Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31828 Publications
Comparison of the Solution Behaviour of a Pyrite/Calcite Mixture in Batch and Unsaturated Sand Column
Kuechler, R.; Noack, K.;
The successful application of reaction transport algorithms to calculating the chemical evolution of natural systems requires accurate methods to compute the rates of mineral/fluid surface reactions. Regarding the transport of radio-nuclides in mining dumps the dissolution of minerals is of special importance. The use of a kinetic rate law of the mineral dissolution verified for unsaturated conditions will allow a realistic modeling of the mineral weathering in the environment. Dissolution rates of minerals in an aqueous solution are determined by surface reaction rates, the morphology of the mineral’s surface and, in case of the unsaturated zone, by the degree of the water saturation. For this process, it is decisive which portion of the particle surfaces is in con-tact with percolating water. To study the differences of mineral dissolution under saturated and unsaturated conditions batch and column experiments were carried out with a pyrite/calcite mixture. The experimental results were verified by calculations. Comparing the dissolution in batch with that in the column experiment, which was performed with a water flow velocity of 0.64 cm/d and analyzed in the region with a water saturation of 0.11, one can conclude that only the small portion of about five per cent of the grain surface is chemically reactive in this unsaturated flow.
Keywords: pollutant transport, unsaturated soil, pyrite/calcite dissolution, transport modelling

Publ.-Id: 7811 - Permalink


Development of a neutron time-of-flight source at the ELBE accelerator
Klug, J.; Altstadt, E.; Beckert, C.; Beyer, R.; Freiesleben, H.; Greschner, M.; Grosse, E.; Junghans, A. R.; Naumann, B.; Noack, K.; Schneider, S.; Seidel, K.; Wagner, A.; Weiss, F.-P.;
The ELBE electron beam at Forschungszentrum Rossendorf, Dresden, with energies up to 40 MeV, can be used to produce a beam of intense neutron pulses in a liquid-lead radiator, where bremsstrahlung photons created by the electrons produce neutrons in (gamma,xn) reactions. The 5 ps electron beam pulses create very short neutron pulses, giving an energy resolution of less than 1 % with a flight path of 3.9 m. A beam repetition rate of 1.6 MHz enables measurements with neutron energies from 200 keV to 10 MeV – an interval where neutron cross section measurements are needed for fission, fusion, and transmutation. The neutron beam will be shaped by a 2.4 m long collimator made from borated polyethylene and lead, reducing the background of scattered neutrons and of photons at the sample position. Monte Carlo simulations with MCNP4C3 were performed to optimise the collimator composition. About 92 % of the neutrons at the experiment site retain their correct energy-to-ToF correlation. The neutron energy resolution is 0.4 % (FWHM) at the maximum intensity. For neutron-capture gamma rays, a BaF2 scintillation detector array of up to 60 crystals is being built, whereas for neutron detection, Li-glass scintillators and a 1 m2 plastic scintillator wall will be used.
Keywords: photoneutron source, collimator design, MCNP simulations
  • Contribution to proceedings
    New Trends in Nuclear Physics Applications and Technology, 22.06.2006, Pavia, Italy
    Journal of Physics: Conference Series 41, 296

Publ.-Id: 7810 - Permalink


Gerichtete Erstarrung von Pb-Sn-Legierungen unter Einwirkung eines rotierenden Magnetfeldes
Eckert, S.; Willers, B.; Michel, U.;
Bereits seit einiger Zeit ist bekannt, dass man durch gezieltes Rühren einer erstarrenden, metallischen Schmelze mit mechanischem Antrieb oder mit Hilfe zeitabhängiger Magnetfelder in aktiver Weise Einfluss auf die Gefügeausbildung nehmen kann. Diese sogenannte, erzwungene Konvektion begünstigt beispielsweise globulitisches gegenüber dendritischem Wachstum und bewirkt eine Kornfeinung. Allerdings können Strömungen im Schmelzbad während der Erstarrung auch unerwünschte Makroseigerungen hervorrufen.
Der Einsatz elektromagnetischer Felder zum Rühren des Schmelzbades ist vor allen Dingen aus zweierlei Gründen attraktiv: (a) diese Methode bietet die Möglichkeit einer völlig kontaktlosen Einflussnahme und (b) eine unmittelbare und einfache Kontrolle der Intensität der Strömung kann über die elektrischen Regelparameter Strom und Frequenz vorgenommen werden. Zusätzlich sind verschiedene Arten von Magnetfeldern (Wanderfelder, pulsierende Felder, statische Felder) im Prinzip beliebig kombinierbar. Damit ergibt sich die Möglichkeit, grundsätzlich verschiedene Strömungsmuster je nach Bedarf zu erzeugen.
Das Ziel unserer Forschung besteht in der Anwendung maßgeschneiderter Magnetfelder während der Erstarrung zur effizienten Herstellung homogener, feinkörniger, globulitischer Gefüge. Zunächst soll mit Hilfe von Modellexperimenten, die die Komplexität des Problems überschaubar halten, mehr Informationen über die physikalischen Zusammenhänge zwischen der Erstarrung metallischer Legierungen und einer erzwungenen Konvektion in der Restschmelze gesammelt werden. Dazu wurden Pb-Sn-Legierungen in einer einfachen zylindrischen Geometrie unter Einwirkung eines rotierenden Magnetfeldes (RMF) gerichtet erstarrt.
Keywords: solidification, convection, CET, macrosegregation, rotating magnetic field
  • International Foundry Research 58(2006)2, 38-46

Publ.-Id: 7809 - Permalink


Improvement of high temperature oxidation resistance of TiAl
Schütze, M.; Donchev, A.; Yankov, R.; Richter, E.; Keywords: high temperature corrosion, TiAl, ion implantation
  • Lecture (Conference)
    14.th Int. Conf. Surface Modification of Materials by Ion Beams, 05.-09.09.2005, Kusadasi, Turkey

Publ.-Id: 7808 - Permalink


Microstructure of nitrogen implanted stainless steel after wear experiments
Manova, D.; Hirsch, D.; Richter, E.; Mändl, S.; Neumann, H.; Rauschenbach, B.; Keywords: ion implantation, nitrogen, stainless steel, wear, structure
  • Poster
    14.th Int. Conf. Surface Modification of Materials by Ion Beams, 05.-09.09.2005, Kusadasi, Turkey

Publ.-Id: 7807 - Permalink


Elaboration de Siliciures de Fer par Bombardement Ionique
Ayache, R.; Boubelleou, A.; Richter, E.; Kermiche, F.; Keywords: ion beam synthesis, FeSi2
  • Poster
    2.nd Algerian Crystallography Congress, 17.-21.04.2005, Constantine, Algeria

Publ.-Id: 7806 - Permalink


Stellar rates for the 26Mg(p,y)26Al reaction studied via AMS
Arazi, A.; Faestermann, T.; Fernandez, J.; Kurz, K.; Korschinek, G.; Poutivtsev, M.; Richter, E.; Wallner, A.; Keywords: nuclear reaction, AMS
  • Lecture (Conference)
    10th International Conference on Accelerator Mass Spectrometry, 05.-10.09.2005, Berkeley, California, USA

Publ.-Id: 7805 - Permalink


Hitzbeständige TiAL-Legierungen
Richter, E.; Keywords: TiAl, high temperature corrosion
  • Lecture (others)
    Werkstoff-Forum, 11.-15.04.2005, Hannover, Deutschland

Publ.-Id: 7804 - Permalink


Correlation between PIII nitriding parameters and corrosion behaviour of austenitic stainless steel
Mändl, S.; Manova, D.; Neumann, H.; Pham, M. T.; Richter, E.; Rauschenbach, B.;
In this work, nitrogen plasma immersion ion implantation (PIII) treatment of austenitic stainless steels 1.4301 and 1.4571 was performed to investigate the influence of the process conditions on the corrosion properties. Short treatment, high voltage and high temperature result in a decreased corrosion potential while no correlation to layer thickness, nitrogen concentration or lattice expansion was found. Except for the possibility of small CrN agglomerates at high temperatures, no direct explanation for the results can be provided and it is argued that intrinsic stress accumulation and relaxation may be responsible.
Keywords: plasma immersion ion implantation, stainless steel, nitriding, corrosion
  • Surface & Coatings Technology 200(2005), 104-108

Publ.-Id: 7803 - Permalink


Ion implantation and transient melting: A new approach to formation of superconducting MgB2 phases
Piekoszewski, J.; Kempinksi, W.; Stankowski, J.; Prokert, F.; Richter, E.; Stanislawski, J.; Werner, Z.; Szymczyk, W.;
An attempt to synthesize superconducting MgB2 inter-metallic compound from the liquid state is presented. The process consists of two steps. In the first one, boron ions are implanted into a magnesium substrate. In the second one, the near-surface region of such system is melted by short, intense hydrogen plasma pulses without necessity of annealing in Mg vapor. A magnetically modulated microwave absorption method was used to detect superconducting regions in the obtained MgB2 layer. Percolation between nano-regions (islands) of MgB2 has not been observed. However, a superconducting state of the insulated islands has been experimentally proven with transition temperatures TC as high as 31 K.
Keywords: ion implantation high energy pulse melting, superconductivity, MgB2, phase formation, XRD
  • Acta Physica Polonia A 106(2004), 861-868

Publ.-Id: 7802 - Permalink


Low Energy Ion Beam Synthesis of SiNanocrystals for Nonvolatile Memories –Modeling and Process Simulations
Müller, T.;
es ist kein Abstrakt vorhanden.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-439 2005

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Publ.-Id: 7801 - Permalink


Structural and optical properties of beta-FeSi2 phase prepared by ion beam synthesis
Ayache, R.; Bouabellou, A.; Eichhorn, F.; Richter, E.;
Semiconducting iron disilicide (β-FeSi2) was prepared by ion beam synthesis (IBS) in (111)Si P-type by implantation at 440 ˚C of 195 KeV Fe ions with a dose of 2.1017 Fe+/cm2 followed by annealing in a N2 atmosphere at 900 ˚C for 4 h. Characterization of samples included Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD) pole figure, and Raman spectroscopy. A mixture of β-FeSi2 and α-FeSi2 was observed in the as-implanted state. A Photoluminescence (PL) measurement at 12K indicates the luminescence peak at the energy of about 0.81 eV corresponding to the band gap energy of β-FeSi2 phase.
Keywords: ion beam synthesis, FeSi2, phase formation, RBS
  • Reviews on Advanced Materials Science 8(2004), 97-100

Publ.-Id: 7800 - Permalink


Magnesium suppression for 26Al measurements using AlO-ions
Arazi, A.; Faestermann, T.; Fernandez, J. O.; Frischke, D.; Knie, K.; Korschinek, G.; Maier, H. J.; Richter, E.; Rugel, G.; Wallner, A.;
Measuring the resonance strengths of the 25Mg(p,γ)26Al reaction at energies of astrophysical interest poses a very difficult task for the usual prompt γ-ray detection method. Here we describe an alternative method in which targets are first irradiated and the produced 26Al nuclei are off-line counted by means of AMS. An overall efficiency of 4 × 10−5 could be achieved extracting AlO− from the ion source. For this purpose, a careful chemical treatment of the samples and the use of a gas filled magnet were necessary.
Keywords: astrophysics, magnesium
  • Nuclear Instruments and Methods in Physics Research B 223-224(2004), 259-262

Publ.-Id: 7799 - Permalink


Development and biocompatibility of hard Ti-based coatings using plasma immersion ion implantation assisted deposition
Mukherjee, S.; Maitz, M. F.; Pham, M. T.; Richter, E.; Prokert, F.; Möller, W.;
The hard Ti-based coating TiAlN has been produced by plasma immersion ion implantation-assisted deposition (PIIIAD) on austenitic stainless steel. In PIIIAD, the substrate is exposed to cathodic arc plasma comprising of metallic ions corresponding to the cathode composition, and the substrate is biased pulsed negative. The pulsed bias of the substrate renders alternate phases of deposition (during the bias off time) and implantation and deposition (during bias on time), thereby controlling deposition temperature, reduction of compressive stresses, increase of crystallinity and enhancing adhesion of coating to substrate. The deposition has been carried out in a neutral as well as reactive nitrogen environment, which leads to nitrogen-containing coatings. In addition to TiAlN, also, Ti, TiN and TiAl were produced to investigate the effect of the different elements. All the coatings are tested for their suitability as biocompatible coatings, and hence, the adherence of osteoblast progenitor cells to these coatings was investigated in correlation with deposition parameters and surface morphology. The results identify the coatings that are wear resistant and suitable for orthopaedic implants.
Keywords: Titan coatings, plasma immersion ion implantation, ion assisted deposition, biocompatibility
  • Surface & Coatings Technology 196(2005), 312-316

Publ.-Id: 7798 - Permalink


Carbon ion implantation in pure aluminium at low fluences
Foerster, C. E.; Fitz, T.; Dekorsy, T.; Prokert, F.; Kreißig, U.; Mücklich, A.; Richter, E.; Möller, W.;
This work presents selected results from carbon ion implantation into pure Al matrix. The carbon ions were implanted with an ion energy of 25 keV and fluences of 1×1021 and 2×1021 C+/m2 at room temperature (RT) and elevated temperature of 400 °C. Elastic recoil detection analysis (ERDA), grazing incidence X-ray diffraction analysis (GIXRD), Raman spectroscopy and high resolution electron microscopy (HRTEM) show the formation of embedded Al4C3 precipitates with carbon concentrations below its stoichiometric level. At RT ion implantation, the Al4C3 precipitates have an average grain size in the order of 2–4 nm. For carbon ion implantation at 400 °C, the precipitates grow up to approximately 20 nm in diameter and are randomly distributed in the implanted region. The carbon excess, not bound in the Al4C3 precipitates, forms highly disordered C–C clusters of approximately 0.2–0.4 nm in size. Implantation at a temperature of 400 °C reduces drastically the carbon clusters content due to the growth of the Al4C3 precipitates.
Keywords: plasma immersion ion implantation, carbon ion, aluminium, phase formation
  • Surface & Coatings Technology 192(2005), 317-322

Publ.-Id: 7797 - Permalink


Wear reduction in AISI 630 martensitic stainless steel after energetic nitrogen ion implantation
Mändl, S.; Fritzsche, B.; Manova, D.; Hirsch, D.; Neumann, H.; Richter, E.; Rauschenbach, B.;
A significant wear reduction by several orders of magnitude is the common result for austenitic stainless steels after energetic nitrogen implantation at medium temperatures around 380 °C. In contrast, martensitic stainless steels are rarely investigated. In this investigation, one steel grade, stainless steel AISI 630/DIN 1.4542, is treated using low energy nitrogen implantation at 380 and 600 °C, high voltage nitrogen plasma immersion ion implantation (PIII) and combined carbon/nitrogen PIII at 380 °C. Using PIII, an expanded martensitic lattice extending several micrometers into the sample was observed, whereas Fe4N and CrN were formed after low energy implantation at 380 and 600 °C, respectively. All samples show a hardness of up to 2000 HV and a wear reduction by two orders of magnitude. Additional metallographic cross-sections confirm the microstructure derived from XRD data.
Keywords: ion implantation, stainless steel, nitrogen
  • Surface & Coatings Technology 195(2005), 258-263

Publ.-Id: 7796 - Permalink


The role of lid layers on the performance of von Karman type dynamos
Stefani, F.; Xu, M.; Gerbeth, G.;
The von Karman sodium (VKS) experiment is intended to investigate the hydromagnetic dynamo effect in a highly turbulent flow. Although much effort has been spent in the optimization of the flow structure and the lateral boundary conditions in order to minimize the critical magnetic Reynolds number, no dynamo effect has been seen in the recent experiments. The measured induced magnetic fields deviate significantly from the computed ones. In order to understand these experimental result, we focus on the role of lid layers, i.e. layers of liquid sodium between the impellers and the end walls of the cylinder. It is shown that static lid layers yield a moderate increase of the criticial Rm by approximately 12 per cent. A more dramatic increase by 100 until 200 per cent can occur when some rotational flow is taken into account in those layers. Possible solutions of this grave problem are discussed for the real dynamo facility.
  • Lecture (others)
    Seminarvortrag, Ecole Normale Superieure de Lyon, Laboratoire de Physique, 03.11.2005, Lyon, France

