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Nuclear Safety Research

BIENNIAL SCIENTIFIC REPORT 2007-2008 I Volume 3

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FZD Biennial Scientific Report 2007-2008 I Volume 3Volume 1 Advanced Materials ResearchVolume 2 Cancer ResearchVolume 3 Nuclear Safety Research

Published by Forschungszentrum Dresden-RossendorfConcept and editorial work Dr. Christine Bohnet & Anja Bartho, FZDDesign and layout WA Preußel, CoswigPhotos FZD employeesAvailable from Forschungszentrum Dresden-Rossendorf

Public RelationsBautzner Landstr. 40001328 Dresden / GermanyPhone: +49 351 260 2450Email: [email protected]://www.fzd.de

ISSN 1437-322XWissenschaftlich-Technische BerichteFZD-509, March 2009

Copying is welcomed, provided the source is quoted.

In addition to the Biennial Scientific Reports, the Annual Online Report of the FZD, withresearch and other highlights of the past year, is available under: www.fzd.de/online-report

Cover picture: FZD scientist Jan Schuhknecht working inthe radionulide lab of the Institute of Safety Research. Photo: Rainer Weisflog

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PREFACE …………………………………………………………… 2

FOCUS ……………………………………………………………… 4

FACILITIES FOR EUROPE

TOPFLOW Facility:Looking through impenetrable walls ……………......…………… 6

The Rossendorf Beamline (ROBL)Selenium-79 – a radionuclide highly mobile in the environment? ……………………………....................…… 8

RESEARCH

Fast neutrons for transmutation of nuclear waste ………….…… 12

Counter-current flow limitation experiments at the TOPFLOW test facility ………………............................… 15

Ultra high speed electron beam X-ray tomography for two-phase flows ………...............................................…..… 18

Advanced measuring techniques for liquid metal flows in fast neutron nuclear reactors ……....................................…... 20

Flux dependence of defect cluster formation in neutron irradiated weld material …………...............…….…… 22

Analytical neutron transport solution for a pulsed subcritical transmutation system …………....….........… 24

THEREDA - Thermodynamic Reference Database for nuclear waste disposal in Germany ……….…................…… 26

Colloidal carbon nanotubes and their influence on dissolved uranium ………….........……................... 28

Interaction of actinides with isolated bacterial cell wall components ……............................................ 30

Humic substances and their influence on the mobility of actinides in clay formations ...................................… 32

Mobilization of actinides through bioligands secreted by microbes ……………...........................… 34

FACTS & FIGURES ………………………………........…………… 37

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Preface

The mission of the Forschungszentrum Dresden-Rossendorf (FZD) is excellence in long-termresearch in socially important issues like energy, health, and advanced material technologies. Instrategic collaborations with partners from research and industry the FZD contributes to solve majorchallenges of modern society. Scientific work at the research center focuses on three questions:

◆ How does matter behave in strong fields and at small dimensions?◆ How can cancerous tumors be identified in the early stages and treated effectively?◆ How can the public and the environment be protected from technical risks?

Corresponding to these questions, the Forschungszentrum Dresden-Rossendorf pursues the three program topics “Advanced Materials Research”, “Cancer Research”, and “Nuclear SafetyResearch”. This Biennial Scientific Report highlights the scientific achievements of the “NuclearSafety Research” program, covering the years 2007 and 2008. The first part introduces the overallfocus of the program as well as the large-scale facilities that are used for research, and the secondpart consists of eleven articles highlighting research projects that were conducted by scientists of the following institutes:

◆ Safety Research◆ Radiochemistry◆ Radiation Physics

In 2007, the FZD was evaluated by the German Council of Science and Humanities (Wissenschafts-rat). In its final evaluation report, published in July 2008, the Council unanimously recommendedthat the FZD – a Leibniz institution – should become a member of the Helmholtz Association. Thereport emphasizes: “Since the last evaluation by the German Council of Science and Humanities, the FZD has continuously worked on long-term and highly complex research topics, thus expandingits scientific profile towards a major research center. This top-level research on a strategic and long-term basis in politically and socially important issues suggests an increased financial commitment ofthe Federal Republic of Germany.”

To highlight a few noteworthy events in 2007 and 2008, one must mention the magneto-hydrodynamic (MHD) project of the FZD, which forms a major part of the Collaborative ResearchCenter (SFB) 609 “Electromagnetic flow control in metallurgy, crystal growth, and electrochemistry”.The German Science Foundation (DFG) decided in autumn 2008 to prolong the funding for anotherfour years. Moreover, Dr. Frank Stefani, member of the MHD group, and Prof. Günther Rüdiger(Astrophysikalisches Institut Potsdam, AIP) earned the highly prestigious ”Society needs Science2008“ award of the “Stifterverband für die deutsche Wissenschaft” for the first experimentaldemonstration of the magneto-rotational instability. The PROMISE experiment (Potsdam Rossen-dorf Magnetic InStability Experiment) was conducted in close collaboration between FZD and AIP.

A new focus at the Institute of Radiochemistry, which has been conducting research on actinides,like uranium, for many years, is the interaction of actinides with the bio-system on the cell or evenmolecular level. Because of the Institute’s unique position for uranium and transuranium chemistryin biological systems in Germany, it is a valued partner institution in almost all related research

Roland SauerbreyScientific Director

PREFACE

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projects in Europe. Within the EU program ACTINET - “Network of Excellence for ActinideSciences”, for example, the radiochemistry station of the Rossendorf Beamline at the ESRF inGrenoble provides about one-third of its beam-time to mainly young researchers allowing them to gain hands-on experience as part of their training.

Research on transmutation is a newly established issue of the Institutes of Safety Research andRadiation Physics. The neutron source needed for the experiments was commissioned towards the end of 2007. The orientation towards research on the safety of Generation IV reactors and of transmutation facilities is a common aim of the FZD Institutes of Radiation Physics and SafetyResearch, together with the Institute for Energy Management, and for Nuclear and Particle Physics,of the Technische Universität Dresden.

To strengthen the international visibility of the FZD in the scientific community, the FZD served as the local organizer of the IEEE Meetings “Medical Imaging Conference (MIC)” and “NuclearScience Symposium (NSS)”. The 2008 IEEE-NSS-MIC Conference took place in Dresden fromOctober 19 to 25, and scientists of the Nuclear Safety Research program were actively engaged in it. Just to give one example, Dr. Uwe Hampel presented the world record for ultra high-speedelectron beam X-ray tomography. It is noteable that his conference paper received the highestranking by the responsible MIC committee. All in all, the Dresden IEEE Conference attracted morethan 2,700 participants, thus being the largest IEEE-NSS-MIC Conference ever. We are very gratefulto the German Science Foundation (DFG) and the Saxon State Ministry of Higher Education,Research and the Arts (SMWK) for their essential contributions of funding for the Conference.

The success of a research institution strongly depends on the motivation and dedication of talentedyoung scientists. The FZD has put a lot of effort into attracting junior scientists from Germany andabroad. Our six institutes strive for excellent working conditions and support of their staff, the FZDas a whole offers Ph.D. seminars to about 120 doctoral students, a tenure track program for out-standing postdoctoral staff, special workshops for young scientists such as communication to themedia, presentation in English, training for young science managers, etc. The FZD supports high-level training as well for its technical staff and its almost 60 trainees. In 2008, the FZD received the“Audit Beruf und Familie” (Career and Family Certificate) from the Hertie Foundation, underliningthe particular importance attached to the healthy balance of family and career at the FZD.

Finally, this preface gives me the opportunity to thank our funding institutions, the Saxon StateMinistry of Higher Education, Research and the Arts (SMWK) and the Federal Ministry of Educationand Research (BMBF), for their continued support, our national and international scientific coop-eration partners for many successful joint research endeavors, and the entire staff of the FZD fortheir dedicated work.

Prof. Dr. Roland Sauerbrey

Nuclear Safety Research program at the Forschungszentrum Dresden-Rossendorf

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Frank-Peter Weiss, Gert Bernhard, Thomas E. Cowan

This program is focused on the protectionof the public and the environment againstindustrial hazards. For this purpose, ourresearch mainly aims at assessing andenhancing the safety, efficiency, and sus-tainability of nuclear reactors of currentand future designs as well as of thegeological disposal of radioactive waste. It is the particular goal to evaluate andminimize the risks related to the nuclearfuel cycle. This includes the relics of formeruranium mining, power generation in

nuclear reactors, as well as the reductionand the final geological disposal ofradioactive waste. Many of the scientificmethods and tools used in nuclear engin-eering are also successfully adapted tonon-nuclear fields, for example to optimizeindustrial processes by customized flowcontrol.

The Nuclear Safety Research program isimplemented by the Institute of Radio-chemistry, the Institute of RadiationPhysics, and the Institute of SafetyResearch. It includes research in the fieldsof radioecology, reactor safety, neutron

physics, and thermal fluid dynamics.Whereas radioecology focuses on theidentification of the chemical interactionand the mobility of radionuclides,especially of actinides, in the geo- and the bio-spheres, our research in neutronphysics aims at improved measurement ofthe neutron-induced transmutation ofradionuclides in order to minimize long-lived radioactive waste. The reactor safetyresearch is directed towards the develop-ment of physical simulation tools used fornuclear reactor accident analysis and thedescription of ageing phenomena inirradiated reactor construction materials.

Complementing this, in our research on thermal fluid dynamics we study transient multi-phase flows and magneto-hydrodynamic (MHD) phenomena to provide the basis foradvanced process simulation. The development and validation of tools for processsimulation, accident analysis, and long-term safety assessment of the disposal of radio-active waste, with the emphasis on thermo and fluid dynamic computation methods,constitute the framework for our research.

The Nuclear Safety Research program is supported by large-scale experimental userfacilities operated by the FZD such as the Radiation Source ELBE, the Rossendorf Beamline ROBL at the ESRF in Grenoble, and the Transient Two-Phase Flow Test Facility(TOPFLOW). In addition, close collaborations exist with the other research programs ofthe FZD, which are devoted to Cancer Research and Advanced Materials Research.Within the framework of the latter the MHD group deals with the optimization of flowsin crystal growth and metallurgy. Further collaborations are related for example to thedevelopment of biological metal templates with modified magnetic properties for theDresden High Magnetic Field Laboratory (HLD). In the fields of irradiation-inducedmaterials and ageing and surface layer characterization, we benefit considerably from the expertise at the Institute of Ion Beam Physics and Materials Research. Moreover, wecontribute to the development of new macromolecules for nuclear medicine by ourcompetence in laser spectroscopy.

The reactor safety and radioecology research is integrated in the German Alliances forCompetence in Nuclear Technology (Kompetenzverbund Kerntechnik), and forCompetence in Radiation Research (Kompetenzverbund Strahlenforschung).

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FOCUS

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Uwe Hampel, Dirk Lucas, Helmar Carl

The multi-purpose thermal hydraulic testfacility TOPFLOW (Transient Two-PhaseFlow Test Facility) is one of the majorresearch facilities at the FZD, and isdesigned for studying thermal hydraulicphenomena of steam-water two-phaseflows at high pressures and temperatures(Fig. 1). It is devoted to basic and appliedresearch on two-phase flow phenomena,which play a key role in many industrialprocesses such as in nuclear power plants,chemical reactors, and oil processing [1].TOPFLOW, with its maximum steampower generation capacity of 4 MW,allows performing steam-water two-phase

flow experiments at industrially relevantpressures of up to 7 MPa and saturationtemperatures of 286 °C. Current projectsfocus on computational fluid dynamics(CFD) code validation for two-phase flows,experimental investigation of nuclearreactor safety issues such as pressurizedthermal shock scenarios, and test of in-dustrial plant components like valves andnozzles. TOPFLOW is the reference testfacility of the German Alliance for CFD in nuclear reactor safety.

One of the distinctive features of theTOPFLOW facility is the availability of ad-vanced two-phase flow instrumentation. Akey instrument is the wire mesh sensor [2],

which was developed at the FZD and hasbecome an important two-phase flowmeasurement tool at TOPFLOW and inmany other facilities worldwide. The sensor(Fig. 3) allows visualization of the flowstructure of complex two-phase flows withhigh spatial (2 mm) and temporal reso-lution (up to 10,000 images per second).Recently, a new technique called ultra fastelectron beam X-ray tomography has beeninstalled at TOPFLOW which allows non-invasive flow measurement with similarperformance. Such advanced measure-ment technology combined with standardindustrial and scientific flow instrumen-tation, for example high speed and IRcameras, needle probes for void and flow

TOPFLOW Facility:Looking through impenetrable walls

Facilities for Europe

Fig. 1: TOPFLOW – scheme of the test facility.


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temperature measurement, and gammaray densitometry, allow the study of flowphenomena with unprecedented disclosureof flow details, such as phase and inter-facial area distribution.

