the established one-dimensional thermal hydraulic analyses, since CFD allows to substitute geometry-dependent empirical closure relations by more physically justified closure laws that are formulated on the scale of the structures of the gas-liquid interface. In this way, modelling becomes much more independent from geometrical and thermodynamic boundary conditions and the scale-up to the real reactor scale becomes more reliable than in case of traditional thermal hydraulic codes.

TOPFLOW is not a dedicated integral test modelling a specific reactor type. It was rather de-signed as a multi-purpose facility for different single-effect experiments. This offers numer-ous possibilities for experiments to study basic two-phase flow phenomena as well as to per-form applied research for the industries. The latter includes, for instance, investigations of innovative and passive safety systems for nuclear reactors, like the emergency condenser for boiling water reactors, a model of which is a major component of TOPFLOW. A carefully designed instrumentation including advanced two-phase flow sensors of own development delivers experimental data of high quality, that reflect the addressed phenomena and processes in the necessary detail.

An important role plays the availability of measuring information from wire-mesh sensors with a high spatial resolution of 3 mm, which deliver sequences of complete two-dimensional gas fraction distributions from the entire cross section of both pipes DN50 and DN200 with a frame rate of 2500 Hz. These sensors were upgraded to operational parameters of 280 °C and 65 bar. First results on void profiles and bubble size distributions as well as the evolution of the flow structure along a vertical pipe obtained in this parameter range will be presented.

Another new method used at TOPFLOW is the strategy to install a test facility inside a tank pressurized with air of up to 50 bar and operate if in pressure equilibrium with the inner at-mosphere of the tank. The advantages can be summarised as follows: (1) the test facility itself can have strange shapes that are unfeasible for pressurised components, (2) the manufacture of the test itself will be cheap, since no pressure carrying components are needed, (3) thin walls make it easy to apply instrumentation, for instance optical measurements through glass walls or temperature field measurements by directing an infrared camera to a thin metal wall, (4) no expensive and time consuming licensing procedures are necessary, because the test is housed in the tank designed for the maximum overpressure.
Keywords: two-phase flow, gas-liquid flow, nuclear thermal hydraulics, measuring technology
  • Lecture (Conference)
    11th Workshop on Two-Phase Flow Predictions, 05.-08.04.2005, Merseburg, Germany

Publ.-Id: 7052 - Permalink

Changes of Bacterial Community Structure of a Uranium Mining Waste Pile Sample Induced by Additon of U(VI)
Geissler, A.; Selenska-Pobell, S.; Scheinost, A.;
Bacteria can interact in different ways with uranium. Therefore, they play a major role in biogeochemical cycling of this element. Natural bacterial communities were studied of several different soil samples collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). The 16S rDNA retrieval showed that the communities were predominated by members of -Proteobacteria and Holophaga/ Acidobacterium. In order to analyse the influence of U(VI) on the natural bacterial community structure, one of the studied soil samples, containing originally 40 mg/kg U, was supplemented with nearly 60 mg/kg U(VI) as uranyl nitrate. After four weeks of incubation, selective sequential extractions revealed, that most of the added U(VI) was weakly complexed, hence remained bioavailable. The predominant bacterial populations were shifted from -Proteobacteria and Holophaga/Acidobacterium to Pseudomonas sp., Arthrobacter sp. and Geobacter sp.. Column experiments are in progress in our laboratory, which will help to improve our understanding of the influence of U(VI) on the natural bacterial community. The influence of aeration was also studied on the changes of the bacterial community structure induced by the addition of U(VI).
  • Lecture (Conference)
    Uranium Mining and Hydrogeology IV, 11.-16.09.2005, Freiberg, Germany
  • Contribution to proceedings
    Uranium Mining and Hydrogeology IV, 11.-16.09.2005, Freiberg, Germany
    Uranium in the Environment. Mining Impact and Consequences (B.J. Merkel, A. Hasche-Berger, eds.), Berlin: Springer, 3-540-28363-3, 199-205

Publ.-Id: 7051 - Permalink

Spectroscopic and microscopic characterization of gold nanoparticles formed by cells and S-layer sheets of Bacillus sphaericus JG-A12
Merroun, M.; Rossberg, A.; Hennig, C.; Romero-Gonzales, M.; Scheinost, A.; Selenska-Pobell, S.;
The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The cells of this strain are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters. It was demonstrated that this strain is enveloped by a surface layer protein (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different kind of molecules and also nucleation sites for formation of metal nanoclusters like Pd, for example. In this study we demonstrate that the cells of B. sphaericus JG-A12 and their purified and recrystallized S-layer are capable to bind effectively Au(III) from salt solutions. Moreover, in the presence of reducing agents such as molecular H2, Au(III) is reduced to metallic nanoclusters. Reduced gold nanoclusters were regularly distributed and sized according to the pores of the protein lattice. The metallic nature of the clusters was confirmed by different techniques such as EXAFS, XANES, UV-Vis spectroscopy and by X-ray powder diffraction. The size of the gold nanoparticles was estimated to be about 10 Å. Changes in functional groups in the cells and S-layer due to gold binding were observed by FT-IR microscopy. The cellular localization of the deposited Au(III) and of the gold nanoclusters was defined using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). The results demonstrated that B. sphaericus JG-A12 might be used to prepare gold nanoparticles that can be tailor-made for particular applications.
  • Lecture (Conference)
    The European Material Conference, 31.05.-03.06.2005, Strasbourg, France
  • Contribution to proceedings
    The European Material Conference, 31.05.-03.06.2005, Strasbourg, France

Publ.-Id: 7050 - Permalink

Influence of U(VI) on natural bacterial community of a soil sample from a uranium mining waste
Geissler, A.; Scheinost, A.; Selenska-Pobell, S.;
Bacteria have evolved several different mechanisms to tolerate uranium or to use U(VI) as terminal electron acceptor in anaerobic respiration. Because of this, bacteria play a major role in geomicrobiological cycling of uranium and can be used for the bioremediation of uranium-contaminated sites. In this work natural bacterial communities were investigated by the use of 16S rDNA retrievals in several soil samples from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). Inductively coupled plasma mass spectrometry (ICP-MS) and selective sequential extraction (SSE) analysis were used for the geochemical characterization of the soil samples. The 16S rDNA analysis showed that the natural bacterial communities were predominated by -Proteobacteria and Acidobacteria. SSE analysis demonstrated that the uranium was weakly complexed and bound by Mn(hydr)oxides or Fe(hydr)oxides. The soil samples contain in addition to uranium also other heavy metals like arsenic for example. In order to understand how U(VI) influences the structure of natural bacterial community, one of the studied samples with the lowest indigenous amount of U was supplemented with 60 mg/kg U(VI) in form of uranyl nitrate. After four weeks of incubation, SSE analysis and 16S rDNA retrieval were done in parallel. The SSE analysis demonstrated that most of the supplemented uranium was weakly complexed and remained probably bioavailable. The 16S rDNA retrieval showed that populations of Pseudomonas, Arthrobacter and Geobacter were stimulated by the addition of U(VI) to the soil sample. For more profound understanding of the influence of U(VI) on natural bacterial community, column experiments are running in our laboratory.
  • Poster
    15th Annual Goldschmidt Conference, 20.-25.05.2005, Moscow, Idaho, USA
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 69(2005)10, A230

Publ.-Id: 7049 - Permalink

Surface Bond Structure of Uranium Adsorbed onto Mine Water Colloids
Ulrich, K.-U.; Weiß, S.; Rossberg, A.; Scheinost, A.; Foerstendorf, H.; Zänker, H.;
The sorption complexes of uranium to colloidal ferrihydrite (Fh) were investigated by EXAFS and ATR FT-IR spectroscopy in mildly acidic solution (pH 5.5) in presence and in absence of atmospheric CO2. EXAFS has shown that sulfate, silicate, and carbonate are not involved as ligands bidentately bound onto the adsorbed U. Hence a new surface bond structure of U on hydrous ferric oxides is proposed which tightly fits the experimental EXAFS data. However, ATR FT-IR spectra suggest ternary uranyl carbonato surface complexes under these conditions open to the atmosphere. The conflicting spectroscopic results can be harmonized by proposing a monodentate linkage of the carbonate ligands.
  • Poster
    15th Users Meeting, 08.-11.02.2005, Grenoble, France

Publ.-Id: 7048 - Permalink

Synthese und Charakterisierung von fettsäuretragenden Technetiumkomplexen und deren Vorstufen
Jung, C. M.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-391 2003


Publ.-Id: 7047 - Permalink

Velocity measurements in metallic melts
Eckert, S.; Gerbeth, G.; Gundrum, T.; Stefani, F.;
Various developments of velocity measuring techniques, their test in different liquid metals, and applications in hot melts are reported. A Mechano-Optical Probe (MOP) performing local measurements up to temperatures of about 700°C has been developed and successfully tested. The Ultrasound Doppler Velocimetry (UDV) can be considered as another attractive technique to get velocity data from opaque flows. To extend the application range to higher temperatures and to abrasive liquids a new integrated ultrasonic sensor with an acoustic wave guide has been designed. First successful measurements in a CuSn melt of about 620°C and in liquid Al of about 750°C were carried out. A fully contactless investigation of the mean velocity field is possible by magnetic tomography. Local measurements of the induced magnetic field and the application of inverse reconstruction techniques allow an analysis of the flow structure. A first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure is presented.
Keywords: Velocity measurements, liquid metal, Ultrasound Doppler velocimetry, Magnetic flow tomography
  • Lecture (Conference)
    2005 ASME Fluids Engineering Division Summer Meeting, 19.-23.07.2005, Houston, TX, United States
  • Contribution to proceedings
    2005 ASME Fluids Engineering Division Summer Meeting, 19.-23.07.2005, Houston, TX, United States
    Proceedings of the American Society of Mechanical Engineers Fluids Engineering Division Summer Conference, (2005)6, 49-56

Publ.-Id: 7045 - Permalink

Memory devices obtained by Si+ irradiation through poly-Si/SiO2 gate stack
Dimitrakis, P.; Normand, P.; Vontintseva, E.; Stegemann, K.-H.; Heinig, K.-H.; Schmidt, B.;
iIon irradiation induced interface mixing was used to generate silicon nanoclusters at the SiO2-Si interface of metal-oxide-semiconductor (MOS) structures aiming at electronic memory applications. No particular processing issues have been encountered during integration of this technique in standard submicronic C-MOS technology. The memory properties of the fabricated structures as a function of the Si+-irradiation dose and post-irradiation temperature and time have been examined through electrical measurements of capacitors and transistors. Low-voltage operating devices that can endure more than 106 programming/erasing cycles have been successfully achieved. While excellent device uniformity and reproducibility have been observed over 6-inch wafers, more research is still required to improve charge retention and ensure the standard 10-year retention time needed for true non-volatile memory applications.
  • Lecture (Conference)
    2nd Conf. on Microsystems, Microelectronics and Nanotechnology 2004, 14.-17.11.2004, Athene, Greece
  • Open Access LogoJournal of Physics: Conference Series 10(2005), 7-10

Publ.-Id: 7044 - Permalink

Impact of Humic Acid on the Uranium Migration in the Environment
Sachs, S.; Geipel, G.; Mibus, J.; Bernhard, G.;
The remediation of contaminated areas and facilities of the former uranium mining and milling in Saxony and Thuringia (Germany) requires detailed knowledge on the uranium migration in natural aquifer systems. Humic acids (HA), polyelectrolytic organic macromolecules, are of importance for the mobilization of radiotoxic and toxic metals in the environment due to their ability for complex and colloid formation. In addition, HA are characterized by redox properties that can influence the oxidation state of metal ions which effects their speciation and consequently their migration behavior.

In order to improve the knowledge on the interaction between HA and uranium we characterized the redox properties of different HA (Eh values, Fe(III) redox capacities) and studied the stability of the oxidation state of U(VI) in presence of HA on a time-scale of several weeks. We obtained a spectroscopic proof for the reduction of U(VI) to U(IV) by HA with pronounced redox functionalities applying laser-induced photoacoustic spectroscopy.

This demonstrates a possible relevance of HA for the migration of tetravalent actinides. Therefore, we investigated the transport behavior of the redox couple U(IV)/U(VI) in presence of HA in quartz sand by column experiments. Retardation factors and eluate recoveries were determined. We found that HA influences the transport of both, U(IV) and U(VI). In presence of HA both redox species migrate nearly as fast as the groundwater flow. In case of U(VI) HA exhibits a significant mobilizing effect. There are strong indications for a similar impact on the U(IV) transport.
Keywords: Humic acid, uranium, redox processes, migration, reduction
  • Lecture (Conference)
    Uranium Mining and Hydrogeology UMH IV, 11.-16.09.2005, Freiberg, Germany
  • Contribution to proceedings
    Uranium Mining and Hydrogeology UMH IV, 11.-16.09.2005, Freiberg, Germany
    Uranium in the Environment. Mining Impact and Consequences (B.J. Merkel, A. Hasche-Berger, eds.), Berlin: Springer, 3-540-28363-3, 107-116

Publ.-Id: 7043 - Permalink

Interaction of Uranium from Seepage Water with Hydroxyapatite
Mibus, J.; Brendler, V.;
The ability of hydroxyapatite Ca10(OH)2(PO4)6 (HAP) to immobilize metal ions, particularly lanthanides and actinides, is well known. The long-term stability of this fixation is proven by natural analogue studies. Thus, HAP is a potential filling material in engineered barriers in abandoned mining areas as well as in the near-field of underground repositories for nuclear and toxic waste.
The interaction of U(VI) with HAP was studied in batch and unsaturated column experiments and by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We investigated a seepage water from Schlema (Saxony) with a Uranium concentration of 10-5 M and a syn-thetic HAP packed in a matrix of purified quartz sand.
The batch sorption experiments show 100 % adsorption of UO22+. The break-through curves measured in the column experiments with continuous pulse injection yield a retardation factor Rf = 33.2 ± 1.5 compared to the conservative tracer tritiated water. This value corresponds to the strong adsorption behavior. An elution of the column with ten pore volumes of a uranium-free solution revealed a distinct tailing and a uranium recovery near unity. Thus, the sorption process proved reversible. The TRLFS measurements facilitate a differentiation of uranium bound to the HAP surfaces and to the quartz matrix. Furthermore, the surface speciation of uranium could be identified. Finally, a numerical model using the reactive transport code Crunch describes the transport behavior of uranium.
Keywords: uranium, hydroxyapatite, adsorption, column experiments, spectroscopy
  • Contribution to proceedings
    Uranium Mining and Hydrogeology IV, 11.-16.09.2005, Freiberg, Germany
  • Poster
    Uranium Mining and Hydrogeology IV, 11.-16.09.2005, Freiberg, Deutschland

