Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

New reactor designs comprise passive elements for decay heat removal. Computational-Fluid-Dynamics codes are an appropriate tool for the assessment of the efficiency of those components. Most of these codes are based either on the Finite-Volume or the Finite-Element method. Because of the importance for reactor safety these numerical tools have to be thoroughly validated using results from experimental setups.
The governing mechanism in passive components for decay heat removal is natural convection and heat transfer with internal heating. To assess the capability describing mixed convection flow, post test calculations of an IAHR benchmark exercise were performed. The commercial codes CFX-4® and ANSYS/FLOTRAN® were used, representing the Finite-Volume Method and the Finite-Element Method respectively.
This paper presents a discussion of the problems and capabilities of each code to calculate complex flow regimes and temperature fields.

The behavior of PWRs during cold water or boron dilution transients is strongly influenced by the distribution of coolant
temperature and boron concentration at the core inlet. This distribution is the needed input to 3-dimensional neutron kinetics to
calculate the power distribution in the core. It mainly depends on how the plugs of cold or unborated water formed in a single loop
are mixed in the downcomer and in the lower plenum.

To simulate such mixture phenomena requires the application of 3-dimensional CFD (computational fluid dynamics) codes. The
calculations are based on the CFD Code CFX-4. The results of the simulation have to be validated against mixture experiments at
scaled facilities.

Therefore, in the framework of a research project funded by BMBF, the institute created a 1:5 mixture facility representing first the
geometry of a German pressurized water reactor and later the European Pressurized Water Reactor (EPR) geometry.

In the Forschungszentrum Rossendorf a measurements techniques test loop was constructed. Air water flow in a vertical tube was investigated using different two phase flow measuring techniques. The paper describes the used measuring techniques and some performed experiments. The code CFX-4.2 with its implemented two phase models was used, to simulate bubbly flow and to compare calculated void profiles with the measured results.

The behavior of PWRs during cold water or boron dilution transients is strongly influenced by the distribution of coolant temperature and boron concentration at the core inlet. This distribution is required as an input to 3-dimensional neutron kinetics to calculate the power distribution in the core. It mainly depends on how the plugs of cold or unborated water formed in a single loop are mixed in the downcomer and in the lower plenum [1]. The reactivity insertion due to penetration of unborated coolant into the core depends on the degree of mixing. Weak mixing can result in recriticality and possibly in significant power release. The same is true for cold water insertion into the core due to overcooling of a coolant loop in the case of a steam line break. Coolant mixing is also of interest under steady state normal operation conditions. Slight differences in the cold leg temperatures can occur due to small asymmetries in the primary circuit loops.

To simulate such mixture phenomena requires the application of 3-dimensional CFD (computational fluid dynamics) codes. The results of the simulation have to be validated against mixing experiments at scaled facilities. The calculations are accomplished using the CFD Code CFX-4.2 [2].

As a first step, steady state mixing conditions in the downcomer and lower plenum are considered. Qualitatively different flow fields were found in different reactor types depending from the downcomer geometry. Calculated results were compared with experiments.

At the Gesellschaft für Schwerionenforschung in Darmstadt a therapy unit for heavy ion cancer treatment has been established in collaboration with the Deutsches Krebsforschungszentrum Heidelberg, the Radiologische Universitätsklinik Heidelberg and the Forschungszentrum Rossendorf.

For quality assurance the dual-head positron camera BASTEI (Beta Activity meaSurements at the Therapy with Energetic Ions) has been integrated into this facility. It measures ß⁺-activity distributions generated via nuclear fragmentation reactions within the target volume.
BASTEI has about 4 million coincidence channels. The emission data are acquired in a 3D regime and stored in a list mode data format. Typically counting statstics is two to three orders of magnitude lower than those of typical PET-scans in nuclear medicine.

Two iterative 3D reconstruction algorithms based on ISRA (Image Space Reconstruction Algorithm) and MLEM (Maximum Likelihood Expectation Maximization), respectively, have been adapted to this imaging geometry. The major advantage of the developed approaches are run-time Monte-Carlo simulations which are used to calculate the transition matrix.
The influences of detector sensitivity variations, randoms, activity from outside of the field of view and attenuation are corrected for the individual coincidence channels.

Performance studies show, that the implementation based on MLEM is the algorithm of merit. Since 1997 it has been applied sucessfully to patient data. The localization of distal and lateral gradients of the ß⁺-activity distribution is guaranteed in the longitudinal sections. Out of the longitudinal sections the lateral gradients of the ß⁺-activity distribution should be interpreted using a priori knowledge.

The ratio between magnetic and nuclear small angle neutron scattering (SANS) can provide additional information about the composition and structure of the scattering inhomogenities. The method fails if the material system does not meet the two-phase approach. In this case, by using the indirect transformation method, the ratio can more generally be defined and related to the dependence of the scattering particle size. The method is derived and applied to model systems with two types of non-magnetic spheric inhomogenities in a ferromagnetic matrix.

Solidified liquid metal ion sources (LMISs) operating with Au alloy wetted hair-pin emitters can be used as high-intensity electron point sources for application in the field of ultrahigh vacuum techniques. A nanotip emitter on a solidified LMIS emitter can be formed by quenching during ion emission mode. I - V characteristics and the performance of the electron emitting LMIS are presented.

Technical Reports on VVER transients were provided by IVO, NRI, KI, STCNRS and INRNE. The present report gives a survey of the transients documented by the five organisations mentioned. The main actions and effects observed during each transient are briefly described. An overview of the information contained in the five Technical Reports is provided in tabular form. The tables comprise information on the initial states, the measured parameters, and the time regime of the measurement. For each reactor type, VVER­440 and VVER­1000, respectively, one transient is recommended for coupled codes validation in the current project.

Despite the great success of dynamo theory during the last decades an experimental verification of magnetic field self-excitation in conducting fluids is still missing. We summarize the outcomes of a workshop held in Riga in June 1998 on various experimental approaches to this topic. The Riga dynamo
experiment is presented in more detail.