Another unique feature of TOPFLOW is a large pressure chamber (Fig. 2) whichserves as a pressurized laboratory forexperiments in complex flow domaingeometries. The latter allows operating

thermal hydraulic test rigs of up to 7 mlength and 2 m height in pressureequilibrium which enables optical andinfrared flow observation through thinwalls or glass windows.

Currently, the TOPFLOW facility is used inthe framework of three major projects. Thefirst of them is devoted to CFD validationand model development for applications innuclear reactor safety [3]. It is funded bythe German Federal Ministry of Industry(BMWi). In the second project, PressurizedThermal Shock (PTS) phenomena arestudied in detail, as they represent a crucialreactor safety issue for aged reactor pres-sure vessels during emergency core coolingin a loss-of-coolant scenario. The project isa collaboration of seven industrial andscientific partners: Commissariat à l’EnergieAtomique (CEA) France, Electricité deFrance (EdF), AREVA NP France, Institut deRadioprotection et de Sûreté Nucléaire(IRSN) France, Paul Scherrer Institute (PSI)Switzerland, ETH Zürich, Switzerland, andFZD. The third project, which is conductedin cooperation with Nederlandse AradolinieMaatschappij B. V. (NAM) Netherlands,aims at the investigation of critical flowconditions in a steam nozzle.

Beyond these projects, there are an addi-tional 8 institutions worldwide which makeuse of TOPFLOW experimental data in theframework of bilateral collaborations.

References[1] Gas/liquid flow in large risers,

N.K. Omebere-Iyari, B.J. Azzopardi, D. Lucas, M. Beyer, H.-M. Prasser, International Journal of Multi-Phase Flow 34, 461 – 476 (2008)

[2 Evolution of the structure of a gas-liquid two-phase flow in a large vertical pipe, H.-M. Prasser, M. Beyer, H. Carl, S. Gregor, D. Lucas, H. Pietruske, P. Schütz, F.-P. Weiss, Nuclear Engineer-ing and Design 237, 1848 – 1861 (2007)

[3] Gas-liquid flow around an obstacle in a vertical pipe, H.-M. Prasser, M. Beyer, T. Frank, S. Al Issa, H. Carl, H. Pietruske, P. Schütz, Nuclear Engineer-ing and Design 238, 1802 – 1819 (2008)

Project partners· Commissariat à l’Energie Atomique, France· Electricité de France, France· Institut de Radioprotection et de Sûreté Nucléaire, France

· AREVA NP, France· Paul Scherrer Institute, Switzerland· ETH Zürich, Switzerland· Nederlandse Aradolinie Maatschappij B. V., Netherlands

· Université Catholique de Louvain, Belgium· Computational Dynamics Limited, UK· University of Nottingham, School of Chemical, Environmental and Mining Engineering, UK

· Norwegian University of Science and Technology, Trondheim, Norway

· Idaho National Lab, USA· Rensselaer Polytechnic Institute, USA· Gadjah Mada University, Yogyakarta,Indonesia

· Royal Melbourne Institute of Technology, Australia

Fig. 3: The evolution of upwardsteam-water two-phase pipe flow in vertical pipes is currently a majorsubject of study at TOPFLOW. Avariable gas injection unit allowsfeeding in steam bubbles into thepipe at different heights (left). Thesteam distribution within the flow is measured using a high-pressure,high-temperature wire mesh sensor(centre). The sensor delivers gasfraction distribution data with highspatial and temporal resolution. The right image shows an axial sliceof the flow with gas bubblesautomatically detected and labelledby 3D image processing algorithms.

Fig. 2: TOPFLOW pressurized vessel for the opera-tion of test sections and components in pressureequilibrium with the vessel atmosphere. Thistechnology allows the application of optical and IRmeasurement techniques at pressures up to 50 bars.

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Andreas C. Scheinost

The Rossendorf Beamline (ROBL) at theEuropean Synchrotron Radiation Facility(ESRF) in Grenoble, France, offers theunique opportunity to investigate thechemical state of radionuclides at very lowconcentrations (down to a few parts permillion). The beamline is therefore ideallysuited for fundamental research requiredto assess the safe disposal of nuclearwaste, which is one of the great challengesof society in the 21st century.

Current deep-geological disposal conceptsare considered to be highly efficient inretaining cationic (positively charged)radionuclide species, which include fissionproducts like cesium and strontium, as wellas soluble actinide species. Anionic (nega-tively charged) radionuclide species,

however, may pass through these barrierseasily since anion adsorbing mineral sur-faces (mostly Fe(III) oxides) are scarce inthe oxygen-depleted conditions of deepgeological formations. Especially theradioisotope selenium-79 is of highconcern because, firstly, it forms solubleanionic species at three of its fouroxidation states (-II, IV and VI), and,secondly, it has a very long half-life of one million years. Consequently, severalnational risk assessment reports havepredicted that selenium-79 will dominatethe radioactive dose released from nuclearwaste repositories into the biosphere forone million years into the future afterclosure.

Yet selenium may not only occur as solubleanions, but also as elemental Se and metalselenides (Se oxidation states 0 and -II),

solids with extremely low solubility. IfSe(IV) or Se(VI) were reduced to theselower oxidation states, then these insolublesolids may precipitate out of solution,thereby preventing selenium migration. Infact, anoxic waste repositories are rich inFe(0) and Fe(II)-containing surfaces, whichcould promote selenium reduction by acoupled redox reaction (Se is reduced, Fe is oxidized). Although this process ispredicted to proceed based on thermo-dynamics, it may be prevented by slowreduction kinetics. Earlier attempts to investigate the reduction processexperimentally were hampered by thedifficulty to maintain strictly anoxicconditions during sample preparation and the selenium speciation steps, whichcommonly have to be performed at variouslab facilities, as well as by the slow redoxkinetics.

The Rossendorf Beamline (ROBL)Selenium-79 – a radionuclide highly mobile in the environment?

Fig. 1: Reduction of aqueous SeIV at the surface of Fe0 and FeII nanoparticles and formation of Se0 and Se-II nanoparticles.


A recent collaboration between the FrenchNational Center for Scientific Research(CNRS), the universities of Grenoble,Bordeaux and Le Mans in France, Umea in Sweden and the FZD, supported byACTINET – European Network ofExcellence, has now finally brought amajor breakthrough by bringing togetheran array of techniques, including X-rayAbsorption Spectroscopy (XAS) at theRossendorf Beamline of the ESRF, High-Energy X-ray Scattering (HEXS) at the ESRF Beamline ID-15B, cryogenic X-rayPhotoSpectroscopy (XPS) at the Universityof Umea (Sweden), Moessbauer spectro-scopy at the University of Maine (France),and by ensuring an oxygen-free transportchain from the anoxic glove box at theUniversity of Grenoble to the spectroscopyfacilities.

The selenite reduction mechanisms wereinvestigated in a range of iron(II) systemsrepresenting the different barriers in atypical nuclear waste repository: (1) nano-particulate zerovalent iron, green rust, and

magnetite which occur at the surface ofcorroding steel containers for spent nuclearfuel; (2) the clay mineral montmorillonitewith adsorbed or structural Fe(II) whichoccurs in the bentonite backfill surroundingthe waste containers; (3) mackinawite,siderite, and magnetite which are typicalFe(II)-minerals ubiquitous in geologicalbedrock and aquifer sediments.

X-ray Absorption Near-Edge Structure(XANES) spectroscopy was used to followthe redox state of selenium over time. Incontrast to the otherwise slow reductionkinetics of selenium, selenite reduction wascompleted within 24 hours (sometimeswithin 10 to 30 min) in the presence ofnanoparticulate zero-valent iron, mag-netite, green rust, and mackinawite (Fig. 1), in line with a fast electron transferrate at the surfaces of these metallic orsemiconducting solids. In contrast, thelarge band-gap of the Fe(II)-carbonatesiderite and of Fe(II)-montmorilloniteresulted in much slower reaction kinetics,where even after reaction times of 1 to 2

months only partial selenite reduction wasobtained.

In the Fe(II)-montmorillonite system, wewere able to follow the oxidation state ofFe by using Fe-57 Moessbauer spectro-scopy (Fig. 2). Even before adding theredox partner Se, 1/4 of Fe(II) was rapidlyoxidized within a few minutes. In contrast,Se reduction was slow, with only 3/4completed within one month. No furtherFe(II) oxidation was observed during thistime, suggesting that the iron oxidationand selenium reduction reactions are notdirectly coupled. By combining surfacecomplexation modeling, Density Func-tional Theory (DFT) quantum chemicalcalculations and thermodynamics, acomplex reaction scheme was elucidated,where Fe2+ forms an activated surfacecomplex, followed by oxidation of iron and formation of hydrogen from water.This hydrogen species remains sorbed tothe montmorillonite surface and is thenlater available for Se(IV) reduction.

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Fig. 2: Kinetically decoupled redox reaction between aqueous SeIV and FeII sorbed to edge sites of a layered alumino-silicate, montmorillonite.

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Using Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy, weidentified a range of amorphous andnanoparticulate reduced Se phases,including red (amorphous) and gray(triclinic) elemental Se, and FeII selenidephases similar to tetragonal FeSe andFe7Se8. The Fe(II) selenides formed at thesurface of magnetite, green rust, andmackinawite, i.e. during rapid Se reduc-tion, while elemental Se formed onlyduring slow Se reduction. This differencecould be explained by the concentration ofa reduced intermediate species, aqueousHSe-, which favors formation of FeII

selenides.

Now what about the effect of seleniumreduction on selenium concentration insolution? Elemental selenium and iron(II)selenides have an extremely low solubility(in the order of 10-9 M). If particle sizes

reach the lower nanometer range,however, surface tension may drasticallygrow, thereby increasing solubility byseveral orders of magnitude in comparisonto larger crystals. This effect was notobserved in our experiments. WheneverSe(IV) was completely reduced, Se concen-tration dropped below the detection limit(about 10-8 M) close to the values of bulkminerals.

This low solubility is already an importantrequirement to keep selenium transport bygroundwater in aquifers small. Given theappropriate physico-chemical conditions(low ionic strength and a pH far apart fromthe point of zero charge of the particles),selenium nanoparticles may form stablecolloidal suspensions which are thentransported through the pore space ofaquifers with a speed even faster than thatof a conservative (non-sorbing) solute.

Our investigations showed, however, notendency of the nanoparticles to detachfrom the surfaces and to form mobilecolloids.

Our research suggests that radioactiveselenium will be retained by the steelcontainers constituting the first confine-ment for nuclear waste, even if thesecontainers are corroding. The clay backfillsurrounding the containers, as well as theFeII minerals naturally occurring in aquifersediments, provide further protection ofthe biosphere from radioactive selenium-79. In conclusion, our study shows for the first time that the risk associated withselenium-79 may be much smaller thanpreviously assumed, providing an im-portant step towards the safe disposal of nuclear waste.

References[1] Electron transfer at the mineral/water

interface: Selenium reduction by ferrous iron sorbed on clay, L. Charlet, A.C. Scheinost, C. Tournassat, J.M. Greneche, A. Géhin, A. Fernández-Martínez, S. Coudert, D. Tisserand, J. Brendle, Geochimica et Cosmochimica Acta 71(23), 5731 – 5749 (2007)

[2] Selenite reduction by mackinawite, mag-netite and siderite: XAS characterization of nanosized redox products, A.C. Schein-ost, L. Charlet, Environmental Science & Technology 42, 1984 – 1989 (2008)

[3] X-ray absorption and photoelectron spectroscopy investigation of selenite reduction by FeII-bearing minerals,

A.C. Scheinost, R. Kirsch, D. Banerjee, A. Fernandez-Martinez, H. Zaenker, H. Funke, L. Charlet, Journal of Contamin-ant Hydrology 102, 228 – 245 (2008)

[4] Immobilization of selenite on Fe3O4 and Fe/FeC3 ultrasmall particles, R.L.d.A. Loyo, S.I. Nikitenko, A.C. Scheinost, M. Simonoff, Environmental Science & Technology 42(7), 2451 – 2456 (2008)

[5] Synthesis of a Se0/calcite composite using hydrothermal carbonation of Ca(OH)2 coupled to a complex seleno-cystine fragmentation, G. Montes-Hernandez, A. Fernández-Martínez, L. Charlet, F. Renard, A.C. Scheinost, M. Bueno, Crystal Growth & Design 8(7), 2497 – 2504 (2008)

Project partners· Laboratoire de Géophysique Interne et Tectonophysique, Université Joseph Fourier, Grenoble, France

· Centre Nationale de la Recherche Scientifique, Gradignan, France

· Chimie Nucléaire Analytique et Bioenviron-nementale, Université de Bordeaux, Gradignan, France

· Laboratoire de Physique de l’Etat Condensé, Université de Maine, Le Mans, France

· Department of Chemistry, Environmental and Biogeochemistry, Umeå University, Umeå, Sweden


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RESEARCH INSTITUTE OF RADIATION PHYSICS

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Arnd R. Junghans

The partitioning of nuclear waste andtransmutation of long-lived isotopes tonuclides with shorter lifetime is animportant topic in international research to provide sustainable sources of energywhich are free of greenhouse gasemissions (see Fig. 1). Different designsinvolving critical reactors or sub-criticalaccelerator-driven systems (ADS) are beingstudied in view of their transmutationcapabilities, as well as new concepts toproduce less waste via very high burn-up.The Generation IV International Forum(GIF) has selected six nuclear energy

systems for which research and develop-ment are ongoing to confirm their viabilityand to demonstrate their expected per-formance that includes the objective ofproducing less waste.

