Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

The paper describes a first experimental test of a new electromagnetically based bubble detection method in an electrically conducting fluid. A reliable and contin-uous bubble detection method is important for a lot of liquid metal flows, in particular, flows of reactive liquid metals like sodium or lithium. Moreover, the method is suitable for the detection of any inhomogeneity having different electrical conductivity compared to the bulk flow.
The experimental approach for the detection of inhomogeneities was developed at RWTH Aachen for an early slag detection in steel production. The method is based on the fact that a primary electromagnetic field is changed by the motion of an electrically conducting fluid. This change is very sensitive to any inhomogeneities in the flow which have a different electrical conductivity compared to that of the fluid. The signals of suitably arranged secondary coils are evaluated in order to separate the influence of the inhomogeneity. In the experiments performed at the sodium facility of RCR we were able to detect single bubbles which were of diameters in the range 0.5 - 2 mm.
Compared to usual, mainly acoustically based detection methods the following advantages of the electromagnetic approach are obvious:

• No time delay between bubble occurence in the coil region and the signal.
• High sensitivity up to single bubble detection.
• Contactless method. No need to install sensors at hot walls, even a thermal isolation between the coils and the channel is possible.
• Every flowing bubble is detected whereas acoustic methods are able to detect acoustically active bubbles only.

Magnetic fields provide the possibility to influence the convective flow pattern in an predefined contactless way, in particular, to suppress and control oscillatory instabilities. Therefore, there is increasing interest now in the use of magnetic fields in a variety of materials processing technologies like crystal growth from the melt or directional solidification.
Available knowledge is very limited on the influence of a steady magnetic field (described by the Hartmann number Ha) on convective motions, described by the Grashoff number Gr (buoyancy), and by the Marangoni number Ma (thermocapillarity at free surfaces) in low Prandtl number fluids like liquid metals. Therefore, in the present paper we present theoretical results on the prototype problem of an infinitely extended fluid layer heated either from the side or from the bottom, and exposed to a steady external magnetic field.
In the first part we consider the stability of a unidirectional thermocapillary flow set up by a temperature gradient parallel to the free surface. The magnetic field is supposed to be parallel to the free surface. In this case the magnetic field has no influence on the basic flow, the stability of which is well known without magnetic field. The restriction to disturbances propagating in the same direction as the magnetic field allows to obtain an analytical solution of the stability problem and an explicit expression for the dispersion relation. The hydrothermal wave instability is suppressed by the magnetic field, the critical Marangoni number grows proportionally to Ha. The most unstable wave pattern is stretched along the field lines. The wave number of the most unstable mode decreases as Ha-4/5 for Ha >> 1.
The second part of this communication is devoted to the analysis of the thermocapillary instability in a layer with both temperature gradient and magnetic field being perpendicular to the free surface. Although this problem has been extensively treated in the past, the ...

Thermocapillary driven motion is considered in a horizontal electrically conducting fluid layer heated from the side and exposed to a magnetic field coplanar to the layer. The hydrothermal wave instability and its control by the magnetic field is studied by a linear stability analysis. The special assumption of disturbances traveling crosswise the basic flow allows an analytical solution of the problem. For a particular class of perturbations considered here, the critical Marangoni number and the wavelength of the most unstable mode increase directly with the strength of the applied magnetic field.

It is well known now that in a liquid metal duct flow exposed to a strong transverse magnetic field turbulent fluctuations can persist even when the mean flow can be regarded as laminar with respect to the overall pressure drop. It was also found, that these fluctuations can even be increased under distinct conditions. This effect is in line with the model of two-dimensional MHD turbulence. While 3D turbulence elements are effectively damped by the magnetic field, 2D eddies with axes in the direction of the B-field are not influenced by this damping mechanism. The use of this 2D turbulence allows an enhancement of the heat/mass transport perpendicular to the flow direction without a significant influence on the overall pressure drop.
There is an ongoing research in the FZR MHD group on local transport phenomena in a turbulent LM duct flow exposed to a transverse magnetic field. Measurements were performed at the FZR sodium facility. The advantage of sodium is that high MHD parameters (Ha = 3000, N = 800) can be reached with moderate values of the magnetic field (B = 0.5 T). On the other hand the properties of sodium cause considerable difficulties with respect to any local measurements in such a flow (velocity, fluctuation intensities). Thus the idea was created to use small gas bubbles (argon) as local tracers for the investigation of local transport mechanisms. In the case of our experimental conditions a volumetric gas flow ratio lower than 0.09 clearly indicates a pure bubbly flow regime. The bubbles are injected by means of a single injector in the center of the channel cross section or in the vicinity of a channel wall. The injector was located in the region where the flow enters into the magnetic field. A traversing mechanism allows to move the B-field-region. Single wire resistivity probes are used for measuring the local void fraction and the number of bubbles.
The measured local dispersion of bubbles shows a significant anisotropy which clearly corre ...