We present numerical simulations for the Riga dynamo experiment, which is intended
to verify the magnetic field self-excitation in a helical flow of a conducting fluid.
Testing a wide variety of axial and azimuthal velocity profiles we show the importance
of the global helicity for the efficiency of the dynamo. Predictions are made on
the shape of the arising magnetic field and the back-reaction of the
Lorentz force on the flow.

The critical magnetic Reynolds number (Rm) of the Riga dynamo experiment depends
strongly on the shape of its velocity profiles. For given motor power ressources it is
necessary to optimize these profiles in order to achieve self-excitation of the magnetic
field. We present a number of one- and two-dimensional calculations for a variety of
axial and azimuthal velocities. Particularly, we test velocity profiles with maximal
helicity (Bessel function profile). For these velocity profiles the critical Rm can
be reduced by 20 per cent compared to the value for the solid body rotation profile.
The used two-dimensional finite difference solver allows to study the effect of
axially varying profiles, too. In addition, we present some two-dimensional
calculations for further dynamo experiments in cylindrical geometry, including
the flow topologies s1t1, s2t1 and s2t2. The influence of the flow direction and
the effect of a surrounding conducting medium on the critical Rm is investigated
in detail.

We present numerical results on the control of 2-D and 3-D instabilities in the wake of a circular cylinder by means of externally applied magnetic fields. 2-D instability (vortex shedding) can clearly be suppressed with increasing field strength. However, 3-D instability is influenced in a nonmonotonic way, triggered by changes to the 2-D flow. 3-D instability can exist below the 2-D stability threshold, which may lead to a reversal of the order of instabilities for fixed field strength. Strong fields seem to amplify 3-D instability.

In 1995 at the integral test facility ISB-VVER in Elektrogorsk near Moscow natural circulation experiments were performed, which were scientifically accompanied by the Forschungszentrum Rossendorf. These experiments were the first of this kind at a test facility, which models VVER-1000 thermalhydraulics. Using the code ATHLET which is being developed by "Gesellschaft für Anlagen- und Reaktorsicherheit", pre- and posttest calculations were done to determine the thermalhydraulic events to be expected and to define and tune the boundary conditions of the test. The conditions found for natural circulation instabilities and cold leg loop seal clearing could be confirmed by the tests. Besides the thermalhydraulic standard measuring system, the facility was equipped with needle shaped conductivity probes for measuring the local void fractions.

The OECD has defined a benchmark for coupled Cartesian neutron kinetics/thermohydraulics code systems. In the first phase, a plant simulation with point kinetics was requested. The purpose was to test the model response.
In this presentation, the dependence of the results obtained by means of the ATHLET-code from several important parameters is investigated. It was found, that the nodalization of the steamline in the vicinity of the break has an influence on the pressure behaviour and on the time of the return-to-power.

The fifth dynamic benchmark was defined at the 7th AER-Symposium, held in Hörnitz, Germany in 1997. It is the first benchmark for coupled thermohydraulic system/three-dimensional hexagonal neutron kinetic core models. In this benchmark the interaction between the components of a VVER-440 NPP with the reactor core has been investigated. In this presentation, the first results obtained by means of the codes DYN3D/ATHLET (Forschungszentrum Rossendorf), BIPR8/ATHLET (Kurchatov Institute Moscow) und HEXTRAN/SMABRE (VTT Energy Espoo) were compared. Both thermohydraulics and neutron kinetics parameters show dif-
ferences.

A new nodal method HEXNEM2 for hexagonal geometry is described. The method is based on a two-dimensional expansion of
the intranodal fluxes. Polynomials up to the second order and exponential functions are used in each group. By this method the singular
terms occurring in the transverse integration methods are avoided. Side averaged and corner point values of fluxes and currents are used
for the coupling of nodes. A calculation scheme for the outgoing partial currents at the sides and similar expressions for the corners from
given incoming values are used in the inner iteration which gives a fast running scheme. The method is tested against 2-dimensional
hexagonal benchmark problems for the VVER-type reactors. The results show that the multiplication factor and nodal powers are predicted
accurately. A considerable improvement can be shown of the results for the VVER-1000 benchmarks compared with the method developed
previously for the code DYN3D and the simpler method HEXNEM1.

A summary of magnetic field effects on surface driven flows will be given. Own work in the fields
- hydrothermal waves controlled by magnetic fields,
- Marangoni flows at liquid metal surfaces,
- thermoelectrically driven flows,
- levitated spheres and drops,
- Marangoni motion of drops
will be summarized. In addition, literature results about magnetic field influence on floating zone crystal growth or the use of magnetic fields in laser or electron beam welding bill be given. The second part of the lecture will concentrate on possible experiments with magnetic fields under microgravity. Proposals will be presented for discussion for crystal growth with magnetic fields, thermoelectricity, electromagnetic gas injectors, or magnetic field control of electrochemical processes. Emphasis will be put on the problem of diagnostics being inherent to all activities.

A summary of MHD effects and technical applications will be given based on a classification of the different actions of external magnetic fields and/or external electrical currents. An overview of the different alternating fields (rotating, pulsating, travelling) and static magnetic fields, and their interaction with liquid metal melts will be given. Special emphasis will be put on applications in crystal growth where a contactless melt flow control is important for the convective motions in many growth technologies. Typically steady magnetic fields are used to damp such flows. Surprisingly, active flow driving forces due to alternating magnetic fields can be of stabilizing character, too. Numerical results for the combined action of DC and AC magnetic fields will be presented for two problems: vertical Bridgeman and silicon Czochralski crystal growth. Recent results on MHD turbulence and some destabilizing actions of steady magnetic fields will shortly be mentioned. Special attention will be given to the problem of measuring techniques in liquid metal melts since this is a crucial question for any experimental activities in the field. For instance, any activity for code validation will require model experiments which, in turn, quickly lead to serious measuring problems. Some new results and ideas will be discussed.