In the considerations for waste reduction,the possible use of fast (i.e. un-moderated)neutrons coming directly from the fissionprocess is of great importance as most ofthe proposed systems use a fast neutronspectrum. Reliable predictions of therelevant physical processes, and theoptimization of the related facilities,depend on the availability of high-qualitynuclear data. The data needs have been

investigated by the working party onevaluation co-operation (WPEC) of theOECD Nuclear Energy Agency. Twoimportant research fields were identified tobe the inelastic scattering of fast neutronson structure materials in reactors andtransmutation devices, and the neutron-induced fission process of minor actinidenuclei.

The EURATOM framework programscontinue to foster European research in thefield of nuclear transmutation: The neutrontime-of-flight facility nELBE at the For-schungszentrum Dresden-Rossendorf ispart of the Integrated InfrastructureInitiative (I3) entitled “European Facilitiesfor Nuclear Data Measurements”(EFNUDAT), which has been created by a consortium of 10 experimental facilitiesin 7 European countries for nuclear datameasurements. Joint Research Activities(JRA) within this I3 include the dataacquisition using fast digitizers, qualityassurance of nuclear data, and thedevelopment of neutron producing targettechnology.

Photoproduction of neutrons at ELBEELBE is the first superconducting electronlinear accelerator combined with a neutrontime-of-flight facility. Time-of-flightmeasurements take advantage of a highpulse repetition rate of 100kHz to 500kHz.This is nearly a factor of 1000 higher thanthe pulsed operation at normal-conductingaccelerators. The instantaneous neutronand photon flux is lower, which can lead toimproved background conditions from thescattered photon flash.

The nELBE neutron time-of-flight facility is now operational for experiments at theELBE superconducting linear accelerator.

Fast neutrons for transmutation of nuclear wasteResearch

Fig 1: Evolution in time of the radiotoxicity of the waste from a conventional uranium reactor and itscomponents. This graph was prepared by the Nuclear Energy Agency (NEA), a specialized agency withinthe Organization for Economic Co-operation and Development (OECD). This plot includes effectsresulting from a possible incorporation of waste components decaying by α-decay or fission. Theradiotoxicity of plutonium and other (minor) actinides decay to the natural level of the uranium ore onlyafter 10 to 100 thousand years, and thus their removal by transmutation is especially important.Source: Physics and Safety of Transmutation Systems – A Status Report, p. 9, OECD 2006

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Fast neutrons in the energy range from~ 0.1 to 10 MeV are produced by thepulsed electron beam from ELBE impingingon a liquid lead circuit as a radiator. InFig. 2, the experimental neutron energyspectrum at nELBE is shown in comparisonwith a neutron spectrum typical of the

neutron induced fission of 235U. Theenergy spectrum measured at nELBE has avery similar shape as the fission spectrumfrom fast neutrons, demonstrating that theenergy range relevant for reactions withfast neutrons in reactor and transmutationsystems can be investigated. The short

beam pulses of ~10 ps provide the basisfor an excellent time resolution for neutrontime-of-flight experiments, giving anenergy resolution of about < 1% at 1MeVwith a short flight path of ~6.5 m. A neutron source strength of ~5 x 1010

neutrons per second has been reached,resulting in a neutron intensity on target of~3 x 104n/(cm2s) using an electron bunchcharge of 77pC at 100kHz pulse repetitionrate.

The neutron flux – which determines thestatistical accuracy of a cross sectionmeasurement carried out in a given time –depends on the primary beam intensityand on the amount of converter targetmaterial exposed to the beam in theneutron source. A liquid lead circuit is usedto cope with the very high beam powerdeposition (P ≈ 5 kW/g) and to allowefficient cooling. It was designed and builtin a collaborative effort of the FZDinstitutes of Radiation Physics and ofSafety Research [1]. The liquid lead circuithas been operated for more than 800hours without any significant failures.

Experimental setup at nELBEIn two experiments, the inelastic neutronscattering of 56Fe and the total neutroncross section σtot of 181Ta have beenmeasured. The total neutron cross sectionhas been determined in a transmissionexperiment in the energy range from300 keV to 8 MeV. Between 800 keV and1600 keV only very sparse data existed uptill now. The energy resolution obtained atnELBE was 0.7% at 2 MeV neutronenergy. The relative statistical error in thecross section was about 2% after 33h ofbeam time.

The time-of-flight, and thus the neutronenergy, is determined with plasticscintillators with a low detection threshold,as shown in Fig. 3. Measurements with a235U fission chamber from the Physikalisch-Technische Bundesanstalt (PTB)Braunschweig allowed to determine theabsolute neutron intensity of the beam. By comparison of data with and without a Cd-shield, an upper limit for the relativethermal neutron flux of less than 8x10-5

was determined.

Rossendorf Beamline


Advanced Materials Research

Cancer R

esearch

TOPFLOW-FacilityHigh Magnetic Field Lab.

PET-Center

Ion Beam Center

Radiation Source ELBE

Fig 2: Neutron energy spectrum measured at nELBE (red curve) using a 235U fission chamber, anelectron beam energy of 25 MeV and a 652 cm neutron flight path. The peaks on the low energy sideof the spectrum are due to the fine structure of the dipole strength distribution in the isotopes of theneutron radiator. The blue curve is a neutron spectrum from the fission of 235-U induced by fastneutrons with En = 10 MeV, taken from the evaluated nuclear data file ENDF/B-VII.0 (scaled to themeasured data).

Fig. 3: The inelastic neutron scattering experiment from downstream direction. The neutron beamtravels through the Barium-Fluoride (BaF2) detector array in the middle of the picture and passes the235U fission chamber from Physikalisch-Technische Bundesanstalt (PTB) on the right side, to be stoppedin a beam dump. The target is located at the center of the BaF2 array, for example a sample of 56Fe,from which neutrons are scattered. Neutrons are detected by plastic scintillation counters on the leftside (yellow). The simultaneously emitted photons are measured in the BaF2 array.

RESEARCH INSTITUTE OF RADIATION PHYSICS

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Inelastic neutron scattering is beinginvestigated using a compact 4π-array ofBaF2 scintillators which consist of up to 42 hexagonally shaped crystals (19 cmlong by 53 mm diameter, see Fig. 3). By adouble time-of-flight measurement, theenergy of the incoming neutron and of thescattered neutron can be determined. Thescattered neutrons are detected by an

array of 5 plastic scintillators (100 cm longby 4.2 cm wide by 1.1 cm thick). By usingthe photon and neutron detectors incoincidence, inelastic neutron scatteringcan be identified. Both detector typesreach time resolutions below 1 ns, and arethus well suited for a proper time-of-flighttagging. Fig. 4 shows the coincident(incident and scattered) neutron spectrum

from the double time-of-flight measure-ment, in which scattering from the 1st and2nd excited state can be separated. Theexperiment also allows to measure theangular distribution of the scatteredneutrons.

OutlookThe experimental program to measureinelastic neutron scattering and totalneutron cross sections in the fast neutronrange from 0.1 to 10 MeV has begun atnELBE. Structural materials that arerelevant for nuclear transmutation systemsare being investigated currently.With the higher intensity available with thesuperconducting radiofrequency (SRF)injector of ELBE, neutron induced fissioncross section of actinides can be investi-gated. Minor actinides will be analyzed in afission ionization chamber prepared withthin films of the radioactive target material.The radiochemical requirements arestringent: isotopically pure material needsto be used to create homogeneous thinfilms, with an areal density of typically100 mg/cm2, to be able to register thefission fragments with good signal to noiseratio. The sample and target preparationfor minor actinides is being conducted aspart of the joint research activities of theEFNUDAT project as well.

Reference[1 ]A photo-neutron source for time-of-

flight measurements at the radiation source ELBE, E. Altstadt, C. Beckert, H. Freiesleben, V. Galindo, E. Grosse, A.R. Junghans, J. Klug, B. Naumann, S. Schneider, R. Schlenk, A. Wagner, F.-P. Weiss, Annals of Nuclear Energy 34, 36 (2007)

Project partner· Physikalisch-Technische Bundesanstalt (PTB) Braunschweig, Germany

Fig. 4: Double time-of-flight measurement of the incoming neutron and the scattered neutronfrom a natFe target. The lines indicate the region where, within the given energy resolution, the1st up to the 4th excited state of 56Fe should be located.

Fig. 5: The nELBE photo-neutron source together with the final section of the electron beam line. Theelectron beam focused by quadrupole magnets (painted blue) hits the liquid lead inside a cylindrical vacuumchamber, where high-intensity neutron pulses are produced. Afterwards, the beam is stopped in a lead-shielded beam dump. The liquid lead is circulated with an induction pump through a heat exchanger in a thermally insulated and electrically heated circuit.

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Christophe Vallée, Matthias Beyer, Dirk Lucas, Horst-Michael Prasser1

In the event of a loss-of-coolant-accident(LOCA) in a pressurized water reactor,emergency strategies have to be mappedout in order to guarantee the reliableremoval of the decay heat from the reactorcore. During a hypothetical small breakLOCA with failure of the high pressureemergency core cooling system, the decayheat has to be released to the secondarycircuit over the steam generators, via atwo-phase natural circulation in theprimary circuit. If the water level in thereactor pressure vessel falls below the hotleg inlet, steam only flows to the steamgenerator. In this case, the natural circu-lation breaks down and switches to the

reflux condenser mode, which means thatthe steam coming from the reactorpressure vessel condenses in the vertical U-tubes of the steam generator. As it flowsdown the tubes, part of the condensatehas to stream back over the hot leg to theupper plenum in counter-current to thesteam flow.

The horizontal stratified counter-currentflow of condensate and steam is onlystable for a certain range of flow rates. Incase of high steam flow rates, part of thecondensate can be clogged in the hot legmarking the beginning of the counter-current flow limitation (CCFL): the hot legand steam generator are flooded, whichdecreases the water level in the reactorpressure vessel and reduces the core

cooling. The simulation of CCFLconditions, which are dominated by 3Deffects, requires the use of a computationalfluid dynamics (CFD) approach. Thesemethods are not yet mature and have tobe validated by sound experiments beforethey can be applied to nuclear reactorsafety analyses. Therefore, dedicatedexperimental data are needed with highresolution in space and time, ideally atreactor typical conditions. For thesepurposes, a model of the hot leg of apressurized water reactor was built at theTOPFLOW test facility of the FZD.

The hot leg modelThe hot leg model (Figs. 1 and 2) is de-voted to optical measurement techniques,so a flat test-section design was chosen

Counter-current flow limitation experiments at the TOPFLOW test facility

Fig. 1: Schematic view of the experimental setup.

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with a width of 50 mm. The test sectionrepresents the hot leg of the GermanKonvoi pressurized water reactor at aheight scale of 1:3, which corresponds to a channel height of 250 mm in the straightpart of the hot leg. The test-section ismounted between two separators, onesimulating the reactor pressure vessel andthe other being connected to the steamgenerator inlet chamber. This allowsperforming co-current as well as counter-current flow experiments. The hot legmodel is operated in the pressure chamberof the TOPFLOW facility (Fig. 1), which isused for high-pressure experiments underpressure equilibrium with the insideatmosphere of the chamber. This newoperation method was developed at theFZD and enables the application of opticalobservation techniques at reactor typical

conditions (i.e. pressures up to 5 MPa andtemperatures up to 264°C). The presentedexperiments focus on the flow structureobserved in the region of the riser and ofthe steam generator inlet chamber (Fig.2,right) during counter-current flow. Theywere carried out in the frame of a currentresearch project funded by the GermanFederal Ministry of Economics andTechnology.

As an example, one of the experimentsperformed at a system pressure of 5.0 MPaand a temperature of 262°C may serve to explain the phenomena. During thisexperiment, a constant water flow rate of 0.72 kg/s was injected into the steamgenerator separator while the gas flow rateinjected into the reactor pressure vesselsimulator was gradually increased to reach

counter-current flow limitation conditions.The measurement of global parameters(e.g. flow rates, water levels, pressures)was complemented by high-speed videoobservations for local information on theflow structure (Fig. 3). Thanks to therectangular cross-section geometry, thepictures of the flow deliver a detailed viewof the stratified interface as well as of thedistribution of dispersed structures (drop-lets and bubbles). This kind of visualizationof steam/water flows over large windowsat reactor typical conditions is a world first.

