Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

33397 Publications

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

Permalink: https://www.hzdr.de/publications/Publ-7777
Publ.-Id: 7777


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

Permalink: https://www.hzdr.de/publications/Publ-7776
Publ.-Id: 7776


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

Permalink: https://www.hzdr.de/publications/Publ-7775
Publ.-Id: 7775


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

Permalink: https://www.hzdr.de/publications/Publ-7774
Publ.-Id: 7774


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

Permalink: https://www.hzdr.de/publications/Publ-7773
Publ.-Id: 7773


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

Permalink: https://www.hzdr.de/publications/Publ-7772
Publ.-Id: 7772


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

Permalink: https://www.hzdr.de/publications/Publ-7771
Publ.-Id: 7771


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

Permalink: https://www.hzdr.de/publications/Publ-7770
Publ.-Id: 7770


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

Permalink: https://www.hzdr.de/publications/Publ-7769
Publ.-Id: 7769


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

Permalink: https://www.hzdr.de/publications/Publ-7768
Publ.-Id: 7768


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

Permalink: https://www.hzdr.de/publications/Publ-7767
Publ.-Id: 7767


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

Permalink: https://www.hzdr.de/publications/Publ-7765
Publ.-Id: 7765


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7764
Publ.-Id: 7764


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

Permalink: https://www.hzdr.de/publications/Publ-7763
Publ.-Id: 7763


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

Permalink: https://www.hzdr.de/publications/Publ-7762
Publ.-Id: 7762


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

Permalink: https://www.hzdr.de/publications/Publ-7761
Publ.-Id: 7761


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

Permalink: https://www.hzdr.de/publications/Publ-7760
Publ.-Id: 7760


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

Permalink: https://www.hzdr.de/publications/Publ-7759
Publ.-Id: 7759


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

Permalink: https://www.hzdr.de/publications/Publ-7758
Publ.-Id: 7758


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.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7757
Publ.-Id: 7757


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7756
Publ.-Id: 7756


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

Permalink: https://www.hzdr.de/publications/Publ-7755
Publ.-Id: 7755


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

Permalink: https://www.hzdr.de/publications/Publ-7754
Publ.-Id: 7754


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

Permalink: https://www.hzdr.de/publications/Publ-7753
Publ.-Id: 7753


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

Permalink: https://www.hzdr.de/publications/Publ-7752
Publ.-Id: 7752


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

Permalink: https://www.hzdr.de/publications/Publ-7751
Publ.-Id: 7751


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

Permalink: https://www.hzdr.de/publications/Publ-7750
Publ.-Id: 7750


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

Permalink: https://www.hzdr.de/publications/Publ-7749
Publ.-Id: 7749


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

Permalink: https://www.hzdr.de/publications/Publ-7748
Publ.-Id: 7748


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7747
Publ.-Id: 7747


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

Permalink: https://www.hzdr.de/publications/Publ-7746
Publ.-Id: 7746


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

Permalink: https://www.hzdr.de/publications/Publ-7745
Publ.-Id: 7745


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

Permalink: https://www.hzdr.de/publications/Publ-7744
Publ.-Id: 7744


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7743
Publ.-Id: 7743


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7742
Publ.-Id: 7742


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7741
Publ.-Id: 7741


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7740
Publ.-Id: 7740


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

Permalink: https://www.hzdr.de/publications/Publ-7739
Publ.-Id: 7739


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

Permalink: https://www.hzdr.de/publications/Publ-7738
Publ.-Id: 7738


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7737
Publ.-Id: 7737


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

Permalink: https://www.hzdr.de/publications/Publ-7736
Publ.-Id: 7736


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

Permalink: https://www.hzdr.de/publications/Publ-7735
Publ.-Id: 7735


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

Permalink: https://www.hzdr.de/publications/Publ-7734
Publ.-Id: 7734


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

Permalink: https://www.hzdr.de/publications/Publ-7733
Publ.-Id: 7733


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 Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-438 2005

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7732
Publ.-Id: 7732


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7731
Publ.-Id: 7731


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

Permalink: https://www.hzdr.de/publications/Publ-7730
Publ.-Id: 7730


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

Permalink: https://www.hzdr.de/publications/Publ-7729
Publ.-Id: 7729


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7728
Publ.-Id: 7728


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7725
Publ.-Id: 7725


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7724
Publ.-Id: 7724


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

Permalink: https://www.hzdr.de/publications/Publ-7722
Publ.-Id: 7722


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7721
Publ.-Id: 7721


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7720
Publ.-Id: 7720


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7719
Publ.-Id: 7719


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

Permalink: https://www.hzdr.de/publications/Publ-7718
Publ.-Id: 7718


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 Logo Archives of Thermodynamics 26(2005)4, 49-59

Permalink: https://www.hzdr.de/publications/Publ-7717
Publ.-Id: 7717


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

Permalink: https://www.hzdr.de/publications/Publ-7716
Publ.-Id: 7716


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

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7715
Publ.-Id: 7715


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

Permalink: https://www.hzdr.de/publications/Publ-7713
Publ.-Id: 7713


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 Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-437 2005

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7712
Publ.-Id: 7712


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

Permalink: https://www.hzdr.de/publications/Publ-7711
Publ.-Id: 7711


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

Permalink: https://www.hzdr.de/publications/Publ-7710
Publ.-Id: 7710


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

Permalink: https://www.hzdr.de/publications/Publ-7709
Publ.-Id: 7709


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

Permalink: https://www.hzdr.de/publications/Publ-7708
Publ.-Id: 7708


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

Permalink: https://www.hzdr.de/publications/Publ-7707
Publ.-Id: 7707


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

Permalink: https://www.hzdr.de/publications/Publ-7706
Publ.-Id: 7706


X-ray investigation of low-energy ion-beam induced lateral surface nanostructures on semiconductor surfaces

Grenzer, J.; Hazra, S.; Chini, T. K.; Bischoff, L.; Pietsch, U.; Sanyal, M. K.
Low energy ion beams are widely used to alter the surface properties of semiconductors. We have used two different ways to create lateral nanostructures, either using an artificial patterning by a focused ion beam or by a tilted non-focused ion beam achieving a self-organizing ripple formation. X-ray grazing-incidence diffraction is a powerful tool to investigate such lateral nano-structures. Choosing the angle of incidence smaller or slightly larger as the critical angle of total external reflection one can probe the fine structure of an in-plane Bragg diffraction in a depth between about 5 to several 100 nm.
Keywords: ion beam implantation, ion beam errosion, x-ray diffraction
  • Invited lecture (Conferences)
    IUMRS ICA2004, 16.-18.11.2004, Hsinchu, Taiwan

Permalink: https://www.hzdr.de/publications/Publ-7705
Publ.-Id: 7705


Depth resolved strainanalysis of lateral nanostrucutres by x-ray grazing incidence diffraction