Publ.-Id: 7041 - Permalink

In situ speciation of actinides with a newly developed spectro-electrochemical cell
Hennig, C.; Tutschu, J.; Rossberg, A.; Scheinost, A. C.; Bernhard, G.;
Natural aquatic and terrestrial environments exert large variations in redox state due to oxygen diffusion on one hand and microbial processes on the other hand. Actinides with their large number of oxidation states are especially susceptible to these redox changes, forming different aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell, which allows to study the structure and speciation of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell is gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement. First U LIII-edge X-ray absorption spectra have been obtained from aqueous solutions of U(VI) and U(IV) in high concentrated chloride solutions.
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-418 Januar 2005, 9-14


Publ.-Id: 7040 - Permalink

MoBeE, Prozesssteuerung an der Molekularstrahl-Epitaxie-Anlage
Heer, R.; Wagener, M.; Winnerl, S.;
Dokumentation zu einem IDL-basierten Steuerprogramm für die Prozesssteuerung einer MBE-Anlage
  • Other report
    Jülich: Interner Bericht FZJ-ZEL-IB-500104, 2004
    86 Seiten

Publ.-Id: 7038 - Permalink

Identification and validation of ductile damage parameters by the small punch test
Kuna, M.; Abendroth, M.;
The small punch test (SPT) is a suitable miniaturized test method to determine the actual and local material state in structural components under operating conditions. A combined experimental-numerical approach is presented to identify material parameters of plastic deformation and ductile damage behaviour from the SPT. Neural networks (NN) are generated and trained by finite element simulations to obtain the relation between a load displacement curve of the SPT and the matching material parameters. These parameters, identified from the SPT, are validated by reference values determined from smooth and notched tensile specimens. Next, the same parameters are used to simulate the ductile crack growth in fracture specimens by means of finite elements. This way, even fracture thoughness data J_Ic of the materials could be successfully predicted. These findings substantiate the feasibility to gain comprehensive material characteristics from the SPT and their transferibility to quantify the ductile failure of strucural components.
Keywords: Small punch test, ductile damage, neural networks, finite elements, parameter identification
  • Contribution to proceedings
    15th European Conference of Fracture (ECF 15), 11.-13.08.2004, Stockholm, Sweden

Publ.-Id: 7037 - Permalink

Geochemische Prozesse bei der Ausbreitung von Schadstoffen aus einem Endlager für radioaktive Abfälle
Altmaier, M.; Brendler, V.; Bosbach, D.; Kienzler, B.; Marquardt, C.; Neck, V.; Richter, A.;
Die Studie beinhaltet die Sichtung, Zusammenstellung und Bewertung der zur Bearbeitung sicherheitstechnischer Fragestellungen benötigten Daten für die Modellierung geochemischer Prozesse. Der Abschlussbericht basiert auf den im Rahmen dieses Projektes erstellten Zwischenberichten. Die nach Sichtung und, soweit möglich, kritischer Begutachtung ausgewählten Daten sind in einem separaten Anhang in tabellarischer Form zusammengestellt.
Keywords: geochemical modeling, safety engineering, radioactive waste, repository, sorption, aquatic species, interaction
  • Other report
    Karlsruhe: Forschungszentrum Karlsruhe, 2004
    520 Seiten
  • Lecture (others)
    Workshop BfS: Sicherheitstechnische Einzelfragen der Endlagerung, 28.-29.09.2005, Hannover, Germany

Publ.-Id: 7036 - Permalink

Exploring the Spatial Resolution of the Photothermal Beam Deflection Technique in the Infrared Region
Seidel, W.; Foerstendorf, H.; Glotin, F.; Ortega, J.-M.; Prazeres, R.;
In photothermal beam deflection (PTBD) spectroscopy generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry. Recent resulrs of PTBD experiments are presented with a high spatial resolution which is near the diffraction limit of the infrared pump beam.
  • Poster
    26th International Free Electron Laser Conference & 11th FEL User Workshop, 29.08.-03.09.2004, Trieste, Italy
  • Contribution to proceedings
    26th International Free Electron Laser Conference & 11th FEL User Workshop, 29.08.-03.09.2004, Trieste, Italy
    Proceedings of the 26th International Free Electron Laser Conference & 11th FEL User Workshop, 679-680

Publ.-Id: 7035 - Permalink

Anwendung des Master-Curve-Konzeptes zur Zähigkeitscharakterisierung inhomogener Reaktordruckbehälterstähle
Viehrig, H.-W.; Wallin, K.;
Die auf dem “Master-Curve” (MC)-Konzept basierende ASTM-Prüfvorschrift E 1921 ist für die Ermittlung einer Referenztemperatur T0 homogener Stähle mit einer kubisch-raumzentrierten (ferritischer) Grundstruktur konzipiert. In der Realität sind große Schmiederinge, Grobbleche und insbesondere Schweißverbindungen makroskopisch oft nicht homogen. Aus diesem Grund wurden auf dem MC-Konzept basierende Verfahren entwickelt, mit denen sich Referenztemperaturen von inhomogenen Stähle ermitteln lassen. An russischen Reaktordruckbehälterstählen des Typs 15Kh2MFA werden J-Integral basierte Bruchzähigkeitswerte KJc beim Ein-satz von Spaltbruch gemessen und nach der Standard MC-Methode und den modifi-zierten Verfahren ausgewertet.
The Master Curve (MC) approach of defining reference transition temperature, T0, has been standardized in ASTM Standard Test Method E 1921. The basic MC approach for analysis of fracture test results is intended for macroscopically ho-mogeneous steels with a body centred (ferritic) structure only. In reality, the steels are seldom fully macroscopically homogeneous. In this paper, new comparatively simple extensions of the MC are applied on forgings of Russian reactor pressure vessel steel 15Kh2MFA. J-integral based fracture toughness values KJc measured at the onset of cleavage fracture were evaluated with the basic MC evaluation, the lower tail modification of the SINTAP procedure, a bimodal estimation and a maxi-mum likelihood estimation of the random inhomogeneity.
Keywords: fracture toughness, cleavage fracture, Master Curve approach, reactor pressure vessel steel, inhomogeneous structure
  • Lecture (Conference)
    37. Tagung des DVM-Arbeitskreises Bruchvorgänge, 22.02.2005, Hamburg-Harburg, Germany

Publ.-Id: 7034 - Permalink

Quasi-particle model of strongly interacting matter
Bluhm, M.; Kämpfer, B.; Soff, G.;
The successful quasi-particle model is compared with recent lattice data of the coefficients in the Taylor series expansion of
the excess pressure at finite temperature and baryon density. A chain of approximations, starting from QCD to arrive at the model expressions for the entropy density, is presented.
Keywords: Equation of state, Strongly interacting matter, Lattice QCD
  • Contribution to proceedings
    8th International Conference on Strangeness in Quark Matter 2004, 15.-20.09.2004, Cape Town, South Africa
  • Contribution to WWW
  • Journal of Physics G 31(2005), S1151-S1154

Publ.-Id: 7033 - Permalink

Synthesis of 18F-labeled acyclic purine and pyrimidine nucleosides intended for monitoring gene expression
Grote, M.; Noll, B.; Noll, S.;
Non-invasive imaging of genes which are introduced into cells is a useful method for gene therapy monitoring. The labeling of acyclic purine and pyrimidine nucleoside derivatives with fluorine-18 required for the HSV-1 tk imaging approach with Positron Emission Tomography (PET) 18 is described. The methoxytritylated and tosylated precursors were radiolabeled using a K[18F]F/kryptofix 2.2.2TM complex, followed by removal of the protecting groups under acidic conditions and HPLC purification. The radiochemical yields of the 18F-tracers amount to 5 - 15 % (decay corrected) after a synthesis time of 85 - 95 min, the radiochemical purity was > 98 % with an average specific activity of 19 GBq/μmol at the end of synthesis.
Keywords: fluorine-18, PET, gene expression, HSV-1 tk
  • Radiochimica Acta 93(2005)9-10, 585-588

Publ.-Id: 7032 - Permalink

Speciation of Colloid-borne Uranium by EXAFS and ATR-IR spectroscopy
Ulrich, K.-U.; Rossberg, A.; Foerstendorf, H.; Weiß, S.; Zänker, H.; Jenk, U.;
Molecular speciation is a prerequisite for reliable assessment of contaminant migration in the environment. We use sophisticated techniques for concentrating colloids (e.g. ultracentrifugation, ultrafiltration) in combination with Extended X-ray Absorption Fine Structure (EXAFS) and Attenuated Total Reflectance Infrared (ATR IR) spectroscopy to investigate the speciation of colloid-borne uranium in waters which occur in abandoned ore mines. Mine flooding was simulated in a 100 L scale by mixing acid mine water of elevated U concentration and near-neutral groundwater from an aquifer above the mine until pH~5.5 was reached. The generated colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, sil-ica, and carbon compounds. EXAFS analysis at the U-LIII absorption edge suggested a bidentate surface complex of UO22+ on FeO6 octahedra, but two minor backscattering contributions in the vicinity of the absorber remained unexplained. Since only Al could be excluded as backscattering atom, we studied U sorption on Fh at pH 5.5 in presence and in absence of sulfate, silicate, and atmospheric CO2 to clarify the bond structure.

EXAFS showed the unknown backscattering contributions in all the sorption samples regardless of the presence or absence of the tested components. Contrary to structural models in the literature, bidentately complexed carbonate ligands cannot explain the results when using U concentrations around 0.1 mM. But ATR-IR spectra showed that U(VI) carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately, which is currently being studied. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. Monte-Carlo Target Transform Factor Analysis was employed to test if the EXAFS spectra could be fitted by a struc-ture including exclusively Fe, U, and O atoms. We propose a new model in which the bidentately bridged UO22+ is oriented in a way that yields a distance of ~2.9 Å to the O atom of an adjacent, edge-shared FeO6 octahedron. This model predicts a second Fe shell at ~4.35 Å which tightly fits the experimental data.

Summarizing, uranium may form different sorption complexes with colloidal Fh: a binary bidentate uranyl complex with modified orientation, and ternary U carbonato complexes with monodentate linkage of the carbonate ligands, depending on specific conditions.
  • Lecture (Conference)
    Uranium Mining and Hydrogeology - UMH IV, 11.09.2005, Freiberg, Germany
  • Poster
    Uranium Mining and Hydrogeology - UMH IV, 11.-16.09.2005, Freiberg, Deutschland
  • Contribution to proceedings
    Uranium Mining and Hydrogeology - UMH IV, 11.-16.09.2005, Freiberg, Germany
    Uranium in the Environment. Mining Impact and Consequences (B.J. Merkel, A. Hasche-Berger, eds.), Bergakademie Freiberg: Springer, 3-540-28363-3, 137-147

Publ.-Id: 7031 - Permalink

Application of the normalization method for the determination of J-R curves
Dzugan, J.; Viehrig, H.-W.;
The performance of the normalization method (NM) is evaluated and compared with the standard unloading-compliance method of fracture-toughness analysis for a broad spectrum of different materials and specimen geometries. The critical J-integral values based on the normalization method are summarized and compared with the results of unloading compliances tests. The results demonstrate the applicability of the normalization method for the J-R curve determination for a range of steels. The normalization method yields results, which deviate as much as 15 % from the values obtained with the unloading compliance method, and thus results of acceptable accuracy can e attained with this method.
Keywords: Fracture mechanics; Fracture toughness; Normalization method; Unloading compliance
  • Materials Science and Engineering A 387(2004), 307-311

Publ.-Id: 7030 - Permalink

Results and Conclusions from Fracture Toughness Tests in IAEA CRP-5
Viehrig, H.-W.; Planman, T.; Server, W. L.;
This paper provides a summary of Master Curve fracture toughness test results on small surveillance-type single- edge bend (SE(B)) and one-inch thick compact tension (1T-CT) specimens of the IAEA reference reactor pressure vessel (RPV) steel JRQ and other national RPV steels from numerous laboratories throughout the world. The JRQ test blocks distributed to the different laboratories were mainly from test plate 6JRQ. The mean fracture toughness of the 6JRQ plate material generally can be described satisfactorily with the standard Master Curve method from ASTM E 1921-02. The mean T0 values shows in accordance with previous investigations that a bias of around 10 K exists between the T0 values of CT and SE(B) specimen types so that CT specimens give higher T0. The analyses of both JRQ and national RPV steels confirm that the procedures specified in ASTM E 1921-02, as well as the SINTAP procedure, are generally valid and applicable for characterizing RPV type steels and even steels showing distributed inhomogeneity.
Keywords: reactor pressure vessel steel, cleavage fracture toughness, Master Curve, inhomogeneity
  • Lecture (Conference)
    IAEA Specialists meeting "Irradiation effects and mitigation in Reactor Pressure Vessel", 28.05.2004, Gus Khrustalny, Russia

Publ.-Id: 7029 - Permalink

Wavelet transformation for image analysis and signal processing: some estimations and real applications
Chukalina, M.; Funke, H.; Dubrovskii, Y.; Golossio, B.; Shapoval, S.; Ivanov, D.; Volkov, V.; Simionovici, A.; Somogyi, A.;
wird nachgereicht
  • Contribution to proceedings
    The 6-th Open Russian-German Workshop on Pattern Recognition and Image Understanding, 25.-30.08.2004, Village Katun of Altai Region, Russia, 153-156

Publ.-Id: 7028 - Permalink

Sage of wavelet transform for extraction of the information needed to describe an object
in Russian
Chukalina, M.; Funke, H.;
wird nachgereicht
  • Contribution to proceedings
    Book of Proceedings. Intelligent systems AIS-04 IEEE Conference, 03.-10.09.2004, Divnomorskoe, Russia
    Proceedings, 194-198

Publ.-Id: 7027 - Permalink

An approach to the analysis of EXAFS spectra based on the wavelet transformation
in Russian
Chukalina, M.; Funke, H.;
wird nachgereicht
  • Izvestija Akademii Nauk SSSR 60(2004)2, 235-238
  • Contribution to proceedings
    Book of Proceedings on X-ray optics, 02.-06.05.2004, Nizhnii Novgorod, Russia, 106-111