At the beginning of the experiment, thecounter-current flow is stable (Fig. 3-a): a thin supercritical water layer (i.e. Froudenumber > 1) flows down the riser to thereactor pressure vessel simulator. Just smallwaves are observed, which do not affect

(a) stable counter-current flowt = 60.00 sm· G = 0.81 kg/sm· L,d = 0.71 kg/s

(b) during counter-current flow limitationt = 80.25 sm· G = 0.92 kg/sm· L,d = 0.23 kg/s

(c) during counter-current flow limitationt = 125.28 sm· G = 0.99 kg/sm· L,d = 0.08 kg/s

Fig. 2: The test section in front of the pressure chamber (left) and the transparent part of the hot leg model (right).

Fig. 3: Evolution of the flow during a steam/water counter-current flow limitation experiment performed at 5.0 MPa and 262°C with m· L = 0.72 kg/s.

steamwater

riser

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the flow. After an increase of the steamflow rate from 0.81 to 0.92 kg/s, wateraccumulates in the horizontal part of thechannel due to a flow reversal at theinterface. The high gas velocity generateswaves and slugs at the water surface(Fig. 3-b): bubbles are entrained in theliquid phase and the interface is torn intodroplets, especially at wave crests. Theslugs collapse in the riser but dropletsdetach at the slug front, transporting waterto the steam generator inlet chamber. Atthe junction between horizontal channeland riser, a recirculation zone is observed:the water flowing down the riser from thesteam generator inlet chamber is deflectedby the slugs arriving from the other direc-tion. The discharge water flow through thetest-section (m· L,d) can be obtained from thewater level increase in the reactor pressure

vessel simulator. At this stage, it has beenreduced to 0.23 kg/s. With a further in-crease of the steam flow rate to 0.99 kg/s,the discharge water flow is reduced to0.08 kg/s. As a consequence, the flowshows highly mixed two-phase zones(Fig. 3-c). Big slugs are observed whichflow up the riser and transport water intothe steam generator separator, where thewater accumulates.

Results of counter-current flow limitationare usually presented in a flooding diagramby plotting the dimensionless superficialvelocity J* of the air versus that of thedischarge water, which is measured fromthe water level increase in the reactorpressure vessel simulator. The floodingcurve (Fig. 4) indicates the maximum waterflow rate for a given gas flow rate and

therefore delimits the possible combin-ations of flow rates from the impossibleones. Fig. 4 compares the data obtainedfrom the experiments in the hot leg modelwith different results obtained for similargeometries (i.e. a horizontal conduitconnected to a riser) available in theliterature: Richter et al. (1978), Ohnuki et al. (1986), Weiss et al. (1988) andWongwises (1996). The overall agreementwith previous investigations performed inpipes shows that the rectangular cross-section of the hot leg model does notinfluence counter-current flow limitation.In the near future, image processingmethods will be applied in order to extractlocal quantitative information from thehigh-speed camera images. This will beused for comparison with computationalfluid dynamics simulations.

References[1] Experimental study on the air/water

counter-current flow limitation in a model of the hot leg of a pressurized water reactor, Deendarlianto, C. Vallée, D. Lucas, M. Beyer, H. Pietruske, H. Carl, Nuclear Engineering and Design 238/12 (2008), 3389 – 3402

[2] Air/water counter-current flow experi-ments in a model of the hot-leg of a pressurized water reactor, C. Vallée, Deendarlianto, M. Beyer, D. Lucas, H. Carl, Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 131/2, 022905 (2009)

[3] Experimental investigation and CFD simulation of horizontal stratified two-phase flow phenomena, C. Vallée, T. Höhne, H.-M. Prasser1, T. Sühnel, Nuclear Engineering and Design 238/3 (2008), 637 – 646

Project partners· ETH Zürich, Switzerland1

· Gadjah Mada University, Yogyakarta, Indonesia

· Université Catholique de Louvain, Belgium

Fig. 4: Flooding curve (delimitation between combinations of flow rates which are possible - part below the curve - and the impossible ones) of the hot leg model obtained from steam/waterexperiments at 3 system pressures compared to previous investigations plotted in terms of the non-dimensional superficial velocity J* for gas vs. water.

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Ultra high speed electron beam X-ray tomography for two-phase flows

Uwe Hampel, Frank Fischer

Multiphase flows occur in many industrialareas, such as in nuclear light waterreactors, chemical reactors, hydrodynamicmachines, oil exploration, biochemicalprocessing and water management. A keyissue to understand the physical principlesgoverning such flows is the availability ofadequate measurement techniques whichenable to measure and visualize multiphaseflows at very high speed and with highspatial resolution. A good candidate tech-nology is X-ray computed tomography(CT). However, standard computedtomography scanners as used in medicineare much too slow since they employmechanically moving parts for scanning.

For industrially relevant multiphase flows,velocities in the range of 1 m/s and higherare common. Therefore, a tomographytechnique is required which can scan theflow at rates of 1000 frames per secondand even higher. This can be achieved byelectron beam tomography, which offersboth high spatial and temporal resolutionalong with non-intrusiveness and goodlinearity in density resolution.

In order to use this technology for flowmeasurement, we developed a dedicatedelectron beam CT scanner which wasoptimized for very fast image generationup to 7 kHz frame rate. The functionalprinciple of the scanner is displayed inFig. 1. Within the scanner an electronbeam of 150 keV maximum energy isgenerated by means of an electron gun.The beam first passes an electron lenssystem, which provides beam centeringand focusing, and then an electromagneticdeflection system, which allows rapidbeam deflection in two directions. On the farther end of the scanner resides a

semicircular target made of a tungstenalloy which stops the electrons, therebyproducing X-rays within a small focal spot(see Fig. 4). By fast scanning of the beamacross the target using the beam deflectionunit, a moving focal X-ray spot is producedwhich rapidly circulates around the target.This electron beam system replaces therotating X-ray tube of standard medical CTscanners and enables scanning frequencieswell above 1 kHz.

For measuring the X-ray attenuationcaused by an object residing in the centreof the target, a circular X-ray detector isarranged at the inner side of the openingin the scanner head. This detectorcomprises 240 fast semiconductor pixels

which can be sampled at a rate of up to1 MHz by dedicated detector electronics.Additional components include a highvoltage supply, vacuum system, beammonitoring system and control PC. Thedeveloped scanner, which is named ROFEX(ROssendorf Fast Electron beam X-rayscanner), can be operated at beam powersof up to 10 kW at scanning rates of up to7,000 frames per second. The spatialresolution is about 1 mm and objects of upto 100 mm diameter can be investigated.A limiting factor is the maximum X-rayenergy of 150 keV, which prohibits thepenetration of steel or other dense ma-terials. Fig. 2 shows the scanner mountedat a vertical test section of the TOPFLOWfacility. Here, the test section is a 50 mm

Fig. 1: Principle of the ultra fast electron beam X-ray CT.

Fig. 2: ROFEX scanner at a vertical test sectionof the TOPFLOW facility.

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pipe made of a titanium alloy with 1.5 mmwall thickness, which will be used to studysteam-water two-phase flows under pres-sures of up to 7 MPa and a correspondingsaturation temperature of 284 °C.

As an example, Fig. 3 shows X-ray tomo-graphy images taken with the ROFEXscanner from a bubble column. Such

devices are frequently used in chemicalindustry where gases and liquids arebrought into contact for reaction. Efficientreaction is ensured when gas is finelydispersed into the liquid while slug flowregimes are to be avoided because of lowinterfacial area density and pulsating masstransfer. In such devices, the flow patternsand their transitions follow complex

evolutions which are not yet fullyunderstood. In the given example, theROFEX scanner acquired cross-sectionalimages of the 60 mm column with a rateof 1 kHz. For the first time, this enables acomplete visualization of the gas-liquidstructure including the phase boundary,which is necessary to measure furtherprocess parameters, such as the local gashold-up and interfacial area density.

With the development and commissioningof an ultra fast electron beam X-ray CTscanner, for the first time world wide, weare able to image complex and highlydynamic multiphase flows in unpreced-ented spatial and temporal detail. In thisway only, it will be possible to understandand perhaps model the complex physics ofmultiphase flows. This will greatly enhanceour ability to optimize technical processesinvolving such flows and to assess safetyissues associated with the operation ofnuclear and chemical installations.

References[1] Ultra fast limited-angle type X-ray

tomography, M. Bieberle, F. Fischer, E. Schleicher, D. Koch, K. S. D. C. Aktay, H.-J. Menz, H.-G.Mayer, U. Hampel, Applied Physics Letters 91, 123516 (2007)

[2] Simulation study on electron beam X-ray CT arrangements for two-phase flow measurements, M. Bieberle, E. Schleicher, U. Hampel, Measurement Science and Technology 19, 094003 (2008)

[3] An ultra fast electron beam X-ray tomo-graphy scanner, F. Fischer, D. Hoppe, E. Schleicher, G. Mattausch, H. Flaske, R. Bartel, U. Hampel, Measurement Science and Technology 19, 094002 (2008)

Project partners· Institut für Kernenergetik und Energie-systeme, Universität Stuttgart, Germany

· Fraunhofer-Institut für Elektronenstrahl- und Plasmatechnik Dresden, Germany

Fig. 3: Optical image (left) and three-dimensional ROFEX images (right) of the gas distribution in a bubble column.

➊ ➋ ➌ ➍

Fig. 4: CAD-drawing (exploded view) of the ROFEX scanner: 1 - electron beam gun; 2 - beam tube;3 - target; 4 - fast X-ray detector.


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Sven Eckert, Dominique Buchenau, Gunter Gerbeth

Design and optimization of the thermalhydraulics of liquid metal cooled nuclearreactors are based on numerical simu-lations of the heat and mass transferprocesses of the related flow field. How-ever, velocity measurements in opaqueliquid metal flows still represent a challeng-ing task as commercial measuring systemsare not available for such melts. During thelast 10 years, considerable effort has beenspent at the FZD on the development andqualification of techniques to measure the

velocity in liquid metal flows. Significantprogress has been achieved especially inthe field of non-invasive measuringtechniques, with new developmentsconcerning electromagnetic flow metersand the Ultrasound Doppler method,respectively.

A multitude of different electromagneticflow-meter designs are known, themajority of which, however, need anelectrical contact to the liquid metal inorder to measure the electric potentialdifference. The working conditionsrelevant to nuclear systems, such as high

temperatures, interfacial effects orcorrosion, prohibit this approach. A liquidmetal flow inside an external magneticfield gives rise to electrical currents in themelt which cause a deformation of theapplied magnetic field. Such a deformationcan be measured outside the fluid volume,and this information can be used toreconstruct the velocity field. Based on this principle, new types of inductive flowmeters were developed at the FZD, whichoperate in a fully contactless manner. Aschematic view of the new flow meter isshown in Fig. 1. Operation is based on the detection of the asymmetry of themagnetic field caused by the flow. Besidesthe voltage difference between the tworeceiver coils, the device also provides twoadditional quantities: phase and frequency.Such additional information significantlyimproves the reliability of the measuredflow rate [1]. The feasibility and therobustness of our approach were success-fully demonstrated at various liquid metalloops of temperatures up to 550 °C, e.g. at the lead-bismuth (PbBi) loop of theBelgian Nuclear Research Centre SCK•CENin the framework of the European projectEUROTRANS (“European research pro-gram for the transmutation of high-levelnuclear waste in an accelerator drivensystem”).

Because of its ability to work in opaquefluids and to deliver complete velocityprofiles in real time, the UltrasoundDoppler Velocimetry (UDV) technique hasbecome very attractive for liquid metalapplications. Measurements can be donethrough the channel wall as well as indirect contact with the liquid metal. Manyapplications in the nuclear field are relatedto liquid metal two-phase flows. For suchkinds of flows, it was successfully shownthat the UDV technique can simultan-

Advanced measuring techniquesfor liquid metal flows in fast neutron nuclear reactors

Fig. 1: Schematic view of the electromagnetic flow meter.

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eously deliver both the bubble and theliquid velocity [2]. In the case of hotmetallic melts the user is confronted with a number of specific problems: first of all,the application of conventional piezo-electric transducers is usually restricted tomaximum temperatures below 200 °C.Moreover, the transmission of a sufficientamount of ultrasonic energy from thetransducer into the fluid has to beguaranteed. Therefore, the acousticcoupling and the wetting conditions areimportant issues. A new concept of anultrasonic transducer with integratedacoustic wave guide was designed [3] inorder to achieve a thermal and chemicaldecoupling between the transducer andthe hot liquid metal. Stainless steel wasselected as wave-guide material. Theultrasonic sensor consisting of the piezo-electric element and the acoustic waveguide is shown in Fig. 2. The wave guide isfabricated from a stainless steel foil with athickness of 0.1 mm, which is wrappedaxially around a capillary tube. It is closedat the front end by means of laser beamwelding. This surface is in direct contact

with the melt and has to be preparedbefore the measurements to obtain asufficient wetting with the liquid metal.Typically, the wave guides have an outerdiameter of about 8 mm and a lengthbetween 200 and 1000 mm. The opera-bility of such wave guides has beendemonstrated in PbBi at 300 °C as well as in liquid aluminum and CuSn alloys attemperatures up to 750 °C.