Publ.-Id: 7795 - Permalink


Industrial CFD Applications of Free Surface and Cavitating Flows
Zwart, P.-J.; Höhne, T.; Vallée, C.;
The FZR performed parallel experimental and numerical investigations in order to better understand the mechanisms leading to slug formation. For the CFD simulation, the code CFX-5 was used, applying the two fluid model with the free surface option. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying slug flow.
Keywords: Horizontal two-phase flow, Slug flow, CFD
  • Contribution to proceedings
    VKI Lecture Series, 27.04.2005, Rhode-Saint-Genèse, Belgium
    VKI Lecture Series 4.1

Publ.-Id: 7793 - Permalink


CFD analyses for stirred tank reactor: mixing behaviour of different density liquids
Hristov, H. V.; Prasser, H.-M.; Kryk, H.; Hessel, G.; Schmitt, W.;
The aim of this work is to numerically assess the dynamics of the mixing process of two different density liquids in a stirred tank reactor. The mixing of different density liquids is common operation in the process industry which occurs when a higher density liquid is injected into a tank filled with a lighter density one or in the case of impeller malfunctioning when such a system of different density liquids can get stratified. The process might prove to be of significant importance, particularly in the case of reacting liquids for large-scale reactors operating in the industry.
The CFD analyses, performed with the CFX-5 numerical package, were carried out for a non-baffled stirred tank reactor, mechanically agitated by a Pfaudler impeller. Although the non-baffled vessel posses an axi-symmetric behaviour on macromixing scale, the process was regarded as three dimensional in order to demonstrate the local instabilities associated with the blade passage. The dynamic mixing behaviour of two miscible liquids with different densities was numerically predicted from initially stratified conditions to complete mixing. The gas phase was involved in the simulations to investigate the effect of the free surface deformation on the mixing process, which was modelled using the free surface model. The multicomponent model was applied to the liquid phase in which the two different density liquids were present. The suitability of the different turbulence models was also addressed but the k-ε turbulence model was finally employed. The numerical simulations were performed on different size grids to ensure obtaining of grid independent results. However, the grid elements size was kept relatively low because of the dynamic behaviour of the liquid surface central vortex. Additionally, the impeller acceleration was taken into account.
The accuracy of the numerical predictions was evaluated experimentally using a video visualisation technique. The initially stratified lighter (alcoholic) coloured component and the heavier (water) transparent one were brought into motion by the rotating impeller. The mixing process was captured by a digital camcorder and subsequently the images were digitally processed. The procedure was repeated for a number of different initial concentrations of the lighter liquid to obtain the colour-calibration curve. The numerical predictions were evaluated at several locations, close to the vessel central line and wall, for which the optical distortions were minimal. Since the video visualisation technique provides the integral mixing curves at the chosen locations, the predicted concentration values were exported and averaged along the lines corresponding to these locations.
The hydrodynamics of the above described system is of particular concern for many chemical and biochemical reactions engineered to take place in stirred tank reactor. Although the initial conditions were to some extend idealised in order to avoid some complications raised by the presence on an injection, the studies showed strong influence on the density difference on the homogenisation.
  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, 31.05.-03.06.2005, Dresden, Germany
  • Contribution to proceedings
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, 31.05.-03.06.2005, Dresden, Germany
    Proceedings, CD-ROM

Publ.-Id: 7792 - Permalink


Compact Terahertz cyclotron resonance spectrometer in high magnetic fields
Drachenko, O.; Rylkov, V. V.; Leotin, J.;
In this paper we present a very compact cyclotron resonance (CR) spectrometer based on a GaAs/AlGaAs quantum cascade laser emitting at 11.4m. We show its operation under magnetic fields up to 60T and in temperatures up to 80K. We, finally, illustrate our spectrometer with the measurements of InAsxSb1-x alloy.
Keywords: Quantum Cascade Lasers, Magnetic fields, Cyclotron Resonance, InAsSb alloys
  • Lecture (Conference)
    The Joint 30th International Conference on Infrared and Millimeter Waves and 13th International Conf, 19.-23.09.2005, Williamsburg, USA

Publ.-Id: 7791 - Permalink


Electron-phonon interaction in quantum cascade lasers probed by Landau level spectroscopy
Drachenko, O.; Leotin, J.; Sirtori, C.; Page, H.; Semtsiv, M. P.; Ziegler, M.; Dreßler, S.; Müller, U.; Masselink, W. T.;
Resonant electron-LO phonon assisted depopulation of the lower lasing state is one of the common approaches to ensure population inversion and gain of quantum cascade lasers (QCLs) [1]. As a consequence, understanding of the dominating energy relaxation channels is important for development and optimizing of the active region of QCLs, especially built with new or modified materials. In this work we present a method to study the energy of the phonon modes responsible for nonradiative energy relaxation of electrons in the active zone of QCLs. The method is based on the spectrum analysis of the oscillations pattern of QCLs emission intensity as a function of magnetic field applied along the growth direction. These oscillations known as intersubband magnetophonon resonance (IMPR) originate from the resonant phonon assisted scattering of electrons from the upper lasing state into the Landau ladders of lower subbands whenever it is allowed by energy conservation [2] (Fig.1). The IMPR oscillations are periodic in the reciprocal magnetic field. Each lower subband and each phonon mode results in a maximum of the oscillation spectra. Each maximum corresponds to resonant scattering of electrons into the first Landau level of one of the bottom subbands, therefore the difference between intersubband and cyclotron energies gives the energy of phonon modes ensuring the relaxation.
In our experiments we have studied three sets of samples. The first two ones are GaAs/AlGaAs QCLs with different Al concentration in the barriers (33% and 45%) [3]. We clearly demonstrated that in the case of high Al concentration the relaxation via AlAs-like LO phonon can be significant (Fig. 2.). The third set is a In0.73Ga0.27As/AlAs short-wavelength QCL [4]. In this case we found that in spite of the high Al concentration in the barriers and the low GaAs contents in the wells, the nonradiative energy relaxation happens principally via GaAs-like or InAs-like (or mixed modes) phonon emission, while a clear signature of AlAs-like phonons was not observed.

[1] J. Faist et al., IEEE J. Quantum Electronics 38, 533 (2002).
[2] D. Smirnov et al., Phys. Rev. B 66, 125317, (2002); D. Smirnov et al., Phys. Rev. B 66, 121305(R) , (2002)
[3] P. Kruck et al. Appl. Phys. Lett. 76, 3340 (2000) ; H. Page et al., Appl. Phys. Lett. 78, 3529 (2001)
[4] M. P. Semtsiv et al., Appl. Phys. Lett. 85, 1478 (2004).
Keywords: Quantum Cascade Lasers, Phonon spectroscopy, Landau Levels, Magnetic fields
  • Lecture (Conference)
    8th International Conference on Intersubband Transitions in Quantum Wells ITQW’2005, 11.-17.09.2005, North Falmouth, USA

Publ.-Id: 7790 - Permalink


Experimental and analytical investigations for debris transport phenomena in multidimensional water flow
Alt, S.; Seeliger, A.; Krepper, E.; Grahn, A.;
The investigations of insulation debris generation and transport gain in importance regarding the reactor safety research for PWR and BWR considering all types of LOCA as well as short and long term behaviour of emergency core coolant systems.
The background of experimental investigations consists of the generation of a wide data base developing and validating the CFD-models for the description of particle transport phenomena in flow (e.g. drift, subsidence, sedimentation, resuspension, agglomeration and head loss at hold-up devices) under various geometric and fluidic boundary conditions. Separate effect experiments for the investigation of particle transport phenomena in multidimensional water flow, sedimentation and resuspension processes were carried out at plexi glass test facilities (Column, Ring Channel) using modern flow measurement and digital image processing technologies. The behaviour of gravitating insulation particles in aqueous solution (sink rates or settling velocities) and sedimentation processes were observed at the test facility “Column” in 2D-geometry. Experiments for the determination of 2D-transport behaviour of different particle sizes in horizontal carrier flow were realised at facility “Ring Channel”. Experimental results were generated with constant cross section area along the whole channel length as well as with varied cross section areas (e.g. barriers) and strainers.
Model developments for CFD simulations of insulation material transportation, suspension, resuspension and the clogging and penetration at strainers are described. The check of model parameters and functions based on the separate effect experiments.
The paper includes the presentation of experimental results generated at the facilities, the theoretical concepts for modelling these phenomena with CFD-codes and the comparison between simulated and measured data.
Keywords: insulation debris transport, cfd modelling, comparison to experiments
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), Paper 116, 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France

Publ.-Id: 7789 - Permalink


Air-water flow in a vertical pipe with sudden changes of superficial water velocity
Krepper, E.; Prasser, H.-M.; Frank, T.;
For further model development and the validation of CFD codes for two-phase flow applications experiments were carried out with a sudden change of the superficial velocity of water in a vertical pipe of 51.2 mm diameter. Measurements of the cross sectional gas volume fraction distributions were taken by two wire-mesh sensors (24x24 points, 2500 Hz) mounted in a short distance (16 mm) behind each other. This sensor assembly was placed 3030 mm downstream of the gas injection. The change of the superficial water velocity was jump-like reduced and in a second series of tests jump-like increased. The tests enable the observation of the restructuring process of bubbly flow between two steady state conditions. The experimental results for tests showing a monodisperse bubble size distribution were compared to CFD calculations using the code CFX-5. Applying the two fluid approach, the momentum interaction between the liquid and gas phase was considered. For the experimental conditions of dispersed bubbly flows without or with neglectable bubble coalescence & breakup the main flow features observed in the experiments could be reproduced qualitatively and quantitatively by the numerical simulation. Further research will be undertaken for the investigation of flow regime transition from gaseous phase volume fraction wall peak to core peak dominated flows. Further investigations will also include compressibility effects for the disperse bubbly phase.
Keywords: two phase measurement technique, experiments, two phase flow, cfd modelling, euler/euler approach, bubble forces
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France

Publ.-Id: 7788 - Permalink


Two fluid model LES of a bubble column
Reddy Vanga, B.; Lopez De Bertodano, M.; Krepper, E.; Zaruba, A.; Prasser, H.-M.;
The hydrodynamics of a rectangular bubble column operating in the dispersed bubbly regime has been numerically investigated using a two-fluid model Large Eddy Simulation (LES). Experimental data was obtained to validate the numerical model. LES computational fluid dynamic calculations of the transient flow for the bubble column were performed to account for the turbulence in the liquid phase. The computational mesh is of the same scale as the bubble size. The sub-grid scale Reynolds stresses were calculated using the Smagorinsky model. Furthermore, the effect of the bubbles on the turbulence in the continuous phase was modeled using Sato’s eddy viscosity model for bubble-induced turbulence. LES facilitates the direct numerical resolution of length scales that play an important role in the transport of bubbles, avoiding the need for constitutive models like the turbulent diffusion force to account for diffusion of the gas phase under the influence of the large eddies. Mean quantities, in particular the void fraction and the average velocity of the bubbles, were computed by averaging over a time period that was longer than the dynamic time scales of the turbulence. A systematic analysis of the effect of the interfacial momentum transfer terms on these quantities has been conducted. The bubble column was locally aerated using a sparger located in the center of the bottom plate. The model was validated with experimental data (Reddy Vanga, 2004) obtained using wire-mesh tomography measurements for void fraction and bubble size distributions. The experiments were performed for various aspect ratios (height of water column to width ratio) and superficial gas velocities.
Keywords: Two-Fluid Model, Large Eddy Simulations, Bubble Column, Lift Force, Wall Force
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France

Publ.-Id: 7787 - Permalink


Numerical investigations for insulation particle transport phenomena in water flow
Krepper, E.; Grahn, A.; Alt, S.; Kästner, W.; Kratzsch, A.; Seeliger, A.;
The investigation of insulation debris generation, transport and sedimentation gains importance regarding the reactor safety research for PWR and BWR considering the long term behaviour of emergency core coolant systems during all types of LOCA. The insulation debris released near the break during LOCA consists of a mixture of very different particles concerning size, shape, consistence and other properties. Some fraction of the released insulation debris will be transported into the reactor sump where it may affect emergency core cooling. Open questions of generic interest are e.g. the sedimentation of the insulation debris in a water pool, possible re-suspension, transport in the sump water flow, particle load on strainers and corresponding difference pressure.
A joint research project in cooperation with Institute of Process Technology, Process Automation and Measuring Technology (IPM) Zittau deals with the experimental investigation and the development of CFD models for the description of particle transport phenomena in coolant flow. While experiments are performed at the IPM-Zittau, theoretical work is concentrated at Forschungszentrum Rossendorf.
In the present paper the basic concepts for CFD modelling are described and first results including feasibility studies are shown. During the ongoing work further results are expected.
Keywords: insulation debris transport, cfd methods, comparison to experiments, strainer clogging model
  • Contribution to proceedings
    Nuclear Energy for New Europe 2005, 05.-08.09.2005, Bled, Slovenia
  • Lecture (Conference)
    23rd CADFEM Users Meeting 2005, 09.-11.11.2005, Bonn, Germany
  • Contribution to proceedings
    23rd CADFEM Users Meeting 2005, 09.-11.11.2005, Bonn, Germany

Publ.-Id: 7786 - Permalink


CFD modeling of subcooled flow boiling for nuclear engineering applications
Koncar, B.; Krepper, E.; Egorov, Y.;
In this work a general-purpose CFD code CFX-5 was used for simulations of subcooled flow boiling. Some important modelling issues were investigated: heat flux partitioning, turbulence modelling and non-drag forces. The subcooled boiling model, available in a custom version of CFX-5, has been used here. The special treatment of the wall boiling boundary, based on analytical temperature wall function, assures the grid invariant solution. The calculations been validated against the published experimental data of high-pressure flow boiling in a vertical pipe covering a wide range of conditions (relevant also to the pressurized water reactor).
Keywords: cfd methods, two phase flow, boiling, comparison to experiments
  • Contribution to proceedings
    International Conference "Nuclear Energy for New Europe 2005", 05.-08.09.2005, Bled, Slovenia

Publ.-Id: 7785 - Permalink


Inhomogeneous MUSIG model – a population balance approach for polydispersed bubbly flows
Frank, T.; Zwart, P.; Shi, J.-M.; Krepper, E.; Lucas, D.; Rohde, U.;
Many flow regimes in Nuclear Reactor Safety (NRS) Research are characterized by multiphase flows, where one of the phases is a continuous liquid and the other phase consists of gas or vapour of the liquid phase. In the range of low to intermediate volume fraction of the gaseous phase the multiphase flow under consideration is a bubbly or slug flow, where the disperse phase has to be characterized by an evolving bubble size distribution due to bubble breakup and coalescence processes. The paper presents a generalized inhomogeneous Multiple Size Group (MUSIG) Model, where the disperse gaseous phase is divided into N inhomogeneous velocity groups (phases) and where each of these groups is subdivided into M bubble size classes. Bubble breakup and coalescence processes between all bubble size classes are taken into account by appropriate models. The derived inhomogeneous MUSIG model has been validated against experimental data from the TOPFLOW test facility at the Research Center Rossendorf (FZR). Comparisons of gas volume fraction and velocity profiles with TOPFLOW-074 testcase data are provided, showing the applicability and accuracy of the model for polydispersed bubbly flow in large diameter vertical pipe flow.
Keywords: cfd methods, two phase flow, bubble size classes, comparison to experiments
  • Contribution to proceedings
    International Conference Nuclear Energy for New Europe 2005, 05.-08.09.2005, Bled, Slovenia

Publ.-Id: 7784 - Permalink


Investigation of flashing-induced instabilities at CIRCUS test facility with the code ATHLET
Schäfer, F.; Manera, A.;
The CIRCUS test facility has been built to study the start-up phase of a natural-circulation BWR. During the start-up so called flashing-induced instabilities can arise. These instabilities are induced by flashing, due to steam production in the long adiabatic riser section, which is placed above the core to enhance the flow rate. Flashing occurring in the riser causes an unbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations.