Eine kontaktlose Beeinflussung der konvektiven Strömung in der Schmelze ist in vielen Kristallzüchtungstechnologien von großer Bedeutung. Gewöhnlich werden stationäre magnetische Felder benutzt, um solche Strömungen zu dämpfen. Überraschenderweise können auch aktive Strömungsantriebskräfte, die von instationären magnetischen Feldern erzeugt werden, von stabilisierendem Charakter sein. Wir stellen Resultate der numerischen Simulation der kombinierten Wirkung von homogenen und linearen stationären Magnetfeldern für die Silizium-Czochalski-Kristallzüchtung und von homogenen und rotierenden Magnetfeldern für die Bridgman-Anordnung vor. Es werden bei der Czochalski-Geometrie nicht nur die thermische Konvektion und die Rotation des Kristalls und des Tiegels in Betracht gezogen, sondern auch der Einfluß der antreibenden und/oder dämpfenden elektromagnetischen Kräfte sowie der Einfluß des induzierten elektrischen Stromes und der thermokapillar angetriebenen Strömungen an der freien deformierbaren Schmelzoberfläche. Aufgrund der hohen Reynolds-Zahl der Strömung ist die numerische Simulation laminar nicht mehr möglich. Es werden vergleichende Rechnungen mit einem Null-Gleichungs-Turbulenzmodell, das auf der Prandtl´schen Mischungsweg-Hypothese basiert, und einem anisotropen k-epsilon Turbulenzmodell durchgeführt.

The flow around bodies moving in weakly electrically conducting fluids can be controlled by applying electromagnetic forces originating from electrodes and permanent magnets suitably placed on the surface of the body. Here we consider the
possibility of separation control for a two-dimensional bluff body and an inclined flat plate by inducing Lorentz forces parallel to the surface. We present physical and numerical experiments at diameter/chord Reynolds numbers in the range of 300--4,000 for the circular cylinder and 2,000--20,000 for the plate. Both steady and time-periodic forcing are applied. The physical experiments are conducted in an open channel with sodium hydroxide as the working fluid. Dramatic separation delays are observed on both bodies for a modest expenditure of energy. Special attention is drawn to lift enhancement due to separation delay for the inclined plate. Direct numerical simulations at low Reynolds numbers confirm the physical tendencies of the experiments.

The flow around bodies (cylinder, plate) can be controlled by applying electromagnetic forces originating from electrodes and permanent magnets suitably placed on the surface of the body. There is a large variety for applying those forces with respect to the geometrical arrangement and the electrical current feeding the electrodes. The goals of this approach are flow stabilization, drag reduction or manoeuvrability of the body in an electrically low-conducting fluid like seawater. We present experimental and numerical results for a low Reynolds-number range of 200 < Re < 4000. Experiments were performed using a copper sulphate electrolytic solution and a sodium hydroxide loop. Flows are considered around a cylinder and over a plate, with
Lorentz forces being parallel to the body surface. Experimental results will be presented for the body drag and the wake flow structures depending on different
regimes of electromagnetic forcing. In particular, we distinguish between the
regimes of direct, frequency-variable sinusoidal or pulsed electric currents. Numerical results confirm the physical tendencies at least for lower Reynolds numbers. Parameter ranges will be given for an optimal electromagnetic flow control in terms of drag reduction and flow laminarization. The energetic balance will be discussed.

Specimen reconstitution, i.e. the incorporation of a small piece from a previously tested specimen into a compound specimen, allows to multiply the number of tests. That is especially important if the available material is restricted and new parameters have to be measured. For this purpose a technique was developed to reconstitute Charpy size single-edge notch specimens (SENB) from broken halves of Charpy V-notch specimens. The essential tools for producing reconstituted specimens are a stud arc welding set-up and an electric wire discharge machine. The reconstitution technique applied is in accordance with the ASTM- guideline E-1253. The fraction of the insert that is affected by the reconstitution technique is determined by measurements of temperature and hardness gradients and by metallographic examination. The specimen reconstitution technique has been validated for SENB specimens of Charpy geometry. The test methods comprised instrumented impact testing of Charpy V specimens and elastic- plastic fracture toughness testing with precracked and side grooved SENB specimens.

Der Traum von magnetohydrodynamischen (MHD)-Generatoren und MHD-Schiffsantrieben hat sich nicht erfüllt. Die magnetisch gesteuerte Kernfusion läßt auf sich warten. Doch die Stille trügt:; MHD-Technologien halten erfolgreich Einzug in Metallurgie und Verfahrenstechnik, MHD-Experimente eröffnen neue Perspektiven für die nichtlineare Physik und Turbulenzforschung, und selbst das klassische Problem der Entstehung des Erdmagnetfeldes scheint seiner experimentellen Verifikation nahe zu sein.

The Riga dynamo experiment is an attempt to show the
self-excitation of a magnetic field in an electrically conducting fluid.
Due to the absence of any scale separation effects, the precise shape of
the velocity profile has a strong influence on the values
of the critical magnetic Reynolds numbers (Rm).
Several numerical codes have been developed and used for the determination
of these critical Rm for arbitrary velocity profiles.
Helicity maximizing
profiles are shown to provide smaller critical Rm than the
solid body rotation flow. We outline how the velocity profiles
have been optimized in an iterative process including flow measurements,
constructive improvements and numerical calculations.