With both measuring techniques, contact-less flow-rate sensor and UltrasoundDoppler Velocimetry, we contribute to the European projects EUROTRANS andVELLA (“Virtual European lead labora-tory”). They are related to the develop-ment of a PbBi based target for nuclearspallation sources in transmutationsystems, where transuranium elements are irradiated with fast neutrons in order to reduce the proportion of long-livedisotopes enclosed in nuclear waste. Liquidmetal measuring techniques are also partof the upcoming European project CP-ESFR in the field of liquid sodium cooledfast reactors. Moreover, there are many

industrial applications requiring velocitymeasurements in molten metals rangingfrom molten tin in float-glass production toliquid steel casting, where such techniquescould successfully be applied.

References[1] Verfahren und Anordnung zur kontakt-

losen Messung des Durchflusses elektrisch leitfähiger Medien, J. Priede, G. Gerbeth, D. Buchenau, S. Eckert, Patent DE 10 2006 018 623 B4 (2008)

[2] The flow structure of a bubble-driven liquid metal jet in a horizontal magnetic field, C. Zhang, S. Eckert, G. Gerbeth, Journal of Fluid Mechanics 575 (2007), 57 – 82

[3] Velocity measurement techniques for liquid metal flows, S. Eckert, A. Cramer, G. Gerbeth, in “Magnetohydrodynamics – Historical Evolution and Trends”, S. Molokov, R. Moreau, H.K. Moffatt (eds.), Springer-Verlag (2007), 275 – 294

Collaboration· DFG Collaborative Research Center SFB 609, Technische Universität Dresden, Germany

Fig. 2: Concept of an ultrasonic sensor with integrated acoustic waveguide: schematic view (left) and picture of a sensor for melt temperatures up to 750°C (right).

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Frank Bergner, Uwe Birkenheuer, Andreas Ulbricht

The core-belt region of the reactorpressure vessel (RPV) of a nuclear powerplant (NPP) is exposed to intense neutronirradiation, and the fast neutrons causedegradation of the mechanical properties.In order to guarantee the structuralintegrity of the RPV throughout itsoperational lifetime, surveillance programsare implemented prior to initial commis-sioning of a nuclear power plant.According to these programs specimens ofthe RPV steel are inserted into capsulesand placed in special surveillance channels.At these positions, the fast neutron flux(number of neutrons per unit area and unittime) exceeds the flux at the RPV wall by a“leading factor” (typically between 1.5and 12). The specimens are taken from thesurveillance capsules at regular intervals inorder to undergo mechanical tests in hotcell labs (Fig. 1). The mechanical propertiesare then assumed to be characteristic of

the RPV material at an instant of timecorresponding to the irradiation time of thespecimen multiplied by the leading factor.However, this procedure is only applicableif flux effects are either completely absent,i.e. degradation depends on fluence only,or result in a conservative prediction of thebehavior of the RPV material. At this point,the basic interest in the dependence of themechanical properties and the underlyingmicrostructure on neutron flux becomesevident.

How to separate flux effects on themicrostructureThe primary irradiation parametergoverning the degradation of materialproperties is neutron fluence, Φ, i.e.neutron flux, ϕ, multiplied by exposuretime, t. Neutron flux is a secondaryparameter, though of primary technicalimportance. In order to separate fluxeffects from the dominant dependence onfluence, it is necessary to vary the value offlux while keeping the value of fluence

constant. An appropriate pair of sampleswas selected from German irradiationprograms. Identical samples of weldmaterial containing 0.22 wt% Cu wereexposed to fluxes, ϕ1 = 0.06 x 1012 cm-2s-1

and ϕ2 = 2.08 x 1012 cm-2s-1 (E > 1 MeV),differing by a factor of 35. The neutronfluence, Φ = ϕ t = 2.2 x 1019 cm-2, wasmade to agree for both conditions bychoosing irradiation times, t1 = 11.6 yearsvs. t2 = 122 days.

Samples of these material conditions wereanalyzed by means of small-angle neutronscattering (SANS) at the beamline V4 ofthe Helmholtz Centre Berlin for Materialsand Energy. The results are presented inFig. 2 in terms of scattering curves, i.e.measured scattering cross section vs.scattering vector, Q (see insert), and interms of reconstructed size distributions ofthe irradiation induced defects [1].We have observed that (1) the totalvolume fraction of irradiation induceddefect-solute clusters (hatched area forblue curve) agrees for both values ofneutron flux and assumes a value of0.52 vol.%, and (2) the peak radius of thesize distribution (marked for the greencurve) is increased for low-flux irradiationby the factor 2 (0.85 nm vs. 1.6 nm).Mechanical impact testing of the samematerial did not reveal any significantdependence of the brittle-to-ductiletransition temperature shift, ∆T41, on flux(119 K vs. 111 K). It is important to notethat the latter result is consistent withstate-of-the-art surveillance procedures.From the viewpoint of physical under-standing we have to answer twoquestions: Why does the cluster sizeexhibit a pronounced flux dependence,and why, in spite of that, is there nodifference in the shift of the transitiontemperature?

Flux dependence of defect cluster formation in neutron irradiated weld material

© R

. Wei

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Simulating cluster growth by meansof reaction rate theoryThe constituents of our rate theory modelare the balance equations for point defects(vacancies and self-interstitial atoms) andfor Cu-clusters. We assume the ratio ofirradiation enhanced and thermal Cu-diffusivity to be given by the ratio ofsteady-state and equilibrium concentrationof vacancies. Based on asymptotic consid-erations of the equations involved in themodel, we have found that there are twodifferent flux regimes (Fig. 3). In the low-flux regime, the growth rate of Cu-richclusters is independent of flux. In this case,the dominant process causing the loss ofvacancies is the disappearance at sinks likegrain boundaries or dislocations. The high-

flux regime with vacancy-interstitialrecombination as prevailing mechanism ofvacancy loss is characterized by an inverseproportionality of the growth rate with thesquare root of flux. The rate theory modelalso yields an expression for the transitionflux estimated to be 0.7 x 1012 cm-2s-1

under the present conditions. In otherwords, the investigated low-flux irradiationof the weld material belongs to the flux-independent regime whereas for high-fluxirradiation a reduced rate of cluster growthis expected in qualitative agreement withthe experimental observation. Existingdisagreement on the magnitude of the fluxeffect is attributed to the effect of thealloying elements not yet taken intoaccount in the model.

In order to bridge the gap betweennanoscale features and macroscopicmechanical properties, it is important tonote that state-of-the-art models generallypredict the material’s resistance to plasticdeformation (strength) to depend on bothvolume fraction and size of irradiationinduced defect-solute clusters. Increase ofstrength is in turn correlated with thetransition temperature shift. Thus, ourexperimental findings rule out any modelthat predicts a pronounced size depend-ence. The results substantiate the hypo-thesis that the mechanical properties aremainly determined by the total volumefraction of the clusters whereas cluster sizeseems to be of minor influence [2]. How-ever, this hypothesis has to be confirmedby further studies.

References[1] Flux dependence of cluster formation in

neutron-irradiated weld material, F. Bergner, A. Ulbricht, H. Hein1, M. Kammel2, Journal of Physics: Condensed Matter 20, 104262 (2008)

[2] SANS response of VVER440-type weld material after neutron irradiation, post-irradiation annealing and reirradiation, A. Ulbricht, F. Bergner, J. Böhmert, M. Valo3, M.-H. Mathon4, A. Heinemann2, Philosophical Magazine 87, 1855 (2007)

Project partners· AREVA NP GmbH, Erlangen, Germany1

· Helmholtz Centre Berlin for Materials and Energy, BENSC, Germany2

·VTT Technical Research Centre of Finland, Espoo, Finland3

· Commissariat à l’Energie Atomique, Centre de Saclay, France4

· Centro de Investigaciones Energéticas Medioambientales y Tecnológicas, Madrid, Spain

· Electricitè de France, Site des Renardieres,France

· Gesellschaft für Reaktorsicherheit, Köln, Germany

· Kurchatov Institute, Moscow, Russia· Studiecentrum voor Kernenergie•Centre d'Etude de l'énergie Nucléaire, Mol, Belgium

Fig. 2: Scatteringcurves for RPV weldmaterial (insert) andreconstructed sizedistributions ofirradiation induceddefects (low flux ingreen, high flux in blue, black symbols:unirradiated).

Fig. 3: Cluster growthrate normalized withthe limiting rate at zeroflux vs. neutron fluxnormalized with thetransition flux.

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Bruno Merk, Frank-Peter Weiss

The underground storage in deepgeological repositories has been acceptedworldwide as the strategy for the finaldisposal of radioactive waste. Partitioningand Transmutation (P&T) is an appropriatemeans to reduce the share of extremelylong-lived radionuclides, which also helpsto relieve safety requirements at thedisposal site and to reduce the necessaryisolation time. The development of theaccelerator driven system (ADS) tech-nology for the transmutation of mainlyplutonium and minor actinides isvigorously pursued in the EURATOMframework program. ADSs are dedicatedburners of long-lived radionuclides.

ADSs connect a proton accelerator with a subcritical reactor core (see Fig. 1). By spallation reactions in a heavy metaltarget, the accelerated protons generateneutrons in the center of the system. Theseexternal source neutrons maintain thechain reaction, thus enabling continuouspower production at a quasi-stationarylevel in the subcritical core. The neutronflux in the core decays rapidly as soon asthe external neutron source is switched off.The neutron physical behavior of ADSs iscurrently under investigation in the Euro-pean Integrated Project EUROTRANS ofthe 6th EU Framework Program. Kineticneutron physics experiments for ADStechnology are performed in the ECATSdomain of this project at the YALINABooster facility in Minsk, Belarus, and lateron at the GUINEVERE facility at the Bel-gian Nuclear Research Centre (SCK•CEN).

In order to optimize the design and safetyof ADSs, it is important to be able toproperly analyze the space-time behaviorof the neutron flux in current, andplanned, European experiments. Mostly,analysis of subcritical kinetic experiments is

still based on methods originally developedfor the analysis of experiments in criticalreactors. However, the use of thesemethods is limited since they were derivedfrom the zero dimensional point kineticsequations. The point kinetics in turnrepresents an approximated solution of thediffusion equation. Recent analyses of suchkinetic experiments using these methodshave shown unacceptable deviationsbetween experiments and theoreticalpredictions. Detailed mathematical andphysical investigations reveal that due to

their limitations neither the point kineticsnor the diffusion equation can properlyreproduce the kinetic system behavior ofsubcritical systems. In order to handle thisproblem, we have established a newapproach solving the time dependenttelegrapher’s or P1 equation. Analyticapproximation solutions have beendeveloped and applied to the pulsedneutron source problem described above.The results of these new approximationsolutions are compared to the diffusionequation.

Analytical neutron transport solutionfor a pulsed subcritical transmutation system

secondary coolant forconventional powergeneration argon

circulation

proton beam inevacuated tube

heatexchanger

protons

directionof leadcirculation

argon

liquidlead

lead target

neutrons

proton accelerator(cyclotron)

reactor core

Source: Ansaldo

Fig. 1: Scheme of an acceleratordriven system (ADS)Source: Spiegel 22/1998

The lead atoms in the center of the subcritical reactor corebreak into pieces due to thebombardment with acceleratedprotons from the cyclotron. This reaction, called spallation,creates neutrons, which maintainthe chain reaction in thesubcritical reactor core anddetermine the power level. Theadvantageous safety featuresresulting from subcriticality allow a higher loading of minoractinides to be transmuted in thecore than is possible in criticalreactors. The liquid lead isadditionally used for heatremoval from the reactor core tothe heat exchangers. As soon asthe proton source is shut down,the chain reaction in the reactorstops immediately.

25

In their textbook “The physical theory ofneutron chain reactors”, Weinberg andWigner already characterized the tele-grapher’s equation as the correct timedependent P1 approximation to Boltz-mann’s neutron transport equation. Thetelegrapher’s equation is second order withrespect to time, compared to the first orderdiffusion equation. Due to this property,the P1 solution is capable of describingretardation effects, which include theoccurrence of a well-defined wave front ofneutron propagation and the existence ofa residual disturbance persisting at allpoints traversed by the wave front.Contrary to this, the propagation velocityof a neutron flux perturbation is infinite inthe diffusion equation. A change in theexternal source immediately produces adisturbance everywhere in the system. Thislimitation of the diffusion becomes crucialin future ADS operation. The differencescan be especially observed in kineticexperiments measuring large variations ofthe neutron flux on very short time scales,where the influence of the propagatingneutron flux wave front cannot always beignored.