The technical need for instability postponement, turbulence suppression and flow control in material processing as well as the seek for low-cost alternatives to space-technologies for crystal growth are currently leading to an increased interest in the interaction between thermocapillary flows in electrically conducting fluids and magnetic fields. While the interplay between isothermal flows and magnetic fields is well understood, our physical understanding of the influence of magnetic fields on thermocapillary flow phenomena, i.e. flows driven by surface tension gradients, leaves still much to be desired.
The goal of the püresent communication is to demonstrate that a magnetic field acting on the thermocapillary flow of a low Prandtl number fluid causes the fluid to behave like a high Prandtl number fluid. This important feature is exemplified by considering the linear stability of a unidirectional thermocapillary flow set up by a temperature gradient parallel to the free surface of an unbounded planar fluid layer. The magnetic field is supposed to be normal to the free surface. Our problem is the magnetic counterpart to the work of Smith & Davis. We report results of a comprehensive study of the critical Marangoni number for the onset of hydrothermal waves as a function of the Hartmann number and of the Prandtl number. For weak magnetic field the instability mechanism in liquid metals is found to be the same as in the nonmagnetic case for low Prandtl numbers. For sufficiently strong magnetic field the basic flow and the most unstable perturbation are confined to a thin Hartmann boundary layer below the free surface which leads to a decrease of the effective viscous diffusion time-scale as Ha-2. Our Computations reveal that at a certain value of the Hartmann number, when the effective viscous time equals the thermal diffusion time, the character of the instability changes discontinously. The new type of instability is reminiscent of the instability mechanism w ...

In the present paper the time-dependent, two-dimensional, incompressible MHD flow around a circular cylinder is investigated numerically using a finite difference method in stream function-vorticity formulation. The calculations are restricted to the typical situation of liquid metal flows under laboratory conditions where the magnetic Reynolds number is small. The flow is investigated in the parameter range of Re < 10000 and magnetic interaction parameter N < 20 (N = Ha²/Re).
To validate the numerical method, a comparison with the few published numerical results (MOCHIMARU, TSINOBER) is performed, and a good agreement is found. Furthermore, the influence of different outer boundary conditions is tested.
The two cases of a magnetic field aligned to the flow as well as perpendicular to it are investigated in detail. The influence of the magnetic forces on the flow is shown in stream function and vorticity isoline plots for different Reynolds numbers and interaction parameters. The vorticity and pressure distribution at the cylinder surface and the induced magnetic field are calculated and compared with experimental results. The occurrence of a large, but slow recirculation eddy behind the cylinder for a strong aligned magnetic field is discussed. The motion of the fluid becomes more and more stagnant in that region for increasing magnetic fields.
The downstream wake is characterized by the velocity profiles, and the farfield of the vorticity is discussed.
As expected, the influence of the magnetic field on the flow in general is a stabilizing one. In particular, the suppression of an instationary wake flow can be achieved by the magnetic forces. A stability line in the (Re,N)-plane is extracted from the numerical simulations. This result will be compared with a linear stability analysis based on a Galerkin approach.