This paper gives an overview about experimental results and the physics of the instabilities. The thermo-hydraulic code ATHLET is used to investigate the dynamic behavior of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

This work is part of the NACUSP project (Natural Circulation and Stability Performance of BWRs) within the European-Union 5th Framework Programme.
Keywords: BWR, ATHLET, CIRCUS, flow instabilities
  • International Journal of Nuclear Energy Science and Technology 2(2006)3, 209-218

Publ.-Id: 7783 - Permalink


Accurate determination and benchmarking of radiation field parameters relevant forpressure vessel monitoring. A review of some REDOS project results
OšMera, B.; Boehmer, B.; Ballesteros, A.; Konheiser, J.; Kyncl, J.; Hordosy, G.; Keresztúri, A.; Belousov, S.; Ilieva, K.; Kirilova, D.; Mitev, M.; Smutný, V.; Polke, E.; Zaritsky, S.; Töre, C.; Ortego, P.;
Plant life management needs a reliable estimation of radiation field parameters, including their uncertainty, to avoid the use of conservative approaches. The particular objectives of the REDOS project are the improvements of the RPV monitoring, the improvement of the neutron – gamma calculation methodologies through the LR-0 engineering benchmarks for WWER-1000 and WWER-440, and the accurate determination of radiation field parameters in the vicinity and over the thickness of the RPV. This paper is mainly devoted to the comparison and analysis of the experimental and calculated LR-0 data (WP-3). The LR-0 benchmark data consist of neutron spectra (WWER-440 Mock-ups) and neutron + photon spectra (WWER-1000 Mock-up) in several points from the barrel simulator to the outer surface of RPV and evaluated integral fluxes, space – energy indices, like the spectral indices and attenuation factors in measuring points.
Keywords: reactor, neutron, gamma, benchmark, WWER-1000, WWER-440, REDOS, LR-0
  • Lecture (Conference)
    Twelfth International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, Tennesse, United States
  • Journal of ASTM International 4(2007)10
    DOI: 10.1520/JAI100279
  • Contribution to proceedings
    12 th International Symposium on Reactor Dosimetry, 08.-13.05.2005, Gatlinburg, United States, 08.-13.05.2005, Gatlinburg, United States
    Reactor Dosimetry: 12th International Symposium, West Conshohocken: ASTM, 978-0-8031-3412-6

Publ.-Id: 7782 - Permalink


Optisches Koppelelement für eine Durchflusszelle
Arnold, T.; Großmann, K.; Krawczyk-Bärsch, E.;
Die Aufgabe der Erfindung besteht darin, ein optisches Koppelelement zur mikroskopischen Charakterisierung von Proben in Durchflusszellen zu entwickeln, um einen direkten Kontakt des Objektivs mit der Durchflusslösung zu vermeiden und dabei die Verluste in der numerischen Apertur des Objektivs so gering wie möglich zu halten.
  • Patent
    Patentanmeldung 10 2005 051 406 A1
  • Patent
    PCT-Anmeldung PCT/DE2006/001806

Publ.-Id: 7781 - Permalink


Messsensor
Arnold, T.; Großmann, K.; Krawczyk-Bärsch, E.;
Messsensoren, die sich innerhalb einer durchstrahlbaren Probe befinden, können mikroskopisch visualisiert werden.
  • Patent
    Patentanmeldung 10 2005 051405 A1
  • Patent
    PCT-Anmeldung PCT/DE2006/001805
  • Patent
    DE 10 2005 051 405 B4 - 23. Aug. 2007

Publ.-Id: 7780 - Permalink


Mikroskopzusatz
Arnold, T.; Großmann, K.; Krawczyk-Bärsch, E.;
Es soll die Anpassung der Kryotechnik an das Mikroskop für die Messung von lebenswissenschaftlichen, aquatischen und mikrobiellen Proben und in Kopplung mit der Fluoreszenzmikroskopie erreicht werden.
  • Patent
    Patentanmeldung 10 2005 051 386 A1
  • Patent
    PCT-Anmeldung PCT/DE2006/001804

Publ.-Id: 7779 - Permalink


Anordnung zur Messung der lokalen elektrischen Impedanz und der Temperatur in Fluiden
Schleicher, E.; Da Silva, M. J.; Hampel, U.;
Aufgabe der Erfindung ist es, eine Anordnung zur schnellen und gleichzeitigen Messung der lokalen elektrischen Impedanz und der Temperatur in Fluiden vorzuschlagen.
  • Patent
    DE 10 2005 046 662 B3 - 22. März 2007
  • Patent
    PCT / DE2006 / 0001590

Publ.-Id: 7778 - Permalink


Channeling X-rays at the ELBE radiation source
Wagner, W.; Azadegan, B.; Panteleeva, A.; Pawelke, J.; Enghardt, W.;
A new setup for the measurement of electron channeling radiation has been taken into operation at the ELBE radiation source. First experiments at electron energies of 14.6 and 17 MeV using diamond type-IIa crystals were aimed at the verification of the dependence of the yield of channeling radiation on the crystal thickness. While the dissipative approach assuming an experimentially decreasing occupation function with an ernergy-dependent characteristic occupation length (locc) is able to describe the yield up to a thickness of about 2locc multiple scattering remarkable influences the yield at larger crystal thickness
  • Lecture (Conference)
    International Workshop on Charged and Neutral Particle Channeling Phenomens, Channeling 2004, 02.-06.11.2004, Frascati, Italy
  • Contribution to proceedings
    International Conference on Charged and Neutral Particles Channeling Phenomena, 02.-06.11.2004, Rome, Italy
    Proceedings of SPIE, International Conference on Charged and Neutral Particles Channeling Phenomena, 5974 (Dec. 2005), B1-B9

Publ.-Id: 7777 - Permalink


Untersuchungen zum Verhalten von freigesetztem Isolationsmaterial in ruhender und horizontaler Kühlmittelströmung
Alt, S.; Hampel, R.; Kästner, W.; Lischke, W.; Seeliger, A.; Krepper, E.; Grahn, A.;
The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multidimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data will be use for CFD-modelling and validation. The anticipated modeling concepts are presented and their feasibility is demonstrated. During the ongoing work further results are expected.
Keywords: insulation materials, experiments
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
    CD-ROM

Publ.-Id: 7776 - Permalink


Can we predict critical heat flux in fuel assemblis by CFD methods?
Burtak, F.; Krepper, E.;
The presentation describes the industrial needs for the nuclear fuel elemet design particularly concerning the mixing vanes of spacer grids. Actual informations can be gained only by very expensive experiments. The actual state and the capabilities of CFD to support this process is referred.
Keywords: fuel elements, hot channel, critical heat flux, experiments, CFD simulations
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany

Publ.-Id: 7775 - Permalink


Practical calculation of bubble column flow with CFX-5
Frank, T.; Krepper, E.; Eickenbusch, H.;
The presentation describes the setup of a multiphase simulation on the example of the simulation of a bubble column. The results are compared to experiments performed in the FZR applying high speed video and a wire mesh sensor. The comparison shows, that the correct simulation of the non drag forces is essential to reproduce the correct flow pattern. Considering all forces, an excellent agreement toe the measured results can be achieved.
Keywords: CFX, multiphase CFD, bubble column, measurements, bubble forces
  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, 31.05.-03.06.2005, Rossendorf, Germany

Publ.-Id: 7774 - Permalink


WWER radial reflector modeling by diffusion codes
Petkov, T.; Mittag, S.;
The two commonly used approaches to describe the WWER radial reflectors in diffusion codes, by albedos on the core-reflector boundary and by a ring of diffusive assembly size nodes, are discussed. The advantages and disadvantages of the first approach are presented first, then the Koebke's equivalence theory is outlined and its implementation for the WWER radial reflectors is discussed. Results for the WWER-1000 reactor are presented. Then the boundary conditions on the outer reflector boundary are discussed. The possibility to divide the library into fuel assembly and reflector parts and to generate each library by a separate code package is discussed.
  • Lecture (Conference)
    15-th Symposium of AER, 03.-07.10.05, Znojmo, Czech Republic
  • Contribution to proceedings
    15th Symposium of AER, 03.-07.10.05, Znojmo, Czech Republic
    Proceedings, Budapest: Kiadja a KFKI Atomenergia Kutató Intézet, 963-372-6328, 39-50

Publ.-Id: 7773 - Permalink


Mathematical models in the DYN3D-FLOCAL code – consequences on reactor analysis results
Rohde, U.; Grundmann, U.;
The lecture gives an introduction into the computational modeling of transients in nuclear reactors. The physical models and numerical methods used in the code DYN3D for the simulation of reactivity initiated accidents in Light Water Reactors are briefly described. The importance of correct numerics for nuclear safety analysis is outlined. Examples are given, how numerical errors and not properly chosen methods can influence the results of transient analyses. Particularly, the importance of low-diffusive numerical schemes for the modelling of transport phenomena like transport of low-borated slugs of coolant is stressed.
Keywords: nuclear reactor simulations, reactivity initiated accidents, physical models, numerical methods, 3D neutron kinetics, thermal hydraulics, nuclear reactor safety
  • Invited lecture (Conferences)
    Course on Mathematical Modelling, 24.11.2005, Plzen, Czechia

Publ.-Id: 7772 - Permalink


Solarstrahlungskarten und Erträge von PV-Anlagen: Ergebnisvergleich in Sachsen
Drews, A.; Heinemann, D.; Rindelhardt, U.;
Während bei großen PV-Anlagen (etwa > 100 kW) die Messung der Einstrahlung in Modulebene inzwischen zum Standard der installierten Messtechnik gehört, sind die Betreiber von kleineren Anlagen zur Überwachung der korrekten Funktion ihrer Anlage auf den Vergleich mit externen Daten angewiesen. Dazu werden von verschiedenen Anbietern z.B. monatliche Überprüfungen der Erträge unter Berücksichtigung der meist aus Satellitendaten bestimmten lokalen Globalstrahlung und der konkreten Anlagenkonfiguration vorgeschlagen. Andererseits werden auch monatliche bzw. jährliche Einstrahlungskarten veröffentlicht, die es jedem Anlagenbetreiber grundsätzlich ermöglichen eigene Einschätzungen der erzielten Erträge vorzunehmen. Das letztgenannte Vorgehen soll anhand einiger Anlagen aus Sachsen verifiziert werden.
Die Untersuchungen wurden für das Jahr 2004 vorgenommen. Dazu stand der vom DWD erstellte Solarstrahlungsatlas zur Verfügung. Er basier auf den Bodenmessungen von fast 40 über Deutschland verteilten Messstationen. Da diese Messungen nicht flächendeckend sind, werden sie mit aus Satellitendaten abgeleiteten Globalstrahlungsinformation kombiniert.
Eine zweite Einstrahlungskarte wurde an der Universität Oldenburg aus Satellitendaten erzeugt. Sie wurde (ausschließlich) aus Bildern des meteorologischen Satelliten Meteosat-7 mit einer für Deutschland angepassten Version der Heliosat-1 Methode abgeleitet. Die räumliche Auflösung der Karte beträgt ca. 5 x 5 km.
Für die Verifikation wurden aus über 200 PV-Anlagen in Sachsen die 20 Anlagen mit den höchsten Jahreserträgen in 2004 ausgewählt. Dieses Auswahlprinzip garantierte, dass nur (verschattungsfreie) Anlagen mit optimaler Ausrichtung sowie in technisch einwandfreien Zustand einbezogen wurden. Die Erträge der Anlagen lagen durchweg über 900 kWh/kW, ihre räumliche Verteilung ist im Bild 1 zu sehen.
Die Einstrahlung im Jahr 2004 wich in Sachsen nur geringfügig vom solaren ""Normaljahr" ab (Globalstrahlung in Dresden ca. 4% über langjährigem Mittelwert). Nach beiden Karten treten in Sachsen (abgesehen von den höheren Mittelgebirgsregionen) Einstrahlungen zwischen 1040 und 1100 kWh/m² auf, als Gebiet höchster Einstrahlung wird übereinstimmend ein Gebiet westlich von Meißen ausgewiesen. Letztere stimmt auch mit den Werten der Bodenstationen überein. Für die übrigen Gebiete treten zwischen den Karten teilweise Unterschiede in der Einstrahlung von mehr als einer Klasse (20 kWh/m²) auf.
Der Vergleich der Standorte der betrachteten PV-Anlagen mit den von den Karten angegebenen Einstrahlungsgebieten (unterteilt nach Klassen mit 20 kWh/m² führte zu einem überraschenden Ergebnis: Die Anlagenstandorte scheinen eher gleichverteilt als mit den Einstrahlungsgebieten korreliert.
Ein belastbarer Vergleich von jährlichen Einstrahlungen aus Karten mit den Erträgen von (gut orientierten und technisch einwandfreien) PV-Anlagen an konkreten Standorten ist offenbar nicht ohne weiteres möglich.
Als mögliche Ursachen kommen – neben Fehlern in der Datenbasis der Karten - Interpolationsfehler und eine zu starke Generalisierung bei der grafischen Darstellung in Betracht. U.U. muss auch auf monatliche Einstrahlungskarten zurückgegriffen werden, um eine bessere Verifikation der Anlagenerträge zu erreichen.
Keywords: Photovoltaic, performance
  • Contribution to proceedings
    21. Symposium Photovoltaische Solarenergie, 08.-10.03.2006, Staffelstein, Germany
    Tagungsband "Photovoltaische Solarenergie", Regensburg: OTTI, 450-455
  • Poster
    21. Symposium Photovoltaische Solarenergie, 08.-10.03.2006, Staffelstein, Deutschland

Publ.-Id: 7771 - Permalink


Betriebserfahrungen mit der ersten sächsischen Photovoltaik-Megawattanlage in Meerane
Rindelhardt, U.; Schröder, A.;
Im Jahr 2004 wurde in Meerane die erste Megawatt-Anlage in Sachsen in Betrieb genommen. Sie liegt in einer vom DWD ermittelten "Sonneninsel" westlich von Chemnitz. Die Anlage befindet sich in einem Gewerbegebiet südlich von Meerane hinter einer Lärmschutzwand an der Autobahn A4. Auf einer Fläche von 2,5 Hektar wurden insgesamt 417 Tische zur Aufnahme der Module errichtet, die Gesamtleistung beträgt 1066 kW. Die Anlage wurde im April 2004 in Betrieb genommen, eine komplette Datenerfassung (einschließlich Einstrahlung und Modultemperatur) erfolgte ab August 2004. In den ersten Monaten traten mehrfach Abschaltungen der Wechselrichter, ausgelöst durch zu geringen Isolationswiderstand des PV-Generators, auf. Ab August 2004 lief die Anlage weitgehend fehlerfrei.
Der Wechselrichter-Wirkungsgrad lag durchgehend bei 95 %, und das Performance Ratio bei 0,76.
Im Zeitraum August 2004 bis Juli 2005 wurde ein normierter Ertrag von 927 kWh/kW erreicht (siehe Bild 1). Durch aufgetretene technische Störungen trat ein Verlust von etwa 20 kWh/kW auf, so dass bei störungsfreiem Betrieb ein Ertrag von 950 kWh/kW erreicht worden wäre. Da der betrachtete Zeitraum bezüglich der Einstrahlung als "Normaljahr" angesehen werden kann, kann auch künftig im Mittel mit diesem Ertrag gerechnet werden.
Keywords: Photovoltaic, power plant
  • Poster
    21. Symposium Photovoltaische Solarenergie, 08.-10.03.2006, Staffelstein, Deutschland
  • Contribution to proceedings
    21. Symposium Photovoltaische Solarenergie, 08.-10.03.2006, Staffelstein, Germany
    Tagungsband "Photovoltaische Solarenergie", Regensburg: OTTI, 275-279

Publ.-Id: 7770 - Permalink


CFD-modelling of subcooled boiling and application to simulate a hot channel of a fuel assembly
Krepper, E.; Egorov, Y.;
The paper contributes to the advanced CFD simulation of subcooled boiling in forced convective flows, with special attention given to the momentum transfer between continuous liquid and vapour bubbles. A wall boiling model, implemented in CFX-5 (Egorov, Menter, 2004) and based on the two-fluid approach, is used here together with the state-of-the-art model correlations for the non-drag forces, available in CFX-5. The paper describes the main concepts of modelling mass, heat and momentum transfer between the phases. Published experimental results for flow in a pipe are used for the model validation.
The model is applied to the simulation of subcooled boiling flow in a hot channel of a fuel rod bundle. Influence of mixing vanes, attached to the spacer grids of fuel assembly in order to enhance the heat transfer, is taken into account. The simulation results demonstrate the capability of the model to estimate the effects of geometrical design on the flow physics.
Keywords: cfd modelling, boiling, phase transition
  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, 31.05.-03.06.2005, Dresden, Germany

Publ.-Id: 7769 - Permalink


Numerical investigations of insulation debris transport phenomena in water flow
Grahn, A.; Krepper, E.;
The paper includes the description of separate effect test facilities used for investigations with regard to the fragmentation and the transport behaviour of different insulation materials in multidimensional aqueous flow. The instrumentation of the rigs is specified, in particular modern digital image processing technologies. First experimental results are shown and discussed generated at three acrylic glass test facilities. The experimental data will be use for CFD-modelling and validation. The anticipated modeling concepts are presented and their feasibility is demonstrated. Particularly a model for description of the behaviour of a strainer is presented.
Keywords: insulation material, flow behaviour, experiments, cfd methods
  • Lecture (Conference)
    Workshop on Multi-Phase Flow: Simulation, Experiment and Application, 31.05.-03.06.2005, Rossendorf, Germany

Publ.-Id: 7768 - Permalink


Application of Best Practice Guidlines for the use of computational fluid dynamics in the reactor safety analysis
Höhne, T.;
Die Kühlmittelvermischung in Druckwasserreaktoren ist für zum einen für die Reaktorsicherheit, zum anderen aber auch die wirtschaftliche Betriebsführung von Bedeutung. Bei Borverdünnungsstörfällen ist die Vermischung des unterborierten Kühlwassers mit dem vorliegenden Kühlmittelinventar auf dem Weg zum Reaktorkern einzige effektive Schutzmechanismus gegen einen Reaktivitätsstörfall. Im Notkühlfall bestimmt die Vermischung die thermische und damit mechanische Belastung der Druckbehälterwand.