Grenzer, J.
Quantum well semiconductor heterostructures are increasingly important systems in the development of smaller, faster and more efficient electronic and optoelectronic devices. One way to modify the electronic band structure is to exploit quantum size effects requiring device engineering on a nanometer length scale. In particular, the lateral patterning of a strained stressor layer allows to achieve a lateral carrier confinement in a buried single quantum well as a result of the strain relaxation. The strain relaxation at free surfaces of the stressor layer induces a lateral inhomogeneous strain distribution and subsequently a lateral change of the optical properties within the single SQW. To exploit this effect in a device the structure has to be planarized by a second epitaxial step. The lateral carrier confinement of the initially free standing nanostructure can almost be maintained using a two step overgrowth process. The layout of the lateral nano structure (layer thicknesses and composition, shape) is predicted by finite element calculations of the strain distribution. The achieved optical properties are measured by photoluminescence; the strain field is probed by X-ray grazing-incidence diffraction.
Keywords: x-ray diffraction
  • Lecture (others)
    eingeladener Vortrag am Institut für experimentelle Physik, 11.05.2005, Warschau, Polen

Permalink: https://www.hzdr.de/publications/Publ-7704
Publ.-Id: 7704


A modified rf ion source with a ceramic bottle

Friedrich, M.
The generation of negative He ions for acceleration at tandem accelerators requires an ion source with alkali vapor charge exchange canal. The diffusion of the Li or Rb vapor into the surrounding vacuum chamber limits the operation time of the ion source and increases the necessary maintenance. On the other hand, the modified rf ion source at the Rossendorf single ended 2 MV Van de Graaff accelerator has a life time of some thousands hours. The installation of this ion source inside the terminal of the Rossendorf 5 MV tandem accelerator would allow high-energy implantation of He ions in the energy range of 1-5 MeV without the difficulties of the charge-exchange canal. To reduce the risk for breaking of the ion source glass bottle under the pressure of the insulating gas a ceramic source bottle has been tested. First results of its operation at the 2 MV VdG are presented.
Keywords: Ion sources, Electrostatic accelerators, Helium ions
  • Lecture (Conference)
    39th Symposium of Northeastern Accelerator Personnel (SNEAP), 16.-20.10.2005, Port Jefferson, USA

Permalink: https://www.hzdr.de/publications/Publ-7703
Publ.-Id: 7703


Investigation of WWER RPV steel and cladding from Greifswald NPP

Rindelhardt, U.; Konheiser, J.; Viehrig, H.-W.
The investigation of the well documented different irradiation/annealing states of the four former NPP Greifswald units are a special advantage to assess the reactor pressure vessel integrity and to check the corresponding rules and codes.
The results of new, more accurate calculations of the neutron fluence will be given. Further, the change of the RPV dismantling strategy required a new approach for the trepanning procedure. The new procedure will be shortly described and the cold test results of the new developed drilling machine are shown. Finally some aspects of the material investigation program are discussed.
Keywords: RPV steel, embrittlement, NPP Greifswald
  • Invited lecture (Conferences)
    IAEA-Workshop “Improved Reactor Pressure Vessels (RPV) Structural Integrity Assessment for NPPs”, 18.-21.10.2005, Madrid, Spain

Permalink: https://www.hzdr.de/publications/Publ-7702
Publ.-Id: 7702


Die Erholung der sächsischen Talsperrenökosysteme von der atmosphärischen Versauerung im Vergleich zu hydrochemischen Trends im Einzugsgebiet der Talsperre Kleine Kinzig (Nordschwarzwald)

Ulrich, K.-U.; Meybohm, A.; Hoehn, E.
Aufgrund des enormen Ausstoßes an Schwefeldioxid und Stickoxiden sowie des basenarmen Grundgesteins von Erzgebirge und Vogtland litten zahlreiche sächsische Staugewässer etwa seit Mitte der 1960er Jahre unter der atmosphärischen Versauerung. Dies betraf auch einige Trink¬wassertalsperren. Nach der Wiedervereinigung wurden weder Kosten noch Aufwand gescheut, um geeignete Technologien zur Aufbereitung des weichen, sauren Rohwassers zu entwickeln, die Wasserwerke zu modernisieren und auf die Einhaltung der geforderten Grenzwerte einzustellen.
Innerhalb des letzten Jahrzehnts verringerten sich die Schwefeldioxid-Emissionen beträchtlich. Der Literatur zufolge gibt es große regionale Unterschiede bei der Erholung der Oberflächengewässer von der atmosphärischen Versauerung. Entsprechende Trends sind in vielen deutschen Mittelgebirgen nur schwach ausgeprägt oder überhaupt nicht nachweisbar. Dies begründet die Motivation, den Datenbestand der Landestalsperrenverwaltung Sachsen am Beispiel von sieben versauerten Talsperren und 22 Zuflüssen hinsichtlich der Trends ausge¬wählter hydrochemischer Parameter für 11 Jahre (1993-2003) mit dem Saisonalen Mann-Kendall Test statistisch auszuwerten und mit anderen Regionen zu vergleichen. Beispielsweise stehen im Nordschwarzwald für die Zuflüsse der Trinkwassertalsperre Kleine Kinzig entsprechende Datensätze aus den Jahren 1989 bis 2003 zur Verfügung.
Der Vortrag stellt die charakteristischen Trends im Zusammenhang mit der regionalen Entwicklung der Emissions- und Depositionssituation und vor dem Hintergrund forstlicher Bodenschutzkalkung dar. Als Hauptfaktor für den in 85% der untersuchten sächsischen Gewässer signifikanten Konzentrationsrückgang von Protonen und Sulfat wird die Abnahme der Depositionsraten um mindestens Faktor 3 angesehen. In etwa 20% der Gewässer, bei denen die insgesamt applizierte Dolomitdosis im Einzugsgebiet 7 t ha-1 überschritt, fanden sich steigende Trends der Calcium- und/oder Magnesiumkonzentration, die jedoch nicht signifikant waren. Der direkte Beitrag der Bodenschutzkalkung zur Entsäuerung und nachhaltigen Erhöhung des Pufferungsvermögens der Oberflächengewässer wird als relativ gering eingeschätzt. Der starke Konzentrationsrückgang von Protonen und damit einhergehend von toxischen Aluminiumver¬bindungen bildet die Grundlage für eine Wiederbesiedelung der Gewässer durch säure¬empfindliche Organismen. Veränderungen in der Dominanzstruktur des Phytoplanktons gab es bereits in mehreren Talsperren im Vogtland. Dort hat sich auch gezeigt, dass mit dem Auftreten einer planktivoren Fischart extreme Schwankungen im Bestand bis hin zu Massensterben durch zeitweise Erschöpfung der Nahrungsressourcen einhergehen. Die Räuber-Beute-Effekte sowie episodisch auftretende Säureschübe können die Etablierung von größerer planktischer Filtrierer (z.B. Daphnien) stark verzögern.
  • Invited lecture (Conferences)
    15. Limnologisches Gespräch des Zweckverbandes Wasserversorgung Kleine Kinzig (WKK), 20.10.2005, Alpirsbach-Reinerzau, Germany

Permalink: https://www.hzdr.de/publications/Publ-7701
Publ.-Id: 7701


Perturbation theory for non-selfadjoint operator matrices and its application to the MHD α²-dynamo

Günther, U.; Kirillov, O.
We consider singular boundary value problems for linear non-selfadjoint m-th order N×N matrix differential operators on the interval (0,1]∋ x. The coefficient matrices in the differential expressions and the matrix boundary conditions are assumed to depend on the spectral parameter λ as well as on a vector-valued parameter distribution p(x). For simplicity, we restrict our attention to setups with a (boundary) singular point (x=0) of regular (Fuchsian) type.