Publ.-Id: 7026 - Permalink

Wavelet analysis and its application to the Tunneling and X-ray spectroscopy
in Russian
Chukalina, M.; Funke, H.; Dubrovskii, Y.;
The capabilities and limitations of wavelet analysis are demonstrated for the illustrative case of two practial applications: investigation of magneto-tunneling signals and the extended x-ray absorption fine structure (EXAFS) of uranium. A brief introduction to wavelet analysis is given. The term "window size" of the mother wavelet function is defined; this concept underlies one of the ideas for a criterion of optimal choice of the mother wavelet function. The capabilities of a software package developed by the authors are demonstrated; this software was used for all the calculations done in the course of this study.
  • Low Temperature Physics 30(2004)11, 1235-1243

Publ.-Id: 7025 - Permalink

Wavelet analysis of Extendet X-ray Absorption Fine Structure Data
Funke, H.; Chukalina, M.; Rossberg, A.;
Extended Xray absorption fine structure data evaluation usually begins with the Fourier transform of the spectrum. We suggest the wavelet transform as a complement to the Fourier transform. While the Fourier transform analyzes the distances to the backscattering atoms, wavelet transform additionally reveals the wavenumber dependence of the scattering. Thus wavelet analysis can differentiate between heavier and lighter backscattering atoms, even if they are almost equidistant from the central atom. First the method of operation and the advantage of the wavelet analysis will be demonstrated by simple models. Then it is applied to the interpretation of extended Xray absorption fine structure spectra concerning the complexation of UraniumVI with the carboxylic groups acetic, formic, and glycolic acid. The wavelet transform analysis suggests clearly for the system Uraniumformic acid both, UU and UCC, structural elements. In contrast to the clear separation of different scattering paths by wavelet transform, Fourier transform analysis was not able to resolve the two different backscattering processes.
  • Physica Scripta T115(2005), 232-234

Publ.-Id: 7024 - Permalink

Effects of data scatter and inconsistency in sorption modeling
Richter, A.; Brendler, V.; Nebelung, C.;
Surface Complexation Models (SCM) can describe sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. The effect of parameter uncertainty in blind predictions is illustrated by the example of Np(V) sorption onto hematite.
The Diffuse Double Layer (DDL) model was chosen as SCM submodel to keep the number of parameters at a minimum. From the surface species reported so far, =FeOH2+, =FeO-, =FeONpO2, =FeONpO2(HCO3)22-, =FeOHCO2, and =FeOCO2- were selected with their normalized DDL reaction constants log Kn, taken from the RES³T database (Brendler et al., 2003).
The modeling was performed with the FITEQL code, version 3.2. The predictions were evaluated by comparison with the experimental results by Kohler et al. (1999), comprising of 52 data points for the Np(V) sorption at varied pH, ionic strength, solid/liquid ratio, Np content, and air PCO2. When focusing on the conventional distribution coefficient KD, the maximum deviation for all data subsets is less than one order of magnitude, a spreading considered to be reasonable in performance assessment applications.
Because the protolysis constants can not be varied independently, the point of zero charge (PZC) and delta pK were calculated based on experimental pK1 and pK2. Consequential we generated 20 independent pK data sets with the aid of Gaussian-distributed random numbers. None of these parameter sets did deliver unacceptable blind predictions for the distribution coefficients.
The formally large scatter of pK values as extracted from literature is actually not critical. Even the use of inconsistent values from other electrostatic models will yield similar results. For well-defined mineral systems, provided a suitable database is accessible, the SCM approach seems to be promising.
(References: Brendler V. et al. (2003), J. Cont. Hydrol., 61, 281-291.; Kohler M. et al. (1999), Radiochim. Acta, 85, 33-48.)
Keywords: sorption, database, diffuse double layer model, surface complexation, neptunyl, hematite
  • Lecture (Conference)
    15th Annual Goldschmidt Conference 2005, 20.-25.05.2005, Moscow (Idaho), United States
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 69(2005)10, A421

Publ.-Id: 7022 - Permalink

Study of micromechanical properties of ion-beam mixed tungsten-on-steel layers
Piatkowska, A.; Jagielski, J.; Gawlik, G.; Matz, W.; Richter, E.; Mozetic, M.; Zalar, A.;
The relations linking structure, microhardness and adhesion were studied for ion-beam mixed tungsten layers deposited on the surface of high-speed steel. The 45 nm thick W layer were mixed with 340 keV Kr ions at temperatures ranging fro, RT up to 450°C. The increase of mixing temperature results in partial crystallization of the layers and the increase of the layer hardness. Substantial increase of layer adhesion has been observed in scratch tests for all mixed samples.
Keywords: ion-beam mixing; thin layers; adhesion; micromechanical properties

Publ.-Id: 7020 - Permalink

Recursive Coupling of Thermal and Mechanical FE-Models of a Creeping Pressure Vessel with a Heated Melt Pool
Willschuetz, H.-G.; Altstadt, E.; Weiss, F.-P.;
To gain a better understanding of the behavior of the reactor pres
sure vessel lower head in case of a core meltdown scenario in a light water reactor experiments have been conducted worldwide. Especially for experiments including a heated melt pool in the lower head like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes and the dislocation of the melt pool due to the expanding vessel.
Therefore a 2D Finite Element Model with 3 different sub models is developed based on the code ANSYS® Multiphysics. A thermal sub model includes planar and contact elements for conductive heat transfer. Additional surface elements are used to simulate convection and radiation from outer surface areas and a radiation matrix is used to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers there is no turbulence model that correctly simulates the heat transfer. Therefore an Effective Conductivity Convectivity Model is implemented to simulate the heat transfer from the melt pool to its boundaries.
The resulting temperature field of the vessel wall is applied to the mechanical sub model of the vessel. To describe the visco-plastic deformation a numerical creep data base was developed where the creep strain rate is evaluated in dependence on the current total strain, temperature, and equivalent stress. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The third sub model uses hyperelasticity and contact elements to move the melt pool along with the creeping vessel wall.
In this paper the differences between the results of a simple coupled and a recursive coupled FE-simulation are highlighted. Due to the thermal expansion at the beginning and the accumulating creep strain later on the shape of the melt pool and of the vessel wall are changing. Despite the fact that these relative small geometrical changes take place relatively slowly over time, the effect on the temperature field is rather significant concerning the mechanical material behavior and the resulting failure time. Assuming the same loading conditions the change in the predicted failure time between the simple and the recursive coupled model is in the order of magnitude of the total failure time of the simple model. The comparison with results from the FOREVER-experiments shows that the recursive coupled model is closer to reality than the single step model.
Keywords: Severe Accident with Core Melt Down, FE-Model, Recursive Coupling of Thernal and Mechanical Model, Prediction of Vessel Failure
  • Lecture (Conference)
    ICAPP 2005, International Congress on Advances in Nuclear Power Plants, 15.-19.05.2005, Seoul, Korea
  • Contribution to proceedings
    ICAPP 2005, International Congress on Advances in Nuclear Power Plants, 15.-19.05.2005, Seoul, Korea
    ICAPP 2005 Proceedings on CD-ROM, Paper 5629, Seoul: Korean Nuclear Society

Publ.-Id: 7017 - Permalink

The effect of parameter uncertainty on blind prediction of Np(V) sorption onto hematite using the Diffuse Double Layer Model
Richter, A.; Brendler, V.; Nebelung, C.;
The aim of this work is to illustrate the effect of parameter uncertainty (protolysis constants) in surface complexation modeling. As example the blind prediction of Np(V) sorption onto hematite was selected, applying the Diffuse Double Layer Model (DDLM).
None of the pK parameter sets randomly generated within a space of two standard deviations did deliver unacceptable predictions for the distribution coefficients. Thus the formally large spreading of the pK values as extracted from literature (even after normalization and extrapolation to infinite dilution) is actually not critical. For well-defined mineral systems, provided a suitable database is accessible, the DDLM approach seems to be promising.
Keywords: sorption, database, diffuse double layer model, uncertainty analysis, neptunyl, hematite
  • Radiochimica Acta 93(2005)9/10, 527-532

Publ.-Id: 7016 - Permalink

Magnetfeldgesteuerte Formfüllung
Cramer, A.; Eckert, S.; Galindo, V.; Gerbeth, G.;
Den gestiegenen Anforderungen bei der Herstellung immer komplexerer, dünnwandigerer und auch größerer Feingussteile kann mit der gezielten elektromagnetischen Strömungsbeeinflussung der Schmelze über magnetische Felder begegnet werden. Hierbei kann auf kontaktlose Weise die Zuströmung hinsichtlich einer optimalen Füllung der Gießform kontrolliert werden. Die aufgabenspezifische Auswahl aus einer Vielzahl technisch realisierbarer Feldarten und die Parametrierung erfordert die Kenntnis der typenspezifischen Wirkungsweise auf die Strömung und der jeweils zu erwartenden Stärke des Einflusses. Das erste Kapitel liefert deshalb einen Einstieg in die Grundlagen der Strömungskontrolle mit Magnetfeldern.

Im realen Prozess sind in-situ Untersuchungen der Strömungsvorgänge in der Regel nicht möglich. Eine Beurteilung des Endproduktes kann zwar, in begrenztem Umfang, den Einfluss magnetischer Felder auf dessen Qualität liefern, nicht aber die Wirkkette oder gar ein umfassendes Verständnis. Die Auslegung der Felder stützt sich von daher meist auf numerische Strömungssimulationen oder Modellexperimente. Warum etwa Wasserexperimente für die weitaus meisten metallurgischen Prozesse ungeeignet und numerische Simulationen alleine nicht ausreichend sind, wird in Kapitel zwei beschrieben.

Auch in den vergleichsweise „kalten“ Modellexperimenten bleibt die für die Optimierung des Magnetfeldeinsatzes erforderliche Bestimmung von Strömungsgeschwindigkeiten weiterhin problematisch. Die für transparente Flüssigkeiten kommerziell verfügbaren Methoden LDA (Laser Doppler Anemometrie), PIV (Particle Image Velocimetry) oder auch das Einbringen von Farbstoffen und/oder Schwebeteilchen zur Visualisierung sind auf Grund der Undurchsichtigkeit von Metallschmelzen nicht anwendbar. Kapitel 3 gibt einen Überblick über die für Flüssigmetallströmungen geeigneten Messtechniken.

Im Hauptkapitel 4, welches sich mit Beispielanwendungen beschäftigt, wird zunächst über den erfolgreichen Einsatz einer Magnetfeldbremse, von der Auslegung des Feldes bis hin zur Implementierung, im industriellen Aluminium-Feinguss berichtet. Dem schließt sich eine Beschreibung einer weitergehenden Prozessoptimierung mittels eines linearen Mehrphasen-Wechselfeldes an, welche das Potenzial des „Maßschneiderns“ von Magnetfeldern demonstriert. Den Abschluss bildet die Erstarrung im rotierenden Magnetfeld, die als ein weiteres Beispiel für die Vielfalt der elektromagnetischen Kontrolle im Bereich der Metallurgie dienen möge.
  • Invited lecture (Conferences)
    VDG-Seminar, "Technologie des Feingießens", 12.-13.10.2004, Bad Dürkheim, Germany
  • Contribution to proceedings
    VDG -Qualifikationslehrgang, 12.-13.10.2004, Bad Dürkheim, Germany
    "Technologie des Feingießens"

Publ.-Id: 7013 - Permalink

Local velocity measurements in electromagnetically forcedconfined flows
Cramer, A.; Stefani, F.; Gundrum, T.; Varshney, K.;
For a physical modelling of hot and chemically aggressive metallic melts in industrial processes, the according experiments are done mostly on water. Besides the fact that the important influence of magnetic fields on the flow cannot be studied at all, the majority of these results are meaningless owing to the non-matching similarity criteria, such as for instance the Prandtl number in the case when thermal gradients are involved. Realistic models rely on low melting point metals the flow of which is not easily measurable by „of the shelf“ equipment.
Rather than giving a systematic review of the measuring techniques available for liquid metal flows, the presentation will concentrate on electric potential probes (EPP) and the up and coming ultrasonic Doppler velocimetry (UDV). These methods will be compared with respect to their applicability and characteristics such as sensitivity, dynamic range, and spatial as well as temporal resolution. Several practically orientated examples have been selected to demonstrate the state of the art performance of both these techniques.
In crystal growth processes rotating magnetic fields (RMFs) are often employed for homogenisation purposes while it is mandatory to keep the flow almost stationary. Well below the threshold of linear stability, the transition from the Stokes-regime to a laminar boundary layer flow was quantified by EPP.
The flow mapping capabilites of UDV have turned out to be a powerful tool for the determination of topological details of the convective pattern.
Scaling laws known from theory may be proved by precision measurements. This was done for the ~Ta2/3-dependence in the RMF by EPP and the ~B-characteristic in a single-phase AC (pulsating) magnetic field by UDV.
Whereas „Kolmogorov-like“ spectra were obtained from the swirling flow, large scale structures with the according low frequency oscillations were found within the recirculation. A video prepared from a sequence of the correlated velocity information contained in each UDV-profile impressively shows the spatio-temporal behaviour of such coherent structures.
To complete with the modern developments in velocity measuring techniques in electrically conduction fluids, the principles of the inverse reconstruction from measurements of the flow-induced magnetic field outside the fluid volume will be outlined. A first benchmark of this method clearly shows its robustness and the ranges of applicability.
  • Invited lecture (Conferences)
    Seminarreihe der Forschergruppe Magnetofluiddynamik, 20.10.2004, Ilmenau, Germany

Publ.-Id: 7012 - Permalink

Numerical and experimental studies on electomagnetic stirring
Stiller, J.; Frana, K.; Grundmann, R.; Cramer, A.; Varshney, K.; Gerbeth, G.;

We present direct numerical simulations (DNS) of the flow in a finite cylinder driven by a rotating magnetic field. The main idea is that externally applied magnetic field can be used to control the motion of the liquid during the growth of single crystals in a good electrical conductors. The experiments have demonstrated that rotating magnetic field produced much better solid-solution or alloyed crystals and reduce small-scale spatial oscillations of the additive concentration in nearly pure crystal. The subject is complicated by the fact that the Taylor-Görtler instability of the side layer and the instability of the Bödewadt-type horizontal layer occur in the flow depending on the aspect ratio and magnetic Taylor number Employing the rigid-body and low-frequency approximations the mathematical model reduces to the Navier-Stokes equations with a priori known Lorentz force. A second-order finite-element method combined with Adams-Bashforth time integrations is used for discretization.
The transient and early turbulent flow regimes have been investigated in detail by numerical computation. Some characteristic features such as dominating large structures and homogenous rotating core have been identified in flow. Furthermore, weak secondary flow appear near the top and bottom of the walls due to existence of the Bödewadt layers.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7011 - Permalink