On the NOKO (emergency condenser) test station constructed at Jülich Research Centre, the operating performance and
effectiveness of the emergency condenser of the boiling water reactor 1000 have been determined in well over 200 tests. It has been
possible to check that the tests were in close agreement with a modified version of ATHLET

Thermocapillary Marangoni convection of liquid gallium was studied experimentally and numerically. A specially designed experimental setup ensured an oxide-free surface of the liquid gallium for a very long time. The convective flow at the free surface was found to be directed opposite to both buoyancy-driven and ordinary thermocapillary convection. The anomalous direction of the thermocapillary flow was explained by the presence of a small amount of a surface-active contaminant - lead adsorbed at the free surface. Two different approaches were used to describe the observed phenomenon. First, the flow was treated as a pure thermocapillary convection with a modified dependence of the surface tension on temperature so that to reproduce the measured velocity distribution. Second, a novel physical model was devised for the flow driven by the gradient of the surface tension induced by the temperature dependence of the concentration of the adsorbed layer of contaminant. In contrast to the ordinary thermocapillary convection in low-Prandtl-number liquids, there is a strong coupling between the flow and the driving force in the proposed model resulting in velocity profiles very similar to those observed in the experiment.

Neutral Re(I) carbonyl complexes with multidentate thioethers of the general formula [ReBr(CO)₃(R-S(CH₂)₂S-R')] were obtained by ligand exchange reaction starting from [ReBr₃(CO)₃]^2-. The thioether ligands bear functional groups (R, R'', such as the carboxyl, propargyl and hydroxyl moiety, which can act as anchor groups for biologically active molecules. First representatives of Re(I) and Tc(I) carbonyl thioether complexes, meant to target CNS neuroreceptors and hormone receptor-positive breast tumors, are described.

Two different instability mechanisms of electromagnetically levitated bodies are analyzed. The first is due to the virtual coupling between the electric current passing through the magnetic system and the variation of position of the body. This mechanism can result in unstable mass center oscillations of a levitated solid body. Another type of instabilities may occur because of the coupling beween the motion and the electric currents induced in the body. This effect can cause a spontaneous rotation of the body setting in as the frequency of the alternating magnetic field exceeds certain critaical threshold depending on the configuration of the field. This instability can be suppressed by an axial steady magnetic field of strength comparable to that of the levitating field.

We study the linear stability of a thermocapilary-driven convection in a planar unbounded layer of an electrically conducting low-Prandtl-number liquid heated from the side and subjected to a transverse magnetic field. The thresholds of convective instability for both longitudional and oblique disturbances are calculated numerically and also asymptotically by considering the Hartmann and Prandtl numbers as large and small parameters, respectively. The magnetic field has a stabilizing effect on the flow with the critical temperature gradient for the transition from steady to oscillatory convection increasing as square of the the field strength. So increases also the critical frequency, while the critical wavelength reduces inversely with field strength. These asymptotics develop in a strong enough magnetic field when the instability is entirely due to the jet of the base flow confined in the Hartmann layer at the free surface. In contrast to the base flow, the critical disturbances, having a long wavelength at small Prandtl numbers, extend from the free surface into the bulk of the liquid layer over a distance exceeding the thickness of the Hartmann layer O(Pr-1/2) times. For Ha ? Pr-1/2 the instability is influenced by the actual depth of the layer. For such moderate magnetic fields the instability threshold is sensitive to the thermal properties of the bottom of the layer and the dependences of the critical parameters on the field strength are more complicated. In the latter case, there is a number of various instability modes possible depending on the thermal boundary conditions and the relative magnitudes of Prandtl and Hartmann numbers.

In the present paper we are concerned with the control of wake instabilities in the flow of an electrically conducting fluid around a circular cylinder by means of external magnetic fields. Besides the Reynolds number (Re) a second parameter N appears describing the strength of the magnetic body force. This offers, depending on the direction of the magnetic field, a large variety of flow configurations and therefore different transition regimes. We perform a numerical simulation of the unsteady two-dimensional flow and characterize the different flow regimes. Strong magnetic fields are capable to stabilize the 2-D flow and to suppress the shedding of vortices. We present curves of neutral 2-D stability in the (Re,N)-parameter plane separating steady and periodic flow regimes. We further perform a linear 3-D stability analysis of the 2-D flow being either steady or periodic and show how the magnetic field influences the 3-D instabilities. We pay special attention to the case when the magnetic field is aligned with the oncoming flow. Here we find 3-D instability in parameter regions above the 2-D stability curve in the (Re, N)-plane where the flow is 2-D stable (steady). This firstly confirms a general result of Hunt (J.C.R. Hunt, Proc. Roy. Soc. A 293 (1966) 342) obtained from a stability analysis of parallel flows and shows that the magnetic field influences 2-D and 3-D instabilities in a different way.

Rotating magnetic fields are of growing interest for crystal growth technologies from the melt. For a few millitesla they provide a controlled motion within the melt, thus controlling the heat and mass transfer and the temperature fluctuations. This paper gives numerical results for the stability thresholds of rotating magnetic field and buoyancy driven melt convections, also by additionally superimposing a steady magnetic field. Some numerical results are given for a possible explanation of the surprising stabilizing action of the rotating magnetic field on a pre-given buoyant flow.

Small-angle neutron scattering (SANS) experiments were performed at KWS2 facility of the KFA Jülich for investigating the defect structures, which are produced by neutron irradiation in Russian Cr-Mo-V alloyed reactor pressure vessel steel. Irradiation and post-irradiation annealing considerably change both SANS intensity and its course in the Guinier plot, which was analysed by the Glatter method. As a rule, bimodal size distribution functions were found with a first maximum at a radius of 1-2 nm and a second maximum at 6-8 nm. Irradiation increases the first maximum annealing reduces it.

The formation of point defects and precipitates after neutron irradiation of VVER-440-type reactor pressure vessel steel was investigated by small angle neutron scattering experiments. Irradiation at 60 °C increased the number of point defects, decreased the precipitates, which already exist in the unirradiated state, and formed a new typ of fine-scaled precipitates. Post-irradiation annealing near the operational temperature of the nuclear power plants (270 °C) provoked a slight decrease of the content of point defects and of the irradiation-induced precipitates. The content of these precipitates which are also present in the unirradiated state did not change by annealing.