Based on a bi-orthogonal solution ansatz, we study perturbations of simple and multiple eigenvalues under small variations of the parameter distribution p(x). Special attention is paid to perturbations of semi-simple multiple eigenvalues (diabolical points; characterized by coinciding geometric and algebraic multiplicity and corresponding diagonal spectral decomposition of the operator) as well as to perturbations of non-derogatory eigenvalues (branch points, exceptional points; with non-trivial Jordan structures in the spectral decomposition) with one eigenvector (geometric multiplicity one) and several associated vectors forming a Keldysh chain of length equal to the algebraic multiplicity of the eigenvalue. Explicit formulae describing the bifurcation of the eigenvalues are derived.

As application, the general technique is utilized for the investigation of the spectral properties of spherically symmetric MHD α²-dynamos. Specifically, we provide an analytical description for the occurrence of spectral branch points under transitions from idealized boundary conditions to physically realistic boundary conditions. Furthermore, we develop a gradient technique with respect to the α-profile α(x) of the dynamo which allows us to search for most efficient α-perturbations to trigger magnetic field reversals.
Keywords: non-selfadjoint matrix differential operators, singular boundary value problems, perturbation theory, spectral analysis, spectral bifurcations, branch points, diabolical points, exceptional points, magnetohydrodynamics, dynamo theory
  • Lecture (Conference)
    4th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 23.-25.11.2005, Stellenbosch, South Africa

Permalink: https://www.hzdr.de/publications/Publ-7700
Publ.-Id: 7700


Bundle stratification of PT-symmetric 4×4 matrix systems and fourth-order spectral branch points of MHD α²-dynamos

Günther, U.; Kirillov, O.; Stefani, F.
The spectra of PT-symmetric quantum systems are, in general, highly complicated complex varieties over the parameter spaces of these systems. Parameter space regions of exact PT-symmetry with purely real eigenvalues adjoin other regions with broken PT-symmetry and pairwise complex conjugate eigenvalues. The boundaries between different regions correspond to (exceptional) hypersurfaces in the parameter space and have certain system defined codimensions. Hypersurfaces (strata) of lower codimension may intersect at sub-hypersurfaces (sub-strata) of higher codimension forming in this way a hierarchical structure of dimensionally nested hypersurfaces of increasing codimension (and increasing "exceptionality"), i.e. they form a so called stratified manifold.

In case of matrix systems, the most general parameter space can be identified with the matrix space itself. Endowing this space with a natural fiber bundle structure, regarding matrix orbits (equivalence classes) over a given Jordan structure as fibers, the hierarchical hypersurface structure of the spectral variety can be studied with the help of nested Jordan structures. As result, one arrives at a so called bundle stratification.

We perform such a bundle stratification explicitly for a PT-symmetric 4×4 matrix systems and use the obtained results to comparatively analyze the spectral structure of the spherically symmetric α²-dynamo of magnetohydrodynamics in the vicinity of a fourth-order branch point.
Keywords: non-selfadjoint operators, spectral theory, branch points, exceptional points, fiber bundles, stratification, PT-symmetric quantum mechanics, magnetohydrodynamics, dynamo theory
  • Lecture (Conference)
    4th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 23.-25.11.2005, Stellenbosch, South Africa

Permalink: https://www.hzdr.de/publications/Publ-7699
Publ.-Id: 7699


High-speed complex admittance/permittivity needle probe for investigation of multiphase flows

Da Silva, M. J.; Brückner, F.; Schleicher, E.; Hampel, U.
For the investigation of three- or multiphase flows, which are of interest for instance in the chemical engineering or in oil extraction and processing, there are only few suitable measuring techniques. For this reason we have developed a high-speed complex admittance/permittivity needle probe. Such probes are able to distinguish the different phases or components of a flow by measuring the complex value of the electrical admittance/permittivity at a high data rate (up to 10,000 samples/s). The performance of the system as well as its ability to differentiate some organic substances has been analyzed. A preliminary time resolved experiment in a gasoline-air-water flow is also presented.
Keywords: needle probe, admittance measurement, permittivity measurement, multiphase flow
  • Contribution to proceedings
    23rd IEEE Instrumentation and Measurement Technology Conference, 24.-27.04.2006, Sorrento, Italy
    Proceedings, 0-7803-9360-0, 1937-1941
  • Lecture (Conference)
    IEEE Instrumentation and Measurement Technology Conference, 24.-27.04.2006, Sorrento, Italy

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7698
Publ.-Id: 7698


Influence of Mg, Ca, Sr and Ba on formation of geochemical relevant uranyl species

Geipel, G.
The uranyl tricarbonato complex is one of the most important uranyl species under environmental conditions. The tendency to form stable metal-uranyl tricarbonato complexes was found particularly for the interaction with alkaline earth elements. However, under comparable chemical conditions the formation of these complexes is very different. While magnesium tends mainly to the formation of a MgUO2(CO3)32+ - complex, in the case of calcium the Ca2UO2(CO3)3(aq.) complex is the most stable and the formation of the CaUO2(CO3)32+ - complex is very limited. In the corresponding systems with strontium as well as for barium only the MeUO2(CO3)32+ - complex is formed. The stability constants of the MeUO2(CO3)32+ - complexes increase in the series Mg, Ca , Sr and Ba. The formation of Me2UO2(CO3)3 – complexes for Mg, Sr and Ba occurs only in a small concentration range and the formed complexes tends to precipitate. The Me2UO2(CO3)3 – complexes for Mg and Ca form stable minerals as bayleyite and liebigite. However several other mineral modifications as zellerite, fontanite, sharpite and rabbittite underline the geochemical importance of this class of compounds.
Analogous phenomena can be expected in the alkaline earth uranyl phosphate systems and results for the formation of species of the type Mex(UO2PO4)y will be presented.
Keywords: Uranium, TRLFS, minerals, complex formation
  • 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, 36-36
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-7697
Publ.-Id: 7697


Atomistic study of the mobility of small interstitial clusters in silicon

Posselt, M.; Gao, F.
In this work a comprehensive atomistic study is performed in order to get a better understanding of the mechanisms of di- and tri-interstitial diffusion at different temperatures and to obtain more data for their diffusivities and migration barriers. A classical potential approach is employed since it allows the investigation of defect migration under relatively realistic conditions, by considering a large computational cell, a very long simulation time, and different initial conditions. In order to test the potential employed, at first the structure and energetics of di- and tri-interstitials are determined and the results are compared with the data obtained by tight-binding and density-functional-theory calculations.
The migration of mono-, di- and tri-interstitials is investigated for temperatures between 800 and 1600 K. The defect diffusivity, the self-diffusion coefficient per defect and the corresponding effective migration barriers are calculated. Compared to the mono-interstitial, the di-interstitial migrates faster, whereas the tri-interstitial diffuses slower. The mobility of the di- and the mono-interstitial is higher than the mobility of the lattice atoms during the diffusion of these defects. On the other hand, the tri-interstitial mobility is lower than the corresponding atomic mobility. The migration mechanism of the di-interstitial shows a pronounced dependence on the temperature. At low temperature a high mobility on zigzag-like lines along a <110> axis within a {110} plane is found, whereas the change between equivalent <110> directions or equivalent {110} planes occurs seldom and requires a long time. At high temperature a frequent change between equivalent <110> directions or {110} planes is observed. During the diffusion within {110} planes the di-interstitial moves like a wave packet so that the atomic mobility is lower than that of the defect. On the other hand, the change between equivalent {110} migration planes is characterized by frequent atomic rearrangements. The visual analysis of the tri-interstitial diffusion reveals complex migration mechanisms and a high atomic mobility. The implications of the present results for the explanation of experimental data on defect evolution and migration are discussed.