Application of RMF during solidification and ist influence on the microstructure of solidified PbSn Alloys
Willers, B.; Eckert, S.; Michel, U.; Haase, I.; Zouhar, G.; Nikritjuk, P. A.; Eckert, K.;
It is already known that the microstructure of a metallic alloy can be affected in a significant way due to the convection in the liquid phase during solidification. A time varying magnetic field can be applied to produce a flow field in the melt which influences the nucleation and growth processes. The aim of our research program is to find an strategy to refine the microstructure of castings by an optimal combination of magnetic field intensity, field frequency and cooling rate. Furthermore, the basic mechanisms controlling the solodification by magnetic fields are investigated.
  • Lecture (Conference)
    International Workshop on "Flow Control by Tailored Magnetic Fields (FLOWCOMAG)", 01.-02.04.2004, Dresden, Germany

Publ.-Id: 7010 - Permalink

Stirring with Rotating Magnetic Fields: Numerical and Experimental Results
Stiller, J.; Cramer, A.; Frana, K.; Varshney, K.;
This work is concerned with the convection in a finite cylinder driven by a rotating magnetic field. Both direct numerical simulation (DNS) and experiments have been carried out to study the characteristics of this kind of confined flows. A decoupling of the mathematical model into the Navier-Stokes equations and an a priori known Lorentz force was achieved in the usual manner by employing the rigid-body and the low-frequency approximations. Adams-Bashforth time integration has been combined with a second-order finite element method for the discretisation. Utilising the upcoming technique of Ultrasonic Doppler Velocimetry (UDV) allowed for a mapping of the meridional velocity components throughout an entire section of the container. In a more quantitative fashion potential difference measurements (PDM) were performed to support and validate the numerical results.
  • Lecture (Conference)
    International Workshop on "Flow Control by Tailored Magnetic Fields (FLOWCOMAG)", 01.-02.04.2004, Dresden, Germany

Publ.-Id: 7009 - Permalink

Magnetohydrodynamik drag reduction and efficiency
Shatrov, V.; Gerbeth, G.;
Two cases are considered in order to study possible drag reductions due to the action of electromagnetic forces.
1. A direct numerical simulation of a turbulent channel flow is performed. The unsteady Navier-Stokes equations and Poisson electric potential equation are solved at a Reynolds number Re=3000 and 6000, based on the laminar centreline velocity V0 and channel half-width d. The tau-collocation spectral method developed by J. Kim. et al. is used. The Crank-Nikolson method for the viscous and a third-order Runge-Kutta method for the nonlinear term and the Lorentz force are applied. The resolution was 64x65x64 in the streamwise, wall-normal and spanwise directions. For an electromagnetic actuator consisting basically of a spanwise oscillating force, we analysed the drag reduction and its efficiency for various load number. It is shown that a load number of order one leads to a significant increase of the efficiency in comparison to the standard case of high small load number.

2. For the flow around a sphere we found an internal alternating electromagnetic field source which leads to a strong drag reduction. The analysis is done in the Stokes approximation analytically and then at Reynolds number Re ~ 300 numerically using a pseudospectral code. A simple gradient-type optimisation was applied in order to tailor the magnetic field source for the purpose of a reduced drag. We considered the simplified case (decoupling of fluid flow and electromagnetic fields) of large load numbers, with the drawback that the strong drag reductions obtained are certainly inefficient from the energetical point of view.
  • Lecture (Conference)
    Interational Workshop "Flow Control by Tailored Magnetic Fields", 01.-02.04.2004, Dresden, Germany

Publ.-Id: 7008 - Permalink

Experiments on the magnetic field influence on liquid metal two-phase flows
Zhang, C.; Eckert, S.; Gerbeth, G.;
The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC longitudinal magnetic field was examined. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4×10-13. The liquid metal was in a cylindrical container at rest. Bubble and liquid velocities were measured using the Ultrasound Doppler Velocimetry (UDV). The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. Whereas for small bubbles (de £ 4.6 mm) an increase of the drag coefficient with increasing magnetic interaction parameter was observed, the application of the magnetic field reduces the drag coefficient of larger bubbles (de ³ 5.4 mm). The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddies in the wake. The Strouhal number St decreases with increasing magnetic interaction parameter.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7007 - Permalink

Electromagnetic levitation: global instabilities and the flow inside a molten sample
Priede, J.; Gerbeth, G.; Shatrov, V.; Gelfgat, Y.;
Electromagnetic levitation is a well-known technique for containerless processing of metals and alloys both in the solid and in the molten state. In experiments the levitated bodies often times show different types of instabilities resulting in a rotating and oscillating motion of the sample. We present results on the reason of such spontaneous instabilities. The theoretical predictions are verified by model experiments using solid Al or Mg spheres. These instabilities can obviously be avoided by system parameters below the corresponding non-dimensional threshold. If this is not possible, an active damping method using DC magnetic fields has been developed. The DC field can either be produced by permanent magnets or by an electromagnetic superposition to the levitation coils. Experiments will be shown demonstrating the stabilization effect due to the DC magnetic fields.
Numerical simulations for the flow inside the molten levitated sample will be given as well as results for the linear stability of this internal flow. Flow and flow stability are also analyzed for the case of a molten droplet subject to a global rotation. It is shown that the global rotation may have a significant stabilizing influence on the internal flow field.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7006 - Permalink

Silicon diffusion in sol-gel derived isotopically enriched silica glasses
Bracht, H.; Staskunaite, R.; Haller, E. E.; Fielitz, P.; Borchardt, G.; Grambole, D.;
We performed silicon diffusion experiments with sol-gel derived isotopically enriched silica glasses at temperatures between 1050°C and 1300°C. The diffusion profiles were measured by means of time-of-flight secondary ion mass spectrometry. Samples annealed in closed silica ampoules under argon or dry air reveal enhanced Si diffusion compared to Si diffusion in fused silica. On the other hand, annealing in a large alumina tube under 18O2 ambient yields Si and O diffusion coefficients which approach the results for thermally grown SiO2. The enhanced Si diffusion in sol-gel derived glass is proposed to be due to water residues which lead to the formation of silanol SiOH groups.
Keywords: Pacs numbers:42.70.Ce, 66.30.Hs, 81.20.Fw
  • Journal of Applied Physics 97(2005)046107, 046107-1-046107-3

Publ.-Id: 7005 - Permalink

Flow control by tailored magnetic fields
Gerbeth, G.;
Electromagnetic fields provide a tool to influence the flow and, in turn, the heat & mass transfer in electrically conducting fluids. An attractive feature for metallurgical or crystal growth applications is the contact-less form of this control. There have been many studies in the past analysing the changes in the transport phenomena which take place by application of some type of magnetic field. In general, steady magnetic fields suppress flows and alternating magnetic fields drive some motion. The variety of magnetic field actions is very big which allows for an inverse approach: a pre-defined flow control is possible by tailored magnetic field systems. There is a basic fluiddynamic interest in such type of flow control, but applications in crystal growth, solidification, metal casting, welding, seawater flow control and others are very close, too.
On the other hand, there is a growing community dealing from a theoretical and computational point of view with optimization, optimal or sub-optimal control and flow control in general. We expect that Magnetohydrodynamics (MHD) establishes an interesting example for it as it provides an active, well-controllable influence on the flow which can directly be tested in experiments. The flow itself is often not of direct interest but acts as a kind of intermediate agent for more general goals like the resulting heat & mass transfer, the resulting microstructure in solidification, or integral results as drag of lift. Hence, it is in many cases a highly non-trivial question which flow field might be a desirable one for the more general objectives of the various processes.
Such type of inverse MHD approach has not yet been realized on its full scale, i.e., starting from a theoretical optimization problem and its numerical implementation up to the experimental demonstration. However, several examples exist of partly addressing this approach, and some of them will be shortly presented: Cz-Si crystal growth with AC and DC magnetic fields, aluminum investment casting with magnetic field control, tailored DC field stabilization of the melt extraction process for metallic fibres, electromagnetic levitation with DC field sample stabilization, seawater flow control for drag reduction and lift enhancement, and float-zone crystal growth with a tailored magnetic field control in order to shape the solid-liquid phase boundary. The latter case will be presented in more detail demonstrating its capabilities for the float-zone crystal growth and solidification studies with NdFeB alloys.
  • Lecture (Conference)
    Sino-German Workshop on EPM, 11.-13.10.2004, Shanghai, China

Publ.-Id: 7004 - Permalink

Nx1 MUSIG model -- implementation and application to gas-liquid flows in a vertical pipe
Shi, J.-M.; Frank, T.; Rohde, U.; Prasser, H.-M.;
A multiple velocity multiple size group (NxM MUSIG) model was developed for inhomogeneous poly-dispersed multiphase flows in cooperation with ANSYS CFX. The model is constructed by incorporating the population balance equation into the multi-fluid modeling framework. The dispersed phase is allowed to be classified into $N$ continuum fields (velocity groups) according to their hydrodynamic behaviors; each group allowing an arbitrary number of sub-size classes. This model has generalized all possible class model variants and is applicable to large-scale computations. As a pre-investigation for the CFX5.8 development, the Nx1 variant was implemented based on CFX5.7 and applied to investigate as-liquid flows in a vertical pipe. The results confirm that this model is capable of predicting the separation of bubbles of different sizes and the development of the gas volume fraction along the pipe.
Keywords: Poly-disperse, bubble, multi-fluid model, population balance
  • Lecture (Conference)
    22nd CAD-FEM User Meeting 2004 and CFX & ICEM CFD Conference, Nov. 10-12, 2004, Dresden, Germany, 12.11.04, Dresden, Germany

Publ.-Id: 7003 - Permalink

Modeling of the evolution of bubbly flow along a large vertical pipe
Lucas, D.; Krepper, E.; Prasser, H.-M.;
A detailed experimental database, obtained for a large pipe with an inner diameter of 195 mm and length of 9 m was used for the validation of models applied in CFD codes for the simulation of bubbly flow. Since the bubbles were injected via holes at the pipe wall, especially very useful information on the bubble migration from the pipe wall towards the pipe center were obtained by measurements at different distances between gas injection and measuring plane. The bubble migration is determined by the forces acting on the bubbles. A simplified model, introduced earlier, but with some new extensions, described in this paper, was used to analyze the data. The comparison of results from a simulation and the experimental findings give the advice, that the turbulent dispersion force according to the FAD model is too strong compared with the radial drag. Up to now no appropriate models for bubble coalescence and break-up are available, which can be applied for a wide range of gas and liquid volume flow rates. Nevertheless for selected combinations of volume flow rates, the calculated bubble size distributions and radial gas volume fraction profiles show an acceptable agreement with the experimental data.
Keywords: bubbly flow, pipe flow, bubble forces, CFD
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    Paper 051
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Nuclear Technology 158(2007), 291-303

Publ.-Id: 7001 - Permalink

Plasma Simulations of the SHIP Experiment at GDT
Anikeev, A. V.; Bagryansky, P. A.; Collatz, S.; Noack, K.;
The concept of the Synthesised Hot Ion Plasmoid (SHIP) experiment at the gas dynamic trap (GDT) facility of the Budker Institute Novosibirsk was already presented at the 29th EPS Conference. During the last year several numerical simulations were made by means of the Integrated Transport Code System (ITCS) to determine the best experimental scenario for getting high plasma parameters. This contribution presents important results of the recent numerical simulations of SHIP by means of the ITCS modules which had to be partly modified.
Keywords: plasma physics, plasma simulations, gas dynamic trap, SHIP experiment, Monte Carlo method
  • Lecture (Conference)
    5th Int. Conference on Open Magnetic Systems for Plasma Confinement, 05.-09.07.2004, Novosibirsk, Russia
  • Contribution to proceedings
    5th International Conference on Open Magnetic Systems for Plasma Confinement,, 05.-09.07.2004, Novosibirsk, Russia
    Open Magnetic Systems for Plasma Confinement, Dexter, Michigan: Beljan Ltd.
  • Fusion Science and Technology 47(2005)1T, 212-214

Publ.-Id: 7000 - Permalink

Laser-Induzierte Breakdown Detektion (LIBD) aquatischer Actinidenkolloide
Hübener, S.;
In dem Seminarvortrag mit Lehrcharakter wird einleitend auf die Bedeutung von Actinidenkolloiden in der Radioökologie und Methoden der Kolloidforschung eingegangen. Detailliert wird die LIBD abgehandelt, gegliedert nach physikalischen Grundlagen, experimentellen Anordnungen, wobei das Gerätesystem des Instituts für Radiochemie vorgestellt wird und Anwendungen der LIBD. Dazu werden Beispiele aus der Literatur und eigene Messungen an natürlichen Wässern und zur Bestimmung der U(IV)-Löslichkeit vorgestellt. Abschließend werden die Anwendung der LIBD zur Aerosoldetektion und die Laser-Induzierte Breakdown Spektroskopie diskutiert.
Keywords: colloids, colloid detection, laser induced breakdown detection, uranium(IV) solubility
  • Lecture (others)
    Seminar des Labors für Radio- und Umweltchemie der Universität Bern und des Paul Scherrer Instituts, 14.01.2005, Villigen, Switzerland

Publ.-Id: 6999 - Permalink

Stability Analysis of Natural Circulation BWRs at Low Pressure Using the Codes FLOCAL and ATHLET
Manera, A.;
The capabilities of the in-house code FLOCAL and of the code ATHLET (developed by GRS, Germany) to reproduce instabilities of natural circulation BWRs at low pressure will be shown. FLOCAL consists of a 4-equations two-phase model. This code is the thermalhydraulic module of the three-dimensional neutronic codes DYN3D, also in-house development of FZR. The code ATHLET is a general-purpose thermalhydraulic code which has the possibility of using 4, 5 or 6-equations two-phase model. This code has been coupled with DYN3D. The results of the simulation obtained with the two codes are compared with experiments carried out with facilities built at Delft University of Technology (The Netherlands) and at Paul Scherrer Institute (PSI, Switzerland). The phenomenology of the instabilities is very well reproduced by the two codes. Good quantitative agreement is found as well.
Keywords: stability, BWRs, natural circulation
  • Invited lecture (Conferences)
    BWR Owners’ Group Global Technical Exchange Conference – BWR Stability-, 05.05.2004, Valencia, Spain