Im Projekt FLOMIX-R wurde eine breite und einzigartige experimentelle Datenbasis zur Kühlmittelvermischung geschaffen. An drei europäischen Versuchsanlagen wurden Experimente zur Kühlmittelvermischung in unterschiedlichen Situationen durchgeführt – Vermischung unter stationären Betriebsbedingungen, Vermischung eines Pfropfens unterborierten Wassers beim Pumpenstart und Vermischung kalten Notkühlwassers. Dank räumlich und zeitlich hochauflösender Messtechnik wurden Einsichten in die Details der Vermischungsphänomene gewonnen. Darüber hinaus wurden Messdaten zur Kühlmittelvermischung an einer realen Reaktoranlage (KKW Paks in Ungarn) verfügbar gemacht.

Die umfangreichen Messdaten bieten eine Grundlage für die Validierung von CFD-Codes. Im Projekt wurden ausgewählte Experimente durch eine Reihe von Projektpartnern mit den CFD-Codes CFX und FLUENT nachgerechnet. Dabei wurde zur Qualitätssicherung nach sogenannten ”Best Practice Guidelines” (BPG) vorgegangen. Die BPG stellen eine Strategie zur Minimierung numerischer Fehler dar. Erst nach einer erfolgten Fehlerminimierung kann die Qualität physikalischer Modelle, insbesondere von Turbulenzmodellen, bewertet werden. Im Rahmen der Anwendung der BPG wurden wichtige Erfahrungen zum Einfluss der Berechnungsgitter, der numerischen Verfahren, der Randbedingungen und der Geometrie gewonnen. Zur Bewertung der Güte der Modelle wurden quantitative Vergleiche zwischen Rechnung und Messung durchgeführt. Zusammenfassend kann festgestellt werden, dass CFD-Methoden für eine ingenieurtechnische Anwendung auf Probleme der turbulenten Vermischung reif sind, aber viele Detailprobleme noch zu klären sind.
Keywords: Best Practice Guidelines, CFD, ROCOM, Coolant Mixing
  • Invited lecture (Conferences)
    Course Mathematical Modelling, 24.11.2005, Pilsen, Czech Republic

Publ.-Id: 7767 - Permalink


Simulation of molten salt reactor dynamics
Krepel, J.; Rohde, U.; Grundmann, U.;
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 of two physical peculiarities of the liquid fueled reactor: the delayed neutrons precursors are drifted by the fuel flow and the fission energy is immediately released directly into the coolant. 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. In these considered transients, the response of the MSR is characterized by the immediate change of the fuel temperature with changing power and fast negative temperature feedback to the power. The response through the graphite temperature is slower. Furthermore, for big MSR cores fueled with U233 the graphite feedback coefficient can be positive. In this case the addition of erbium to the graphite can ensure the inherent safety features. The DYN3D-MSR code has been shown to be an effective tool for MSR dynamics studies.
Keywords: MSR, molten, salt, reactor, dynamics
  • Contribution to proceedings
    Nuclear Energy for New Europe 2005, 05.-08.09.2005, Bled, Slovenia
  • Lecture (Conference)
    Nuclear Energy for New Europe 2005, 05.-08.09.2005, Bled, Slovenia

Publ.-Id: 7765 - Permalink


The Feasibility of In-Beam PET for Therapeutic Beams of 3He
Fiedler, F.; Crespo, P.; Parodi, K.; Sellesk, M.; Enghardt, W.;
At present in-beam PET is the only possibility for an in-situ monitoring of the particle delivery in hadron tumor therapy and there is a unique clinical implementation at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt. Several heavy ion treatment facilities are under construction, which will provide a large variety of ions from protons to oxygen. This requires a precise knowledge of the spatial distribution of beam induced positron emitters in the irradiated volume. For the 3He-case experiments at GSI with three mono-energetic 3He-beams of 130.03 AMeV to 207.92 AMeV and mean intensities varying from 2E8 to 3.6E8 ions/s has been carried out. The beams were stopped in homogeneous thick targets consisting of PMMA, graphite and water, which were placed in the center of the field of view of the PET-scanner at the experimental carbon ion therapy at GSI. Results on the production rate and the spatial distribution of 3He ion induced beta+-activity will be presented and compared with data from 12C-irradiation. From these, the accuracy and resolution for determining the range of the 3He primary beams is deduced. Furthermore, energy dependent thick target cross sections for different reaction channels leading to positron emitters will be estimated from the experimental data.
Keywords: In-beam PET, heavy ion therpay, therapy monitoring
  • Contribution to proceedings
    IEEE Nuclear Science Symposium & Medical Imaging Conference, 23.-29.10.2005, Fajardo, Puerto Rico
    Conference Record 2005
  • Lecture (Conference)
    IEEE Nuclear Science Symposium & Medical Imaging Conference, 23.-29.10.2005, Fajardo, Puerto Rico
  • IEEE Transactions on Nuclear Science 53(2006)4, 2252-2259
    DOI: 10.1109/TNS.2006.877854

Publ.-Id: 7764 - Permalink


Experimental investigation of the hydrodynamics of confined bubble plumes in water and viscous media
Reddy Vanga, B. N.; Zaruba, A.; Krepper, E.; Prasser, H.-M.; Lopez De Bertodano, M. A.;
Wire-mesh tomography measurements of void fraction and bubble size distribution in a rectangular bubble column 10 cm wide and 2 cm in depth have been conducted. Experiments were performed in an air-water and ethylene glycol system with the column operating in the dispersed bubbly flow regime. Experiments were performed for plumes with different aspect ratios (ratio of the height of the stationary liquid column to the width of the test section) between 2.2 to 13. The behaviour of the long plumes (larger aspect ratio) was found to be significantly different than that of the short plumes (aspect ratios 2 to 4). The oscillating nature of the bubble plume is preserved over the entire height of the water column for the short plumes. The longer plumes are characterized by two distinct regions, the near injector oscillating region and a further downstream region where the flow attains a ‘fully developed’ condition and the bubbles rise in a string like motion spread throughout the cross-section of the bubble column. The void fraction distribution in the oscillating region of the long plume exhibits a center-peak profile. A ‘wall peak’ has been observed in the measured void fraction profiles (for higher gas flow rates) in the downstream fully developed region of the long plume. The effect of column height and superficial gas velocity on the void distribution has been investigated. This paper presents the measurement principle and the experimental results for short and long plumes in an air-water system and for short plumes rising in viscous media. The results of the visualization experiment characterizing the structure of the bubble plume and the oscillation frequency of the bubble plumes are reported. Bubble velocities in the non-oscillating region of the long plume have been calculated using digital image processing of high-speed camera images.
Keywords: bubble column, bubble plume, wire-mesh sensor, image processing
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
    Proceedings on CD-ROM, #456

Publ.-Id: 7763 - Permalink


Sorption von Uran an Geomaterialien - Experiment und Modellierung
Hollenbach, B.;
In der vorliegenden Arbeit wurde das Transportverhalten von U(VI) bei der Migration durch Quarz und Gibbsit untersucht. Experimentell erfolgte diese Untersuchung in Säulenversuchen unter ungesättigten Bedingungen. In die Betrachtung wurden 3 Säulen mit unterschiedlichen Quarz- und Gibbsit- Anteilen einbezogen. (Säule 1: Quarz, Säule 2: Gibbsit/Quarz = 1/10, Säule 3: Gibbsit/Quarz = 1/4)
Die aufgebrachte Kontaminationslösung hatte eine Urankonzentration von 5 x 10-6 mol/L. Aus den Ergebnissen der Kationenanalyse des Eluats konnte eine Durchbruchskurve des Urans aufgezeichnet werden. Im Rahmen dieser Arbeit erfolgte jedoch nur ein Durchbruch des Urans in der Quarzsäule. Das Geomaterial der Säule 1 (Quarz) und der Säule 3 (Gibbsit/Quarz: 1/4) wurde im Anschluss an die Sorptionsuntersuchung in Scheiben a 0,5 cm geschnitten. Nach einem Säureaufschluss erfolgte die Bestimmung der Urankonzentration in den einzelnen Scheiben. Im Ergebnis erkennt man, dass die Retardierung des Urans durch zwei Prozesse erfolgte: Adsorption an der Mineraloberfläche und Präzipitation einer Festphase. Der zweite Teil dieser Arbeit beinhaltete die Vorausberechnung der U(VI)-Migration durch die Säulen mit Hilfe des Programms MCOTAC. Diese Berechnung erfolgte für die Quarzsäule und es zeigte sich eine gute Übereinstimmung der Ergebnisse aus Experiment und Modellierung.
  • Other report
    Hochschule für Wirtschaft und Technik Dresden: Diplomarbeit (Studiengang Chemieingenieurwesen), 2005
    68 Seiten

Publ.-Id: 7762 - Permalink


Experimental investigations on bubble turbulent diffusion in a vertical large-diameter pipe by means of wire-mesh sensors and correlation techniques
Manera, A.; Prasser, H.-M.; Lucas, D.;
Experiments with air-water flows have been carried out in a vertical pipe of ~194 mm diameter and 9 m long and a wide range of superficial liquid and gas velocities has been covered. At a distance of 7.6 m from the air injection, two wire-mesh sensors are installed, located at a distance of 63.3 mm from each other. The wire-mesh sensors measure sequences of instantaneous two-dimensional gas-fraction distributions in the cross-section in which they are mounted with a spatial resolution of 3 mm and a frequency of 2500 Hz. The spatial cross-correlations of the gas-fraction signals have been evaluated and on their basis turbulent diffusion coefficients have been estimated.
It is found that for a given liquid superficial velocity a sudden increase of the diffusion coefficient takes place when the superficial gas velocity is increased above a certain value. The abrupt increase of the diffusion coefficient occurs in correspondence of the transition from mono- to bimodal bubble size distributions.
The experimental diffusion coefficients are compared with the prediction of the Sato’s model (experimental gas-fraction profiles and bubble size distributions are given as input). Even if this model has been developed for bubbly flow, the general trends are well captured also in the churn-turbulent regime.
Keywords: Two-phase flow, eddy diffusivity, cross-correlation, bubble-induced turbulence
  • Contribution to proceedings
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, Avignon, France

Publ.-Id: 7761 - Permalink


Strategies for the start-up procedure of natural circulation Boiling Water Reactors
Manera, A.;
The economy of existent NPP designs suffers for the complexity of the safety systems (which have to be redundant and diversified). Nuclear reactors can be made more competitive and reliable by adopting a simpler design and passive safety systems. Following this philosophy, the design of natural-circulation BWRs was developed. In this type of reactors the coolant circulation is gravity-driven and is ensured as long as heat is produced in the core (if a sufficient water level is maintained) without the need of any active system. The elimination of the recirculation systems (pumps and related piping and components) simplifies the design and excludes a whole series of transients and initiating events that can lead to accidents (pump trips, LOCAs due to failures of the recirculation piping, etc.). Unfortunately, natural circulation systems may exhibit thermal-hydraulic instabilities under low-power and low-pressure conditions. Hence, appropriate start-up procedures have to be planned in order to avoid flow oscillations. In the paper strategies for the start-up of natural circulation BWRs are discussed.
Keywords: BWRs, natural circulation, start-up
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany
    CD-ROM
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2005, 10.-12.05.2005, Nürnberg, Germany

Publ.-Id: 7760 - Permalink


Out-of-phase flashing-induced instabilities in a natural circulation two-phase system with parallel channels
Manera, A.;
For the first time flashing-induced out-of-phase oscillations are observed in a natural circulation loop operated at low pressure. Both regular (symmetric) and irregular oscillations patterns have been found. Simulations with the best-estimate thermal-hydraulic code ATHLET (developed by GRS, Germany) have been performed to get deeper insight in the phenomenology of the instability.
The main characteristics of the flow oscillations are illustrated and the relation between fluid travelling time and oscillation period is studied.
  • Contribution to proceedings
    4th International Conference on Transport Phenomena in Multiphase Systems, 26.-30.06.2005, Gdansk, Poland

Publ.-Id: 7759 - Permalink


Integritätsbewertung von Reaktordruckbehältern
Viehrig, H.-W.;
Der RDB ist Teil der druckführenden Umschließung eines Kernreaktors und schließt den Reaktorkern mit nahezu dem gesamten radioaktiven Inventar ein. Er fungiert als Hauptbarriere gegen den Austritt von Radioaktivität in der Umgebung, er ist vielfältig mit anderen Komponenten eines Kernreaktors verflochten und sein Ausfall ist nicht durch andere Komponenten kompensierbar. Während des Betriebes kommt es zu zeitabhängigen Veränderungen der Eigenschaften des RDB, die unter dem Begriff Alterung zusammengefasst werden. Im engeren Sinne ist Alterung dabei als die Degradation der Werkstoffeigenschaften infolge von Temperatur (thermische Alterung), Korrosion, Verschleiß oder Bestrahlung (Strahlenversprödung) aufzufassen. In einem weiteren Sinne ist Alterung auch als konzeptionelle und technologische Alterung zu verstehen, die letztlich aus der Weiterentwicklung von Wissenschaft und Technik resultiert. Derartige Alterungserscheinungen sind zu erfassen und durch geeignete Gegenmaßnahmen zu kompensieren oder wenigstens angemessen zu berücksichtigen, um Betriebsdauer und Sicherheitsniveau der Anlage abzusichern. Die uneingeschränkte Nutzung eines RDB bis zum Ende der Betriebsdauer des KKWs auf einem unverändert hohen Sicherheitsniveau ist nur durch ein ganzheitliches und umfassendes Programm von Maßnahmen und Instrumentarien zu gewährleisten. Entscheidend werden dafür die Weichen bereits bei der Auslegung gestellt, indem hochzähe, strahlenversprödungsresistente Werkstoffe verwendet werden, die Neutronenbelastung durch einen ausreichend breiten Wasserspalt reduziert wird, die fortschreitende Materialalterung durch ein gut konzipiertes repräsentatives Überwachungsprogramm erfasst und Herstellung und Konstruktion gute Prüfbarkeit ebenso wie die Vermeidung von Spannungsdiskontinuitäten absichern. Betriebliche Maßnahmen können die Beanspruchung bei Betrieb oder im Störfall reduzieren, die Neutronenflussdichte durch ein geeignetes Beladeregime senken oder mit aktualisierten Überwachungsprogrammen die Charakterisierung des Materialzustandes verbessern. Als ultimo ratio steht die Ausheilglühung zur Verfügung, deren Praktikabilität inzwi-schen bereits erwiesen ist. Mit vergleichsweise geringem Aufwand, aber hoher Effektivität sind Überwachungsmaßnahmen einzusetzen. Die wiederkehrende ZfP mit verfeinerten Methoden, die immer kleinere Fehler mit Sicherheit nachzuweisen gestatten, liefert eine realistische Grundlage für die Belastungsanalyse, deren Konservativität mit verbesserten FEM-Modellen herabgesetzt werden kann. Diesem Ziel dienen auch genauere Neutronenfluenzbestimmungen oder die Qualifizierung des Messsystems zur Kontrolle der Betriebsbelastungen. Schließlich erweist sich nicht zuletzt die Einführung neuer Konzepte zur Sprödbruchsicherheitsanalyse als wertvoll. Als ein hinsichtlich seiner Einführung bereits fortgeschrittenes Beispiel dieser Art wurde das Master-Curve-Konzept nach Wallin vorgestellt. Dieses Konzept wird gegenwärtig zur Bestimmung einer bruchmechanisch definierten Übergangstemperatur benutzt, mit der die KIc-Universalkurve der Regelwerke materialspezifisch auf der Temperaturachse positioniert werden kann. Die so ermittelten Referenztemperaturen liegen ca. 40 - 60 K niedriger als die bisher verwendeten Referenztemperaturen, die auf den NDT- oder den Charpy-V-Übergangstemperaturen beruhen. Auf diese Weise kann eine unnötige Konservativität der Bewertung abgebaut werden. Das wurde bereits in realen Anwendungsfällen zweifelsfrei nachgewiesen.
Keywords: nuclear power plant, reactor pressure vessel, operation time, integrity assessment, pressurized thermal shock, fracture toughness, Master Curve Concept, neutron embrittlement, surveillance programme, trend curve, aging, thermal annealing
  • Invited lecture (Conferences)
    124. Sitzung des Arbeitskreises Dresden der Gesellschaft für zerstörungsfreie Prüfung e.V., 27.10.2005, Dresden, Germany