[1] P. Pichler, D. Stiebel, Nucl. Instr. Meth. B 186 (2002) 256.
[2] M. J. Caturla, T. Diaz de la Rubia, L. A. Marques, G. H. Gilmer, Phys. Rev. B 54 (1996) 16683.
[3] M. Posselt, Mater. Res. Soc. Symp. Proc. 647 (2001) O2.1.1.
[4] G. H. Gilmer, T. Diaz de la Rubia, D. M. Stock, M. Jaraiz, Nucl. Instr. Meth. B 102 (1995) 247.
[5] S. K. Estreicher, M. Gharaibeh, P. A. Fedders, P. Ordejon, Phys. Rev. Lett. 86 (2001) 1247.
Keywords: Si, intrinsic defects, diffusion, simulations
  • Poster
    11th Int. Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 25.-30.09.2005, Giens, France

Permalink: https://www.hzdr.de/publications/Publ-7696
Publ.-Id: 7696


A modified concerted exchange mechanism for antisite pair recombination in cubic and hexagonal silicon carbide

Posselt, M.; Gao, F.
The antisite pair is one of the defect species which can be formed during ion beam processing of SiC. It consists of two neighboring atoms on “wrong” lattice sites, namely a Si atom on a C site and a C atom on a Si site. In general the experimental analysis of the different defect types formed during ion irradiation is difficult. Theoretical investigations on defect kinetics and defect evolution can be therefore very helpful to interpret the results of the annealing experiments with the irradiated samples. The antisite pair could not yet be identified unambiguously by experimental methods. Recently, the DI low temperature photoluminescence (PL) center has been correlated with the antisite pair [1]. In that theoretical work it is assumed that the antisite pair is stable up to a temperature of 2000 K. However, the thermal stability of the antisite pair has not yet been investigated. To our knowledge, there is only one work that is related to this topic [2]. Based on Pandey’s concerted exchange originally proposed for silicon [3], the antisite pair formation is studied by static potential energy calculations.

This work shows results of a systematic atomistic study on the thermal stabilty of the antisite pair and on the mechanisms of recombination in cubic (3C) and hexagonal (4H) SiC. At first the structure and energetics of the antisite pair is determined for T = 0 K. The results are compared with literature data which were obtained by the density-functional theory (DFT). The comparison shows that the interatomic potential used in the atomistic simulations yields reasonable data. The thermal stability of the antisite pair was investigated by molecular dynamics (MD) simulations at temperatures between 800 and 2500 K. Due to the statistical nature of the recombination process, it was necessary to perform several statistically independent simulations at every temperature. This was done by using different initial random numbers. The lifetime of the antisite pair was determined by different methods: (i) The evolution of the potential energy of the atoms which belong to the antisite pair and/or the potential energy of the atoms belonging to the defect and to the defect environment were analyzed. (ii) The time dependence of the recombination parameter was followed. (iii) The defect configuration was monitored visually. It is found that the thermal stability of the antisite pair is relatively low. It can be therefore not correlated with the DI low temperature PL center which is stable up to 2000 K. These results are confirmed by DFT-based MD simulations. The detailed study of the atomic rearrangements during the antisite pair recombination revealed a modified concerted exchange mechanism. Due to the different atomic sizes in SiC, this process is not identical with the concerted exchange proposed for Si [3] and considered by Rauls et al. [2] in order to explain the antisite pair formation in cubic SiC. Investigations of antisite pair recombination in hexagonal (4H) SiC yield results which are slightly different to those obtained for the cubic polytype.

[1] A. Gali, P. Deak, E. Rauls, N. T. Son, I. G. Ivanov, F. H. C. Carlsson, E. Janzen,
W. I. Choyke, Phys. Rev. B 67 (2003) 155203.
[2] E. Rauls, Z. Hajnal, A. Gali, P. Deak, T. Frauenheim, Materials Science Forum
353-356 (2001) 435.
[3] K. C. Pandey, Phys. Rev. Lett. 57 (1986) 2287.
[4] F. Cargnoni, C. Gatti, L. Colombo, Phys. Rev. B 57 (1998) 170.
[5] M. Tang, L. Colombo, J. Zhu, T. Diaz de la Rubia, Phys. Rev. B 55 (1997) 14279.
Keywords: SiC, intrinsic defects, simulations
  • Poster
    11th Int. Autumn Meeting on Gettering and Defect Engineering in Semiconductor Technology (GADEST), 25.-30.09.2005, Giens, France

Permalink: https://www.hzdr.de/publications/Publ-7695
Publ.-Id: 7695


X-ray absorption spectroscopy - experimental possibilities and limitations

Hennig, C.
X-ray absorption spectroscopy allows to investigate the electronic structure (XANES) and interatomic distances and coordination numbers (EXAFS) not only in solid compounds aut also in non-crystalline and liquid samples. Basic principles and limitations of the technique will be discussed. The use of NEXAFS in comparison with XPS will be demonstrated.
Keywords: XAS, XPS, EXAFS, XANES, NEXAFS, Actinides
  • Invited lecture (Conferences)
    ACTINET - Theoretical User Lab: Experiment / Theory Workshop, 24.10.2005, Karlsruhe, Germany

Permalink: https://www.hzdr.de/publications/Publ-7694
Publ.-Id: 7694


Structure investigation of actinides in solution by combining EXAFS with electrochemistry

Hennig, C.
Natural aquatic and terrestrial environments comprise large variations in redox states. Actinides with their variable oxidation states are especially susceptible to these redox conditions. They form aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability.

Therefore, we developed a spectro-electrochemical cell to study the speciation and structure of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. Due to the specific safety requirements for handling radioactive materials the electrochemical cell is equipped with two safety compartments and a special electrode arrangement.
  • Invited lecture (Conferences)
    eingeladener Vortrag am ITU Karlsruhe, 21.10.2005, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-7693
Publ.-Id: 7693


P0503-Verfahren zur Behandlung von Halbleiter-Substratoberflächen, die mittels intensiven Lichtimpulsen kurzzeitig aufgeschmolzen werden

Voelskow, M.; Skorupa, W.; Anwand, W.
Es soll der Vertikalaufbau der mittels der Lichtimpulsbestrahlung zu schmelzenden Oberflächenschichten so modifiziert werden, dass eine weitgehend ebene und nicht facetierte Schmelzfront erreicht wird.
  • Patent
    DE 10 2005 036 669 A1
  • Patent
    EP 06013986

Permalink: https://www.hzdr.de/publications/Publ-7692
Publ.-Id: 7692


Sättigbarer Absorber

Dekorsy, T.; Neuhaus, J.; Helm, M.
Mit der Erfindung soll ein sättigbarer Absorber realisiert werden, der aus einer Halbleiter-Heterostrukur mit mindestens einem Quantenfilm besteht und dessen charakteristische Absorptionswellenlänge im Bereich des intraroten elektromagnetischen Spektrums liegt und abgestimmt werden kann.
  • Patent
    DE 10 2005 022 436 A1