Publ.-Id: 6998 - Permalink

Evidence of Self-Aligned Si Nanocluster delta-Layers in Buried SiO2 Films Induced by Ion Irradiation
Röntzsch, L.; Heinig, K.-H.; Schmidt, B.;
An abstract was not required.
  • Poster
    International School on Radiation Effects in Solids, 17.-29.07.2004, Erice, Italy

Publ.-Id: 6997 - Permalink

Evidence of Self-Aligned Si Nanocluster delta-Layers in Buried SiO2 Films Induced by Ion Irradiation
Röntzsch, L.; Heinig, K.-H.; Schmidt, B.;
Nanoparticles embedded in a host matrix are systems with a high internal structural gradient which exhibit exciting electronic, optical, and/or magnetic properties. With regard to applications, the position of the nanoparticles, their size and their size distribution have to be well defined which has been a severe challenge for materials scientists. "Bottom-up" approaches are promising alternatives to the conventional "top-down". Usually, they are driven by self-organization mechanisms of matter.
Aiming at novel non-volatile flash memories [1], we have studied the synthesis of Si nanoclusters (NCs) in a thin SiO2 layer which is embedded between the (100)-Si substrate and a poly-Si capping layer. For this application, Si NCs of equal size are required which are located in the buried oxide layer at a given distance from the Si-SiO2 interface. In a previous work [2] we presented a theoretical concept which suggests that such a Si multi-dot structure can be achieved in a two-step process. At first, the layer stack poly-Si/SiO2/(100)Si is irradiated with Si ions of medium energy (50keV) which leads to ion mixing of the Si-SiO2 interfaces. During annealing, phase separation takes place in the course of which the Si-SiO2 interfaces recover rapidly. Excess Si of the tails of the mixing profiles remains in the oxide, precipitates, and – in a self-organizing manner – grows up to a Si NC delta-layer which is ~3nm apart from the Si-SiO2. Because of the very low mass contrast of Si NCs to the surrounding SiO2 and their tininess, the Si NC delta-layer structure is outside the visibility limit of common XTEM.

In this contribution, we present for the first time experimental evidence which proves the mechanism of Si NC delta-layer formation addressed above. For this purpose, the sample structure portrayed previously was modified. In order to enhance the mass contrast of the Si NCs we "decorate" the Si NCs with Ge. A 5nm thin Ge layer was inserted in between the capping and the oxide layer. In the course of annealing, Ge diffuses through the oxide and attaches to the growing Si precipitates due to the energetically favourable Si-Ge bond. Differently from delta-layer of pure Si NCs, the SixGe1-x NC delta-layer is indeed observable in XTEM because of the considerably higher mass contrast to the surrounding SiO2. Without the presence of Si NCs, which act as seeds to which Ge monomers attach, no NC delta-layer would be visible at the position of interest. Consequently, the existence of Si NCs which align in a collective manner at a distinct distance of ~3nm from the Si channel is successfully proven.

This work was supported by the GROWTH Program of the European Community (GRD1-2000-25619).

[1] S. Tiwari, F. Rana, H. Hanafi, A. Hartstein, E. F. Crabbe, and K. Chan, "A Silicon nanocrystals based memory", Appl. Phys. Lett. 68, 1377 (1996).
[2] K.-H. Heinig, T. Müller, B. Schmidt, M. Strobel, and W. Möller, "Interfaces under ion irradiation: growth and taming of nanostructures", Appl. Phys. A 77, 17 (2003).
  • Lecture (Conference)
    EURESCO Conference on Cluster Systems and Nanotubes, 12.05.2004, Giens, France
  • Poster
    EURESCO Conference on Cluster Systems and Nanotubes, 08.-12.05.2004, Giens, France

Publ.-Id: 6996 - Permalink

Self-Organization of Nanocluster delta-Layers at Ion-Beam-Mixed Si-SiO2 Interfaces
Röntzsch, L.; Heinig, K.-H.; Schmidt, B.;
The Multidot Nano-flash Memory suggested by Tiwari [APL69(1996)1232] is a promissing candidate for succeeding the common Floating Gate Flash Memory.
Its most challenging configurational feature is a layer of insulated Si nanoclusters (NCs) within the oxide of a MOS-like structure.
Here, we present experimental evidence that the theoretical concept predicting the self-organization of delta-layers of Si NCs at ion irradiated interfaces is valid (cf. Heinig [APA77(2003)17]).
In this approach of "bottom-up" structuring, unconventionally, a 15nm thin buried SiO2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiOx (x<2) -- where x is a function of depth -- is formed which is not stable.
During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the Multidot Memory device, the principal character of which is a 2D layer of Si nanoclusters of (d~3nm) which is embedded in a 3D SiO2 matrix at a distance of ~3nm from the Si substrate.
The experimental handicap that tiny Si NCs (d<3nm) which are embedded in SiO2 are not visible in common XTEM is resolved by a novel method which applies Ge as contrast enhancing element in TEM studies of tiny Si NCs.
  • Lecture (Conference)
    DPG Jahrestagung, 08.03.2004, Regensburg, Germany

Publ.-Id: 6994 - Permalink

Complexation of Uranium by Cells and S-layer Sheets of Bacillus sphaericus JG-A12
Merroun, M.; Raff, J.; Rossberg, A.; Hennig, C.; Reich, T.; Selenska-Pobell, S.;
Bacillus sphaericus JG-A12 is a natural isolate recovered from a uranium mining waste pile near the town of Johanngeorgenstadt in Saxony, Germany. The cells of this strain are enveloped by a highly ordered crystalline proteinaceous surface layer (S-layer) with an ability to bind uranium and other heavy metals. By using a phosphoprotein specific staining, Inductive Coupled Plasma- Mass Spectrometry (ICP-MS) analysis and a colorimetric method, purified and recrystallized S-layer proteins were shown to be phosphorylated. We used Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to determine the structural parameters of the uranium complexes formed by purified and recrystallized S-layer sheets of B. sphaericus JG-A12. In addition, the complexation of uranium by the vegetative bacterial cells was studied. The EXAFS analysis demonstrated that in all samples studied, the U(VI) is coordinated to carboxyl groups in a bidentate fashion with an average distance between the U atom and the C atom of 2.88 ± 0.02 Å, and to phosphate groups in a monodentate fashion with an average distance between the U atom and the P atom of 3.62 ± 0.02 Å. Transmission Electron Microscope (TEM) analysis showed that the uranium accumulated by the cells of this strain is located at the cell surface as dense deposits.

Publ.-Id: 6993 - Permalink

Interaction mechanisms of uranium with bacterial strains isolated from extreme habitats
Merroun, M.; Nedelkova, M.; Heilig, M.; Rossberg, A.; Hennig, C.; Scheinost, A.; Selenska-Pobell, S.;
Development of biological methods for removal of heavy metals and actinides are a subject of a great interest due to their low cost and high efficiency at moderate metal concentrations. Many bacterial strains have been isolated that sorb actinides usually at the cell surface. In this paper we describe the isolation of bacterial strains from extreme habitats (such as uranium mining wastes and Siberian deep-well radioactive disposal sites). Phylogenetic analysis of these strains revealed that they are related to α-Proteobacteria and to Actinobacteria. Some of these strains possess the ability to accumulate and tolerate uranium and other heavy metals. Thus, a strain of Microbacterium oxydans (SW3) which was isolated from a uranium contaminated water sample tolerates a concentration of U up to 4 mM and accumulates high amounts (up to 110 mg U/dry biomass at pH 4.5 and an initial uranium concentration of 0.25 mM). X-ray absorption near-edge structure analysis showed that the cells of these strains precipitate U(VI) as autunite-like phase (inorganic uranyl phosphate) at pH 4.5, probably due to the release of inorganic phosphate from the cells. However, at pH 2 uranium formed complexes with organically bound phosphate of the cell surface. At pH 3, both organic and inorganic phosphate uranyl species occur together. We applied Iterative Target Test Factor Analysis /1/ to determine the speciation at different pH values quantitatively from the EXAFS spectra. Transmission electron microscopy and energy dispersive X-ray analysis revealed strain-specific extracellular and/or intracellular uranium accumulations to varying degrees.

/1/ Rossberg, A. et al. 2004. Anal. Bioanal. Chem. 376:631
  • Lecture (Conference)
    Actinides 2005, 04.-08.07.2005, Manchester, Great Britain
  • Contribution to proceedings
    Actinides 2005, Advances in Actinide Science, 04.-08.07.2005, Manchester, Great Britain
    Recent Advances in Actinide Science, Editors: May, I., Alvares, R., Bryan, N.: The Royal Society of Chemistry 2006, 0-85404-678-X, 47-49

Publ.-Id: 6992 - Permalink

Quantitative antimony speciation in shooting-range soils by EXAFS spectroscopy and iterative transformation factor analysis
Scheinost, A.; Rossberg, A.; Hennig, C.; Vantelon, D.; Kretzschmar, R.; Johnson, C.;
wird nachgereicht
  • Poster
    ESRF Users Meeting, 10.-11.02.2004, Grenoble, Frankreich

Publ.-Id: 6991 - Permalink

Application of synchrotron radiation excited X-ray microprobe techniques in material and environmental science
Somogyi, A.; Martinez-Criado, G.; Scheinost, A.; Tucoulou, R.;
Synchrotron radiation excited X-ray microprobe techniques (-XRF/XAS, -XRD, imaging/tomography) give unique possibility for non-destructive, in situ investigation of several sample characteristics (elemental- and crystalline composition, chemical speciation, morphology) and different chemical, environmental processes within inhomogeneous samples. The ID22 X-ray microprobe beamline of the European Synchrotron Radiation Facility (ESRF, Grenoble, France) offers the simultaneous use of these techniques with m spatial resolution in the 6-30 keV energy range.

Material and environmental sciences are two scientific fields often requiring the combined investigation of the elemental distribution, chemical speciation, and crystalline structure of large number of samples with (sub)-micron spatial resolution. The new developments of the ID22 beamline can readily fulfill these requirements, as will be illustrated by the presented examples. The high 1010-5x1011 ph/s intensity of the micro-beam (depending on the spot-size, energy and focusing device) allows for continuous scanning -XRF measurements of sample areas of up to 1 mm2 with 0.6-2 m spatial resolution within <10-12 hours measurement time in case of high enough characteristics X-ray line intensities. Combination of scanning -XRF with -XANES (-EXAFS) gives information about the dependence of the oxidation state/chemical speciation of a given element from the elemental composition. The achromaticity of the commonly used KB focusing mirror makes the change of the excitation energy possible in the 7-18 keV energy region without significant change of the size and position of the focused beam. Thus, XANES measurements at different absorption edges are achievable, which allow to study the correlation among chemical speciation of different elements. Correlation between the chemical characteristics and the crystalline structure of the sample can be investigated by combining these techniques with -X-ray diffraction measurements.
  • Invited lecture (Conferences)
    Dispersive X-Ray Spectrometry, European Conference on Energy, 06.-11.06.2004, Alghero, Italy
  • Contribution to proceedings
    Dispersive X-Ray Spectrometry, European Conference on Energy, 06.-11.06.2004, Alghero, Italy

Publ.-Id: 6990 - Permalink

Quantitative zinc speciation in soil with XAFS spectroscopy: Evaluation of iterative transformation factor analysis
Scheinost, A.; Rossberg, A.; Marcus, M.; Pfister, S.; Kretzschmar, R.;
We employed a combination of selective sequential extractions and bulk XAFS spectroscopy, and extracted spectral XAFS components and their concentrations by iterative transformation factor analysis (ITFA), in order to determine the Zn speciation in a smelter-contaminated, acidic soil. We compared the speciation by ITFA with one we performed earlier using principal component analysis and linear combination fit. ITFA identified 4 different species, two different franklinite-type phases (Zn-Fe spinels), sphalerite (Zn sulfide) and Zn oxalate, the latter forming as a precipitate during chemical extraction with oxalate solution. The second spinel-type phase could be extracted with the help of ITFA, although no appropriate reference sample was available. Spinel 1 and 2 have Zn-O distances of 1.96 and 1.99 Å, and Zn-Fe distances of 3.53 and 3.48 Å, respectively. The results from ITFA gave much better fits of experimental spectra and are better in line with elemental mapping and XAFS microspectroscopy. The major advantage of investigating XAFS data with ITFA is the possibility to derive all species even when part of the references are not available.
  • Physica Scripta T115(2005), 1038-1040

Publ.-Id: 6989 - Permalink

The Rossendorf Beamline at the ESRF: An XAS experimental station for actinide research
Scheinost, A.;
The Rossendorf Beamline is in full operation since 1999. Its X-ray absorption spectroscopy station dedicated to actinide research is unique in Europe, and has served for about 80 different experiments in the past four years. An overview on the current status of operation modes, technical details and access conditions is presented.
  • Lecture (Conference)
    3rd Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light, 14.-16.09.2004, Berkeley, United States

Publ.-Id: 6988 - Permalink

Chemical heterogeneity of humic substances and mobile soil colloids studied by X-ray microscopy and microspectroscopy
Schumacher, M.; Scheinost, A.; Christl, I.; Jacobsen, C.; Kretzschmar, R.;
Humic substances are important sorbents for organic and inorganic contaminants such as heavy metals or radionuclides. They participate in many geochemical processes, affecting the quality of ground and surface waters, or the uptake of nutrients by plants. This property is due to their high surface area, the sorption of ions at charged hydrophilic functional groups and the sorption of non-polar organic compounds by hydrophobic surface sites [1,2].
The bulk chemical porperties of of humic substances can be investigated with a variety of methods like solid-state CP-MAS 13C-NMR spectroscopy, FT-IR spectroscopy, pyrolysis coupled with mass spectrometry or acid-base titrations. Although all of those methods have been applied widely to characterize colloids and their interaction with contaminants, methods which provide both in-situ imaging as well as spectroscopic characterization are rare. The Scanning Transmission X-ray Microscope (STXM) at beamline X1-A at the National Synchrotron Light Source (NSLS) is one of the few methods that may fill in this gap. Carbon X-ray absorption near-edge structure (C-1s XANES) as well as X-ray microscopy was employed to systematically monitor the chemical properties of humic substances. Furthermore, the colloidal fraction of different soil types was extracted and analyzed with C-1s XANES spectroscopy. The objectives of this study are (i) to characterize the spectroscopic features of humic substances and mobile soil colloids with C-XANES spectroscopy and X-ray microscopy and (ii) to evaluate a qualitative as well as quantitative comparison with other spectroscopic methods like solid-state CP-MAS 13C-NMR spectroscopy or FT-IR spectroscopy.