Publ.-Id: 7758 - Permalink


Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids
Ulrich, K.-U.; Rossberg, A.; Foerstendorf, H.; Zänker, H.; Scheinost, A.;
To investigate the molecular structure of U(VI) species associated with colloids forming by the gradual flooding of abandoned uranium mines, we mixed acid mine water rich in Fe(II/III) and U(VI) with near-neutral groundwater at oxic conditions. Iron K-edge and U LIII-edge Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy, and Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy were applied to elucidate the structure of the surface complexes at the molecular level. Since the resulting colloidal bulk consisted mainly of 2-line ferrihydrite, we tested by simplified batch experiments the influence of other matrix ions such as sulfate, silicate, and carbonate on the U(VI) sorption structure at the ferrihydrite surface.
In all samples, U(VI) was bound to ferrihydrite by formation of a mononuclear, edge sharing inner-sphere complex. Monte Carlo simulation yielded a slightly tilted orientation of the UO22+ pentagonal bipyramid relative to the edge sharing Fe(O,OH)6 octahedron. This tilted orientation allows to attribute a previously unexplained EXAFS peak at a distance of ~2.87 Å to a third O-atom of the Fe octahedra at the ferrihydrite surface. The experimental results allow us to reject formation of ternary U(VI) sulfate, silicate, and carbonate surface complexes as source of this peak. Furthermore, both spectroscopic approaches do not give convincing evidence for the formation of ternary U(VI) carbonato surface complexes at pH 5.5 and pH 8.0 and U(VI) concentrations of ≤ 0.012 mM. At U(VI) concentrations of ≥ 0.05 mM, however, ATR-FTIR spectra show an increased splitting of the symmetric and antisymmetric carbonate stretching modes due to a frequency shift which can be assigned to a bidentate linkage of carbonate to the adsorbed UO22+, hence suggesting formation of a ternary surface complex at these experimental conditions. At the higher U(VI) concentrations, the formation of ternary complex species and changes of the coordination may cause a decrease in U(VI) binding strength with increasing carbonate concentration. These effects should be considered in hydrogeochemical scenarios of elevated pCO2 conditions prevalent in many groundwater aquifers.

Publ.-Id: 7757 - Permalink


Sektionsberichte Jahrestagung Kerntechnik 2005 - Sektion 2: Thermo- und Fluiddynamik
Schaffrath, A.; Rohde, U.; Prasser, H.-M.; Scheuerer, M.;
Der Beitrag dokumentiert die Vorträge und Poster der Sektion Thermo- und Fluiddynamik der Jahrestagung Kerntechnik 2005. 17 Vorträge und 1 Poster der Sektion gliederten sich in 3 Themenblöcke: Analytische Thermohydraulik für bestehende Reaktoren, analytische Methoden für künftige Reaktoren sowie Experimente und Betriebsverhalten.
Keywords: nuclear technology, thermodynamics, fluid mechanics, analytical methods, experiments, operational behaviour
  • atw - International Journal for Nuclear Power (2005)10, 594-606

Publ.-Id: 7756 - Permalink


Speciation of colloid-born uranium by EXAFS and ATR-FTIR spectroscopy
Ulrich, K.-U.; Rossberg, A.; Scheinost, A.; Foerstendorf, H.; Zaenker, H.; Jenk, U.;
wird nachgereicht
  • 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, 137-148
  • Lecture (Conference)
    Uranium Mining and Hydrogeology UMH IV, 11.-16.09.2005, Freiberg, Germany

Publ.-Id: 7755 - Permalink


Nuclear-structure and nuclear-astrophysics experimentsat the superconducting electron accelerator ELBE
Schwengner, R.; Rusev, G.; Dönau, F.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Nankov, N.; Schilling, K. D.; Wagner, A.;
The superconducting electron accelerator ELBE at Rossendorf delivers electron beams of energies up to 20 MeV with average currents up to 1 mA for experiments using photon-induced reactions. The bremsstrahlung facility installed at this accelerator and the experimental area were designed such that the production of neutrons and the scattering of photons from surrounding materials is strongly reduced.
We have investigated the nuclides {92}Mo, {98}Mo, {100}Mo and {88}Sr in photon-scattering experiments at electron energies from 6 to 13 MeV. Several hundred dipole transitions were observed in each of the nuclides. The experimental dipole-strength distributions of the nuclei are compared with calculations on the basis of a quasiparticle-random-phase approximation for deformed nuclei. Statistical approaches to the correction of level feeding and decay branches are presented.
We have studied the {92}Mo(\gamma,n), {92}Mo(\gamma,p) and {92}Mo(\gamma,\alpha) reactions at various electron energies via photoactivation experiments. The deduced activation yields are compared with theoretical predictions.
Keywords: Photon scattering, Photoactivation, dipole-strength distributions, QRPA calculations
  • Contribution to proceedings
    XVI International School on Nuclear Physics, Neutron Physics and Nuclear Energy, 19.-26.09.2005, Varna, Bulgaria

Publ.-Id: 7754 - Permalink


Entwicklung von Radiometallverbindungen für die nuklearmedizinische Diagnostik und Therapie
Stephan, H.; Juran, S.;
kein Abstract.
  • Invited lecture (Conferences)
    Institutskolloquium, 24.10.2005, Heidelberg, Deutschland
  • Invited lecture (Conferences)
    Kolloquium Hochschule Zittau/Görlitz, 20.10.2006, Zittau, Germany

Publ.-Id: 7753 - Permalink


Dendritic encapsulation of radiometals by glcydendrimers having a cyclam-core
Stephan, H.; Röhrich, A.; Steinbach, J.; Geipel, G.; Bernhard, G.;
The dendritic encapsulation of radionuclides opens a promising way for the development of novel imaging and therapeutic agents. On the one side, there is the opportunity to enhance the stability of the encapsulated radionuclide by increasing generation of the dendrimer. Most importantly, the biodistribution can be influenced by grafting a multitude of suitable biomolecules on the periphery of the dendritic skeleton. Recently, we could show that the grafting of polyethylene glycol arms on the cyclam core leads to both a higher complex stability and an increasing shielding effect for copper(II).
In this contribution the synthesis of two novel glycodendrimers 1 and 2 having a cyclam-core (cf. Fig. 1) will be presented. The complex formation of these glycodendrimers with copper(II) has been studied by UV-VIS and time-resolved laser-induced fluorescence (TRLFS) measurements showing the formation of stable 1:1 complexes.
The metal complexes of these water-soluble glycodendrimers appear very attractive in view of binding of the diagnostically and therapeutically relevant radionuclides 64/67Cu, 99mTc and 186/188Re.
  • Poster
    BioNanoMaT "Bioinspired Nanomaterials for Medicine and Technologies", 23.-24.11.2005, Marl, Deutschland
  • Contribution to proceedings
    BioNanoMaT "Bioinspired Nanomaterials for Medicine and technologies", 23.-24.11.2005, Marl, Deutschland
    Book of Abstracts, 57

Publ.-Id: 7752 - Permalink


Darstellung und Charakterisierung von Nanopartikeln auf der Basis von [Ti2W10PO40]7- und Chitosan
Stephan, H.; Meißner, T.; Bergmann, R.; Rode, K.; Kraus, W.; Emmerling, F.;
Polynuclear metal compounds may have considerable potential as metallic drugs. Certain polyoxomatelates have been recognized to efficiently penetrate into tumour cells and to act as anti-tumour agents. Among a great variability of different metal-oxygen clusters formed, the Keggin type [XW12O40]x-, seems to be one of the most important compounds for medical applications. The structural characterization of two Keggin cluster anions will be reported (cf. Fig. 1). The lacunary sites of these polyanions are surrounded and stabilized by potassium cations and/or water molecules that form a hydrogen bond network with terminal and point-bridged oxygens of the cluster anion leading to a highly symmetric structure in the solid state.
The hydrolytic stability of the cluster anion [TiW11CoO40]8- is rather poor under physiologically relevant conditions. The degradation of the cluster structure has been observed at a pH of 7.4. In contrast to this, [Ti2W10PO40]7- is very stable under these conditions. This cluster anion rapidly forms associates with the biopolymer chitosan in the nanometer size range. These particles show a high hydrolytic stability. Interestingly, the cell uptake of [Ti2W10PO40]7- in tumor cell lines FaDu (human squamous carcinoma) and HT-29 (human adenocarcinoma) is remarkably enhanced in the presence of chitosan. Deposited in targeted cells, such heavy metal clusters have promising properties to be used in Photon Activation Therapy (PAT).
  • Poster
    BioNanoMaT "Bioinspired Nanomaterials for Medicine and Technologies", 23.-24.11.2005, Marl, Deutschland
  • Contribution to proceedings
    BioNanoMaT "Bioinspired Nanomaterials for Medicine and Technologies, 23.-24.11.2005, Marl, Deutschland
    Book of Abstracts, 67

Publ.-Id: 7751 - Permalink


Fluid flow analysis under the influence of a travelling magnetic field - simulation and experiment
Galindo, V.; Grants, I.; Lantzsch, R.; Gerbeth, G.; Pätzold, O.;
A traveling magnetic field (TMF) system for the application to the VGF growth of GaAs is under development. We report on model studies related to the fluid flow caused by the TMF.
  • Lecture (Conference)
    DGKK-Arbeitskreis Angewandte Simulation in der Kristallzüchtung - 4. Workshop, 03.-04.11.2005, Heigenbrücken, Germany

Publ.-Id: 7750 - Permalink


Experimental investigation of the influence of Lorentz forces on local mass transfer and near wall turbulence by means of electrodiffusion probes
Adolphe, X.; Martemianov, S.; Piteau, A.; Weier, T.; Gerbeth, G.;
Electrodiffusion probes have been applied in order to study the influence of a magnetic field on the near wall mass transfer and the near wall hydrodynamics.
  • Lecture (Conference)
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
    2(2005), 151-154

Publ.-Id: 7749 - Permalink


Riga dynamo experiments
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
A review of the Riga dynamo experiment is given focusing mainly on the measured turbulent properties of the flow-induced magnetic field.
  • Invited lecture (Conferences)
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
  • Contribution to proceedings
    Joint 15th Riga and 6th PAMIR International Conference on MHD, 27.06.-01.07.2005, Riga, Latvia
    1(2005), 15-24

Publ.-Id: 7748 - Permalink


Applications of AC and DC magnetic fields in metallurgical and crystal growth processes
Cramer, A.; Eckert, S.; Galindo, V.; Priede, J.; Gerbeth, G.;
A summary on magnetic field applications in the fields of melt extraction, aluminum casting, electromagnetic levitation and float-zone crystal growth is given.
  • Contribution to external collection
    H. Wada, H.J. Schneider-Muntau (Hrsg.): Materials Processing in Magnetic Fields, Singapore: World Scientific Publishing, 2005, 157-168

Publ.-Id: 7747 - Permalink


How to actualize reversals in dynamo experiments?
Xu, M.; Gerbeth, G.; Günther, U.; Stefani, F.;
The theoretical connection between field reversals and the occurrence of exceptional points in the dynamo operator spectrum is examined.
  • Poster
    IGA 2005 Scientific Assembly, 18.-29.07.2005, Toulouse, France

Publ.-Id: 7746 - Permalink


Magnetic field details of the Riga dynamo experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Gundrum, T.; Stefani, F.;
The back-reaction mechanism of the Riga dynamo is examined. It shows in particular a leading action of the induced magnetic field on the azimuthal velocity component, which finally results in a very smart increase of the motor power in case of the finally saturated magnetic field.
  • Invited lecture (Conferences)
    IAGA 2005 Scientific Assembly, 18.-29.07.2005, Toulouse, France

Publ.-Id: 7745 - Permalink


Uranium speciation in two Freital mine tailing samples: EXAFS, micro-XRD, and micro-XRF results
Scheinost, A.; Hennig, C.; Somogyi, A.; Martinez-Criado, G.; Knappik, R.;
We investigated the uranium speciation in a former WISMUT mine tailing, which was buried for 30 years under mine and construction debris.
Chemical extractions, EXAFS, -XRD, and -XRF reveal two major U pools. The first with a relatively high potential mobility was identified as U(VI) sorbed to layer silicates by inner-sphere complexation; the second pool is represented by the relatively insoluble U(IV) minerals pitchblende and coffinite, and by the U(VI) solids uranyl hydroxide and vanuralite.
Distribution between the two pools seems to be con-trolled by pH. Evidence for reductive precipitation of uraninite was found.
  • 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, 117-126

Publ.-Id: 7744 - Permalink


Uncertainty and sensitivity analyses of the Kozloduy pump trip test using coupled thermal-hydraulic 3D kinetics code
Bousbia Salah, A.; Kliem, S.; Rohde, U.; D’Auria, F.; Petruzzi, A.;
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate three-dimensional coupled code computational tools. This technique is, nowadays, extensively used since it allows decreasing conservatism in the calculation models and performs more realistic simulation and more precise consideration of multidimensional effects under complex transients in NPPs. Therefore, large international activities are in progress aiming to assess the capabilities of coupled codes and the new frontiers for the nuclear technology that could be opened by this technique. In the current paper a contribution to the assessment and validation of coupled code technique through the Kozloduy VVER100 pump trip test is performed. For this purpose, the coupled RELAP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data. Deviations between code predictions and measurements are mainly due to the used models for evaluating and modeling of the Doppler feedback effect. Further investigations through the use of two “antagonist” uncertainty GRS and the CIAU methods, were considered in order to evaluate and quantify the origin of the observed discrepancies. It was revealed on one hand that relative error quantification discrepancies exist between the two approaches, and further enhancements for both methods are needed

Publ.-Id: 7743 - Permalink


Wire-mesh sensors for high-resolving two-phase flow studies at high pressures and temperatures
Pietruske, H.; Prasser, H.-M.;
Wire-mesh sensors are used for a high-speed visualization of a gas-liquid flow as well as for the measurement of void fraction profiles, bubble size distributions and gas velocity distributions. Recent progress was made in designing and constructing such sensors for an application in a hot steam-water mixture. Two types are presented: (1) a sensor with an inner diameter of 52.3 mm with a measuring matrix of 16x16 and (2) a sensor of 195 mm inner diameter with 64x64 measuring points. Both devices can be operated at 7 MPa and a temperature of max. 286 °C. The spatial and temporal resolutions are equal to earlier used sensors for air-water flow at ambient conditions (3 mm, 2500 fps). In the paper, the function of the sensors is illustrated by presenting flow visualizations obtained at two vertical test sections of the Rossendorf TOPFLOW facility. The pipes are approximately 9 m long and have inner diameters equal to the diameters of the measuring cross sections mentioned above. The results show how the flow structure depends on the thermodynamic parameters by comparing measurements performed at 1, 2, 4 and 6.5 MPa and 180, 212, 250 and 280 °C, correspondingly, under adiabatic conditions with earlier air-water tests.
Keywords: two-phase flow, flow pattern, vertical upwards flow, wire-mesh sensors
  • Flow Measurement and Instrumentation 18(2007)2, 87-94
  • Lecture (Conference)
    The 11th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics (NURETH-11), 02.-06.10.2005, 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 533