Permalink: https://www.hzdr.de/publications/Publ-7691
Publ.-Id: 7691


P0501 - Gittersensor

Pietruske, H.; Sühnel, T.; Prasser, H.
Es wird ein Gittersensor vorgeschlagen, welcher auch für den Einsatz bei hohen und wechselnden Temperaturen und Drücken geeignet ist.
  • Patent
    DE102005019739.6: Erteilung-26.10.2006; Nachanmeldung WO (EP,JP,US); EP (CH,DE,ES,FI,FR,GB,IT,NL.SE)

Permalink: https://www.hzdr.de/publications/Publ-7690
Publ.-Id: 7690


On the detector arrangement for in-beam PET for hadron therapy monitoring

Crespo, P.; Shakirin, G.; Enghardt, W.
In-beam positron emission tomography (in-beam PET) is currently the only method for an in-situ monitoring of highly tumour-conformed charged hadron therapy. At the experimental carbon ion tumour therapy facility, running at the Gesellschaft fuer Schwerionenforschung, Darmstadt, Germany, all treatments have been monitored by means of a specially adapted dual-head PET scanner.
The positive clinical impact of this project triggered the construction of a hospital-based hadron therapy facility, with in-beam PET expected to monitor more delicate radiotherapeutic situations.
Therefore, we have studied possible in-beam PET improvements by optimising the arrangement of the gamma-ray detectors.
For this, a fully 3D, rebinning-free, maximum likelihood expectation maximization algorithm applicable to several closed ring or dual-head tomographs has been developed. The analysis of beta+ activity distributions simulated from real-treatment situations and detected with several detector arrangements allows to conclude that a dual-head tomograph with narrow gaps yields in-beam PET images with sufficient quality for monitoring head and neck treatments.
For monitoring larger irradiation fields, e.g. treatments in the pelvis region, a closed-ring tomograph was seen to be highly desirable. Finally, a study of the space availability for patient and bed, tomograph and beam
portal proves the implementation of a closed-ring detector arrangement for in-beam PET to be feasible.
  • Physics in Medicine and Biology 51(2006), 2143-2163

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-7689
Publ.-Id: 7689


Complex Formation of Curium(III) with the Amino Acids L2-Aminobutyric Acid and L-Threonine and the Corresponding Phosphate Ester O-Phospho-L-Threonine

Moll, H.; Bernhard, G.
The complex formation of curium(III) with L2-Aminobutyric acid, L-Threonine and O-Phospho-L-Threonine was determined by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3x10-7 M). The concentrations of L2-Aminobutyric acid and L-Threonine were varied between 0.001 and 0.25 M in the pH range of 2 to 9.6 using 0.5 M NaCl as background electrolyte. In the case of O-Phospho-L-Threonine, lower concentrations were applied varying from 1x10-4 to 0.025 M in the pH range 2.8 to 7.6 using 0.154 M NaCl as background electrolyte.
Curium species of the type MpHqLr were identified from the fluorescence emission spectra. Three Cm–L2-Aminobutyrate complexes could be determined: (i) CmL2+ with a peak maximum at 596.0 nm, (ii) CmL2+ with a peak maximum at 600.8 nm, and (iii) CmL3 with a peak maximum at 603.8 nm. The corresponding formation constants were calculated from TRLFS measurements to be log β101 = 5.17 ± 0.07, log β102 = 9.00 ± 0.07, and log β103 = 11.30 ± 0.09. In the Cm–Threonine system, also three different species could be characterized: (i) CmThr2+ with a peak maximum at 599.6 nm, (ii) CmThr2+ with a peak maximum at 603.2 nm, and (iii) CmThr2- with a peak maximum at 605.7 nm. These species show the following formation constants: log β101 = 6.72 ± 0.07, log β102 = 10.22 ± 0.09, and log β1-22 = -(7.22 ± 0.19). Two species could be identified in the Cm–Phosphothreonine system: (i) CmH2PThr2+ with a peak maximum at 597.0 nm and (ii) CmHPThr+ with a peak maximum at 601.0 nm. The formation constants of the Cm-Phosphothreonine complexes were calculated to be log β121 = 18.03 ± 0.13 and log β111 = 14.17 ± 0.09. Possible structures of the identified curium species will be discussed on the basis of the fluorescence lifetime measurements.
For a better understanding of the actinide interaction processes in biological systems such as microbes and plants on a molecular level, it is essential to explore their complexation with selected bioligands of relevant functionalities as model compounds.

This work was funded by the BMWi under contract number: 02E9985.
Keywords: Amino acids; L2-aminobutyric acid; L-Threonine; O-Phospho-L-Threonine; Aqueous solution; TRLFS; Curium; Complexation
  • 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, 223-223
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-7688
Publ.-Id: 7688


Manufacturing and characterization of Pd-nanoparticles formed on immobilized bacterial cells

Pollmann, K.; Merroun, M.; Raff, J.; Hennig, C.; Selenska-Pobell, S.
Biological ceramic composites (biocers) were used as a template to produce Pd(0)-nanoparticles. The metal binding cells of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 were used as biological component of the biocers and immobilized by using sol-gel technology. Vegetative cells and surface layer proteins of this strain are known to bind high amounts of Pd(II) that can be reduced to Pd(0) particles by the addition of a reducing agent. After embedding into sol-gel ceramics, the cells retained their Pd(II)-binding capability. Pd(0)-nanoclusters were produced by the addition of hydrogen as reducing agent after the sorption of Pd(II). The formed Pd(0) nanoparticles were investigated by EXAFS-spectroscopy. The particles had a size of 0.6-0.8 nm. The thus immobilized Pd nanoparticles possess very interesting physical and chemical properties and are of interest for technical applications.
  • Letters in Applied Microbiology 43(2006)1, 39-45

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7687
Publ.-Id: 7687


Interaction of Uranium(VI) and colloidal Iron(III) oxyhydroxide in an abandonded uranium mine

Ulrich, K.-U.; Rossberg, A.; Scheinost, A.; Reuther, H.; Zänker, H.
Acid mine drainage and process water from the in-situ leaching by sulfuric acid applied on uranium mines usually contain high amounts of iron, uranium, and sulfate besides other elements such as aluminum, manganese, zinc, calcium and silicon. Flooding of abandoned U mines by shallow groundwater initiates de-acidification, oxidation, and hydrolysis reactions by which colloids are formed, dominated by X-ray amorphous Fe(III) oxyhydroxide phases. Previous investigation on a flooding scenario has given spectroscopic evidence that the high affinity of U(VI) onto this type of colloids is due to the formation of mononuclear, inner-sphere surface complexes on 2-line ferrihydrite (Fh) where we suppose two types of coordination: (i) edge-sharing linkage of the UO22+ cation to an Fe(O,OH)6 octahedron stabilized by a hydrogen bond between one axial oxygen atom and the Fh surface, occurring in absence of CO2 and other ligands [1], and (ii) double-corner sharing linkage of the UO22+ cation to two Fe(O,OH)6 octahedra, occurring in the presence of atmospheric CO2 at pH ≤ 8 at the expense of the type (i) surface complex owing to competitive adsorption of carbonate on the Fh surface. Whereas a ternary sorption complex with monodentate linkage of carbonate to the adsorbed UO22+ cannot be ruled out at the tested conditions, ternary complexes with other ligands such as sulfate, nitrate, and silicate could be excluded [1].
The retarding impact of colloids on the transport of U(VI) does not only depend on the structure, but also on the long-term stability of the covalent bond between U(VI) and the solid phase. We started a series of desorption experiments in a simulated groundwater medium and a dilute NaHCO3 solution to study the kinetics of U(VI) desorption from U-loaded Fh. On a longer time scale of decades to centuries, the transformation of Fh to more crystalline phases such as hematite and goethite must be considered as well. We use the common approach of gently heating the samples to accelerate the crystallization of Fh in order to quantify the amount of U(VI) that will be incorporated in the lattice during the aging process as shown for instance by Duff et al. [2]. Recent results of these experiments will be presented.
In conclusion, our results show that the interaction of U(VI) and the highly reactive surface of ferric oxyhydroxide colloids plays a major role in lowering or delaying the release of radiotoxic uranium from flooded U mines into adjacent groundwater aquifers or surface water.