LMMHD two-phase flow modelling strongly depends on the accuracy of the constitutive equations and the corresponding closure laws. Several questions rise from various attempts to model these flows. They are mainly connected with the modification of two-phase flow (interfacial dragging, wall friction, apparent elec- trical conductivity, etc.) due to the electromagnetic forces.
The present paper presents a comprehensive survey of the LMMHD two-phase investigations performed in our two laboratories using different liquid systems, mercury-air (LEGI-IMG) and sodium-argon (FZR), with quite different properties. The remarkable difference in the material properties allow us to reach a wide range of nondimensional parameters.
For theoretical predictions a two fluid model (LEGI-IMG) and a bubbly flow model (FZR) have been developed in order to meet the requirements of the corresponding facilities.
The experiments have been realized in rectangular vertical test sections immersed into a transverse magnetic field. The gas is injected in the entrance region of the magnetic field. The distribution of the local void fraction across the channel cross section was measured by means of single wire resistivity probes. The electrical boundary conditions of the test sections are rather different. While the FZR test section consists of a simple stainless steel channel (thickness of the walls: 5 mm), the LEGI-IMG configuration, which includes segmented copper electrodes and an external load resistance, is more similar to a MHD generator. In the FZR experiment a volumetric quality in the range of 0.06 - 0.09 leads to a pure bubbly flow regime. In contrast to this the LEGI-IMG facility usually work with considerable higher gas flow rates.
We present experimental results showing the dependence of the mean values of the void fraction, the slip ratio and the gas velocity on the magnetic field strength as well as on the mean sodium velocity. These results will be compared with the theoreti ...

The hydromagnetic stability of the flow of an incompressible conducting fluid around a circular cyliner in a uniform magnetic field parallel to the mean flow is investigated with different approaches:

Experiments for 1000 < Re < 9000
a simple analytical model
numerical simulation for Re < 1000.
Main goal of the investigations is to find the stability curce inthe (Re, N)-plane, and to distinguish between 2D and 3D instabilities.
Experimental results will be presented based on hot-wire measurements in the down-stream cylinder wake. The suppression of the vortex street by increasing magnetic fields is clearly identified.
Parallel to the disappearance of the typical Kármán frequency an increase of low frequency fluctuations is observed in the spectrum. This will be discussed in therms of theoretical predictions for long-wave MHD instabilities.
More physical insight into the stability behaviour is obtained by a simple Kolmogorov flow modelling of the cylinder wake and the corresponding stability analysis. Theoretical results will be presented for the 2D case: critical Reynolds number, wave number and Strouhal number as function of the magnetic field.
The critical wave number jumbs form the region of the typical Kármán value to very low values at a distinct magnetic field strength. The simple model is extended to include 3D instabilities in the flow. Limitations of the model and the comparison to experiments will be discussed.
Finally the 2D case for Re < 1000 will be compared with results of a full numerical simulation.

A theoretical analysis of liquid drop unsteady migration under microgravity conditions is presented, if an interfracial tension gradient is generated on the drop surface by a uniform temperature gradient in the surrounding liquid. The effect of buoyancy due to a residual gravity vector aligned parallel to the temperature gradient is included. The relevant equations are solved in the creeping flow limit where in the convective transport of momentum as well as that of the energy is neglected, i.e. at low Reynolds and Marangoni numbers. The flow and the temperature field within and around the drop are obtained after transforming the results from the Laplace transform domain, in which they are derived, to the time domain. The time transient behaviour of the Migration speed depends strongly on the choice of the initial flow and temperature fields. The comparison with other initial conditions from the literature is performed.

A serious disadvantage of a lot of microgravity experiments on Marangoni convection is often times the fact that most of the valuable time under microgravity is lost for preparing the necessary temperature gradient. Therefore, the paper will discuss two possibilities of short-term marangoni experiments where the temperature gradient over a plane fluid layer can be prepared in advance, but keeps the fluid motionless.
At first, a convective motion will be started simply by switching off gravity which can result in long-wave surface capillary waves. Such a motion due to surface deformations is suppressed under earth conditions.
Second, various types of Marangoni motions will be discussed for liquid metals exposed to an external magnetic field. Instability thresholds are increased by the magnetic field, i.e. the liquid can be kept motionless by means of the magnetic field under a given temperature gradient.
The paper will discuss the feasibility of such investigations in drop tower experiments.

The ductile-brittle transition temperature is the usual reference parameter for the safety assessment of the reactor pressure vessel. In large forgings this parameter can change with the distance from the surface. Thus, the safety assessment must consider the effect. To evaluate the significance for the VVER 440-type pressure vessel the relationship among mechanical properties, through-the-thickness position and microstructure was investigated at a forging of 15Kh2MFA steel. The change of the mechanical properties (hardness, strength, transition temperature) are relatively low. The surface-near position is harder and tougher than the deeper range. Both ranges differ in the content of preeutectoid ferrite and in the arrangement, but not in the content of carbides. The Orowan model of the mechanism of precipitation hardening can describe quantitatively the dependence of the yield strength and the number of M23C7 carbides per unit area of section plane found experimentally on the trough-the-thickness position.