We investigate the dispersion of gas bubbles injected from a single orifice into a liquid metal flow subjected to transverse and longitudinal magnetic fields. The local void fraction is detected by means of resistivity probes. The results show a damping of velocity fluctuations corresponding to a decrease in the bubble dispersion with increasing magnetic field. An isotropic distribution of the gas phase is preserved if a longitudinal field is applied, while an anisotropic distribution is observed in case the applied magnetic field is transverse to the flow indicating the existence of quasi-two-dimensional vortices as typical of turbulent MHD flows.

The use of a liquid metal target in the concept of a new generation of spallation sources is recommended due to a number of obvious advantages such as a high heat removal capacity, no structural radiation damage of the target material, no water presence in the proton beam interaction zone, etc.. In the regime of a pulsed proton beam at high repetition rates a considerable high instantaneous power is injected into the fluid during very short time periods. This fact gives rise to strong thermal shock waves resulting in substantial stress loads on the container wall. The addition of small Helium bubbles to the flow is considered as a method to diminish this problem by increasing the fluid compressibility. This study reviews some standard methods of gas
injection and checks their suitability for the application in heavy liquid metals with a high value of surface tension. Another important aspect discussed here is the availability of measuring techniques allowing a reliable characterisation of tiny bubbles in opaque liquid metals.

The production of highly porous metallic substrates requires an effective and well controlled production of metallic fibres with diameters in the range of 50 to 200 microns. The melt extraction, where a quickly rotating wheel extracts fibres directly out of the inductively heated melt, is a promising technology for that purpose. The main limitations of this process are due to turbulence within the melt and a wavy motion on the surface. Both effects give rise to strong and time dependent deformation of the melt surface which, in turn, causes non-stationary conditions of the contact zone between the extraction wheel and the melt. In the patent literature many xamples can be found which try to overcome these problems by submersing mechanical parts directly into, or placing them at least in close vicinity to the melt, aiming at a stabilisation of that contact region. Even made of heat resistant ceramics they suffer from corrosion or cracks and do not work reliable at all. The present work describes a non invasive control mechanism by means of a magnetic field. Model experiments were carried out to study the calm down of the turbulent surface of a inductively stirred melt. The stabilisation of the melt surface has been demonstrated in practise by the installation of a solenoid at a working extraction facility under rough industrial conditions like a powerful induction heating and vacuum.

The microstructural evolution of Russian VVER 440-type RPV steele due to neutron irradiation was investigated by small angle neutron scattering. Irradiation produces nanoscaled precipitates. Their volume fraction and their thermal stability depends on the copper content.

Aluminum precipitates are formed after Al implantation with dose 3x10¹⁷ cm^-2 at 500°C into single crystalline 6H-SiC. The aluminum carbide (Al₄C₃)precipitates are in epitaxial relation with 6H-SiC matrix, having the following orientation relation, [0001]6H-SiC//[0001]Al₄C₃ and [11-20]6H-SiC//[11-20]Al₄C₃, as transmission electron microscopy reveals. The aluminum carbide appears around the maximum of the Al depth distribution. Silicon precipitates were also detected in the same zone.

Monte Carlo calculations based on a three-dimensional pinwise representation of the sources and considering all known geometrical and composition details were used for the determination not only of fluence integrals but also of fluence spectra. This was possible by the application of the specially developed code system TRAMO for Monte Carlo calculations and data preparation. A good statistical accuracy was achieved by successfully modifying variance reduction on the basis of the weight window method. Multigroup data sets based on ENDF/B-VI, JEF-2 and the Russian ABBN library were applied. The influence of different data libraries and numbers of groups was investigated. For the realistic representation of fission sources the burnup and the power history for each fuel pin and height layer was considered.
The calculations were verified and adjusted by activation measurements. ⁵⁴Fe(n,p)⁵⁴Mn, ⁵⁸Ni(n,p)⁵⁸Co, ⁴⁶Ti(n,p)⁴⁶Sc, ⁶³Cu(n, )⁶⁰Co and ⁹³Nb(n,n')Nb^93m detectors were irradiated during fuel cycle 5 in the ex-vessel cavity of the Russian VVER-1000 type reactor Balakovo-3 and analysed afterwards by advanced gamma spectrometric methods. For the detectors with the shortest half-lifes "detector fluences" were calculated considering the change of the fission source distribution during the cycle. The calculated end-of-irradiation activities were compared with those measured. The agreement was found better than expected according to uncertainty considerations. Furthermore, the calculated fluence spectra were adjusted to the experimental activities taking into account the variances and correlations of calculated input spectra, detector sensitivities and measurements. Using the adjustment code COSA2 based on the generalized least squares method best estimate fluence spectra and fluence integrals were obtained.
The investigations reported on were accomplished using reactor data and irradiation facilities provided in connection with the Balakovo-3 Interlaboratory Pressure Vessel Dosimetry Experiment conducted by the Scientific and Engineering Centre of Russian GOSATOMNADZOR.

During a hypothetical accident the reactor pressure vessel internals of boiling water
reactors can be exposed to considerable loads resulting from temperature gradients and pressure waves. The finite element (FE) analysis is an efficient tool to evaluate the consequences of those loads by computing the maximum mechanical stresses in the components. 3 dimensional FE models were developed for the core shroud, the upper and the lower core supporting structure, the steam separator pipes and the feed water distributor. The models of core shroud, upper core support structure and lower core support structure were coupled by means of the substructure technique. All FE models can be used for thermal and for structural mechanical analyses. As an example the FE analysis for the case of a station black-out scenario (loss of power supply for the main circulating pumps) with subsequent emergency core cooling is demonstrated. The transient temperature distributions within the core shroud and within the steam separator pipes as well were calculated based on the fluid temperatures and the heat transfer coefficients provided by thermo-hydraulic codes. At the maximum temperature gradients in the core shroud, the mechanical stress
distribution was computed in a static analysis with the actual temperature field being
the load. It could be shown that the maximum resulting material stresses do not exceed the permissible thresholds fixed in the appropriate regulations. Another scenario which was investigated is the break of a feed water line leading to a non-symmetric subpressure wave within the reactor pressure vessel. The dynamic structural response of the core shroud was assessed in a tranisient analysis. Even for this load case the maximum resulting stresses remain within the allowed limits at any time.