References
[1] Ulrich K.-U., Rossberg A., Scheinost A.C., Foerstendorf H., Zänker H., Jenk U. (2006), in: Merkel B.J., Hasche-Berger A. (Eds.), Uranium in the Environment. Mining Impact and Consequences. Springer, pp. 137-147.
[2] Duff M.C., Coughlin J.U., Hunter D.B. (2002), Geochim. Cosmochim. Acta 66, 3533-3547.
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University, 80-01-03474-7, 47-47
  • Lecture (Conference)
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-7686
Publ.-Id: 7686


Addition of U(VI) to uranium mining waste pile soil samples and resulting changes of natural bacterial community structure

Selenska-Pobell, S.
Changes of natural bacterial community structure induced by addition of uranyl or sodium nitrate to weakly contaminated soil samples from a uranium mining waste pile were studied using the 16S rDNA retrieval. Our results demonstrated that both treatments caused drastic changes in bacterial composition of the studied samples resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Most interesting is the strong propagation of Gamma-Pseudomonas spp. capable to accumulate significant amounts of U(VI) and to build biofilms, hence being able to protect the community from the added toxic metal. At the initial stages of incubation (four weeks after the addition of uranyl nitrate) also U(VI) reducing Geobacter spp. appeared. However, at the later stages of incubation (fourteen weeks after the supplementation) no Geobacter populations were detected anymore. The latter indicated that no biological reduction of U(VI) occurred in these samples most probably because of the lack of electron donors to support this reaction. Interestingly, different U-sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI) treated samples at these late stages of incubation. That indicated that the added U(VI) was immobilized and did not disturb anymore the studied bacterial community.
The drastic changes induced by the addition of U(VI) indicate that bacterial communities are able to protect their members from the toxicity of this radionuclide by propagation of resistant and capable to interact with U(VI) populations. On the other hand, the large number of dead bacteria liberates phosphate-rich and other biopolymers capable to bind U(VI). Hence, bacteria together with the abiotic soil components such as minerals and humic acids play a key role in the immobilization of U(VI) in nature.
  • Lecture (others)
    Kolloquium im Institut für Molekulare Biologie der BAW, 10.10.2005, Sofia, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-7685
Publ.-Id: 7685


Addition of U(VI) to a Uranium Mining Waste Sample and Resulting Changes in the Indigenous Bacterial Community

Geissler, A.; Selenska-Pobell, S.
Changes of natural bacterial community structure induced by addition of uranyl or sodium nitrate to weakly contaminated soil samples from a uranium mining waste pile were studied using the 16S rDNA retrieval. Our results demonstrated that both treatments caused drastic changes in bacterial composition of the studied samples resulting in strongly reducing the originally predominant Acidobacteria and Alphaproteobacteria. The addition of sodium nitrate induced a strong propagation of denitrifying and nitrate reducing populations of Actinobacteria and of Bacteroidetes. The treatment of the samples with uranyl nitrate demonstrated that most part of the mentioned Bacteroidetes and some of the actinobacterial populations do not tolerate high U(VI) concentrations. Most interesting is the strong propagation of Gamma-Pseudomonas spp. capable to accumulate significant amounts of U(VI) and to build biofilms, hence being able to protect the community from the added toxic metal. At the initial stages of incubation (four weeks after the addition of uranyl nitrate) also U(VI) reducing Geobacter spp. appeared. However, at the later stages of incubation (fourteen weeks after the supplementation) no Geobacter populations were detected anymore. The latter indicated that no biological reduction of U(VI) occurred in these samples most probably because of the lack of electron donors to support this reaction. Interestingly, different U-sensitive Bacteroidetes and alphaproteobacterial populations propagated in the U(VI) treated samples at these late stages of incubation. That indicated that the added U(VI) was immobilized and did not disturb anymore the studied bacterial community.
The drastic changes induced by the addition of U(VI) indicate that bacterial communities are able to protect their members from the toxicity of this radionuclide by propagation of resistant and capable to interact with U(VI) populations. On the other hand, the large number of dead bacteria liberates phosphate-rich and other biopolymers capable to bind U(VI). Hence, bacteria together with the abiotic soil components such as minerals and humic acids play a key role in the immobilization of U(VI) in nature.

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7684
Publ.-Id: 7684


On the temperature dependence of the mass spectra of AuGe and AuGeSi liquid metal alloy ion sources

Bischoff, L.; Pilz, W.; Ganetsos, T.; Akhmadaliev, C.; Aidinis, C. J.; Londos, C. A.
This reports on an extensive study of the characteristics of AuGe and AuGeSi liquid metal alloy ion sources as a model system for new semiconductor compatible FIB sources. Such characteristics include ion beam mass spectra. A careful investigation has been undertaken where the emitter temperature is the main variable parameter. This work concerns the temperature dependence of the mass spectra of two needle-type liquid metal alloy ion sources (LMAISs), namely Au77Ge14Si9 (Tm=364°C) and Au73Ge27 (Tm=365°C). The sources are importan for producing SiGe layers. The experimental results, in conjunction with existing theories, strongly points towards the co-existance of twomechanisms for the emission of doubly-charged monomer ions: direct field-evaporation and post-ionisation.
Keywords: liquid metal alloy ion source, temperature, mass spectra
  • Contribution to proceedings
    Second Conference on Microelectronics, Microsystems and Nanotechnology, 14.-17.11.2004, Athens, Greece
    Journal of Physics: Conference Series 10(2005), 214-217, Bristol and Philadelphia: Institute of Physics Publishing, ISSN 1742-6588

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7683
Publ.-Id: 7683


11C-C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [11C]methyl iodide

Wüst, F. R.; Berndt, M.
A novel 11C-C bond formation based on the palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide is described. The conversion of internal alkynes into the corresponding alkenylzirconocenes followed by transmetalation with Pd(PPh3)4 and subsequent cross-coupling with [11C]methyl iodide gave several 11C-labelled alpha,alpha’-dimethyl substituted alkenes. The palladium complex Pd(PPh3)4 proved to be superior to Pt(PPh3)4 or Ni(PPh3)4 as transition metal complex.
The scope and limitations of the novel palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide were tested with various internal alkynes. Radiochemical yields of up to 75% (based upon [11C]methyl iodide) could be achieved
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006)2, 91-100

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7682
Publ.-Id: 7682


Synergism effects between Ni and Cu on the radiation susceptibility of RPV model alloys