Publ.-Id: 7742 - Permalink


Determination of In concentration in InGaAs/GaAs 001 epilayers in the early stage of anisotropic stress relaxation
Sass, J.; Mazur, K.; Eichhorn, F.; Strupinski, W.; Turos, A.; Schell, N.; (Editors)
A method has been developed for determination of In concentration in strained layers of InGaAs/GaAs heterostructures. Chemical composition and lattice strain were evaluated from the reciprocal space maps obtained for asymmetric reflections. It was observed that beginning of
relaxation of the In0.13Ga0.87As/GaAs (0 0 1) system with lattice misfit Delta-a/a = 9.3×10−3 and the critical thickness tc(MB) = 15 nm can be detected for layers of thickness exceeding t∼
70 nm ∼ 4.5tc(MB). The principal relaxation mechanism is due to the slipping of 60° misfit dislocations on the tilted (1 1 1) glide planes. The accuracy of indium concentration measurements was estimated to Delta-x =±0.01.
Keywords: X-ray diffraction; Lattice strain; InxGa1−x As/GaAs (0 0 1) heterostructures

Publ.-Id: 7741 - Permalink


Toxic avengers
Raff, J.; Selenska-Pobell, S.;
Live adapts to survive in the most forbidding conditions - even in former uranium mining and production sites. If man could understand how microbes handle radionuclides, he might one day harness a natural force for remediation.
  • Nuclear Engineering International 51(2006)619, 34-36

Publ.-Id: 7740 - Permalink


Radiopharmakaforschung: Trends und neue Konzepte
Wüst, F.;
Die Leistungsfähigkeit der Nuklearmedizin in der Diagnostik, Therapie und medizinischen Forschung hängt entscheidend vom Fortschritt bei der Entwicklung neuer geeigneter Radiopharmaka ab. Die Auswahl, die Herstellung und die präklinische Evaluation dieser neuen Radiopharmaka ist Gegenstand der radiopharmazeutischen Chemie. Vor dem Hintergrund der rasanten Entwicklungen auf den Gebieten der Biowissenschaften im Post-Genom Zeitalter und der technologischen Fortschritte bei der Instrumentierung der bildgebenden nuklearmedizinischen Verfahren SPECT und PET hat sich die Radiopharmakaforschung in den letzten Jahren zu einer komplexen chemischen Wissenschaft entwickelt. Die Schwerpunkte der aktuellen Radiopharmakaforschung umfassen dabei besonders neue koordinationschemische Entwicklungen auf dem Gebiet der [99mTc]Technetium Radiopharmaka, die Herstellung von sogenannten Nicht-Standard Radionukliden für die PET sowie die Synthese von 11C- und 18F-markierten Radiopharmaka mit hoher spezifischer Radioaktivität.
Weitere wichtige Entwicklungen zeichnen sich durch die zunehmende Ausrichtung der Radiopharmakaforschung auf die Entwicklung von Radiotherapeutika und die Einbeziehung der PET in die Arzneimittelentwicklung und -evaluation ab.
Keywords: [99mTc]Technetium; Nicht-Standard-PET-Radionuklide; spezifische Radioaktivität; Radiotherapeutika; Arzneimittelforschung

Publ.-Id: 7739 - Permalink


In vivo metabolism of oxidized low density lipoproteins: Insights from small animal positron emission tomography (PET) studies
Pietzsch, J.; Bergmann, R.; Wüst, F.; van den Hoff, J.;
The human organism is exposed to numerous processes that generate reactive oxygen or nitrogen species may directly or indirectly cause oxidative modification and damage of proteins. Protein oxidation is regarded as a crucial event in the pathogenesis of various diseases ranging from rheumatoid arthritis to Alzheimer's disease and atherosclerosis. The importance of protein oxidation in respect of altered function is exemplified by oxidation of low density lipoproteins (LDL) which causes altered receptor recognition and, e.g., plays a key role in atherogenesis. However, data concerning the role of circulation oxidized LDL (oxLDL) in the development and outcome of disease are scarce. One reason for this is the shortage of methods for direct assessment of the metabolic fate of circulation oxLDL in vivo. As an attractive alternative to, e.g., LDL iodination methods, a novel methodology based on the radiolabeling of apoB-100 of native LDL (nLDL) and oxLDL, respectively, with the positron emitter fluorine-18 (18F]SFB) was developed. In cotrast to most protein radioiodination methods, radiolabeling of both nLDL and oxLDL using [18F]SFB caused neither additional oxidative structural modifications of LDLlipids and proteins nor alteration of their biological activity and functionality, respectively, in virto. The method was further evaluated with respect to the radiopharmacological properties to both [18F]fluorobenzoylated nLDL and oxLDL by biodistribution and dynamic positron emission tomography (PET) studies in male Wistar rats. These studies demonstrated the methodology to be of value to characterize and to discriminate the kinetics and the metabolic fate of nLDL and oxLDL in small animals in vivo.
  • Recent Research Developments in Molecular & Cellular Biochemistry 2(2005), 153-177

Publ.-Id: 7738 - Permalink


Synthesis of a 11C-labelled taxane derivative by [1-11C]acetylation
Mäding, P.; Zessin, J.; Pleiß, U.; Füchtner, F.; Wüst, F.;
The 11C-labelling of the taxane derivative BAY 59-8862 (1), a potent anticancer drug, was carried out as a module-assisted automated multi-step synthesis procedure. The radiotracer [11C]1 was synthesized by reacting [1-11C]acetyl chloride (6) with the lithum salt of the secondary hydroxy group of precursor 3 followed by deprotection. After HPLC purification of the final product [11C]1, its solid phase extraction, formulation and sterile filtration, the decay-corrected radiochemical yield of [11C]1 was in the range between 12 and 23% (related to [11C]CO2; n = 10). The total synthesis time was about 54 min after EOB. The radiochemical purity of [11C]1 was greater than 96% and the chemical purity exceeded 80%. The specific radioactivity was up to 20 GBq/µmol at EOS starting from 80 GBq of [11C]CO2.
Keywords: taxane, anticancer drug, [1-11C]acetyl chloride, [11C]BAY 59-8862, positron emission tomography
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 357-365
    DOI: 10.1002/jlcr.1059

Publ.-Id: 7737 - Permalink


Influence of sputtering conditions and electron energy on XPSdepth profiling of Ge in SiO2
Oswald, S.; Schmidt, B.; Heinig, K.-H.;
Ge nanocluster formation in SiO2 is of growing interest for new electronic applications. Ion beam synthesis using high-energy Ge implantation connected with thermal annealing is one possible preparation method of such clusters. In addition to investigations of electrical and structural changes during the cluster formation process we also studied chemical changes in the samples using x-ray photoelectron spectroscopy (XPS). This was done with low-energy noble gas ion sputtering for depth profiling. Binding state information one can get from the XPS data by means of factor analysis (FA) in combination with other structural investigations.
However, mixed bonding states probably created by ion beam damage during sputter erosion are dominating the results. It is shown, that by changing the experimental conditions (ion beam impact depth during sputtering, electron information depth during XPS measurement) these mixed states are influenced in an appropriate manner. It is concluded that useful chemical information on the behavior of the implanted Ge can be derived despite of the ion beam damage.
Keywords: XPS, depth profile, data analysis, ion beam effects.
  • Crystal Research and Technology 40(2005)12, 1134-1138

Publ.-Id: 7736 - Permalink


Untersuchung des Einflusses von Gallussäure auf das Redoxverhalten von Uran (VI)
Steudtner, R.;
Im Mittelpunkt der Uranforschung stehen die Wechselwirkungen des Urans mit natürlichen Organika, wie Huminstoffen und Holzabbauprodukte. Diese entstehen durch den natürlichen Zersetzungsprozess und sind teilweise hochmolekulare organische Substanzen mit mehreren funktionellen Gruppen.
Es ist bekannt, dass diese Stoffe einen Einfluss auf den Oxidationszustand des Urans haben. Ein bedeutender Unterschied zwischen den verschiedenen Oxidationsstufen liegt in der Löslichkeit des vierwertigen und sechswertigen Urans begründet. Die sehr geringe Löslichkeit des vierwertigen Urans gegenüber dem sechswertigen Uran führt zu einer Immobilisierung des Urans. Bei der Reduktion durch natürliche Organika könnte es so zu einer lokalen Anreicherung an Uran im Boden führen.

Das Ziel der vorliegenden Arbeit ist es, den Einfluss der Gallussäure (3, 4, 5-Trihydroxybenzoesäure) auf das Redoxverhalten von Uran(VI) zu untersuchen und eine mögliche Reduktion des Uran(VI) zu Uran(IV) spektroskopisch nachzuweisen.

Die Gallussäure wurde dabei als vereinfachte Modellvorstellung für Huminstoffe betrachtet, weil sie eine organische Substanz mit mehreren funktionellen Gruppen ist und reduzierende Eigenschaften gegenüber Metallionen aufweist].
  • Other report
    Hochschule Zittau / Görlitz: Diplomarbeit (Studiengang Chemie), 2005
    65 Seiten

Publ.-Id: 7735 - Permalink


Investigation of insulated buried layers obtained by ion implantation in AlGaAs with various Al concentration
Wierzchowski, W.; Wieteska, K.; Graeff, W.; Gawlik, G.; Turos, A.; Mücklich, A.;
The important element of modern AlxGa1-xAs semiconductor lasers is an insulating buried layer introduced by selective implantation with He or H ions. The difficulty in obtaining of such layers is connected with controlling of strain and defects introduced by implantation, which may disturb the action of the laser. The strain may be however controlled in less complicated laterally homogeneous structures or even single implanted layer.
The insulated buried layers obtained by implantation of 150 keV He ions to AlxGa1-xAs with various concentration of Al and GaAs were studies with different synchrotron diffraction methods exploring both white and monochromatic beam.The selected samples were studied with high resolution transmission electron microscopy. The implantation were performed at room temperature, 80°C and 120°C. The doses were in the range from 2x1016 to 6x1016 cm-2. The synchrotron experiment included taking local rocking curves using small 50x50 µm2 probe beam. The rocking curves exhibit characteristic sequence of interference maxima and enabled the analysis of the strain profiles by fitting the theoretical rocking curves obtained by numerical integration of the Takagi-Taupin equations. The white beam synchrotron back reflection topography revealed a sequence of strain modulation fringes similar to the main interference maxima in the rocking curves. They also confirm the uniformity of applied dose and lack of extended crystallographic defects which could be caused by implantation. The characteristic feature of the evaluated profiles was the existence of the deformed region close to the surface which points that the deformation is mainly caused by point defects produced by incident ions and recoils. The other feature increasing with the temperature of implantation was the flattening of top part of the strain maximum corresponding to the insulating buried layer.
  • Poster
    E-MRS 2005 Fall Meeting, 05.-09.09.2005, Warsaw, Poland

Publ.-Id: 7734 - Permalink


Strain Profiles in the Insulated Buried Layers Obtained by He Implantation in AlGaAs
Wierzchowski, W.; Wieteska, K.; Graeff, W.; Gawlik, G.; Turos, A.; Maurin, J.; Mücklich, A.;
The insulated buried layers formed by 150 keV ions to AlxGa1-xAs with various concentration of Al were studied with synchrotron diffraction methods. Some samples were studied with HRTEM. The implantations were performed at RT, 80 and 120°C. The doses varied from 2x1016 to 6x1016 cm-2. The measurements included taking local rocking curves using small 50x50 µm2 probe beam. The rocking curves exhibited characteristic interference maxima and enabled the analysis of the strain profiles by fitting the theoretical rocking curves obtained by numerical integration of the Takagi-Taupin equations. The white beam synchrotron back reflection topography revealed a sequence of strain modulation fringes similar to the main interference maxima in the rocking curves. The evaluated profiles exhibited the deformed region close to the surface indicating that the deformation is mainly caused by the point defects produced by incident ions and the recoils. The other feature increasing with the temperature of implantation was the flattening of top part of the strain maximum corresponding to the insulating buried layer. This flattening was more distinct for lower concentration of Al. The HRTEM patterns revealed characteristic small gaseous inclusions appeared in the most deformed region in the samples implanted with the highest applied doses.
Keywords: strain, ion implantation, diffraction
  • Contribution to proceedings
    XX Congress of the International Union of Crystallography, 23.-31.08.2005, Florence, Italy
    Acta Crystallographica (2005), A61, C449

Publ.-Id: 7733 - Permalink


Methodenentwicklung zur Analyse von Störfallszenarien mit Frischdampfleck und Borverdünnung mit Hilfe des Codesystems ATHLET-DYN3D - Abschlussbericht Teil 2
Kliem, S.; Grundmann, U.; Rohde, U.;
Es wurde ein Modell zur realistischen Beschreibung der Kühlmittelvermischung innerhalb des Reaktordruckbehälters von Druckwasserreaktoren in den gekoppelten Programmkomplex DYN3D/ATHLET implementiert. Diese Modell basiert auf dem Prinzip der linearen Superposition Dirac-Impuls-ähnlicher Störungen und kann für die Modellierung der Vermischung von Kühlmittel unterschiedlicher Temperatur und/oder unterschiedlicher Borsäurekonzentration eingesetzt werden. Der um das Vermischungsmodell erweiterte Programmkomplex DYN3D/ATHLET wurde für Analyse von Borverdünnungsstörfällen und Frischdampflecks angewandt. Für den Fall „Start der ersten Hauptkühlmittelpumpe bei Vorhandensein eines minderborierten Pfropfens im kalten Strang“ zeigten die Ergebnisse der durchgeführten Parame-terstudie, dass es selbst bei Annahme des maximal möglichen Pfropfenvolumens nicht zu einer Schädigung des Brennstoffes kommt. Mit den Analysen zu einem generischen Frischdampfleckszenario wurde die Anwendbarkeit des Programmkomplexes DYN3D/ATHLET auf die zweite Störfallklasse, in der die Kühlmittelvermischung eine wichtige Rollen spielt, demonstriert.
Im Rahmen der Arbeiten zum Projekt wurde außerdem gezeigt, dass der Einfluss der turbulenten Schwankungen des Geschwindigkeitsfeldes innerhalb des Reaktordruckbehälters auf neutronenkinetische Parameter im Nominalbetrieb und unter Störfallbedingungen nicht zu vernachlässigen ist.