[1] Pignatello J.J., and Xing B. (1996) Environ. Sci. Technol. 30, 1-11.
[2] Grolimund, D., Elimelech, M., Borkovec, M., Barmettler, K., Kretzschmar, R., and Sticher, H. (1998) Environ. Sci. Technol. 32, 3562-3569.
  • Geochimica et Cosmochimica Acta 68(2004)11, A225-A225
  • Poster
    Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Dänemark
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark

Publ.-Id: 6987 - Permalink

Zinc speciation in an artificially contaminated soil: Formation of a new mineral phase within 3 years
Kretzschmar, R.; Pfister, S.; Voegelin, A.; Scheinost, A.;
The bioavailability and toxicity of Zn in contaminated soils strongly depend on its speciation. Initially, Zn speciation is determined by the primary contaminants. Over time, primary phases dissolve and Zn may adsorb to various soil components and eventually become incorporated into newly forming mineral phases. The practical relevance of this process for the attenuation of Zn bioavailability depends on the time scale over which new mineral phases form and the thermodynamic stability of the newly formed phase.
In this study, a field soil (pH 6.4, 1.5% organic carbon, 15% clay) was contaminated with filter dust from a brass foundry containing 98% zincite (ZnO). We followed the dissolution and redistribution of Zn over 4 years using bulk and micro XAFS analysis.
Bulk XAFS shows that within 18 months, most zincite dissolved and Zn attached to various soil components, mainly as an outer sphere complex. Micro XAFS reveals both remnants of undissolved zincite as well as regions of Zn specifically adsorbed to Mn/Fe oxides and beginning formation of a Zn bearing solid phase (phyllosilicate or mixed layered hydroxide). After 36 months, we observe a second shell in the bulk XAFS spectrum (~2.1 Zn @ 3.11 Å; 1st shell 5.8 O @ 2.04 Å), further supporting the formation of a Zn bearing mineral. Micro XAFS data for the same time reveal tetrahedrally coordinated specifically adsorbed Zn in Mn rich zones, Zn attached to organic material as an outer sphere complex, and octahedrally coordinated Zn in large diffuse parts of the soil matrix with a spectrum similar to the bulk XAFS.
Our results show that in a near neutral soil, ZnO dissolved within one to two years. A short transient phase, during which Zn is predominantly bound as an outer sphere complex, was followed by specific Zn adsorption and the onset of the formation of a Zn mineral phase. These results demonstrate that within a few years, Zn may be redistributed and attenuated in a near neutral soil. In ongoing studies, we investigate the long term efficiency of this immobilization process, e.g., during soil acidification.
  • Geochimica et Cosmochimica Acta 68(2004), 361-361
  • Lecture (Conference)
    14th Goldschmidt Conference, 05.-11.06.2004, Copenhagen, Denmark
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark

Publ.-Id: 6986 - Permalink

Fate of uranium in the environment
Scheinost, A.; Bernhard, G.; Selenska-Pobell, S.;
Uranium is present in the Earth’s crust at an average concentration of 2 mg/kg, similar to As and Mo, but ten times higher than Sb. It is enriched in granitic and phosphate rocks, lignite and monazite sands, and occurs in numerous minerals, uraninite (pitchblende), carnotite, and autunite being most abundant. During mining and ore processing (World production of U 35,000 Mg/a), these relatively insoluble, U(IV) and/or U(VI) containing minerals are converted into highly soluble and mobile U(VI) aqueous species, which may present an immediate risk for the environment, or are converted back to less mobile chemical forms. We will give an overview of processes, which influence the fate of U in this greatly perturbed biogeochemical cycle.
Even at low redox potential and in equilibrium with uraninite, the aqueous solution of soils, the vadose zone and aquifers is dominated by U(VI) species. The extremely complex speciation of U(VI) is influenced by pH, dissolved carbonate and the presence of organic ligands. The mobility of these species is reduced by sorption processes to minerals, insoluble natural organic matter, and biota. On the other hand, the presence of carbonate and organic ligands with strong affinity for uranyl may prevent sorption to surfaces and enhance the mobility. The migration of U is furthermore influenced by the formation of, or sorption to mobile colloids.
A strong immobilization of U presents the reduction to U(IV) and the subsequent precipitation as uraninite or other minerals. This process may proceed as a catalytic reaction on inorganic surfaces. Microorganisms, however, which are abundant even in U waste piles with high heavy metal concentrations, may be more important for U(IV) mineral precipitation. Processes involved are a direct biological reduction of U(VI) or an indirect reduction by changing redox potential and pH of the aqueous solution. Microorganisms can reduce the U mobility also by processes like bioaccumulation and biomineralization. Alternatively, particular groups of microorganisms can mobilize U from the ores by direct and indirect (metabolic-conducted) oxidation of U(IV), a process called bioleaching. Microorganisms can also increase the U mobility by releasing chelating ligands into the environment. Thus, they play one of the key roles in the biogeochemical cycling of U.
  • Geochimica et Cosmochimica Acta 68(2004), 526-526
  • Invited lecture (Conferences)
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark

Publ.-Id: 6985 - Permalink

Quantitative antimony speciation in Swiss shooting range soils
Scheinost, A.; Rossberg, A.; Hennig, C.; Vantelon, D.; Kretzschmar, R.; Johnson, C.;
Antimony is used to harden the Pb cores of ammunition. Thus, between 4 and 10 tons of Sb are annually deposited on Swiss shooting ranges by bullets. Due to the relatively rapid weathering of the bullets, Sb is released into the soil, but little is known about its further fate. As part of investigations to determine the geochemical factors that control Sb mobility, we have determined the oxidation state and species of Sb in 6 shooting-range soils, using a combination of EXAFS (extended x-ray absorption fine structure) spectroscopy and ITFA (iterative transformation factor analysis), a technique particularly suited for quantitative speciation in complex matrices [1, 2].
Antimony concentrations varied between 1,000 and 17,000 mg/kg. In spite of a wide range of soil chemical conditions (pH, mineral and organic matter composition), we found only two Sb species. In the first species, Sb is surrounded by 6 O atoms at a distance of 1.97 Å, by 1 Fe atom at 3.09 Å, and by 2 Sb atoms at 3.33 Å. This arrangement suggests pentavalent Sb sorbed onto Fe or Mn oxides by forming a polynuclear inner-sphere sorption complex.
In the second species, Sb is surrounded by 2 O atoms at a distance of 1.98 Å, and by Sb atoms at 2.91 Å, 3.35 Å, 4.30 Å, and 4.52 Å. This structure is consistent with Sb(III) (hydr)oxide.
The (hydr)oxide species prevailed in a very acidic soil (pH 3.1), the sorption complex prevailed in a slightly acidic soil, and mixtures of both species occurred in calcareous soils (pH 7.5).
The results for Sb(V) are in agreement with previous findings suggesting that Sb is bound to Fe oxides. Antimony(III) solubility appears to be controlled by Sb(III) (hydr)oxide. Our results suggest that Sb remains tightly bound in soils, confirming our previous macroscopic observation that Sb is strongly enriched in the uppermost layer of a soil profile [3].

[1] Scheinost A. C., Rossberg A., Marcus M., Pfister S., and Kretzschmar R. (2003) Physica Scripta, in press.
[2] Rossberg A., Reich T., and Bernhard G. (2003) Analyt. Bioanalyt. Chem. 376, 631-638
[3] Knechtenhofer L. A., Xifra I. O., Scheinost A. C., Flühler H., Kretzschmar R. (2003) J. Plant Nutr. Soil Sci. 166, 84-92.
  • Geochimica et Cosmochimica Acta 68(2004), 521-521
  • Lecture (Conference)
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark
  • Contribution to proceedings
    14th Goldschmidt Conference, 05.-11.06.2004, Kopenhagen, Denmark

Publ.-Id: 6984 - Permalink

Metal Oxides in Soils
Scheinost, A.;
wird nachgereicht
  • Contribution to external collection
    in: Encyclopedia of Soils in the Environment, Amsterdam: Academic Press, 2004, 0123485304, 428-438

Publ.-Id: 6983 - Permalink

Laser-induced Spectroscopy: Tools to Study Actinide Speciation in Environmental Concentration Ranges
Geipel, G.;
wird nachgereicht
  • Lecture (others)
    Eingeladener Vortrag, 06.12.2004, Praha, Czech Republic

Publ.-Id: 6982 - Permalink

Aquatische Kolloide II: Eine Übersichtsarbeit zur Probennahme, Probenaufbereitung und Charakterisierung
Hofmann, T.; Baumann, T.; Bundschuh, T.; von D. Kammer, F.; Leis, A.; Schmitt, D.; Schäfer, T.; Thieme, J.; Totsche, K.-U.; Zänker, H.;
Kolloide sind Bestandteile aller aquatischen Systeme. Das Verhalten der Kolloide in der Umwelt, deren Mobilisierung, Transport und Abscheidung und somit auch die Relevanz sind noch nicht vollständig verstanden. Dies liegt zum Teil an der Tatsache, dass die Kolloidanalytik extrem aufwändig ist. Sie gehört nicht zur Standardanalytik eines Wasserlabors. Keine Technik ist bisher zufriedenstellend in der Lage, Kolloide in ihrem gesamten Größenbereich auch bei geringsten Konzentrationen gleichzeitig zu quantifizieren und zu identifizieren. In der Regel ist eine Kombination von verschiedenen Techniken notwendig, um ausreichend Informationen über das Verhalten der Kolloide zu erhalten. Für die Bestimmung der Oberflächeneigenschaften stehen kaum Methoden zur Verfügung. Eine weitere, nicht zu unterschätzende Schwierigkeit ist die Probennahme und Probenaufbereitung. Für die Untersuchung von Kolloiden sind spezielle Probennahmetechniken und Protokolle notwendig, da ansonsten die ungestörten, natürlichen Bedingungen durch (Probennahme-)Artefakte maskiert werden. Dieser Artikel soll in Form einer Übersichtsarbeit Hinweise zur Probennahme geben und die verschiedenen Möglichkeiten der Kolloidanalytik aufzeigen.

Publ.-Id: 6981 - Permalink

Aquatische Kolloide I: Eine Übersichtsarbeit zur Definition, zu Systemen und zur Relevanz
Hofmann, T.; Baumann, T.; Bundschuh, T.; Kammer, F. V. D.; Leis, A.; Schmitt, D.; Schäfer, T.; Thieme, J.; Totsche, K.-U.; Zänker, H.;
Kolloide sind Bestandteile aller aquatischen Systeme. Sie umfassen Feststoffe, deren Größe in zumindest einer Dimension zwischen 1 und 1.000 nm liegt. Sie können anorganischer (z. B. Tonteilchen, Karbonate oder Silikate) oder organischer (z. B. Ruß oder höhermolekulare organische Verbindungen wie Huminstoffe) Natur sein. Auch Bakterien, Viren, Sporen und Algen in diesem Größenbereich können zu den Kolloiden gerechnet werden (häufig als Bio-Kolloide bezeichnet). Kolloide können den Transport von (Schad-)stoffen im Untergrund und in Oberflächengewässern beeinflussen, insbesondere von Spurenelementen und hydrophoben organischen Verbindungen, oder zu unerwünschten Effekten wie Porenraumreduktion (Clogging) führen. Für die Hygiene des Trinkwassers ist das Verhalten von Bakterien, Viren und Sporen (den Bio-Kolloiden) von besonderer Bedeutung. Bisher ist das Verhalten von Kolloiden nur unzureichend verstanden. Dieser Artikel soll einen Beitrag zu dem Verständnis des physikalischen Verhaltens der Kolloide, deren Vorkommen in der aquatischen Umwelt sowie Relevanz in Form einer Übersichtsarbeit leisten.

Publ.-Id: 6980 - Permalink

X-ray tomography: how to evaluate the reconstruction quality?
Chukalina, M.; Golosio, B.; Simionovici, A.; Funke, H.;
Different reconstruction techniques are used to reconstruct the distribution of the physical characteristics, describing a sample under investigation, from a set of tomographic projections. We present a technique for the evaluation of the reconstruction quality. The technique is based on the comparison of two images (phantom and reconstructed image) by means of the correlation coefficient and of the mean square error between them. In parallel, the correlation coefficient and mean square error are calculated for the wavelet transforms of the phantom and reconstructed images. The scales for the wavelet transform are chosen in agreement with the major geometric parameters of the phantom. Then the correlation coefficient of the wavelet transform with the chosen scale yields an evaluation of the quality of the phantom parameters reconstruction. The accuracy of the parameters reconstruction is determined by the mean square error for the selected scale. The phantom used for the analysis is a medium with randomly distributed grains. The distribution is characterized by two parameters: grain size and grain density (average number of grains per unit area). The parameters are used as the scales for the wavelet transform calculation. We make a comparison of the Algebraic Reconstruction Technique (ART) and the Filtered Back Projection Algorithm.
Keywords: X-ray computer tomography; Reconstruction techniques; Quality of the reconstruction; Wavelet transform; Correlation coefficient

Publ.-Id: 6979 - Permalink

Kolloide in Bergwerkswässern
Zänker, H.; Wichter, W.; Ulrich, K.-U.; Moll, H.; Hüttig, G.;
Kolloide in Bergwerkswässern
  • Lecture (others)
    6. Arbeitstreffen des Arbeitskreises "Kolloide" der Wasserchemischen Gesellschaft in der GDCh, 09.03.2004, München, Germany

Publ.-Id: 6978 - Permalink

Die Welt der vernachlässigten Dimensionen
Zänker, H.; Richter, W.; Hüttig, G.; Moll, H.; Brendler, V.; Hübener, S.; Opel, K.;
wird nachgereicht

Beitrag zu "Forschung für Mensch und Umwelt. Jahresbericht 2003 des FZR"
  • Contribution to HZDR-Annual report
    Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-398 Mai 2004, 42-51