An effective quasiparticle description of the thermodynamics of deconfined matter, compatible with both finite-temperature lattice data and the perturbative limit, is generalized to finite chemical potential.
Within this approach, the available 4-flavor lattice equation of state is extended to finite baryon density, and implications for cold, charge-neutral deconfined matter in β-equilibrium in compact stars are considered.

The polarization of a surrounding QCD medium
modifies the induced gluon radiation spectrum
of a high-energy parton at small transverse momenta
for a single interaction and for multiple scatterings as well.
This effect is an analogue of the Ter-Mikaelian effect in QED,
superimposed to the Landau--Pomeranchuk effect,
however it appears in QCD in a different phase space region.

The stability and reactivity of "3+1" ^99mTc mixed-ligand complexes were investigated in vitro and in vivo in the blood of rats. Surprisingly, in whole blood the complexes, which proved to be stable in saline, PBS of pH 7.4 and mostly in plasma, were converted into more hydrophilic metabolites. Small structural differences in the complex molecule have a profound influence on the rate of metabolism of the complexes. Transchelation reactions with glutathione (GSH) were hypothesized and this hypothesis substantiated by challenge experiments. Structural parameters influencing the stability of the complexes and consequences for the radiopharmaceutical design are discussed.

Overexpression of the P-glycoprotein (Pgp), present in the plasma membrane of various tumour cells and in several normal cell types contributes to the multiple drug resistance (MDR) phenotype of many human cancers. As an prerequisite for the therapy it is required to study the expression of Pgp. The available clinical radiopharmaceuticals to study the expression of Pgp include the lipophilic ^99mTc cations (sestamibi, tetrofosmin) as well as [^99mTc]Q57, [^99mTc]Q58, and [^99mTc]Q63. Here we describe the in vitro and in vivo properties of the structurally different complex (3-thiapentane-1,5-dithiolato){[N-(3-phenylpropyl)-N-2(3-quinazoline-2,4-dionyl)-ethyl]amino-ethylthiolato}oxotechnetium(V) (^99/99mTc1) as a potential inhibitor of the Pgp. ⁹⁹Tc1 enhances the net cell accumulation of the Pgp substrates [³H]vinblastine, [³H]vincristine, [³H]colchicine, [^99mTc]sestamibi, [^99mTc]tetrofosmin in RBE4 cells, an immortalised endothelial cell line which expresses Pgp. Also, the cell accumulation of ^99mTc1 could be increased by verapamil and reserpine as known Pgp inhibitors. A multitracer approach was used to study the side effects of ⁹⁹Tc1 on cell metabolism. The cells were simultaneously incubated with [^99mTc]sestamibi, [¹⁸F]FDG and various ³H-labelled tracers. Two-dimensional scatter plots of [^99mTc]sestamibi uptake / [¹⁸F]FDG uptake show typical changes of known Pgp inhibitors including ⁹⁹Tc1. Also the effects of the ⁹⁹Tc1 on the in vivo distribution of [^99mTc]sestamibi and [¹⁸F]FDG in rats are comparable with the effects of verapamil, an established Pgp inhibitor and Ca-channel blocker.
We conclude that ^99/99mTc1 is a transport substrate and a potential inhibitor of the Pgp. Our approach may be useful in the design of further radiotracers with specificity to the Pgp.

During ion beam synthesis of compounds in Si a specific redistribution process is responsible for the modification of the implant profile towards a uniform buried compound layer. This process is referred to as Ostwald ripening. Implantation of substoichiometric doses of reactive species leads to structures consisting of two precipitate bands. Investigations done by taking SEM-micrographs on beveled samples reveal that the structuring depends on the implantation conditions. Furthermore splitting of the precipitate band located deeper in the substrate was observed and is seen as an effect of self-organisation. The development of the structures with time depends on the strength of the ripening process taking place parallel and perpendicular to the surface of the substrate. Using methods of spatial statistics the changes in the precipitate configuration according to the different ripening directions become obivous. Unfortunately, there exists no analytical model to describe the precipitation process in systems with inhomogeneous material distribution. Therefore, all the information retained from the experiments serve as an input for simulations to be done and will help to understand the contributions of different physical mechanisms. The results obtained in the course of the present study are described in terms of the formation of a buried oxide layer as a typical example of this kind.
(Unfortunately, the thesis itself is written in german.)

An effective quasiparticle description of deconfined QCD thermodynamics compatible with both finite temperature nonperturbative lattice data and the asymptotic limit is generalized to finite chemical potential.
Implications for the N _f = 4 flavor lattice data extended to mu > 0 as well as for deconfined matter with realistic quark masses are considered.

A Co/Cu solid solution is prepared by direct implantation of 200 keV Co ions into Cu targets. The maximum concentration at this ion energy is limited to 25 at.% Co due to sputtering. Magnetic measurements show a spin-glass behaviour, as expected for a
solid solution of Co in Cu. At about 630 K the solid solution starts to decompose into
clusters. After heat treatment, the sample shows ferro- and superparamagnetic behaviour, indicating that the size of the clusters is broadly distributed.

We study the pattern formation in a chemical two-layer system, placed in a Hele-Shaw cell. The upper layer is an organic solvent in which a carboxylic acid is dissolved. The lower layer consists of water containing an inorganic base. We report on a novel instability type which is driven by an exothermic neutralisation reaction in vicinity to the interface. This instability combines plume and finger regimes and gives rise to a self-sustained dynamics.

Dendrimere sind aufgrund ihrer Hohlraumfähigkeit und Oberflächenfunktionalität von großem Interesse im Hinblick auf Anwendungen in der Chemie und Medizin. Nutzungen zeichnen sich insbesondere auf den Gebieten medizinische Diagnostik und Therapie ab. Es werden neue Entwicklungen aus diesen Bereichen vorgestellt. Außerdem werden Möglichkeiten der selektiven Bindung und des Phasentransfers am Beispiel von lipophilen Harnstoff-Dendrimeren für Oxoanionen wie Pertechnetat und Nukleotide diskutiert.