A model for the realistic description of the coolant mixing inside the pressure vessel of pressurized water reactors was implemented into the coupled code complex DYN3D/ATHLET. This model is based on the linear superposition Dirac-pulse-like perturbations. The model can be applied to the mixing of coolant of different temperature and/or boron concentration. The coupled code complex DYN3D/ATHLET with the newly implemented model was applied to the analysis of boron dilution and steam line break accidents. The results of a parameter study for the case “Start-up of the first main coolant pump with a slug of lower borated water in the cold leg” have shown, that even under the conditions of the maximum slug volume there is no fuel damage. The applicability to the second class of accidents, where the coolant mixing has to be considered, was demonstrated by the analysis of a generic main steam line break scenario.
Further it was shown, that the influence of turbulent fluctuations of the velocity inside the reactor pressure vessel during nominal and accident conditions on neutron-kinetic parameters cannot be neglected.
Keywords: pressurized water reactor, accident analysis, coupled neutronics-thermohydraulic codes, boron dilution, main steam line break, coolant mixing
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-438 2005

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Publ.-Id: 7732 - Permalink


Direct evidence of self-aligned Si nanocrystals formed by ion irradiation of Si/SiO2 interfaces
Röntzsch, L.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.; Thomas, J.; Gemming, T.;
Energy-filtered transmission electron microscopy proves di-rectly, that ion irradiation and post-irradiation annealing of a Si/SiO2 interface results in the formation of a narrow layer of monodisperse Si nanocrystals in the oxide at a tunnel distance from the interface. Position and size of the Si nanocrystals are in agreement with predictive atomistic computer simulations.
Keywords: Ion Irradiation, Phase Separation Si-SiO2 Interface, Si Nanocluster, Non-volatile Memory

Publ.-Id: 7731 - Permalink


Verhalten des Reaktordruckbehälters bei einem unterstellten Kernschmelzunfall
Willschuetz, H.-G.; Altstadt, E.;
Für das unwahrscheinliche Szenario eines Kernschmelzunfalls in einem Leichtwasserreaktor mit Bildung eines Schmelzesees in der Bodenkalotte des Reaktordruckbehälters (RDB) ist es notwendig, mögliche Versagensformen des RDB sowie Versagenszeiträume zu ermitteln, um die daraus resultierende mögliche Belastung des Sicherheitsbehälters bestimmen zu können. Es wurde ein integrales Modell entwickelt, das die Vorgänge im unteren Plenum beschreibt. Dabei sind zwei prinzipielle Modellbereiche zu unterscheiden: Das Temperaturfeld in der Schmelze und im RDB wird mit einem thermodynamischen Modell berechnet, während für die Strukturanalyse des RDB ein mechanisches Modell verwendet wird.
Zunächst wird das betrachtete Unfallszenario dargestellt.
Das thermodynamische und das mechanische Modell können rekursiv gekoppelt werden, wodurch die wechselseitige Beeinflussung berücksichtigt werden kann. Insbesondere werden damit neben der Temperaturabhängigkeit der Materialparameter und den thermisch induzierten Spannungen im mechanischen Modell auch die Rückwirkungen der Behälterverformung auf das Temperaturfeld selber erfasst.
Als Ergebnis der Arbeiten lässt sich festhalten, dass das gekoppelte Modell prinzipiell in der Lage ist, die Behälterdeformation im Falle der skalierten FOREVER-Experimente exakt zu beschreiben bzw. vorherzusagen. Unsicherheiten bezüglich der Versagenszeit resultieren aus nicht exakt bekannten Materialparametern und Randbedingungen.
Die wesentlichen Ergebnisse lassen sich wie folgt zusammenfassen: Aufgrund des thermodynamischen Verhaltens eines großen Schmelzesees mit inneren Wärmequellen erfolgt die höchste thermomechanische Belastung des RDB im oberen Drittel der Bodenkalotte. Dieser Bereich wird als heißer Fokus bezeichnet. Der untere Bereich der Kalotte weist hingegen eine höhere Festigkeit auf und verlagert sich deswegen bei entsprechender Belastung des RDB im wesentlichen senkrecht nach unten. Bei einer externen Flutung besteht auch bei hohen Innendrücken für einen Reaktor großer Leistung (KONVOI) die Möglichkeit, die Schmelze im RDB zurückzuhalten. Ohne interne oder externe Flutung besteht für das betrachtete Szenario keine Aussicht für eine Schmelzerückhaltung im RDB.
Abweichend von bisherigen Annahmen kann im Hinblick auf die Entwicklung zukünftiger Baulinien festgehalten werden, dass eine Kernschmelzerückhaltung im Reaktordruckbehälter auch für Reaktoren größerer Leistung möglich ist.
Keywords: core melt down, in vessel retention, coupled thermal and mechanical FE-model
  • Invited lecture (Conferences)
    Seminar Energieverfahrenstechnik WS 2005/2006, 20.10.2005-26.01.2006, Dresden, Deutschland

Publ.-Id: 7730 - Permalink


Simulation of the FOREVER experiments: enhancement and approach to a prototypic scenario
Willschuetz, H.-G.;
For the simulation of experiments investigating the behavior of the lower head of a nuclear power station in case of a core meltdown scenario like FOREVER it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes. Therefore a 2D Finite Element Model with 3 different submodels is developed based on the code ANSYS® Multiphysics.
A thermal submodel was build up including planar and contact elements for conductive heat transfer, additional surface elements to simulate convection and radiation from outer surface areas and a radiation matrix 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 no turbulence model is capable for a correct simulation. Therefore an Effective Conductivity Convectivity Model (ECCM) was developed to simulate the heat transfer from the melt pool to its environment.
The resulting temperature field of the vessel wall is applied to the mechanical submodel. To describe the visco-plastic deformation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided.
The third submodel is a kind of fictitious physics environment: it uses hyperelasticity and contact to move the melt pool along with the creeping vessel wall.
In this presentation problems on the numerical side are explained and differences between the results of a simple coupled and a kinematically coupled FE-simulation are highlighted. The final comparison with the experiments shows that the kinematically coupled model is closer to reality than the single step model.
Keywords: core melt down accident, thermal and mechanical simulation, recursive coupling
  • Invited lecture (Conferences)
    Seminar at the chair of Nuclear Power Safety, 12.10.2005, Stockholm, Sveden

Publ.-Id: 7729 - Permalink


Electron-optical-phonon interaction in the In0.73Ga0.27As–AlAs intersubband laser
Drachenko, O.; Galibert, J.; Léotin, J.; Tomm, J. W.; Semtsiv, M. P.; Ziegler, M.; Dressler, S.; Müller, U.; Masselink, W. T.;
The magnetic-field dependence of the operation of a quantum-cascade intersubband laser (QCL) is used to investigate the energetic relaxation of injected electrons through phonon emission. The QCL emits at 3.8mkm and incorporates a strain-compensated active region with a large degree of internal strain. Energies of the relevant electron-phonon scattering responsible for the depopulation of the upper laser level are determined from the analysis of the Landau-level spectra. A comparison of those energies with the Raman spectrum of the active region is used to identify which phonon is primarily involved in the electron-phonon scattering. In spite of the low Ga-content in the (In,Ga)As quantum wells and high Al-content in the AlAs/ (In,Al)As composite barriers, the depopulation of the upper laser level appears to be dominated by the resonant electron-GaAs-likelongitudinal-phonon intersubband scattering. In particular, the contribution due to AlAs-like modes is negligible
Keywords: Quantum Cascade Lasers, Intersubband Magnetophonon Resonance, Phonon spectroscopy
  • Applied Physics Letters (2005)87, 072104-1-072104-3

Publ.-Id: 7728 - Permalink


Reactive plasma immersion ion implantation for surface passivation
Yankov, R. A.; Shevchenko, N.; Rogozin, A.; Maitz, M. F.; Richter, E.; Möller, W.; Donchev, A.; Schütze, M.;
Plasma immersion ion implantation (PIII) using halogen or oxygen plasmas has been employed for the surface passivation of advanced alloys with a view to their applications for high-temperature oxidation protection and in medicine. Special devices have been designed to ensure efficient plasma generation and reduce sample contamination arising from the interaction of the aggressive plasmas with the chamber components under bias. The paper addresses two main applications of PIII, namely oxidation protection of gamma-titanium aluminides (γ-TiAl), and modification of the surface properties of shape-memory superelastic nickel titanium (NiTi) alloys. TiAl intermetallics are of great interest for advanced automobile, aerospace and power generation applications due to their low specific weight and high strength. However, excessive oxidation occurring in these materials at temperatures above 700°C has hindered their widespread use. Samples of technical γ-TiAl alloys have been treated by both beamline implantation of Cl or F, and PIII of Cl using an Ar/Cl gaseous blend or alternative precursor gases. High-temperature oxidation behavior has been examined under conditions of either isothermal or thermocyclic oxidation at 900°C. Optimized implantation processing produces marked improvement in the oxidation behavior of the γ-TiAl samples. On the basis of these results, a commercially viable process for enhancing the high-temperature oxidation resistance of γ-TiAl alloys using PIII of halogens is being developed. NiTi alloys are promising materials for use in biomedicine, provided that the release of Ni ions into the body environment can be sufficiently reduced. Oxygen PIII at substrate temperatures below 250°C results in the formation of a transparent rutile TiO2 surface layer with a Ni content down to below 1 at%. This layer in turn serves as a barrier to the corrosion and out-diffusion of Ni ions. Biocompatibility tests show superior in vitro blood compatibility in comparison with untreated NiTi samples.
Keywords: TiAl alloys, shape-memory NiTi alloys, oxidation protection, biocompatibility, ion implantation, plasma immersion ion implantation
  • Surface & Coatings Technology 201(2007), 6752-6758

Publ.-Id: 7725 - Permalink


Small-angle neutron scattering study of post-irradiation annealed neutron irradiated pressure vessel steels
Ulbricht, A.; Bergner, F.; Dewhurst, C. D.; Heinemann, A.;
Neutron irradiated reactor pressure vessel steel of two different Cu contents exposed to isochronal post-irradiation annealing treatments at stepwise increasing levels of temperature have been investigated. Results of small-angle neutron scattering experiments are reported and compared with the respective unirradiated and as-irradiated conditions. Volume distributions of scatterers and ratios of total to nuclear scattering intensities (A-ratio) were calculated from the measured differential macroscopic scattering cross sections. Finally, total volume fractions of scatterers, peak radii of the volume distribution and partial information on the composition of scatterers were extracted and discussed as a function of annealing temperature. Our measurements indicate that there is a temperature regime characterized by essentially complete dissolution of the irradiation-induced Cu-enriched clusters and another temperature regime characterized by a competition of dissolution and coarsening. An Arrhenius type of behaviour and a remarkable reversibility of the irradiation-induced cluster distribution are observed in the complete dissolution regime.
  • Journal of Nuclear Materials 353(2006), 27-34

Publ.-Id: 7724 - Permalink


Uranium(VI) Adsorption onto Synthetic Humic Substance-Kaolinite Sorbates
Sachs, S.; Bernhard, G.;
The reliable risk assessment of future nuclear waste repositories requires knowledge on the actinide migration behavior in potential host rock formations. Clay formations as possible host rocks are closely associated with natural organic matter, e.g., humic substances, which are known as efficient complexing agents for metal ions. Therefore, the immobilization as well as the release of humic substances by clays can affect the mobilization of actinide ions in the environment.
The impact of humic acid on the U(VI) sorption onto kaolinite was investigated in the ternary model system U(VI) – kaolinite - synthetic humic acid [1]. In the present work, the U(VI) sorption onto a synthetic kaolinite sorbate with humic substances is studied in order to approach natural conditions. For that, we synthesized humic acid M42 [2] in presence of Georgia kaolinite KGa-1b. As synthesis product we obtained a synthetic humic substance - kaolinite sorbate (M42-KS). Due to the fact that this humic substance - kaolinite sorbate was formed during the humic acid synthesis, a different composition of the humic material and different interactions between the humic substances and the kaolinite can be expected compared to the model system investigated in [1]. However, these conditions are probably closer to those found in natural clay systems.
The organic carbon content of two synthetic humic substance - kaolinite sorbates was determined with 5 and 24 mg C/g representing about 9 and 44 mg humic substances/g, respectively. To quantify the influence of the humic material associated with kaolinite we studied the U(VI) sorption onto M42-KS ([U(VI)]: 1· 10-6 M, S/L: 4 g/L, I: 0.01 M NaClO4) in the pH range between pH 3.0 and pH 10.0 by batch experiments. Compared to the humic substance-free system the U(VI) adsorption onto M42-KS is significantly increased between pH 3 and pH 5 which is ascribed to the association of humic substances with kaolinite. Up to pH 8 the U(VI) sorption onto M42-KS is reduced in contrast to the system without humic materials. Under these conditions M42-KS releases humic acid resulting in the formation of soluble U(VI) humate complexes. A further reduction of the U(VI) sorption was observed between pH 8 and 10. This is attributed to the formation of soluble U(VI) humate complexes and/or the formation of U(VI) carbonato complexes that dominate the U(VI) sorption in absence of humic material under these conditions. Differences were found for the U(VI) sorption onto humic substances - kaolinite sorbates with various contents on organic carbon. In addition to that, the U(VI) sorption onto M42-KS differs from that observed in the ternary model system U(VI) – kaolinite - humic acid M42. Probably, these dissimilarities are due to a different composition of the humic materials resulting in different functionalities of the humic substances. These can effect a varying interaction behavior in the system U(VI) - humic substance – kaolinite. Our results indicate that the release of humic materials from natural clays can play an important role for the mobilization of U(VI).

[1] Křepelova, A. et al., In: Forschungszentrum Rossendorf, Wissenschaftlich-Technische Berichte, FZR-419, Rossendorf 2005, p. 50.
[2] Pompe, S. et al., Radiochim. Acta 74, 135 (1996).
Keywords: Humic substances, humic acid, clay, kaolinite, uranium(VI), uranium, sorption
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 46-46
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7722 - Permalink


Investigation of gettering effects in CZ-silicon with SIMS
Krecar, D.; Fuchs, M.; Kögler, R.; Hutter, H.;
Abstract:
The ion implantation is a well-known standard procedure in electronic device technology for precise and controlled introduction of dopants into silicon. Damages caused by implantation act as effective gettering zones, collecting unwanted metal impurities. In this work, the consequences of high-energy ion implantation into silicon and of subsequently annealing were analysed by means of secondary ion mass spectrometry (SIMS). The differences in impurities gettering behaviour were studied in dependence of the implantation dose and annealing time at T = 900 degrees C.
Keywords: Ion implantation, silicon, phosphorus, gettering, Rp-effect, trans-Rp-effect, SIMS

Publ.-Id: 7721 - Permalink


SIMS investigation of gettering centres produced by phosphorus MeV ion implantation.
Krecar, D.; Fuchs, M.; Kögler, R.; Hutter, H.;
Damage caused by ion implantation act as effective gettering region, collecting unwanted metal impurities. In this study the consequences of high-energy ion implantation into silicon and subsequent annealing were analysed by means of secondary ion mass spectrometry (SIMS). The differences in impurity gettering behaviour were studied in dependence of the implantation dose and annealing time at T= 900oC.
Keywords: ion implantation, silicon, metal impurities, secondary ion mass spectrometry, SIMS
  • Contribution to proceedings
    13th Applied Surface Analysis Workshop, AOFA 13(2004), 30.09.2004, Dresden, Deutschland
  • Applied Surface Science 252(2005)1, 278-281

Publ.-Id: 7720 - Permalink


Influence of Humic Acid on U(VI) Sorption Onto Kaolinite Studied by TRLFS and EXAFS
Krepelova, A.; Sachs, S.; Reich, T.; Roßberg, A.; Brendler, V.; Baumann, N.; Bernhard, G.;
Understanding the migration behavior of actinides is important for the reliable long-term risk assessment of potential nuclear waste repositories. Depending on geochemical conditions different materials and processes can influence the behavior of such pollutants in natural aquifer systems. Humic acids (HA) comprise an important part of natural organic materials. HA are soluble in the pH range of natural waters and have the ability for complex and colloid formation. Due to these properties HA can affect the speciation of actinide ions, and therefore, their migration in the environment. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite.
Results from our previous batch experiments were combined with spectroscopic measurements to obtain molecular-level information on the interaction of U(VI) with HA and kaolinite (KGa-1b) in natural systems.
From our batch experiments resulted that the sorption of U(VI) on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 presence and HA concentration. HA affects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system due to the formation of additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA because of desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system. Possibly, ternary U(VI)-humate complexes, e.g. uranyl-carbonato-humate complexes, are formed, which can interact with the kaolinite surface and therefore, enhance the U(VI) sorption onto kaolinite in the presence of HA in this pH region.
We used time-resolved laser-induced fluorescence spectroscopy (TRLFS) in order to characterize the species of U(VI) adsorbed onto kaolinite in the absence and presence of HA. Two adsorbed U(VI) surface species on kaolinite were identified in the pH range of pH 5.0 to pH 8.5. No EXAFS was measured in the system U(VI)-HA-kaolinite, therefore we performed also EXAFS measurements under different experimental conditions with U(VI)-HA-kaolinite sorbates in order to improve the knowledge about the surface complexes of U(VI). Results of the spectroscopic measurements are interpreted and compared with the results in the binary system without HA [1] to study the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes. Obtained results help to improve the understanding of the geochemical interactions of hexavalent actinides in environment.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.
Keywords: EXAFS, TRLFS, Humic Acid, Uranium, Sorption, Kaolinite
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 45-45
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Marianske Lazne, Czech Republic