Publ.-Id: 6977 - Permalink

Local “annealing” and domain patterning of amorphous films by He-ion irradiation
McCord, J.; Fassbender, J.ORC; Liedke, M. O.; Frommberger, M.; Mönch, I.; Gemming, T.; Schäfer, R.; Quandt, E.; Schultz, L.
The magnetic anisotropy in amorphous soft magnetic FeCoSiB films is modified by He-ion irradiation. A realignment of uniaxial anisotropy depending on the applied field direction in the irradiated areas is observed by magnetometry and complementary domain observation by Kerr microscopy. Using irradiation together with photolithography the films were treated locally, resulting in ‘anisotropy patterned’ structures. Complicated periodic domain patterns form due to the confined anisotropy distribution. Overall magnetic properties and domain patterns can be adjusted.
Keywords: magnetism, magnetic anisotropy, Kerr microscopy, ion irradiation, patterning, lithography, soft magnetic, alloys
  • Contribution to external collection
    in: IFW Jahresbericht 2004, Dresden: IFW Dresden, 2005, 14-17

Publ.-Id: 6976 - Permalink

Material related fundamentals of cutting techniques for GaAs wafer manufacturing
Hammer, R.; Bergner, F.; Flade, T.; Jurisch, M.; Kleinwechter, A.; Schaper, M.;
Driven by the requirement of high cutting efficiency and improvement of wafer flatness wire sawing of GaAs single crystals under brittle material removal conditions has been studied. Crack nucleation and crack propagation were investigated by indentation and scratching tests on polished {100}-oriented semi-insulating GaAs wafers. Based on these results a concept has been developed to control the force balance in the cutting slits so that the deflection of the wires perpendicular to the cutting planes is minimal resulting in cuts of high flatness. The concept has been successfully introduced in mass production of GaAs wafers.
Keywords: Semi-insulating GaAs; Ductile-to-brittle transition; Indentation tests; Crack nucleation; Wire sawing
  • Zeitschrift für Metallkunde 96(2005), 785-791

Publ.-Id: 6975 - Permalink

Characterization of 6H-SiC surfaces after ion implantation and annealing using positron annihilation spectroscopy and atomic force microscopy
Brauer, G.; Anwand, W.; Skorupa, W.;
Systematic Slow Positron Implantation Spectroscopy (SPIS) and Atomic Force Microscopy (AFM) studies of various 6H-SiC samples are presented to clear the role of conductivity type, crystal quality, ion implantation (B+, Al+, N+), and annealing (1.650 °C) on the formation of continuous long furrows (undulations) running in one direction across the wafer surface. It is found that the observed changes in surface morphology are primary the result of thermal activation and thus occur independent of conductivity type, crystal quality, and type of ion implantation. In terraces in-between the long furrows, stripe like islands with a discrete height in the nanometer range have been observed which may have some link with the ion implantation chosen. SPIS results clearly indicate the formation of vacancy clusters in n-type material which are connected with the mobility of nitrogen in the samples at elevated temperatures. It is found that defect profiling by SPIS is not influenced by the changes in surface morphology observed due to annealing.
Keywords: 6H-SiC, ion implantation, vacancy-type defects, annealing, slow positron implantation spectroscopy, step bunching, atomic force microscopy
  • Journal of Applied Physics 99(2006), 023523

Publ.-Id: 6974 - Permalink

Strömungsinstabilitäten bei Stoffübergang und chemischer Reaktion an der ebenen Grenzfläche zwischen zwei nicht mischbaren Flüssigkeiten
Grahn, A.;
In verfahrenstechnischen Anlagen der Flüssig-Flüssig-Stoffübertragung kommt es an der Phasengrenze zwischen den nicht mischbaren Flüssigphasen häufig zur Ausbildung hydrodynamischer Instabilitäten. Sie sind mit komplexen Geschwindigkeitsfeldern in den Flüssigphasen, insbesondere in den grenzschichtnahen Regionen verbunden und führen zu einem starken Anstieg der pro Zeiteinheit übertragenen Stoffmenge. Die Lösung der Diffusionsgleichung reicht in diesem Fall zur Vorausberechnung des für Auslegungszwecke bedeutsamen Stoffdurchgangskoeffizienten nicht mehr aus. Chemische Reaktionen stellen Quellen oder Senken von Wärme und Stoff dar, die das Auftreten von Instabilitäten begünstigen und die mathematische Beschreibung zusätzlich erschweren.

Im Rahmen der vorliegenden Arbeit wurden experimentelle und numerische Untersuchungen zum Flüssig-Flüssig-Stoffübergang in einem vertikalen Kapillarspalt durchgeführt. Reaktionsfreie Stoffübergänge und solche mit einer exothermen chemischen Reaktion an der Phasengrenze zeigten eine große Vielfalt von Konvektionsstrukturen, wie Rollzellen, Thermiken und das doppeldiffusive Fingerregime. Die Visualisierung der Transportvorgänge erfolgte durch das Schattenschlierenverfahren. Die Beobachtungen wurden hinsichtlich geometrischer Eigenschaften von Konvektionsstrukturen sowie deren zeitlicher Änderung ausgewertet. Dazu zählten insbesondere das Längenwachstum von Thermiken und horizontale Wellenlängen von Fingerstrukturen.

Zur mathematischen Beschreibung der Phänomene im Kapillarspalt wurde ein Modell entwickelt, welches auf den gekoppelten, zweidimensionalen Transportgleichungen von Impuls, Wärme und Stoff beruht. Es berücksichtigt dichte- und grenzflächenspannungsgetriebene Instabilitätsmechanismen sowie die besonderen Durchströmungseigenschaften des Kapillarspalts. Die Phasengrenze wurde als eben angenommen. Die Lösung der Modellgleichungen erfolgt auf numerischem Wege durch ein Computerprogramm.

Das Modell ist in der Lage, die beobachteten Instabilitätsphänomene qualitativ richtig wiederzugeben. Mit Hilfe von Simulationsrechnungen konnte der Mechanismus aufgeklärt werden, der zum schnelleren Rückgang des Stoffdurchgangskoeffizienten im Rollzellenregime der rein grenzflächenspannungsgetrieben Instabilität im Vergleich zum Vorgang mit überlagerter Dichtekonvektion führt. Des Weiteren gelang der Nachweis des doppeldiffusiven Fingerregimes beim Stoffübergang mit exothermer Grenzflächenreaktion. Die berechnete Erhöhung des Stoffdurchgangskoeffizienten stimmt mit Angaben in experimentellen Arbeiten anderer Autoren überein.
Keywords: Interfacial Phenomena, Marangoni Effect, Rayleigh-Bénard Instability, Double Diffusive Instability, Capillary Gap, Hele-Shaw Cell, Fingering Instability, Liquid-Liquid Mass Transfer, Chemical Reaction, Roll Cell, Thermal, Computational Fluid Dynamics
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-417 2005


Publ.-Id: 6973 - Permalink

THz radiation and Bloch oscillations - old visions and new approaches
Winnerl, S.;
Different ways of generation of THz radiation are reviewed and our scalable emitter for intense pulsed THz radiation is presented. In the second part of the talk issues ralated to Bloch gain such as the fundamental understanding of the role of scattering processes and the role of electric field domains are adressed. Our approach to search for Bloch gain is discussed.
Keywords: THz radiation, semmiconductor superlattices, Bloch gain
  • Lecture (others)
    Conensed matter theory seminar, 15.12.2004, Oulu, Finland

Publ.-Id: 6972 - Permalink

Dynamics of MSR
Krepel, J.; Grundmann, U.; Rohde, U.; Weiss, F.-P.;
Dynamics of the Molten Salt Reactor - one of the 'Generation IV' concepts - was studied in this paper. The graphite-moderated channel type MSR was selected for the numerical simulation of the reactor with liquid fuel. The MSR dynamics is very specific because the fuel flow influences the delayed neutrons distribution. Presently, there are not many accessible numerical codes appropriate for the MSR simulation, therefore the DYN3D-MSR code was developed based on the FZR in-house code DYN3D. It allows calculating of full 3D transient neutronics in combination with parallel channel type thermal-hydraulics. By means of DYN3D-MSR, several transients typical for the liquid fuel system were analyzed. Those transients were initiated by reactivity insertion, by overcooling of fuel at the core inlet, by the fuel pump start-up or coast-down, or by the blockage of selected fuel channels. The results of these transient studies have shown that the dynamic behavior of MSR is acceptable with respect to the reactor safety.
Keywords: Molten Salt, Liquid Fuel, Reactor Dynamics, MSR
  • Contribution to proceedings
    Structural mechanics in reactor technology, SmiRT18, 08.-12.08.2005, Beijing, China

Publ.-Id: 6971 - Permalink

Plasma Immersion Ion Implantation Under Industrially Relevant Conditions
Ueda, M.; Wei, R.; Reuther, H.;
Plasma Immersion Ion Implantation Under Industrially Relevant Conditions
  • Invited lecture (Conferences)
    The Second International Workshop on Particle Beams &Plasma Interaction on Material and, 25.11.2004, Chiang Mai, Thailand

Publ.-Id: 6970 - Permalink

V1000CT-1 benchmark analyses with the DYN3D/RELAP5 and DYN3D/ATHLET coupled code systems
Kozmenkov, Y.; Grundmann, U.; Kliem, S.; Rohde, U.; Weiss, F.-P.;
Plant-measured data provided within the specification of the OECD/NEA VVER-1000 coolant transient benchmark (V1000CT) were used to validate the DYN3D/RELAP5 and DYN3D/ATHLET coupled code systems. Phase 1 of the benchmark (V1000CT-1) refers to the MCP (main coolant pump) switching on experiment conducted in the frame of the plant-commissioning activities at the Kozloduy NPP Unit 6 in Bulgaria. The experiment was started at the beginning of cycle (BOC) with average core expose of 30.7 effective full power days (EFPD), when the reactor power was at 27.5% of the nominal level and 3 of 4 MCPs were operating. The transient is characterized by a rapid increase in the primary coolant flow through the core and, as a consequence, a decrease of the space-dependent core inlet temperature. Control rods were not changing their positions during the transient. Both DYN3D/RELAP5 and DYN3D/ATHLET analyses were based on the same reactor model, including identical MCP characteristics, boundary conditions, benchmark-specified nuclear data library and nearly identical nodalization schemes. In addition to validation of the coupled code systems against measured data, a code-to-code comparison between simulation results has been performed to evaluate relevant thermohydraulic models of the system codes RELAP5 and ATHLET.
Keywords: Coupled code systems, 3D neutron kinetics, code validation, code-to-code comparison, VVER-1000 model, coolant transient benchmark, main coolant pump.
  • Contribution to proceedings
    11th International Top. Meeting on Nuclear Reactor Thermal-Hydraulics, 02.-06.10.2005, Avignon, France
    Proceedings CDROM paper 254
  • Lecture (Conference)
    11th International Top. Meeting on Nuclear Reactor Thermal-Hydraulics NURETH11, 02.-06.10.2005, Avignon, France

Publ.-Id: 6969 - Permalink

Atomistic study of the migration of di- and tri-interstitials in silicon
Posselt, M.; Gao, F.; Zwicker, D.;
A comprehensive study on the migration of di- and tri-interstitials in silicon is performed using classical molecular dynamics simulations with the Stillinger-Weber potential. At first the structure and energetics of the di- and the tri-interstitial are investigated, and the accuracy of the interatomic potential is tested by comparing the results with literature data obtained by tight-binding and density-functional-theory calculations. Then the migration is investigated for temperatures between 800 and 1600 K. Very long simulation times, large computational cells and different initial conditions are considered. The defect diffusivity, the self-diffusion coefficient per defect and the corresponding effective migration barriers are calculated. Compared to the mono-interstitial, the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The mobility of the di- and the mono-interstitial is higher than the mobility of the lattice atoms during the diffusion of these defects. On the other hand, the tri-interstitial mobility is lower than the corresponding atomic mobility. The migration mechanism of the di-interstitial shows a pronounced dependence on the temperature. At low temperature a high mobility on zigzag-like lines along a <110> axis within a {110} plane is found, whereas the change between equivalent <110> directions or equivalent {110} planes occurs seldom and requires a long time. At high temperature a frequent change between equivalent <110> directions or {110} planes is observed. During the diffusion within {110} planes the di-interstitial moves like a wave packet so that the atomic mobility is lower than that of the defect. On the other hand, the change between equivalent {110} migration planes is characterized by frequent atomic rearrangements. The visual analysis of the tri-interstitial diffusion reveals complex migration mechanisms and a high atomic mobility. The diffusivities and effective migration barriers obtained are compared with the few data from the literature. The implications of the present results for the explanation of experimental data on defect evolution and migration are discussed.
Keywords: defects, diffusion, silicon, computer simulations

Publ.-Id: 6968 - Permalink

Structural and chemical characterization of functional SiOxCy:H coatings for polymeric lenses
Fernandez-Hidalgo, P.; Martin-Palma, R. J.; Conde, A.; Gago, R.; Simancas, J.; Garcia-Diego, I.; Egio, A.; Martinez-Duart, J. M.;
The deposition of suitable hard protective coatings onto organic substrates for ophthalmic applications faces several challenges, such as proper surface preparation to ensure the adhesion to the rigid substrate and a delicate balance between hardness and flexibility. In this work it is shown that SiOxCy :H-based protective coatings grown by plasma enhanced chemical vapor deposition (PECVD) from mixtures of hexamethyldisiloxane and oxygen, can be used as protective buffer coatings between the soft and easily scratchable substrate and the antireflection stack that might be applied on top of it. These coatings must show absence of optical absorption and require index matching with the substrate. To meet these conditions, a three-phase multifunctional coating PECVD deposition method has been developed, in which a progressive decrease towards the surface in the carbon content of the SiOxCy:H hard coat has been implemented. Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy characterization of the individual layers that compose the multilayer functional structure has been performed. The comparison of the results obtained from each spectroscopy shows the complementarity of these techniques and allows optimizing the protective coating performance from the optical and mechanical points of view.
  • Journal of Vacuum Science and Technology B 22(2004)5, 2402-2408
    DOI: 10.1116/1.1795834