Ulbricht, A.; Keiderling, U.
After the formation of a high point-defect content of vacancies and self- or solute interstitial atoms during neutron-induced displacement cascade processes, the radiation susceptibility of a reactor pressure vessel (RPV) steel is expressed in its capability of defect clustering. These fine-scaled features are the essential microstructural changes and the reason for the enhanced material ageing under irradiation. Small-angle neutron scattering (SANS) provides statistically reliable results about their size distributions and contents in macroscopic volumina. A possible cluster composition can be derived from their magnetic and nuclear scattering intensities.
The content of Cu is the most essential parameter controlling the radiation susceptibility. Ni rich alloys have a higher radiation susceptibility as Ni poor steels with the same content of deleterious elements as Cu. The synergism of Ni and Cu has a catalytical effect on the radiation defect formation. Cu precipitates were not found.
Keywords: SANS, radiation defects, RPV steel
  • Contribution to external collection
    Y. Kirschbaum, A. Brandt, M. Tovar, D. Bischoff, R. Michaelsen: BENSC Experimental Reports 2004, Berlin: Hahn-Meitner-Institut, HMI - B 601(2005), 2005, ISSN 0936 - 0891, 155

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7681
Publ.-Id: 7681


Changes in zinc speciation in field soil after contamination with zinc oxide

Voegelin, A.; Pfister, S.; Scheinost, A.; Marcus, M.; Kretzschmar, R.
Recent studies on the speciation of Zn in contaminated soils confirmed the formation of Zn-layered double hydroxide (LDH) and Zn-phyllosilicate phases. However, no information on the kinetics of the formation of those phases under field conditions is currently available. In the present study, the transformation of Zn in a field soil artificially contaminated with ZnO containing filter dust from a brass foundry was monitored during 4 years using extended X-ray absorption fine structure (EXAFS)
spectroscopy. Soil sections were studied by í-X-ray fluorescence (í-XRF) and í-EXAFS spectroscopy. EXAFS spectra were analyzed by principal component analysis (PCA) and linear combination fitting (LCF). The results show that ZnO dissolved within 9 months and that half of the total Zn reprecipitated. The precipitate was mainly of the Zn- LDH type (>75%). Only a minor fraction (<25%) may be of Zn-phyllosilicate type. The remaining Zn was adsorbed to soil organic and inorganic particles. No significant
changes in Zn speciation occurred from 9 to 47 months after the contamination. Thermodynamic calculations show that both Zn-LDH and Zn-phyllosilicate may form in the presence of ZnO but that the formation of Zn-phyllosilicate would be thermodynamically favored. Thus, the dominance of Zn-LDH found by spectroscopy suggests that the formation of the Zn precipitates was not solely controlled by thermodynamics but also contained a kinetic component. The rate-limiting step could be the supply of Al and Si from soil minerals to the Zn-rich solutions around dissolving ZnO grains.
  • Environmental Science & Technology 39(2005)17, 6616-6623

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7680
Publ.-Id: 7680


Spektroskopische Untersuchungen zur Wechselwirkung von U(VI) mit Huminsäure unter neutralen pH-Bedingungen

Sachs, S.
Im Vortrag werden Studien zur U(VI)-Komplexierung durch Huminsäuren bei pH 7 vorgestellt. Die Untersuchungen erfolgten mittels konventioneller zeitaufgelöster laser-induzierter Fluoreszenzspektroskopie (TRLFS) sowie mittels Femtosekunden-TRLFS (fs-TRLFS).
Keywords: Humic acid, complexation, uranium, spectroscopy, ternary complexes
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Migration von Actiniden im System Ton, Huminstoff, Aquifer", 04.-05.10.2005, Leipzig, Germany

Permalink: https://www.hzdr.de/publications/Publ-7679
Publ.-Id: 7679


Magnetic-field induced band-structure change in CeBiPt

Kozlova, N.; Hagel, J.; Doerr, M.; Wosnitza, J.; Eckert, D.; Muller, K.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Goll, G.; von Lohneysen, H.; Zwicknagl, G.; Yoshino, T.; Takabatake, T.
We report on a field-induced change of the electronic band structure of CeBiPt as evidenced by electrical-transport measurements in pulsed magnetic fields. Above similar to 25 T, the charge-carrier concentration increases nearly 30% with a concomitant disappearance of the Shubnikov-de Haas signal. These features are intimately related to the Ce 4f electrons since for the non-4f compound LaBiPt the Fermi surface remains unaffected. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surface topology.
  • Physical Review Letters 95(2005), 086403

Downloads:

  • available with HZDR-Login

Permalink: https://www.hzdr.de/publications/Publ-7677
Publ.-Id: 7677


Comparative assessment of coupled RELAP5/PARCS and DYN3D/RELAP5 codes against the Kozloduy-6 pump trip test

Kozmenkov, Y.; Grundmann, U.; Kliem, S.; Rohde, U.
The modeling of complex transients in Nuclear Power Plants (NPP) remains a challenging topic for Best Estimate (BE) three-dimensional coupled code computational tools. Nowadays, this technique is extensively used since it allows decreasing conservatism in the calculation models by performing more realistic simulations based on a more precise consideration of multidimensional effects under complex transients in NPPs. This paper represents a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER-1000 pump trip test. The coupled REALP5/3.3-PARCS/2.6 and DYN3D/3-RELAP5/3.3 code systems are used in simulations. The obtained results are assessed against experimental data and also through the code-to-code comparison.

The DYN3D/RELAP5 computational model of VVER-1000 has been developed and adjusted for simulations with the parallel running scheme (PVM) of RELAP5/PARCS. Also, the macroscopic cross-section library used in the DYN3D/RELAP5 calculations has been adapted to meet the input requirements of PARCS. Prior to the test simulations, the RELAP5/PARCS model of the plant has been assessed in the standalone PARCS and RELAP5 test calculations.
A reasonably good agreement between the experimental data and the calculated results is obtained. For the initial state, the observed discrepancies are mainly due to the absence of ADF correction and the evaluation of the Doppler feedback effect. During the transient, the deviations are mainly due to the combined effect of the measurement uncertainty in the control rod axial position and the estimation of the Doppler effect.
Keywords: Coupled codes, 3D neutron kinetics, code assessment, VVER-1000, plant-measured data, main coolant pump
  • Contribution to proceedings
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-7676
Publ.-Id: 7676


Uncertainty and sensitivity analyses of the Kozloduy pump trip test by coupled RELAP5/PARCS code

Bousbia Salah, A.; Kliem, S.; Rohde, U.
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 simulating and more precise consideration of multidimensional effects under complex transients in NPPs. In the current paper a contribution to the assessment and validation of coupled code technique through the Kolzoduy VVER100 pump trip test is performed. For this purpose, the coupled REALP5/3.3-PARCS/2.6 code is used. The code results were assessed against experimental data and the comparison study shows good agreements between the calculations and the global kinetic and thermal-hydraulic aspects observed experimentally. Further investigations through the uncertainty and sensitivity GRS method, covering kinetic and thermal-hydraulic parameters, have been carried out in order to assess the origin of the observed discrepancies.
Keywords: Coupled Codes, Uncertainty and Sensitivity Analyses, GRS Method
  • Invited lecture (Conferences)
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France
  • Contribution to proceedings
    International Top. Meeting on Mathematics and Computation, Supercomputing, Reactor Physics and Nuclear Applications, 12.-15.09.2005, Avignon, France
    Proceedings

Permalink: https://www.hzdr.de/publications/Publ-7675
Publ.-Id: 7675


EXAFS Investigations of U(IV) species in aqueous solutions with a newly developed spectro-electrochemical cell