Humin- und Fulvinsäuren, die als organische Materialien in natürlichen Systemen in unterschiedlichen Konzentrationen vorkommen, treten über Komplexbildungsreaktionen mit gelösten radioaktiven und toxischen Schadstoffen, z. B. Uran, in Wechselwirkung. Sie beeinflussen somit deren Sorptionsverhalten an geologischen Materialien und folglich deren Migrationsverhalten in wäßrigen Systemen. Demzufolge ist eine Quantifizierung des Einflusses von Huminstoffen auf die Sorption von radioaktiven Schwermetallen für Risikobetrachtungen notwendig.
Der Einfluß von Huminsäure auf die Uranyl(VI)-Sorption wurde an Phyllit untersucht, das im Westerzgebirge in Sachsen (Deutschland) relativ häufig und zusammen mit Uranablagerungen in den ehemaligen Uran-Bergbaugebieten vorkommt. Als organische Materialien wurden sowohl eine aus dem Hochmoor 'Kleiner Kranichsee' isolierte [1], ortsspezifische Huminsäure (Kranichsee-HS) sowie eine 14C-markierte synthetische Huminsäure (Typ M1) angewandt.

Die Sorption wurde sowohl an Phyllit als auch an seinen mineralischen Bestandteilen Muskovit, Albit und Quarz mittels Batch-Experimenten unter aeroben Bedingungen bei konstanter Ionenstärke (0.1 M, NaClO4) im pH-Bereich 3.5 bis 9.5 untersucht. Die Konzentrationen für Uran und Huminsäure betrugen 1o10-6 mol/L bzw. 5 mg/L. Die Ergebnisse der Uran-Sorption werden mit Uran-Sorptionsdaten [2] verglichen, die in Abwesenheit von Huminsäure erhalten wurden.

Verglichen mit seinen mineralogischen Bestandteilen zeigt Phyllit die höchste Huminsäure-Sorption über den gesamten pH-Bereich. Die Huminsäure-Sorption an Muskovit und Albit ist nur im sauren pH-Bereich hoch, sinkt dann jedoch stark mit steigendem pH-Wert. Die Sorption von Uran an Phyllit wird durch Huminsäure im sauren pH-Bereich vergrößert, jedoch im neutralen pH-Bereich nicht beeinflußt. Dagegen wird die Uran-Sorption an den mineralischen Bestandteilen des Phyllits im neutralen pH-Bereich durch Huminsäure stark verringert. D.h., die Uran- und Hum ...

Die Kopplung fortgeschrittener Thermohydraulikprogramme mit dreidimensionalen Neutronenkinetikcodes ordnet sich in das Bestreben ein, konservative Abschätzungen durch "best estimate Rechnungen" zu ersetzen. Der DYN3D-Code wurde im Forschungszentrum Rossendorf für die Analyse von reaktivitätsinduzierten Störfällen in Reaktoren mit hexagonalen Brennelementen entwickelt und beinhaltet neben der 3D-Neutronenkinetik auch Modelle für die Thermohydraulik im Corebereich und für den Wärmeübergang vom Brennstoff zum Kühlmittel. Daher gibt es zwei grundlegende Möglichkeiten für die Realisierung der Kopplung mit dem Thermohydraulikcode ATHLET der Gesellschaft für Anlagen- und Reaktorsicherheit.
Bei der einen Kopplungsart wird nur der Neutronenkinetikteil von DYN3D an ATHLET angekoppelt (interne Kopplung). Diese Kopplung längs des Cores ist sehr eng und auf Grund der vielen zu übergebenden Parameter mit hohem Programmieraufwand verbunden.
Bei der hier vorgestellten Kopplungsart wird der Corebereich ganz aus dem ATHLET-Anlagenmodell herausgeschnitten und vollständig von DYN3D modelliert (externe Kopplung). Die Schnittstellen sind in diesem Fall der Coreeintritt und -austritt. An diesen Schnittstellen sind nur die Drücke, Massenströme, Enthalpien und Borsäurekonzentrationen zu übergeben. Diese Kopplungsart kann sehr einfach durch Zwischenschaltung einer Interfaceroutine realisiert werden. Sie wird durch das "General Control and Simulation Modul" (GCSM) von ATHLET wirkungsvoll unterstützt. Es sind kaum Veränderungen der einzelnen Programme notwendig. Weiterhin hat sie den Vorteil, daß die aufeinander abgestimmten DYN3D-Modelle auch in dem gekoppelten Programm genutzt werden können.
Die Kopplung wurde explizit realisiert, da eine geschlossene implizite Zeitintegration der thermohydraulischen Gleichungen wie in ATHLET entweder rechenzeitintensive Iterationen zwischen den Programmteilen oder umfangreiche Änderungen der Codes erfordern würde. Die explizite Kopplung beider Progr ...

The experiment to the IAEA standard problem exercise No. 4 was a 3.2 mm break on the downcomer head. The high pressure injection cooling was assumed to be not available. As an accident management measure, bleed and feed on the secondary side of the steam generator was applied. Research Center Rossendorf contributed to the experiment of SPE-4 by supplying needle shaped conductivity probes for the measurement of local void fractions in the primary circuit of the PMK-II test facility. In the course of the standard problem exercise No. 4 RCR contributed with post-test calculations using the thermalhydraulic code ATHLET.

The calculations showed, that the code was suitable to reproduce the main events of the test. Reasons for some deviations and modelling problems were discussed.