Publ.-Id: 7719 - Permalink


Migration of Caesium in Bentonite: Influence of the Pore Water Composition
Brockmann, S.; Mibus, J.; Nebelung, C.;
The transferability of empirical distribution coefficients (KD) derived from batch sorption experiments to compacted systems is evaluated in this study. Sorption pa-rameters of Cs+ on bentonite (Wyoming type MX-80) were studied at different dry bulk densities of the clay (1.3, 1.6, 1.9 g/cm3) in both batch tests and diffusion ex-periments. Here, an innovative approach developed at Paul Scherrer Institute (CH) was used for modelling the pore water composition of the compacted clay [1]. The obtained parameters shall be used for long-term prognoses of diffusion processes in the near-field of final repositories of nuclear waste.
The KD values derived from batch and diffusion tests, respectively, differ by ap-proximately 20 to 40 %. This result is acceptable, when taking into consideration the experimental uncertainties of both methods. The use of batch derived KD’s to de-scribe the migration behaviour of Cs+ can be recommended, provided that an ade-quate pore water composition is used.
In contrast, the effective diffusion coefficients (De) of Cs+ in compacted ben-tonite exceed the De’s of tritiated water (HTO) significantly. This effect is attributed to a phenomenon described in the literature as “surface diffusion” indicating an addi-tional diffusive flux of adsorbed species.
Hence, the combination of diffusion coefficients of HTO and batch derived KD’s systematically underestimates the diffusive flux of Cs+. In order to implement this ap-proach in the future, the surface diffusion phenomenon has to be elucidated by ad-vanced spectroscopic methods and to be quantified.
Deviations in the KD are only related to the transient state of the diffusion proc-ess. Thus, they influence the initial state of the transport process. The batch derived KD’s are transferable to the compacted system. However, the use of an adequate diffusion coefficient De is of extreme importance for any prediction of long-term pre-dictions in risk assessment.
Keywords: cesium, bentonite, pore water, sorption, diffusion
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 50-50
  • Poster
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7718 - Permalink


Simulation of condensation in a sub-cooled bubbly steam-water flow along a large vertical pipe
Lucas, D.; Prasser, H.-M.;
Detailed experimental data obtained at the TOPFLOW facility for steam-water vertical pipe flow were used to test the complex interaction of local bubble distributions, bubble size distributions and local heat and mass transfer. Steam is injected into sub-cooled water and condenses during the upwards flow. The model considers a large number of bubble classes (50). This allows the investigation of the influence of the bubble size distribution. The results of the simulations show a good agreement with the experimental data. The condensation process is clearly slower, if large bubbles are injected (4 mm holes). Also bubble break-up has a strong influence on the condensation process because of the change of the interfacial area. Some unsureness arises from the unknown interfacial area for large bubbles and possible uncertainties of the heat transfer coefficient.
Keywords: bubbly flow, phase transfer, bubble size distribution, vertical pipe
  • Open Access LogoArchives of Thermodynamics 26(2005)4, 49-59

Publ.-Id: 7717 - Permalink


Migration of Uranium(VI) in a Phosphate Environment: Column Experiments and Modeling
Mibus, J.; Brendler, V.; Pfingsten, W.;
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 un-derground 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 concentra-tion of 10-5 M and a synthetic HAP packed in a matrix of purified quartz sand.
In common batch sorption experiments, a strong interaction of uranium with the HAP surface was observed. The sorption of uranyl ions onto phosphate groups is eventually as important as their sorption onto silanol groups, outweighing the low phosphate content. From the interpretation of the TRLFS spectra, two surface spe-cies could be distinguished. On the basis of their fluorescence decay time and the shift of the peak maxima related to the free uranyl ion, these two species could be associated with uranium adsorbed to phosphate and silanol surface groups, respec-tively.
The breakthrough curves (BTC’s), measured at different vertical positions of the column, exhibit a strong retardation of uranium compared to the conservative tracer. The breakthrough (i.e., exceeding 50 % of the starting concentration) occurs after about 30 pore volumes. However, the elution part of the BTC’s features a pro-nounced tailing. The release of uranium is controlled by two processes of different rates. We assign the faster sorption/desorption scheme to the uranyl silanol surface species, exhibiting an almost full reversibility. The second observed process creating the long and pronounced tailing in the BTC’s can be explained by the much stronger binding of the uranyl moiety to the phosphate sites.
Keywords: uranium, hydroxy apatite, sorption, transport, modeling
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7, 238-238
  • Poster
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Publ.-Id: 7716 - Permalink


Evidence for In-Medium Changes of Four-Quark Condensates
Thomas, R.; Zschocke, S.; Kämpfer, B.;
Utilizing the QCD sum rule approach to the behavior of the omega meson in nuclear matter we derive evidence for in-medium changes of particular four-quark condensates from the recent CB-TAPS experiment for the reaction gamma + A -> A' + omega (-> pi0 gamma) with A = Nb and LH2.
Keywords: In-Medium Modifications, QCD Sum Rules, Chiral Symmetry, Four-Quark Condensates

Publ.-Id: 7715 - Permalink


Atomistic computer simulation of ion implantation, ion-beam-induced defect formation and defect migration
Posselt, M.;
Ion implantation and subsequent thermal annealing are the standard processes for the electrical doping of semiconductors. Ion implantation is characterized by fast ballistic processes which lead to the deposition of the implanted atoms and to displacements of the target atoms. After the fast relaxation of the displaced atoms a (meta)stable defect structure is formed. Long-term thermally activated processes, especially during thermal annealing, cause defect reduction, rearrangement, and migration. In my talk I will show that computer simulations on the atomic level are a useful tool for the theoretical description of the different physical processes occurring during ion implantation and thermal annealing. The ballistic processes are simulated by the Crystal-TRIM code which is based on the binary collision approximation (BCA). This code is part of different process simulators. Classical molecular dynamics (MD) simulations are employed to investigate defect migration over a period of 10 - 100 ns. The defect diffusivity as well as the microscopic migration mechanisms are studied. A combination of BCA and MD simulations is used to determine the complex defect morphology after the fast relaxation processes are finished. This method allows the effective calculation of the total number and the depth distribution of different defect species (e.g. isolated vacancies and self-interstitials as well as more complex defects) formed on average per incident ion.
Keywords: computer simulation, implantation, defects, Si
  • Lecture (others)
    eingeladener Vortrag am CEA-LETI, 11.10.2005, Grenoble, France

Publ.-Id: 7713 - Permalink


Modelling of in-vessel retention after relocation of corium into the lower plenum
Altstadt, E.; Willschuetz, H.-G.; Sehgal, B. R.; Weiss, F.-P.;
Considering the unlikely core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be investigated for a determination of the loadings on the containment. Worldwide several experiments have been performed accompanied with material properties evaluation, theoretical, and numerical work.
At the Institute of Safety Research of the FZR a finite element model has been de-veloped simulating the thermal processes and the viscoplastic behaviour of the ves-sel wall. An advanced model for creep and material damage has been established and has been validated using experimental data. The thermal and the mechanical calculations are sequentially and recursively coupled. The model is capable of evalu-ating fracture time and fracture position of a vessel with an internally heated melt pool.
The model was applied to pre- and post test calculations for the FOREVER test se-ries representing the lower head RPV of a PWR in the geometrical scale of 1:10. These experiments were performed at the Royal Institute of Technology in Stock-holm. The results of the calculations can be summarised as follows:

• The creeping process is caused by the simultaneous presence of high tem-perature (>600 °C) and pressure (>1 MPa)
• The hot focus region is the most endangered zone exhibiting the highest creep strain rates.
• The exact level of temperature and pressure has an influence on the vessel failure time but not on the failure position
• The failure time can be predicted with an uncertainty of 20 to 25%. This uncer-tainty is caused by the large scatter and the high temperature sensitivity of the viscoplastic properties of the RPV steel.
• Contrary to the hot focus region, the lower centre of the vessel head exhibits a higher strength because of the lower temperatures in this zone. The lower part moves down without significant deformation. Therefore it can be assumed, that the vessel failure can be retarded or prevented by supporting this range.
• The development of a gap between melt crust and vessel wall could not be proofed.

First calculations for a PWR geometry were performed to work out differences and commonalities between prototypic scenarios and scaled experiments. The results of the FOREVER-experiments cannot be transferred directly to PWR geometry. The geometrical, mechanical and thermal relations cannot be scaled in the same way. Because of the significantly higher temperature level, a partial ablation of the vessel wall has to be to expected in the PWR scenario, which is not the case in the FOREVER tests. But nevertheless the FOREVER tests are the only integral in-vessel retention experiments up to now and they led to a number of important insights about the behaviour of a vessel under the loading of a melt pool and pressure.
Keywords: In-vessel retention, Reactor pressure vessel, Core melt down accident, Creep, Damage, ECCM, FEM
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-437 2005

Downloads:

Publ.-Id: 7712 - Permalink


Einfluss von Huminsäure auf die Np(V)-Sorption an Kaolinit
Schmeide, K.;
Die Np(V)-Sorption an Kaolinit in Abwesenheit und Gegenwart von Huminsäure wird mittels Batch-Experimenten untersucht.
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 04.-05.10.2005, Leipzig, Germany

Publ.-Id: 7711 - Permalink


CORPHAD and METCOR ISTC projects
Bechta, S. V.; Khabensky, V. B.; Granovsky, V. S.; Kroushinov, E. V.; Vitol, S. A.; Gusarov, V. V.; Almiashev, V. I.; Mezentseva, L. P.; Petrov, Y. B.; Lopukh, D. B.; Fischer, M.; Bottomley, D.; Tromm, W.; Barrachin, M.; Altstadt, E.; Piluso, P.; Fichot, F.; Hellmann, S.; Defoort, F.;
The ongoing CORPHAD Project (Phase Diagrams for Multicomponent Systems Containing Corium and Products of its Interaction with NPP Materials) started in August 2001. The main aim of the project is to experimentally determine the relevant physicochemical data on phase diagrams of binary, ternary, quaternary and prototypic multi-component systems, which are important for analysis and modelling of a severe accident (SA) and efficient planning of severe accident management (SAM) measures. The data should be directly used for the European NUCLEA database development and validation. The following systems are in the focus of the project: (1) UO2 – FeO, (2) ZrO2 – FeO, (3) SiO2– Fe2O3, (4) UO2 – SiO2, (5) UO2 – ZrO2-FeO, (6) UO2 – ZrO2-FeOy, (7) U-O-Fe, (8) Zr-O-Fe, (9) U-O-Zr, (10) U-Zr-Fe-O, (11) complex corium mixtures.
The experimentally determined data of the listed diagrams include: coordinates of characteristic points (eutectics, peritectics and others); liquidus and solidus concentration curves; component solubility limits in the solid phase; tie line coordinates and temperature-concentration regions of the miscibility gap. Different methodologies are used for the phase diagram study. Classical methods of thermal analysis, like DTA and DSC are combined with methods specifically developed for corium studies.
The METCOR project (Investigation of Corium Melt Interaction with NPP Reactor Vessel Steel) started in April 1999. The objectives of the project are to qualify and to quantify physico-chemical phenomena of corium melt interaction with reactor vessel steel cooled from the outside. The variable parameters of the interaction tests are: oxygen potential in the system, corium composition, interaction interface temperature and heat flux from corium to steel. The medium scale tests with corium mass of about 2 kg are carried out by using high-frequency induction heating of the corium melt in a cold crucible.
The METCOR&CORPHAD work-packages are performed by Russian partners in close collaboration with leading European scientific institutes in the area of corium research as well as with the European nuclear industry.
This paper briefly describes the results obtained in both projects and their possible application for SA analysis and SAM. The paper concludes with recommendations for future research activities in the frame of METCOR and CORPHAD projects.
Keywords: Corium, Phase diagram, Corium-structure interaction, Reactor vessel steel
  • Contribution to proceedings
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France

Publ.-Id: 7710 - Permalink


Vessel rupture: Synthesis of the FOREVER interpretation activity
Altstadt, E.; Willschütz, H.-G.; Sehgal, B. R.; Weiß, F.-P.;
At FZR an integral axisymmetric finite element model has been developed for simulat-ing the late phase of core melt down scenarios in a RPV. The model allows for the calculation of the failure time and the failure mode of a vessel with a heated melt pool. In the thermal submodel the transient temperature field of the melt and of the vessel wall is evaluated. This can be done either with a CFD model or with the Effective Conduction Convection Model (ECCM). Within the mechanical submodel the viscoplastic deformation of the vessel wall is simulated. By use of the material damage the failure time and position can be deter-mined. An additional mechanical submodel is used to evaluate the melt pool deformation. The thermal and the mechanical submodels are recursively and sequentially coupled, i.e. for each time step a thermal dynamic and a mechanical solution is calculated considering a mutual feedback. Besides of the temperature dependence of the material parameters and the thermally induced stresses, which are considered in the mechanical model, also the consequences of the vessel deformation for the temperature calculation are included (change of melt pool geometry, melt level drop, change of heat resistance of the vessel wall through thickness reduction, increase of the effective surface for heat radiation and convection). For the mechanical model a creep data base has been developed based on experimental results of projects of the 4th frame work programme of the EU. The viscoplastic calculation is coupled with the material damage. The creep data base was validated using two pipe rupture experiments. The coupled model for vessel failure was for pre- and post test calculations of the FOREVER experiments performed at the KTH Stockholm. In general, a good agreement of the calculation and the experimental results could be achieved. The FE model can be considered as validated for medium scaled vessel tests. Some sensitivity studies are done to evaluate the influence of the design peculi-arities of the FOREVER experiments in comparison with the prototypic scenarios.
Keywords: In-vessel retention, Reactor pressure vessel, Finite element model, Creep, Damage, Effective conduction convection model
  • Contribution to proceedings
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France
  • Lecture (Conference)
    ERMSAR 2005, 14.-16.11.2005, Aix en Provence, France

Publ.-Id: 7709 - Permalink


Ripple structure of ion beam induced Si wafers
Pietsch, U.; Grenzer, J.; Hazra, S.; Chini, T. K.; Sanyal, M. K.;
Ion beam induced ripple formation in Si wafers was studied by atomic force microscopy (AFM) and non-destructive depth-resolved x-ray grazing incidence diffraction (GID). The formation of ripple structure at high doses (7x1017 ions/cm2), starting from initiation at low doses (1x1017 ions/cm2) of ion beam is evident from AFM, while that in the buried crystalline region below a partially crystalline top layer is evident from GID study. The GID technique reveals that these periodically modulated wave-like buried crystalline features become highly regular and strongly correlated as one increases the Ar ion beam energy from 60 keV to 100 keV. The vertical density profile obtained from the analysis of Vineyard profile shows that the density in the upper top part of ripples is decreased to about 15% of the crystalline density. The partially crystalline top layer at low dose, transforms to a completely amorphous layer for high doses and the top morphology was found to be conformal with the underlying crystalline ripple. Inspection of the amorphous scattering shows that the amorphous form factor of the damaged top layer is strongly textured in azimuth and scales with the ion dose.
Keywords: ion beam errosion, grazing incidence diffraction
  • Lecture (Conference)
    IUCr2005 XX Congress of the International Union of Crystallography, 23.-31.08.2005, Florence, Italy

Publ.-Id: 7708 - Permalink


Grazing-incidence Diffraction and Small angle X-ray scattering
Grenzer, J.;
X-ray grazing incidence diffraction and small angle scattering are a scattering method which combines out-of plane reflectivity under the condition of X-ray total external reflection with in-plane Bragg diffraction and small angle scattering, respectively. The formation of an evanescent wave propagating parallel but close below the sample surface opens the possibility to probe structures at a sample surfaces or close below it.
Keywords: x-ray granzing incidence diffraction, grazing incidence small angle scattering
  • Invited lecture (Conferences)
    6th Autumn School on X-ray scattering from surfaces and thin layers, 18.-21.09.2005, Smolenice, Slovenia

Publ.-Id: 7707 - Permalink


X-ray investigation of focused ion-beam induced semiconductor surfaces - How to make a lateral nanostructure
Grenzer, J.; Bischoff, L.; Pietsch, U.;
We report on the strain and defect analysis of lateral nanostructures created in Ga and Si substrates which was performed utilizing the method of X-ray grazing-incidence diffraction. The substrates were patterned by focused ion beam implantation technique using a Ga or AuGeSi liquid metal ion source.
Keywords: ion beam implantation, grazing incidence diffrtaction
  • Lecture (Conference)
    348. WE-Heraeus-Seminar, Ions at Surfaces: Patterns and Processes, 19.-23.06.2005, Bad Honnef, Germany

Publ.-Id: 7706 - Permalink


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