The deterioration of the mechanical properties of reactor pressure vessel (RPV) steels during their irradiation in a nuclear power plant is known as neutron embrittlement. The microscopic mechanisms of the neutron embrittlement of low alloy RPV steel are not fully understood.
These mechanisms were investigated at the RPV steel of Russian and Czech type 15Kh2MFA. This steel differs from ASTM type A503 or A533 steels mainly in its contents of the carbide forming elements Cr and V. Neutron small angle scattering (SANS) using the SANS-2 facility at the FRG-1 reactor in Geesthacht and anomalous X-ray small angle scattering (ASAXS) using the JUSIFA facility at the HASYLAB in Hamburg were employed.
The difference between the scattering intensities from irradiated and unirradiated specimens give the small angle scattering effect of the radiation damages. Irradiation induced precipitates were found with a mean diameter of = 1...2 nm. The defect volume fraction is depending from the neutron fluence.
From the magnetic scattering contrast (SANS) and the anomalous scattering contrast (ASAXS) information about the chemical composition were got. This results are compared with the idea that the irradiation induced precipitates in 15Kh2MFA steel are carbides.

The state-of art of ultrasonic two-phase flow measurements is characterised by a number of different approaches commonly based on the identification and characterisation of individual voids (bubbles, plugs etc.) applying the techniques of ultrasonic testing. The recorded individual events are integrated to extract parameters as void fraction or volume flow rates. The main limitation of these methods arises from the complicated structure of two-phase flow at higher void fractions which leads to multiple diffractions of the sound beam. The measurement is therefore limited to low void fractions or an easy flow structure.
The main idea of the present work was to overcome these limitations by means of pattern recognition. An ultrasonic beam crossing the two-phase flow is modulated by the changing structure of the voids passing by and therefore the through-transmission signal must contain information about the parameters of the two-phase flow even if information about individual flow effects cannot be derived. Therefore it was supposed that a pattern recognition algorithm trained with signals obtained at known conditions is able to identify the set of the flow parameters (flow rates, void fraction etc.) in an unknown situation.

Die Ergebnisse aus dem einjährigen Betrieb von 43 netzgekoppelten PV-Anlagen in Sachsen werden dargestellt. Schwerpunkte bilden die architektonische Einbindung der Generatoren in die Gebäude, die mögliche Synchronisation zwischen solarer Stromerzeugung und dem Verbrauch von Elektroenergie sowie Erfahrungen bei der Installation und dem Betrieb von netzgekoppelten PV-Anlagen.
Hervorhebenswert sind die Ergebnisse zum möglichen Eigenverbrauch des solar erzeugten Stromes. Es konnte gezeigt werden, daß gerade energiesparende Haushalte stark auf die "Zwischenspeicherung" im öffentlichen Netz angewiesen sind (Eigenverbrauch 20 %). Maximal wird ein Eigenverbrauch von ca. 50 % erreicht.
Die erreichten jährlichen Energieerträge betragen im Mittel 680 kWh/kWp, wobei große Unterschiede zwischen den einzelnen Anlagen gefunden wurden. Als Hauptursache für die unterschiedlichen energetischen Ergebnisse werden Abweichungen der Modulparameter von den Datenblattangaben der Hersteller vermutet.

Der Projektvorschlag für eine kompakte Synchrotronstrahlungsquelle der 3. Generation ROSY wird beschrieben. Die Quelle sol1 für die Materialforschung dediziert sein, die für die Forschung im regionalen Umfeld von Rossendorf prägend ist.
Bei einer Speicherringenergie von 3 GeV wird Synchrotronstrahlung im harten Röntgenbereich mit einer kritischen Energie des Spektrums von Ec = 8,4 keV (hc=0,14 nm) emittiert. Mit einer naturlichen Emittanz von 28 n nm rad wird eine sehr brillante Strahlung zur Verfügung gestellt. Neben der Strahlung aus Ablenkmagneten kann Strahlung aus Wigglern und Undulatoren genutzt werden. Für diese insertion devices sind 8 Einbaumöglichkeiten vorhanden, von denen 4 in nichtdispersionsfreien geraden Strecken liegen. Der Speicherring hat eine vierfache Symmmetrie, einen Umfang von 148 m und ist als modifizierte FODO-Struktur konzipiert. Ein nachträglicher Einbau von supraleitenden Ablenkmagneten zur Erzeugung eines harteren Spektrums und damit zur Ausweitung des Anwendungsbereiches ist möglich.
Der Teil I enthält die wissenschaftliche Begründung fur ROSY und eine Darstellung der Nutzungsmöglichkeiten. Im Teil II werden das Speicherringkonzept und die technischen Details der einzelnen Komponenten beschrieben.