Hennig, C.; Tutschku, J.; Palladino, G.; Poineau, F.; Schmeide, K.; Rossberg, A.; Scheinost, A.; Bernhard, G.
Actinides with their large number of oxidation states are susceptible to redox conditions, forming different aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell which allows to study the structure and speciation of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential.
The safety regulations for handling of radioactive materials at the ESRF prohibit any gas release from samples containing radionuclides. Therefore the electrochemical cell is air-tight and the applied reduction process prevents a water decomposition. The electrochemical cell comprises a double confinement. A well-defined anodic reaction is applied by using Ag as anode in equilibrium with hardly soluble AgCl. Formal cathodic potentials Ecs of the U(VI)/U(IV) couple were verified by cyclic voltammetry. The potential Ecs+E was then kept constant for the subsequent reduction process of U(VI) to U(IV).
The coordination of the U(VI) species before reduction and the electrochemically stabilized U(IV) ions in presence of different ligand systems has been studied by U LIII-edge EXAFS spectroscopy. In non-complexing perchloric acid the U(IV) aquo ion was obtained with 9 spherically arranged atoms in a distance of 2.41 Å. In concentrated chloride solutions we observed between 3 to 9 M [Cl] the complexes U(H2O)8Cl3+, U(H2O)6-7Cl22+ and U(H2O)5Cl3+ with U-O distances of 2.41 Å and U-Cl distances of 2.71 Å [1]. In presence of sulfuric acid, the coordination with SO42- seems to change from bidentate with U(VI) to monodentate fashion with U(IV) at low pH. We observed in presence of formic acid tetranuclear U(IV) species with U-U distances of 3.85 Å. Investigations in carbonate solutions are in progress.
[1] C. Hennig, J. Tutschku, A. Rossberg, G. Bernhard, A.C. Scheinost, Comparative EXAFS investigation of U(VI) and U(IV) aquo chloro complexes in solution using a newly developed spectro-electrochemical cell, Inorg. Chem., submitted
  • Contribution to proceedings
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France
  • Poster
    Migration 2005, 10th International Conference on Chemistry and Migration Behaviour of Actinides and Fission Products in the Geosphere, 18.-23.09.2005, Avignon, France

Permalink: https://www.hzdr.de/publications/Publ-7674
Publ.-Id: 7674


Molekulare Wechselwirkungsmechanismen an der Grenzfläche zwischen Geosphäre und Biosphäre

Raff, J.
Detailkenntnisse der mikroskopischen Prozesse an der Grenzfläche zwischen Biosphäre und Geosphäre sind notwendig für das Verständnis des makroskopischen Verhaltens von Schwermetallen und Radionukliden in der Umwelt. Darauf aufbauend erlaubt die Untersuchung komplexer Systeme die Beurteilung der Relevanz der einzelnen Reaktionen unter natürlichen Bedingungen. Die erhaltenen Ergebnisse sind sowohl für die Risikobeurteilung als auch für die Entwicklung innovativer Sanierungs­verfahren von entscheidender Bedeutung. Anhand ver­schiedener Unter­suchungen zur Immobilisierung von Uran durch Bakterien werden existierende Wechselwirkungs­mechanismen aufgezeigt sowie deren Bedeutung und Anwendungspotential diskutiert.
  • Invited lecture (Conferences)
    Plenarvortrag im Rahmen des 4. Jenaer Sanierungskolloquiums, 29.-30.09.2005, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-7673
Publ.-Id: 7673


Modification of temperature and solute distribution during directional solidification caused by electromagnetically-driven convection

Willers, B.; Eckert, S.; Nikrityuk, P. A.; Eckert, K.
The application of time varying magnetic fields can be considered as an effective tool to organize a well-defined flow structure in the liquid phase affecting the nucleation and solidification parameters. Once a flow occurs in the liquid melt during solidification, nucleation and grain growth are mainly governed by the convective transport of heat and solute. The consequences on the structure of solidified ingots are widely discussed in the literature. So it is known, that the application of mechanical or electromagnetic stirring promotes the formation of fine, equiaxed grains [1-4].
Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Pb Sn alloys from a water cooled copper chill. A rotating magnetic field (RMF) was applied for melt agitation. Thermocouples were used to measure the temperature field during solidification. Profiles of the velocity in the liquid phase were determined by means of Ultrasound Doppler velocimetry (UDV) [5].
Numerical simulations are based on the classical mixture formulation [6]. To calculate the viscosity in the mushy region the model proposed by Roplekar and Dantzig [7] was implemented into the code. The amplitude of the electric currents induced by the RMF are altered if the electrical conductivity of the growing solid phase deviates from that of the liquid phase. Previous investigations [8] showed that for such a situation numerical predictions of the velocity field using a stationary Lorentz force term become questionable. For our calculations presented here the Lorentz force term has been recalculated for each time step.
The comparison between numerical simulations and solidification experiments delivered a good agreement. Due to the permanent changes both of the aspect ratio of the fluid volume and the material properties during solidification the flow field shows a transient behaviour being more complex as known from the stationary, isothermal case. Our results disclose that the forced convection causes distinct modifications of the temperature and concentration field. The electromagnetic stirring promotes the columnar-to-equiaxed transition and causes a considerable grain refinement. Modifications of the grain structure and effects of macrosegregation are discussed with respect to the details of the flow field.

[1] D.B. Spencer, R. Mehrabian, M.C. Flemings (1972), Met. Trans. 3, 1925-1932
[2] W.C. Johnston, G.R. Kofler, S. O?Hara, H.V. Ashcom, W.A. Tiller (1965), Trans. Met. Soc. AIME 233, 1856-1860
[3] W.D. Griffiths, D.G. McCartney (1996), Mater. Sci. Eng. A 216, 47-60
[4] B. Willers, S. Eckert, U. Michel, I. Haase, G. Zouhar (2005), Mater. Sci. Eng. A, article in press
[5] S. Eckert, B. Willers, G. Gerbeth (2005), Met. Mat. Trans. 36A, 267-270
[6] W.D. Bennon and F.P. Incropera (1987), Int. J. Heat Mass Trans. 30, 2161-2170
[7] J.K. Roplekar, J.A. Dantzig (2001), Int. J. Cast Metals Research 14, 79-98
[8] S. Eckert, B. Willers, P.A. Nikritjuk, K. Eckert, U. Michel, G. Zouhar (2005), International Conference on Advanced Solidification Processes, Stockholm, Sweden
Keywords: solidification, PbSn alloys, forced convection, rotating magnetic field
  • Contribution to proceedings
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 28.05.-02.06.06, Opio, France
  • Lecture (Conference)
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 28.05.-02.06.2006, Opio, France

Permalink: https://www.hzdr.de/publications/Publ-7672
Publ.-Id: 7672


Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187] [188] [189] [190] [191] [192] [193] [194] [195] [196] [197] [198] [199] [200] [201] [202] [203] [204] [205] [206] [207] [208] [209] [210] [211] [212] [213] [214] [215] [216] [217] [218] [219] [220] [221] [222] [223] [224] [225] [226] [227] [228] [229] [230] [231] [232] [233] [234] [235] [236] [237] [238] [239] [240] [241] [242] [243] [244] [245] [246] [247] [248] [249] [250] [251] [252] [253] [254] [255] [256] [257] [258] [259] [260] [261] [262] [263] [264] [265] [266] [267] [268] [269] [270] [271] [272] [273] [274] [275] [276] [277]