Fig. 2 provides a qualitative comparison ofthe results obtained with the diffusion andtelegrapher’s equation, the spatial coord-inate pointing to the front and timeevolution to the right. The neutron fluxtransient shown there is initiated by aneutron pulse from an external neutronsource located in the center part of thehomogenized system. The pulse is repre-

sented by a Dirac delta function. Thehomogenized system has to be derivedfrom the real system (Fig. 1) using nu-merical neutron transport methods. Theinitial value of the neutron flux is zero inthe whole system. The experiment startswhen the external source pulse occurs inthe center of the symmetric one-dimen-sional system at time zero. The neutronsspread out immediately in both thediffusion and transport solution. Never-theless, only the solution obtained with theP1 equation depicts a clearly defined wavefront whereas in the diffusion solution theperturbation caused by the external sourcepulse propagates with an infinite velocity.The excessive flux peak occurring in thecenter, immediately after the pulse, is aside effect of this unrealistically highpropagation velocity since the response tothe pulse is created by multiplication in thewhole system. This is an artifact caused bythe diffusion approximation. In fact, thepropagation of the perturbation takessome time until it reaches the outer zoneof the system. The velocity of the wavepropagation approximates the neutronvelocity divided by √ 3.

Obviously, the telegrapher’s or P1 equationprovides additional insight into the systembehavior. Such additional information isindispensible in cases where detailedinformation on the short time behavior ofthe system is required. This applies tocurrent ADS experimental setups, whichimply strong external neutron sources aswell as measurements at time scales of the

order of the prompt neutron generationtime. The neutron wave travels about 20centimeters during one neutron gener-ation. On the one hand, measurement istherefore influenced by the pulses if therepetition rate is low. On the other hand, itis impeded by a time delay if the detectorsare far away from the source. Due to thereasons mentioned above, the approxi-mated neutron transport solutions will beused to develop new analysis methods forkinetic ADS experiments.

References[1] An analytical solution for a one dimen-

sional time dependent neutron transport problem with external source, B. Merk, Transport Theory and Statistical Physics 37: 5-7, 535 – 549 (2008)

[2] An analytical approximation solution for a time dependent neutron transport problem with external source and delayed neutron production, B. Merk, Nuclear Science and Engineering 161, 49 – 67 (2009)

Project partners· Commissariat à l’Energie Atomique, France· Centre National de la Recherche Scientifique, France

· Instituto Tecnológico e Nuclear, Portugal· Studiecentrum voor Kernenergie•Centre d’Etude de l’énergie Nucléaire, Belgium

· Forschungszentrum Karlsruhe GmbH, Germany

· Royal Institute of Technology, Sweden· Centro de Investigaciones Energeticas Medioambientales y Tecnologicas, Spain

· Ente per le Nuove tecnologie, l'Energia e l'Ambiente, Italy

norm. time τ norm. time τ

norm. spatial coordinate

norm

. neu

tron

flu

x Φ

norm

. neu

tron

flu

x Φ

transport solutiondiffusion solution Fig. 2: One-dimensionalspace-time dependentneutron flux following ashort pulse of the externalsource as obtained withthe developed analyticalapproximation solutions.

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RESEARCH INSTITUTE OF RADIOCHEMISTRY

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Vinzenz Brendler, Anke Richter, Sven Gester

The disposal of radioactive waste includingthe assessment of its long-term safety isstill an open question in Germany. Inaddition to the choice of a repository hostrock (salt, granite, clay), a consistent andobligatory thermodynamic referencedatabase is urgently needed. This allows to accurately assess potential failurescenarios and to make well-foundedpredictions about the long-term safety.Waste repository and remediation projects,in Germany especially, require comprehen-sive datasets also covering high tem-peratures and high salinities. However,available databases do not suffice and arelimited in their use. This is partly due tohigh demands on data precision, whichunfortunately results in the completeomission of many reactions having largeruncertainties. Other databases rely onheterogeneous and therefore inconsistentdata leading to incorrect model calcu-lations [1].

A new reference database called THEREDAaims at overcoming these deficiencies byproviding consistent thermodynamicdatasets and enhancing the transparencyand reliability of safety analyses. THEREDAis a joint project by the FZD and otherleading institutions in the field of safetyresearch for nuclear waste disposal inGermany and Switzerland (see list ofpartners). The project is jointly funded bythe German Federal Ministries of Educationand Research (BMBF), Economics andTechnology (BMWi), and Environment,Nature Conservation and Nuclear Safety(BMU).

Fig. 1 depicts the various tasks to beaddressed within this project, and also liststhe different elements for which thermo-dynamic data (free standard enthalpy offormation (∆G0

f), standard enthalpy offormation (∆H0

f), standard entropy (S0),standard heat capacity (C0

p), partial molarvolumina (V0), equilibration constants (log K), and activity coefficients for speciesdissolved in brines and for solid solutions)

have to be collected, evaluated and stored.Both data management and technical realization are integrated into a WWW-based content management system, which also provides a correspondinginteractive graphical user interface (go to“http://www.thereda.de” for the currentstate of the project). The internal relation-ships, data flow and user interactions areillustrated in Fig. 2. One of the major goalsof the project is to rely on open sourcesoftware in order to minimize the risks ofvendor dependence and incompatibilities,and to keep the long-term running costsfor database maintenance low. Thus, majorsoftware components are PostgreSQL(database) and Apache (web server). Forthe same reason all data are stored in ageneric and openly documented ASCIIformat.

Each dataset is documented in detail and isallocated a degree of quality. Informationabout solid phase modification (like “crys-talline” or “amorphous”) is mandatory andspecific marks are designated to indicate

THEREDA - Thermodynamic Reference Database for nuclear waste disposal in Germany

Fig. 1: Tasks and elements addressed in the THEREDA project.

27

whether dissolution / precipitation arekinetically controlled or not. Higher gradesof quality are assigned to thermodynamicparameters derived from experimentaldata, namely from non-thermochemicalexperiments, whereas estimated valuesdetermined from Linear Free EnergyRelationships and other regressions orcorrelations, or from studies of chemicalanalogs, get lower ratings. The funda-mental philosophy here is that omission ofspecies and related reactions almost alwaysgenerates larger errors than using

corresponding data which admit a largeuncertainty. The inherent storage of allassociated data uncertainties will allow for numerical uncertainty and sensitivityanalyses at a later point. Furthermore, thequality of the data sources (primary orsecondary literature, peer-reviewed ornon-certified) is categorized.

In order to guarantee the consistency of datasets within the thermodynamicdatabase, internal conversion paths haveto be strictly followed. Other importantconsistency rules require linking thoseparameters which were originally derivedsimultaneously from the same experi-mental raw data. In addition, someparameters are linked to specific sets ofchemical species and are only valid withinthis combination.

A special feature is that custom-designeddata can be extracted from the databaseand converted to file formats requiredspecifically by geochemical codes (such asEQ3/6, PHREEQC, GWB, ChemApp). Thisallows a widespread use for storage of

radioactive waste or chemo-toxic sub-stances and remediation of contaminatedsites. Respective long-term safety analyseswill be made more reliable, comparableand traceable. Moreover, we anticipatethat THEREDA can serve as an instrumentfor research control. Priorities for futureexperimental programs can be given basedon identifying and ranking gaps within thethermodynamic datasets.

Reference[1] Quality assurance in thermodynamic

databases for performance assessment studies in waste disposal, W. Voigt, V. Brendler, K. Marsh, R. Rarey, H. Wanner, M. Gaune-Escard, P. Cloke, T. Vercouter, E. Bastrakov, S. Hagemann, Pure and Applied Chemistry 79, 883 (2007)

Project partners· Forschungszentrum Karlsruhe, Germany· Gesellschaft für Anlagen- und Reaktor-sicherheit Braunschweig, Germany

· TU Bergakademie Freiberg, Germany· AF-Colenco, Switzerland

Fig. 2: Parameter flow chart and user interactions of the THEREDA project.

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Final repository for nuclear waste(Source: Bundesamt für Strahlenschutz).


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Harald Zänker

Environmental scientists and geochemistsincreasingly require systematic research onthe risks of nanotechnology for man andthe environment. They assume that fearsover possible dangers of some nanotech-nologies may be exaggerated, but notnecessarily unfounded (cf. [1]). Theconcern is that the possible harm, whetherreal or imagined, could slow down the

development of nanotechnology unlessreliable information is gained on what therisks are, and how to avoid them.

Nanostructured materials, in particularengineered nanoparticles, behave ascolloids if released to environmentalwaters, thus resembling natural colloids,which are ubiquitous in natural aquaticsystems and which have been investigatedfor decades (cf. [2]). On the other hand,

artificial nanoparticles differ from theirnatural counterparts. Unlike natural nano-particles, which can vary very much in theirshapes and properties, engineered nano-particles possess well-defined propertiessuch as distinct particle size distributions,particle shapes, functionalities etc.

One type of nanostructured materials thatattract much interest are carbon nanotubes(CNTs). The demand for CNTs is expectedto grow rapidly over the next decade. Asthese materials find their way intoindustrial and consumer products, theirunintended release into the environmentduring production, use and disposal cannotbe precluded. Functionalization may be akey parameter controlling the impact ofCNTs on human health and environment.Even if CNTs should prove to be non-toxic,it is possible that environmental pollutantsbind onto CNTs and that the transport ofpollutants through the environment, aswell as the bioavailability of thesepollutants for aquatic organisms, can be influenced by their interaction withnanoparticles.

CNTs are very hydrophobic and tend toaggregate in aqueous solution because of high Van der Waals interaction forcesalong the tube exterior. As a result, theydo not easily disperse in water. At firstsight, CNTs should therefore not be regard-ed as potential mobile contaminants ofaquatic systems. However, the dispersibilityof CNTs in water can be increased byfunctionalization such as surface oxidationor by addition of surfactants.

We studied the influence of surfacefunctionalization on the colloidal stabilityof CNTs [3]. CNTs were treated withconcentrated HNO3/H2SO4 to simulatepurification steps in CNT production aswell as possible alteration processes after

Colloidal carbon nanotubes and their influence on dissolved uranium

29

hypothetical release to the environment.Various methods were used to characterizethe properties of the pristine and thetreated material. Furthermore, colloidalstability of CNTs in aqueous solution wasinvestigated. In Fig. 1 the temporal de-velopment of the scattered light intensity(a measure of CNT concentration) of thesuspensions after ultrasonication ispresented. It shows that the scattered lightintensity decreased from 1,100 to about30 cps within 24 hours for the pristineCNTs. Simultaneously, a deposition ofblack flocks became visible at the bottomof the sample cell. Hence, pristine CNTs do

not form stable colloids. By contrast, thescattered light intensity of the suspendedmodified CNTs remained nearly constantover a period of more than 14 days(decrease only ~25%), i.e. this colloidalsuspension proved to be stable. This is dueto the generation of deprotonablecarboxylic groups (COOH groups) on theCNT surface during surface oxidation(these groups could also be detected byinfrared spectroscopy). Furthermore, thefigure demonstrates that also humic acid,which is ubiquitous in environmentalwaters, is able to stabilize CNTs as colloidssince it acts as a natural surfactant.

Finally, the sorption of heavy metal ions onCNTs was tested, and uranium was chosenas an example of a toxic heavy metal. Ad-sorption isotherms of hexavalent uraniumon pristine and modified CNTs are depictedin Fig. 2. As can be seen, increasingamounts of uranium are adsorbed by theCNTs with an increasing degree of func-tionalization. A rise in U(VI) sorptioncapacity by more than one order of mag-nitude due to surface modification wasobserved in our experiments. The type ofbinding of U(VI) onto CNTs is assumed tobe surface complexation between theuranyl ions and the carboxylic groups ofthe CNTs.

We think that transport of heavy metalssuch as uranium bound to CNTs throughnatural aquatic systems and even intobiological systems such as human cells(“Trojan Horse effect”) is at least con-ceivable. Considering the intensity of theinteractions between CNTs and someenvironmental contaminants as well as thepossibility that CNTs may act as “vehicles”for contaminants, the properties of CNTs inaquatic systems should be further investi-gated in order to enable prognoses of theirfate, behavior and effects if released to theaquatic environment.