Publ.-Id: 6967 - Permalink

First in-beam PET imaging with LSO/APD array detectors.
Crespo, P.; Kapusta, M.; Pawelke, J.; Moszynski, M.; Enghardt, W.;
The performance and in-beam imaging capabilities of two position-sensitive gamma-ray detectors consisting of Hamamatsu avalanche photodiode arrays (S8550) individually coupled to crystals of cerium-doped lutetium oxyorthosilicate (LSO) are presented. The two detectors were operated in coincidence at the medical beam line of the Gesellschaft für Schwerionenforschung, in Darmstadt, Germany. In a first set of experiments, their imaging performance was tested before, during, and after the irradiation of phantoms of polymethylmethacrylate with carbon ion beams with fluences equivalent to 1000 typical daily therapeutic fractions. Only minor energy, time, and spatial resolution deterioration was observed, with the initial values being recovered after stopping the irradiation. A second set of experiments successfully imaged the depth distribution of positron emitter radionuclides created in a phantom that stopped the high-energy carbon ion beam. The particular details for the in-beam PET acquisition are shortly outlined. The obtained results show that LSO is a suitable material for in-beam PET and that its coupling with avalanche photodiode arrays is feasible for a PET system dedicated to in-beam monitoring of ion therapy.
Keywords: avalanche photodiode (APD), ion therapy, lutetium oxyorthosilicate (LSO), positron emission tomography (PET),proton therapy

Publ.-Id: 6966 - Permalink

Synthesis of silicon nanocrystal memories by sputter deposition
Schmidt, J.-U.;
Aim of this work was, to investigate the preparation of Si NC memories by sputter deposition. The milestones are as follows:
- Review of relevant literature.
- Development of processes for an ultrathin tunnel-oxide and high quality sputtered SiO2 for use as control-oxide.
- Evaluation of methods for the preparation of an oxygen-deficient silicon oxide inter-layer (the precursor of the Si NC layer).
- Characterization of deposited films.
- Establishment of techniques capable of probing the phase separation of SiOx and the formation of Si NC.
- Establishment of annealing conditions compatible with the requirements of current CMOS technology based on experimental results and simulations of Si NC formation.
- Preparation Si NC memory capacitors using the developed processes.
- Characterization of these devices by suitable techniques. Demonstration of their memory functionality.
Keywords: Sputter deposition, Silicon nanocrystals, charge storage, Nanocrystal MOS devices
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-425 2005


Publ.-Id: 6965 - Permalink

Neptunium(V) Reduction by Various Natural and Synthetic Humic Substances
Schmeide, K.;
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Humic Substances in Performance Assessment of Nuclear Waste Disposal: Actinide and Iodine Migration in the Far-Field (HUPA)", 18.-19.10.2004, Karlsruhe, Germany

Publ.-Id: 6964 - Permalink

Untersuchung der Redoxstabilität von Neptunium(V) in Gegenwart natürlicher und synthetischer Huminstoffe
Schmeide, K.;
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 12.-13.10.2004, Heidelberg, Germany

Publ.-Id: 6963 - Permalink

Auswertung der Komplexierungsdatenbasis bezüglich weiterführender Experimente und der Weiterentwicklung des Ladungsneutralisationsmodells
Schmeide, K.; Brendler, V.;
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 11.-12.05.2004, Saarbrücken, Germany

Publ.-Id: 6962 - Permalink

Colloid-chemical Investigation of the Kaitzbach Stream
Schmeide, K.; Zänker, H.; Weiß, S.; Ulrich, K.-U.;
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Humic Substances in Performance Assessment of Nuclear Waste Disposal: Actinide and Iodine Migration in the Far-Field (HUPA)", 26.-27.04.2004, Budapest, Hungary

Publ.-Id: 6961 - Permalink

CFD- analysis of the mixing pattern under various flow conditions at the ROCOM test facility using CFX-5
Höhne, T.; Kliem, S.; Rohde, U.;
The coolant mixing in the downcomer and the lower plenum of pressurized water reactors (PWR) is significant for safety assessment of boron dilution and cold water transients.

The research project FLOMIX-R within the 5th Framework Programme of EC had the objective to obtain experimental data on the relevant coolant mixing phenomena using improved measurement techniques with enhanced resolution in space and time for CFD validation.

Recent experiments at the Rossendorf test facility ROCOM were integrated into this research project. ROCOM is a 1:5 scaled Plexiglas model of a German PWR allowing conductivity measurements by wire mesh sensors for analyzing the mixing pattern at selected positions in the reactor pressure vessel and velocity measurements by LDA technique.

A few benchmark problems based on selected experiments were used to study the effect of different turbulent mixing models under various flow conditions, to investigate the influence of the geometry, the boundary conditions, the grid and the time step in the CFD analyses. In doing the calculations the Best Practice Guidelines for nuclear reactor safety calculations have been followed. Results of this numerical mixing studies will be discussed.
Keywords: FLOMIX-R, CFD, Coolant Mixing, ROCOM, PWR
  • Lecture (Conference)
    13th International Conference on Nuclear Engineering 2005, 16.05.2005, Beijing, China
  • Contribution to proceedings
    13th International Conference on Nuclear Engineering, 16.-20.05.2005, Beijing, China

Publ.-Id: 6960 - Permalink

Numerical modelling of a transient slug mixing experiment of the ROCOM test facility using CFX-5
Höhne, T.;
The coolant mixing is of relevance for two classes of accident scenarios – boron dilution and cold-water transients. Experimental investigations and numerical simulations of coolant mixing in the downcomer and the lower plenum of PWRs was the topic of the EU-Project “FLOMIX-R”. The results of the project showed, that coolant mixing has a high relevance for nuclear safety. The coolant mixing is the only inherent mechanism, which reduces risks of power excursions. For the investigation of the relevant mixing phenomena, the Rossendorf test facility ROCOM has been used. ROCOM is a 1:5 scaled Plexiglas model of the PWR Konvoi allowing conductivity measurements by wire mesh sensors and velocity measurements by the LDA technique. Series of experiments were performed at ROCOM to study the mixing of a slug of lower borated water during the start-up of the first main circulation pump.

The CFD calculations were carried out with the code CFX-5. A complex hybrid mesh with the size of 2 million nodes and 4 million elements was used. The turbulence was modeled with the SST model.

Due to the strong momentum insertion during the pump start-up, a dominating horizontal component of the flow was observed near the inlet nozzle leading to a circumferential flow around the core barrel. Therefore, the injected slug is distributed into two main jets, and the maximum of the tracer concentration at the core inlet appears firstly at the location opposite to the loop where the tracer was injected. For turbulent flows the CFD-Code CFX-5 was validated for turbulent, momentum driven mixing. A better description of the mixing processes inside the RPV is the basis of a more realistic safety assessment concerning boron dilution scenarios.
Keywords: Boron Dilution, CFD, Coolant Mixing, PWR
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 3.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    CD-ROM, paper 481

Publ.-Id: 6959 - Permalink

Numerical modelling of a buoyancy driven flow in a reactor pressure vessel using CFX-5
Höhne, T.; Scheuerer, M.; Kliem, S.;
The influence of density differences between the primary loop inventory and the Emergency Core Cooling water on the mixing in the downcomer of a Pressurised Water Reactor (PWR) was analyzed at the Rossendorf coolant mixing test facility ROCOM. ROCOM is 1:5 scaled model of a German PWR designed for experimental coolant mixing studies. It is equipped with advanced instrumentation, which delivers high-resolution information characterizing either temperature or boron concentration fields. A series of experiments was performed on mixing under the influence of density differences. Water with higher density was injected into the cold leg of the reactor model. Wire mesh sensors measuring the concentration distribution of a tracer added to the injected water were installed in the upper and the lower part of the downcomer. The data were used for CFD code validation. An experiment with 5% of nominal, constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop water was selected for validation of the CFX-5 code. The turbulence was modeled with the BSL Reynolds stress turbulence model and a mesh with two million control volumes was used.

The results of the experiment as well as of the numerical calculations show, that buoyancy effects dominate the mixing. While at higher mass flow rates (close to nominal conditions) the injected slug propagates mainly in circumferential direction around the core barrel, the buoyancy effect partly suppresses this circumferential propagation. The ECC water falls down in an almost straight streamline and reaches the lower downcomer sensor position directly below the affected inlet nozzle. Therefore, the density effects play an important role during natural convection with ECC injection in PWRs. It was important to point out, that CFX-5 is able to cope the specific flow pattern and mixing phenomena.
Keywords: CFD, Turbulence, Buoyancy Driven Flow, PWR, Coolant Mixing
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 3.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    CD-ROM, paper 480

Publ.-Id: 6958 - Permalink

Thermochromatographic Adsorption Studies of Curium and Berkelium
Hübener, S.; Eichler, B.; Taut, S.;
In preparation for thermochromatographic adsorption studies of Lr in metal columns at temperatures up to 2000 K we investigated the metal adsorption of Cm and Bk. Cm was chosen to model Lr as a trivalent metal and Bk as a trivalent actinide having a (divalent) fn+1s2 ground state configuration. 250Bk electroplated on tantalum and 248Bk/246Cm implanted in zirconium foils were used as actinide sources. To carry out an adsorption experiment the actinide sources were placed at the starting position of the thermochromatographic columns and hold for 30 min at 1850 K. Standard enthalpies of adsorption were calculated from the experimental results and compared with calculations using a semi-empirical method. Based on these results, the capability of the method for studying electronic and metallic state properties of the heaviest actinides up to Lr is discussed.
Keywords: heavy actinides, adsorption enthalpies, thermochromatography, metallic state
  • Poster
    Actinides 2005, 3.-9.7.2005, Manchester, UK
  • Contribution to external collection
    R. Alvarez, N.D. Bryan, I. May: Recent Advances in Actinide Science, Cambridge: RSC Publishing, 2006, 0-85404-678-X, 287-289

Publ.-Id: 6957 - Permalink

Experimental modelling and CFD simulation of air/water flow in a horizontal channel
Vallee, C.; Höhne, T.; Prasser, H.-M.; Sühnel, T.;
For the investigation of air/water slug flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter current flows under atmospheric pressure, especially the slug behaviour. Optical measurements were performed with a high-speed camera, and were complemented by simultaneous dynamical pressure measurements.

CFD simulation of the stratified co-current flow was performed using the code CFX-5 applying the two fluid model with the free surface option. The grid contains 400000 control volumes. The tubulence was modeled separately for each phase using the k, w-turbulence model. The results show wave formation up to slug development with closure of the whole channel cross section, where the slug is propagating towards the outlet of the channel with an increasing speed compared to the water velocity and an increase of the pressure level in the channel after the slug front.

The qualitative slug formation in the CFX calculation is in good agreement with the experiment, while the calculated pressure distribution shows higher peak values than the measured one.
Keywords: Multiphase flow, slug flow, CFD, Volume of Fluid model
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 3.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    CD-ROM, paper 479

Publ.-Id: 6956 - Permalink

Validation of coupled codes using VVER plant measurements
Vanttola, T.; Hämäläinen, A.; Kliem, S.; Kozmenkov, Y.; Weiß, F.-P.; Kereszturi, A.; Hadek, J.; Strmensky, C.; Stefanova, S.; Kuchin, A.;
A data set of five transients at different VVER type nuclear power plants was collected in order to validate neutron kinetics/thermal hydraulics codes. Two of these transients ‘drop of control rod at nominal power at Bohunice-3’ of VVER-440 type and ‘coast-down of 1 from 3 working MCPs at Kozloduy-6’ of VVER-1000 type, were then utilised for code validation. Eight institutes contributed to the validation with 10 calculations using 5 different combinations of coupled codes. The thermal hydraulic codes were ATHLET, SMABRE and RELAP5 and the neutron kinetic codes DYN3D, HEXTRAN, KIKO3D and BIPR8. The general behaviour of both the transients was quite well calculated with all the codes. Even an elementary modelling of coolant mixing in reactor pressure vessel under asymmetric transients improved correspondence to the measurements. Some differences between the calculations seem to indicate that fuel modelling and treatment of VVER-440 control rods need further consideration. The simultaneous validation interacted with the data collection effort and thus improved its quality. The complexity of data collection systems and sometimes conflicting data, however, called for compromises and interpretation guides that also taught the analysts balanced plant modelling.
  • Nuclear Engineering and Design 235(2005), 507-519 (2005)

Publ.-Id: 6954 - Permalink

Comprehensive uncertainty and sensitivity analysis for coupled code calculations of VVER plant transients
Langenbuch, S.; Krzykacz-Hausmann, B.; Schmidt, K.-D.; Hegyi, G.; Kereszturi, A.; Kliem, S.; Hadek, J.; Danilin, S.; Nikonov, S.; Kuchin, A.;
The development of coupled codes, combining thermal-hydraulic system codes and 3D neutron kinetics codes, is an important step to perform best-estimate calculations for plant transients of nuclear power plants. For applications in safety analysis, these coupled codes should be validated by benchmark calculations and, preferably, by comparison with plant transient data from operating plants. In addition, the results should be supplemented by applying uncertainty and sensitivity analysis methods, which allow to identify relevant parameters of models and solution procedures affecting the results and to quantify their relative importance. Both objectives were part of the VALCO project. The aspect of validation is presented in [S. Mittag, et al., 2004. Neutron-Kinetic Code Validation against Measurements in the Moscow V-1000 Zero-Power Facility, in press; T. Vanttola et al., 2004. Validation of coupled codes using VVER plant measurements, in press], the aspect of a comprehensive uncertainty and sensitivity analysis for coupled code calculations is the topic of this contribution. The results and experiences obtained by the analysis for two plant transients in a VVER-440 and a VVER-1000, respectively, are presented and discussed.
  • Nuclear Engineering and Design 235(2005), 521-540

Publ.-Id: 6952 - Permalink

Uranium sorption and solubility under conditions relevant for the radioactive waste repository in Morsleben / Germany
Nebelung, C.; Baraniak, L.;
Uranium is of great importance for the Morsleben radioactive waste disposal site. Its retention by both backfilling materials and the overlying rock was determined in batch sorption experiments over a period of 400 days. There, the solution simulated the brines typical for this site. The observed retention at the backfilling and overlying rock materials was in the regions of 95.8 to 100% and 92.7 to 98.1%, respectively. The solubility of solid U3O8 in these brines was determined to be between 5*10-9 and 9*10-6 mol/L uranium.

The project was supported by the BfS under the contract No.: 9M 212230-62
Keywords: sorption, solubility, uranium, Morsleben
  • Poster
    Actinides 2005 Manchester 4th-8th July 2005, conference
  • Contribution to external collection
    May I., Alvare R, Bryan N: Recent advances in Actinide Science, Cambridge, UK: RSC Publishing, 2006, 978-0-85404-678-2, 110-112

Publ.-Id: 6951 - Permalink

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