The potentially bidentate ligand diphenyl(2-pyridyl)phosphine (PPh2py) reacted with (NEt4)2[MI(CO)3X3] complexes (M = Re, Tc) to give (NEt4)[MI(CO)3X2(PPh2py-P)] or [MI(CO)3X(PPh2py-P)2] depending on the amount of the ligand used. The reaction with (NBu4)[TcVINCl4] yielded [TcVNCl2(PPh2py-P)2] whereas from the reaction with (NBu4)[ReOCl4] the complexes [ReVOCl3(PPh2py-P,N)], [ReVOCl3(OPPh2py-O,N)], [ReIVCl4(OPPh2py-O,N) and [ReIVCl3(OH)(OPPh2py-O,N)] have been isolated. Reduction of the metal center occurs using an excess of PPh2py and heating of the reaction mixtures under reflux.
The products have been characterised spectroscopically and by X-ray structure analysis. Monodentate co-ordination via phosphorus has been found for the rhenium(I) carbonyl complexes and [TcVNCl2(PPh2py-P)2]. In the latter compound a trigonal-bipyramidal coordination sphere is formed with the phosphines as axial ligands (bond angle P-Re-P: 161.69(3)°). The chelated complexes show small N-Re-P and N-Re-O bite angles of 63.6° and 77.7 - 82.2° due to the 4-membered or 5-membered chelate rings. The pyridine nitrogen occupies the axial position (trans to "O2-") in [ReOCl3(PPh2py-P,N)] whereas equatorial co-ordination is found in [ReOCl3(OPPh2py-O,N)].

The large cavity homoleptic thioether cages R,R'-S6tricosane] (1-hydroxymethyl-9-methyl-3,7,11,15,18,22-hexathiabicyclo[7.7.7]tricosane) (1) and [R,R'S6hexacosane] (1-hydroxymethyl-10-methyl-3,8,12,17,20,25-hexathiabicyclo[8.8.8]hexacosane) (2) have been synthesized and the structure of 1 and the complex [Ag(2)¥ been elucitated, the latter one showing a polymeric string with Ag+ coordinating by three different cages.

Der Bericht beschreibt Nachrechnungen eines Abblaseexperiments, das vor etwa 10 Jahren am Moskauer Energetischen Institut durchgef|hrt wurde und für das experimentelle Daten des zeitlichen Verlaufes der Druckentlastung im Abblasebehälter und des Dampfgehaltes in verschiedenen Gefäßhöhen vorliegen.
Es wurden die Programme RELAP5/mod2 und ATHLET 1.0 Version E eingesetzt. Wie es sich zeigt, hat die richtige Beschreibung der Zweiphasenströmung an der Ausströmöffnung den größten Einfluß auf die Genauigkeit der Nachrechnung. Hierfür bietet das stationdre 1D-FD-Modell für kritisches Ausströmen des Programms ATHLET die bessere Anpassungsfähigkeit an die gegebenen Versuchsbedingungen.

In der vorliegenden Studie werden Ergebnisse zur Bruchzähigkeit intermetallischer Phasen sowie Erfahrungen bei deren experimentellen Bestimmung aus der Literatur zusammengetragen und diskutiert, ohne dabei Anspruch auf Vollständigkeit zu erheben. Da es für diese Kombination von Prüfaufgabe und Werkstoff bisher kaum gesicherte Erkenntnisse gibt, liegt der Schwerpunkt darauf, bevorzugt angewendete Verfahren herauszuarbeiten und die Gründe für diese Bevorzugung zu machen.

Der Bericht gibt einen Überblick über die Arbeiten der Abteilung Magnetohydrodynamik auf dem Gebiet der elektromagnetischen Umströmungskontrolle in schwach-leitfähigen Flüssigkeiten.

Der Bericht beschreibt Nachrechnungen eines Abblaseexperiments, das vor etwa 10 Jahren am Moskauer Energetischen Institut durchgef|hrt wurde und für das experimentelle Daten des zeitlichen Verlaufes der Druckentlastung im
Abblasebehälter und des Dampfgehaltes in verschiedenen Gefäßhöhen vorliegen.
Es wurden die Programme RELAP5/mod2 und ATHLET 1.0 Version E eingesetzt. Wie es sich zeigt, hat die richtige Beschreibung der Zweiphasenströmung an der
Ausströmöffnung den größten Einfluß auf die Genauigkeit der Nachrechnung.
Hierfür bietet das stationdre 1D-FD-Modell für kritisches Ausströmen des
Programms ATHLET die bessere Anpassungsfähigkeit an die gegebenen
Versuchsbedingungen.

Practical application of dynamic perturbation measurements for on-power determination of important parameters of nuclear reactors by means of delayed reacting neutron detectors is only possible, if a correction method is given to measure the time-dependent neutron flux behaviour without delay and with high accuracy. An improved model of dynamic signal compensation is presented and illustrated by examples of analog and digital correction methods.
Knowing the transfer function of the neutron detector, it is possible to invert a dynamic (prompt jump response) system by transforming the output equation of the state equation system to the input. An analog circuit corresponding this inverse detector kinetics was developed. On the other hand a recursive digital algorithm of high computational speed and accuracy with regard to real-time processing was found.
The improved analog and digital dynamic compensation methods were developed and used in German and Hungarian nuclear power plants with pressurized water reactors of VVER type. By means of the named correction methods the time- and space-dependent neutron flux behaviour during power changes or reactivity perturbations was followed to estimate reactivity coefficients like differential control rod worths or power coefficient.

The ductility of ZrNb1 claddings after exposure to steam between 700 and 1000 °C was determined by ring compression tests at room temperature and compared with the ductility behaviour of Zircaloy. The ductility of ZrNb1 is quickly reduced by steam exposure. Complete embrittlement of ZrNb1 is reached at a relative equivalent oxide-layer thickness of 5 %, in contrast to Zircaloy, where a relative thickness of 17 % is necessary to produce complete embrittlement. The different behaviour of the two alloys is caused by higher oxygen uptake and a more homogeneous oxygen distribution in ZrNb1 after cooling. Between 950 and 1000 °C, there is an additional effect of high hydrogen absorption. Validity of the 17 % criterion for ZrNb1 can no longer be taken for granted in view of these experimental findings.