References[1] Safe handling of nanotechnology,

A.D. Maynard, Nature 444, 267 – 269 (2006)

[2] Environmental colloids and particles, IUPAC series on analytical and physical chemistry of environmental systems, K.J. Wilkinson, J.R. Lead (eds.), Wiley Interscience 2007

[3] Aqueous suspensions of carbon nano-tubes: surface oxidation, colloidal stability and uranium sorption, A. Schierz1, H. Zänker, Environmental Pollution 157, 1088 – 1094 (2009)

Project partners· University of South Carolina, USA1

· Universität Göttingen, Germany· Universität Wien, Austria

Fig. 2: Sorption isotherms of uranium(VI) on pristine and modified CNTs (pH = 5, I = 0.1 M NaClO4,pCO2 = 10 -3.5 atm). The equilibrium surface loading by uranium, qeq, depends on the uraniumconcentration in solution, ceq, and on the intensity of the modification process (duration of sonicationat increased temperature).

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Fig. 1: Sedimentation behavior of pristine CNTs in the absence and presence of humic acid (HA) andsedimentation behavior of modified CNTs (pH 7, cCNT ≤ 100 mg L-1). The suspended CNTs areindicated by the light scattered from the solution at 90° when illuminated by a laser beam.


30

Astrid Barkleit, Henry Moll

Bacteria are very important for the bio-remediation of the environment becausethey are able to adsorb radionuclides andother heavy metals. They significantlyinfluence mobilization and immobilizationof metal ions in the soil. In order to betterunderstand the interaction of heavy metalswith the biosphere, knowledge of thebinding mechanisms on the molecular levelis essential. The main binding sites of bac-terial cell surfaces for heavy metal ions arephosphoryl, carboxyl, hydroxyl, and aminogroups. We investigate the interaction ofvarious actinides with isolated cell wallcompartments, which are assembled like puzzle pieces and are thus able torecognize complex biological systems.

Bacteria can be differentiated into twolarge groups based on the chemical andphysical properties of their cell walls.Gram-positive bacteria have a thickmultilayered peptidoglycan envelope,which amounts to up to 50 % of the dry mass of the cell wall. Gram-negativebacteria only have a thin monolayeredpeptidoglycan envelope (Fig. 1).Peptidoglycan consists of chains of sugarmolecules (polysaccharides = glycan)which are cross-linked with amino acidstrings (peptides). The most importantcompartment of the cell envelope ofGram-negative bacteria is lipopoly-saccharide. It is embedded in the outermembrane of the microbe, sticking outinto the environment. Lipopolysaccharideplays a key role in the protection againstcontaminants and selective assimilation of needed small molecules or metals. Itaccounts for about 30 % of the whole cellwall of Gram-negative bacteria. Whereaslipopolysaccharide contains an especiallyhigh amount of phosphoryl groups for

metal binding, they are missing in pepti-doglycan.

We investigated the interaction processesof isolated lipopolysaccharide biomacro-molecules from Pseudomonas aeruginosaand peptidoglycan biomacromoleculesfrom Bacillus subtilis with uranium(VI) andcurium(III). Uranium is widely spread in theenvironment due to uranium mining andmilling, or applications in industry. Curium,a solely man-made actinide, is highlyradiotoxic and very hazardous once it hasbeen released, for instance from nuclearwaste repositories. Both actinides showexcellent luminescence properties. Hence,we could study their interactions with thebiomacromolecules with time-resolvedlaser-induced fluorescence spectroscopy(TRLFS) over a wide pH range using traceconcentrations. Additionally, potentio-metric titrations were carried out todetermine the deprotonation constants of the biomacromolecules and stabilityconstants of the respective uraniumcomplex species.

Fig. 2 depicts selected luminescencespectra of uranium and curium with

lipopolysaccharide at different pH values.The spectra of the uranium lipopoly-saccharide system show a strong increaseof the luminescence intensity with risingpH and lipopolysaccharide concentration,connected with a strong red shift of thepeak maxima, compared to the freeaquatic uranyl ion UO2

2+(aq). Thisluminescence behavior is characteristic of the formation of very stable uranylcomplexes with organic phosphoryl orinorganic phosphate groups [1]. Threedifferent luminescence lifetimes over themeasured pH range refer to three differentphosphoryl coordinated uranyl lipopoly-saccharide species. In combination withpotentiometry, the composition andstoichiometries of these complexes couldbe identified. Additionally, a uranyllipopolysaccharide species with carboxylcoordination could be determined withpotentiometry only [2].

With increasing pH, the luminescencespectra of curium with lipopolysaccharideshow a red shift of the peak maximum ofthe free aquatic curium ion Cm3+(aq) withthree domains of new peak maxima (Fig.2)connected with three different lumines-

Interaction of actinides with isolated bacterial cell wall components

Fig. 1: Left: Gram-negative bacteria Pseudomonas aeruginosa (scanning electron micrograph (SEM); source: http://commons.wikimedia.org; photo: CDC/ Janice Haney Carr). Right: Scheme of bacterial cell walls of Gram-positive and Gram-negative bacteria.

31

cence lifetimes, indicating the formation ofthree different curium lipopolysaccharidecomplex species. These luminescenceproperties could be assigned to a phos-phoryl coordinated complex, a carboxylcoordinated species, and one withhydroxyl coordination.

Up to pH ~ 5.6 the luminescence spectra of the uranium peptidoglycan system showa slight increase of the luminescence

intensity connected with a red shift of thepeak maxima, and then again a strongdecrease of the luminescence intensitycaused by a quenching uranyl complexspecies. This inferior luminescence be-havior is typically caused by the formationof uranyl carboxyl complexes. Twodifferent luminescence lifetimes could bedetected, referring to two luminescentcomplexes. Again, we could identify theuranyl peptidoglycan species in combin-

ation with potentiometry. We found twocarboxyl coordinated complexes withdifferent stoichiometries, and the quench-ing species was identified as a complexwith carboxyl coordination and an addi-tional coordination through a hydroxyl or amino group [3].

Likewise, the luminescence spectra of thecurium peptidoglycan system show a redshift of the peak maximum to only onenew maximum, connected with also onlyone new luminescence lifetime whichbelongs to the sole curium peptidoglycancomplex species with carboxyl coordin-ation.

The speciation of the various uranium(VI)and curium(III) complexes with lipopoly-saccharide and peptidoglycan biomacro-molecules (Fig. 3) could be calculated with the stability constants determinedwith potentiometry and time-resolvedlaser-induced fluorescence spectroscopy.The comparison of the complexation of uranium and curium with lipopoly-saccharide and peptidoglycan shows thaturanium has a stronger tendency to bindwith phosphoryl groups than curium.Uranium forms stable complexes withcarboxyl or other functional groups only in absence of phosphoryl groups and onlyin the middle pH range (Fig. 3, U-PGNsystem) whereas curium forms similarlystable complexes with carboxyl, phos-phoryl, and hydroxyl groups over a widepH range (Fig. 3, Cm-LPS system). Ingeneral, lipopolysaccharide seems to havea better binding potential for metal ionsover a wider pH range than peptidoglycan.

References[1] Uranium(VI) complexes with phos-

pholipid model compounds – A laser spectroscopic study, A. Koban, G. Bernhard, Journal of Inorganic Biochemistry 101, 750 – 757 (2007)

[2] Interaction of uranium(VI) with lipopolysaccharide, A. Barkleit, H. Moll, G. Bernhard, Dalton Transactions, 2879 – 2886 ( 2008)

[3] Complexation of uranium(VI) with peptidoglycan, A. Barkleit, H. Moll, G. Bernhard, Dalton Transactions, submitted (2008)

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Fig. 2: Samples of luminescence spectra of uranium and curium with lipopolysaccharide (LPS)at different pH values.

Fig. 3: Speciation of the different uranyl and curium lipopolysaccharide (LPS) and peptidoglycan (PGN)species in aquatic solution. P = Phosphoryl coordination. C = Carboxyl coordination. H = Hydroxylcoordination.


32

Susanne Sachs, Katja Schmeide, Adéla Křepelová

The main objective of a final repository forhighly radioactive nuclear waste is to pro-tect people and the environment from therisks caused by the waste. According towaste management concepts, the radio-active waste should finally be stored indeep geological formations (Fig. 1). Inorder to keep the waste safe in the longrun and to isolate it from the biosphere, amulti-barrier system consisting of geologic-al and technical barriers has to be used.

All over the world, scientists are studyingwhether different rock formations, mainlysalt, argillaceous and crystalline rocks, e.g.granite, are acceptable as nuclear wasterepositories. In Germany, all three of thesetypes of rock formations come into con-sideration [1]. A comprehensive databaseon the properties of salt rock and saltformations relevant for the storage ofhighly radioactive nuclear waste is already

available. However, for granite and clayformations further studies are stillnecessary to be able to compare whetherdifferent rock formations are suitable as ahost rock.

Radionuclides with long radioactive half-lives, such as actinides as well as tech-netium-99, iodine-129, and selenium-79,play a prominent role for the safety case of a nuclear waste repository. In order toassess whether these radionuclides aremobile in the surroundings of a nuclearwaste repository in case of an accidentscenario, fundamental knowledge about all conceivable geochemical processes is a prerequisite. Our studies, which werefunded by the German Federal Ministry of Economics and Technology and by theEuropean Commission within the inte-grated project FUNMIG, contribute to thisunderstanding.

The migration behavior of actinides in anaquifer can strongly be affected by humicsubstances (humin, humic and fulvic acids),organic macromolecules ubiquitouslyfound in natural environments. Due totheir solubility in the pH range of naturalwaters, their ability to form complexes andcolloids as well as their redox properties,humic and fulvic acids can influence boththe immobilization and transport ofactinides. Most natural clays are closelyassociated with natural organic matter, e.g. humic acid- and fulvic acid-likecompounds, which can be mobilized fromclay. Both organic compounds associatedwith clay and organic compounds releasedfrom clay can influence the mobility ofmetal ions such as actinides.

In order to determine the influence ofhumic acid on the mobility of actinides in

clay formations, we studied the sorption of Am(III), Np(V) and U(VI) onto kaolinite,which is representative of clay minerals.These actinides were selected as examplesof actinides in different oxidation states.

The sorption experiments showed thathumic acid sorption onto kaolinitedecreases with increasing pH value [2].The sorption of actinides onto kaolinitewas found to be influenced by pH, ionicstrength, presence of CO2, actinideconcentration and humic acid presence.Fig. 2 shows the sorption of Am(III), Np(V)and U(VI) onto kaolinite in absence orpresence of humic acid. As can be seenfrom Fig. 2a, the Am(III) sorption ontokaolinite is very strong over the entire pHrange and is only slightly influenced byhumic acid. In contrast, the Np(V) sorptiononto kaolinite (Fig. 2b) is much lower. It increases with pH up to pH 8.5 anddecreases again at higher pH values. Inpresence of humic acid, the Np(V) uptakeis further decreased between pH 7.5 andpH 10.5. The U(VI) sorption onto kaolinite(Fig. 2c) shows a broad maximum betweenpH 5.5 and pH 8. Humic acid enhances theamount of adsorbed U(VI) in the acidic pHrange and reduces the U(VI) sorption inthe near-neutral pH range compared to thesystem without humic acid.

These results show that humic substancesare able to influence the sorption ofactinides onto kaolinite, and, thus, theirmobility. The increase of the actinidesorption in the acidic pH range comparedto the system without humic acid can beattributed to the humic acid sorption ontothe mineral, a scenario leading to addi-tional binding sites for actinides. Fig. 3shows a scheme for the sorption of metalions and humic substances onto clay

Humic substances and their influence on the mobility of actinides in clay formations

Fig. 1: Nuclear waste disposal in deep geologicalformations.

33

minerals. The reduction of the actinidesorption in the near-neutral pH range canbe attributed to the formation of aqueousactinide humate complexes. The com-parison of the actinide sorption behaviorshows that the sorption of actinidesdepends strongly on their oxidation stateand, thus, their speciation. In case ofU(VI), the species sorbed onto kaolinite inthe absence and presence of humic acidwere identified by time-resolved laser-induced fluorescence spectroscopy [3] andby extended X-ray absorption fine struc-ture spectroscopy [4]. These structural dataare an important basis for modeling theU(VI) sorption onto kaolinite.

The studies described above used an isol-ated humic acid and a pure clay mineral.However, natural clays comprise a mix oforganic matter. Therefore, more complex

interactions are expected. In order toapproach natural conditions and to identifyeffects of humic substances associatedwith natural clays which influence thesorption behavior of metal ions, wedeveloped an artificial humic substance-kaolinite-associate (HSKA) as model sub-stance and studied the sorption of U(VI)onto this product [5]. It was found that thehumic matter associated with kaolinite alsoexhibits an immobilizing as well as a mobil-izing effect on U(VI). However, due tostructural and functional dissimilarities ofthe humic substances, the U(VI) sorptiononto the synthetic HSKA differs from thatof U(VI) in the system U(VI)/humicacid/kaolinite with separately added purehumic acid. Thus, it was concluded thatnatural humic substances associated withclay or free in solution can show differentmobilizing effects on metal ions.

The present results are going to becompared to those for natural organicmatter-containing clays, which we arecurrently studying. In order to imitatenatural conditions more closely, diffusionexperiments are performed to study theinfluence of humic substances on theactinide migration in compacted clay.

References[1] Endlagerung radioaktiver Abfälle in

Deutschland. Untersuchung und Bewer-tung von Regionen mit potenziell geeigneten Wirtsformationen, BGR, Hannover/Berlin, 2007

[2] Uranium(VI) sorption onto kaolinite in the presence and absence of humic acid, A. Křepelová, S. Sachs, G. Bernhard, Radiochimica Acta 94, 825 – 833 (2006)

[3] U(VI)-kaolinite surface complexation in absence and presence of humic acid studied by TRLFS, A. Křepelová, V. Brendler, S. Sachs, N. Baumann, G. Bernhard, Environmental Science & Technology 41, 6142 – 6147 (2007)

[4] Structural characterization of U(VI) surface complexes on kaolinite in the presence of humic acid using EXAFS spectroscopy, A. Křepelová, T. Reich1, S. Sachs, J. Drebert1, G. Bernhard, Journal of Colloid and Interface Science 319, 40 – 47 (2008)

[5] Sorption of U(VI) onto an artificial humic substance-kaolinite-associate, S. Sachs, G. Bernhard, Chemosphere 72, 1441 – 1447 (2008)

Project partner· Institute of Nuclear Chemistry, Johannes Gutenberg Universität Mainz, Germany1Fig. 3: Scheme for the sorption of metal ions and humic substances onto clay minerals.

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Fig. 2: (a): Am(III), (b): Np(V), and (c): U(VI) sorption onto kaolinite in absence and presence of humic acid (HA). Experiments were performed under ambientatmosphere with initial Am(III), Np(V) and U(VI) concentrations of 1·10-6 M, a solid-to-liquid-ratio of 4 g kaolinite/L and an ionic strength of 0.01 M NaClO4.


34

Henry Moll, Gert Bernhard

Today, various human activities areresponsible for the contamination ofshallow and deep groundwater byactinides. These activities include theinjection of low- and intermediate-levelradioactive waste into deep geologicalformations, underground atomic bombtesting, leaching from mine waste, andaccidental leakage from current and futureunderground radioactive waste reposi-tories. The interaction between microbesand hazardous actinides may influencetheir environmental migration behavioronce they have been released.

Microorganisms can interact with actinidesthrough both direct and indirect pathways(Fig. 1).This study, which was partlyfunded by the German Federal Ministry ofEconomics and Technology, focuses on aninvestigation of indirect processes betweenmicrobes and actinides. Indirect processesinclude the formation of soluble complexesof actinides with various bioligands sec-reted by the resident microorganisms.

Microbes like Pseudomonads are ubiqui-tous soil and ground water bacteria. In our institute, we were able to isolate andidentify these microbes in uranium wastepiles or sewage from uranium mill tailings

where they are able to live under harshenvironmental conditions. In environmentspoor in iron, the fluorescent Pseudomonasspecies secrete bioligands, the so-calledpyoverdins. Due to their unique structure,pyoverdins have a great potential to bindmetals. The functional groups that areresponsible for binding the metals are thecatechol group of the chromophore andtwo ligand sites in the peptide chain, i.e.one or two hydroxamate groups and oneor two α-hydroxy acid moieties (Fig. 1). Inthis report, we present results describingthe complexation between the hazardousactinide elements uranium and curium andthe pyoverdins released by Pseudomonas

Mobilization of actinidesthrough bioligands secreted by microbes

Fig. 1: Direct (A-C) andindirect (D) interactionprocesses of microbes withreleased actinides. Thebioligands investigatedhere, the pyoverdins, are highlighted. Asterisksindicate the complexationsites involved in metalbinding.

35

fluorescens (CCUG 32456) cells isolatedfrom the granitic rock aquifers at the Äspöhard rock laboratory (HRL) in Sweden [1, 2]. This study is part of an internationalcooperation between the Institute ofRadiochemistry at the FZD and theGöteborg University (Department of Celland Molecular Biology, Microbiology) inSweden.In this paper, we are able toanswer the following question: besidesiron(III), do pyoverdins also form strongspecies with hazardous and radiotoxicactinides? If the answer to our question isyes, it would have a serious impact on theamount of actinides that can leach out of a nuclear waste disposal site.

Both the actinides (UO22 +, Cm3 +) and the

pyoverdins have excellent properties fordirect speciation studies with spectroscopictechniques. Ultra-violet and visible-light(UV-vis) spectroscopy, as well as time-resolved laser-induced fluorescence spec-troscopy with ultrafast pulses (fs-TRLFS) incombination with a factor analysis baseddata evaluation procedure, provides apracticable method for investigating thespeciation of UO2

2+ in the aqueous P.fluorescens (CCUG 32456) pyoverdinsystem. In our study, the pyoverdinmolecule is denoted LH4 according to the general assumption that pyoverdinmolecules can liberate four labile protonsfrom the complexing sites most likelyresponsible for metal binding. Fourdifferent pyoverdin species, i.e. LH4, LH3

-,LH2

2-, LH3-, and two uranyl pyoverdincomplexes, i.e. UO2LH2 and UO2LH-, couldbe identified by their individual absorption

spectra (Fig. 2). The identified uranium-pyoverdin complexes dominate theuranium speciation in the environmentallyrelevant pH range between 4 and 8 [1].The formation of the uranyl pyoverdincomplexes results in a static fluorescencequenching and, as a consequence, indrastic changes of the fluorescence prop-erties of pyoverdin. Therefore, pyoverdinscould be used as fluorescence probes toinvestigate siderophore-mediated proces-ses, e.g. to measure the uptake of metalsby bacterial cells, in biological systems. Theresults of this study indicate that pyo-verdins present in groundwater at the µMconcentration level can contribute to theincreased dissolution of uranium from, forexample, mine waste. At the RossendorfBeamline (ROBL) at the ESRF, we investi-gated the structure of uranium-pyoverdincomplexes in aqueous solution, by usingextended X-ray absorption fine structure(EXAFS) spectroscopy. The results indicatea strong affinity of uranyl to the catecholfunctionality of the pyoverdin molecule.

The unknown interaction between solublespecies of curium(III) and pyoverdins wasstudied at trace curium(III) concentrations(3x10-7 M) using time-resolved laser-induced fluorescence spectroscopy(TRLFS). Strong Cm3+ pyoverdin speciesare formed, indicating that these uniquebioligands have a great potential tomobilize curium(III) in the biologicallyrelevant pH range [2]. Three Cm3+

pyoverdin complexes, CmH2L+, CmHL,

and CmL-, could be identified by theirindividual emission spectra (Fig. 3). We

were able to observe an indirect excitationmechanism for the curium(III) lumines-cence in the presence of pyoverdinmolecules.

In conclusion, both actinides form strongsoluble pyoverdin species in aqueoussolutions. The chemical reactions betweenboth actinides (UO2

2+, Cm3+) and aqueouspyoverdin species were determined usingdifferent spectroscopic techniques. Thestability constants of these individual reac-tions can be used directly in safety calcu-lations to quantify the actinide-mobilizingeffect of the pyoverdins released, forexample, in the vicinity of a nuclear wasterepository. Such complexation studies ofselected bioligands are essential to explainthe overall interaction processes of acti-nides with microbes at the molecular level.

Rossendorf Beamline



Cancer R

esearch


PET-Center

Ion Beam Center


References[1] Characterization of pyoverdins secreted

by a subsurface strain of Pseudomonas fluorescens and their interactions with uranium(VI), H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicro-biology Journal 25, 157 – 166 (2008)

[2] Curium(III) complexation with pyo-verdins secreted by a groundwater strain of Pseudomonas fluorescens, H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, BioMetals 21, 219 – 228 (2008)

Project partner· Department of Cell and Molecular Biology, Microbiology, Göteborg University, Sweden

Fig. 3: Luminescence emission spectra of the aqueous Cm3+-P. fluorescens(CCUG 32456) pyoverdin species. The spectra are scaled to the same peakarea. L4 - = deprotonated pyoverdin molecule.

Fig. 2: Absorption spectra of the individual components of the aqueousP. fluorescens (CCUG 32456) pyoverdin system with and without UO2

2+.L4 - = deprotonated pyoverdin molecule.

FACTS & FIGURES

37

The Forschungszentrum Dresden-Rossendorf (FZD) is a multi-disciplinary research centerfor natural sciences and technology. It is the largest institute of the Leibniz Associationand is equally funded by the Federal Republic of Germany and the Federal States, inparticular by the Free State of Saxony. At the FZD, around 330 scientists are engaged inthree different research programs of basic and application-oriented research. Scientistsworking in the Advanced Materials Research program investigate the reactions of matterin strong fields and at small dimensions. Research and development in the CancerResearch program is focused on the imaging of tumors and the effective radiationtreatment of cancer. How can humankind and the environment be protected fromtechnical risks? – This question is in the center of research in the Nuclear Safety Researchprogram of the FZD.

In the following Facts & Figures section data presenting the scientific output in theNuclear Safety Research program are given as well as information on staff and funding at the FZD.

Facts & Figures

3838

Advanced Materials Research Cancer ResearchNuclear Safety Research

14

12

10

8

6

4

2

02007 2008

staff scientists third-party funded scientistsguest scientists postdocs

50

40

30

20

10

02007 2008

Patents – FZD

Scientific staff – Nuclear safety research

Number of applications for a patent filed in each researchprogram of the FZD in 2007 and 2008.

Distribution of positions occupied by scientific personnel in theNuclear Safety Research program of the FZD. Third-party fundedscientists, guest scientists, and postdocs represented by thecorresponding figures are given in units of paid full-time posts.*

2007 2008

Research Programs


Cancer Research


Large-Scale Facilities

Sum

Core Funding

T€

19.776

7.729

12.577

14.564

54.646

Third-Party Funding

T€

1.600

1.141

5.086

1.487

9.314

Core Funding

T€

17.822

9.340

13.069

18.401

58.632

Third-PartyFunding

T€

4.622

840

3.660

4.028

13.150

Budget

Share of each research program, as well as of the experimental facilities located at the FZD,of both core and third-party funding during the last two years.

*All figures as of 1st March 2009.

39

FACTS & FIGURES

11

10

8

7

7

6

USA

Bulgaria

China

Australia

Italy

Great Britain

6

6

5

5

5

5

Russia

Czech Republic

Poland

Ukraine

India

Hungary

59

23

20

14

13

11

Japan

Turkey

France

Netherlands

Romania

Spain

4

4

3

3

3

21

Latvia

Portugal

Algeria

Egypt

Israel

others

200

160

120

80

40

02004 2005 2006 2007 2008

140

120

100

80

60

40

20

02004 2005 2006 2007 2008

Publications – Nuclear safety research

Doctoral students – FZD

International guest scientists – FZD

Growth in number of doctoral students at the FZD from2004 until 2008.

Number of peer-reviewed articles by scientists from theFZD’s Nuclear Safety Research program. The figuresinclude reviewed proceedings (2004: 39, 2005: 50, 2006: 53, 2007: 64, 2008: 71).

Distribution of the international guest scientists whovisited the FZD for the purpose of research between 2007 and 2008 according to their countries of origin.

40

Organizational Chart

ADVANCED MATERIALS RESEARCH

CANCER RESEARCH

Research Technology

Dr. Frank Herbrand

Administration

Andrea Runow

Technical Service

Dr. Wolfgang Matz

Institute of Ion Beam Physics andMaterials Research

Prof. W. Möller and Prof. M. Helm

Institute of Radiopharmacy

Prof. Jörg Steinbach

Dresden High Magnetic FieldLaboratory

Prof. Joachim Wosnitza

Institute of Radiation Physics

Prof. Thomas Cowan

NUCLEAR SAFETY RESEARCH

Institute of Radiochemistry

Prof. Gert Bernhard

General Assembly

Scientific Advisory Board Chair: Prof. August Schubiger

Supervisory BoardChairman: Dr. Gerd UhlmannDeputy: Dr. Jan Grapentin

Scientific Technical Council Chair: Prof. Joachim Wosnitza

Works Committee Chair: Siegfried Dienel

Support Staff

Board of Directors Scientific Director Administrative DirectorProf. Roland Sauerbrey Prof. Peter Joehnk

Institute of Safety Research

Prof. Frank-Peter Weiß

March 2009� Advanced Materials Research � Cancer Research � Nuclear Safety Research

Forschungszentrum Dresden-RossendorfP.O. Box 51 01 19 I 01314 Dresden/GermanyScientific Director I Prof. Dr. Roland SauerbreyPhone +49 351 260 2625Fax +49 351 260 2700Email [email protected]

Member of the Leibniz Association

i nuclear safety - hzdr · minimize the risks related to the nuclear ... description of ageing...

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