The deterioration of mechanical properties of reactor pressure vessel (RPV) steel during its irradiation in a nuclear power plant is known as neutron embrittlement. It is for instance manifested as a shift of the ductile - brittle transition temperature toward higher values. The microscopic mechnisms of neutron embrittlement of low alloy RPV steel are not yet fully understood. It is known that dislocation loops, vacancy clusters (voids) and precipitates are formed during irradiation.
The dimensions of radiation induced precipitates are less than 5 nm, in RPV steel 15Kh2MFA they are about 1 - 3 nm. One of the objectives of present research in this field is to throw light on the nature of these precipitates.
In this article the correlation between the results of small angle neutron scattering (SANS) and the ductile - brittle transition temperature are studied and possible mechanisms of neutron embrittlement are discussed.

Abstract Photon production in a longitudinally and transversely expanding gluon plasma with initially little quark admixture is considered. Chemical equilibration of quarks and gluons is followed by rate equations. The yields of hard photons withE2 GeV are insensitive to chemical equilibration and depend mainly on the initial thermalized state. Medium-energy photons withE1 GeV are more frequently produced in case of faster equilibration, despite of faster cooling. For an assumed fast equilibration we follow the evolution of matter through mixed and hadron phases. The transverse momentum kick, due to transverse expansion, of photons from hadron matter is shown to be reduced for an equation of state with reduced latent heat. The photon yield in the regionE>1 GeV from deconfined matter dominates for conditions, estimated to be achieved at RHIC, in case of a weakly first-order confinement transition.

A two-stage achromatic E x B mass seperator has been desinged for a high-current focused ion beam column with collimated beam. The seperator consists of two homogeneous field E x B filters, a stigmator and the seperation aperture. The second-order geometrical and chromatic aberration coefficients are derived and their dependence on magnetic pole piece and electrode geometry are investigated in performing electric and magnetic field calculations. The influence of the mass seperator on the spatial resolution of the column is discussed.

Im Rahmen eines umfangreichen Programmes wurden Untersuchungen zur Anwendbarkeit der Windatlas-Methode (WASP) zur Ermittlung des Windenergiepotentials in Sachsen durchgeführt. Das Ziel der Untersuchungen bestand darin, die erwarteten Grenzen bei der Nutzung von WASP in orografisch gegliedertem Gelände genauer zu ermitteln. Grundlage der Berechnungen waren Messungen von vier Stationen des sächsischen Windmeßprogrammes. Es konnte gezeigt werden, daß in großen Gebieten der Oberlausitz die Windatlas-Methode genutzt werden kann. In den Kammregionen des Erzgebirges wurden widersprüchliche Ergebnisse gefunden, so daß eine Nutzung hier praktisch nur in sehr kleinen Repräsentationsgebieten in der Umgebung einer Meßstation möglich ist.

The maskless ion implatation with the focused ion beam as as a new method for ion beam synthesis of cobalt silicide wires is presented. In order to perform the implantation a special achromatic mass seperator was implemented into the ion column, liquid alloy ion sources for cobalt ions were 30 keV Co+ and 60 keV Co++ ions. The dose dependence for room temperature implantation and the influence of the substrate temperature were investigated.

The Hungarian integral test rig PMK of the KFKI Atomic Energy Research Institute was used as a source of experimental data for the IAEA Standard Problem Exercise SPE-4, a Medium size cold leg Loca with a secondary Bleed-and-feed procedure. The needle shaped conductivity probes developed by the Research Center Rossendorf have been applied in order to obtain information about the void fraction and the structure of the two-phase flow. The primary circuit of the PMK-II test facility was practically fully equipped with probes (with exception of the core simulator and the downcomer). An overview of the signals of all probes and the general chronology of characteristic events are discussed. As a main result the mechanism of the hot leg loop-seal clearing was clarified in detail.

Zur Aktualisierung der Neutronenparameter in der drehbaren Bestrahlungseinrichtung des rekonstruierten BER-II wurde der im Forschungszentrum Rossendorf entwickelte Mehrkomponentenaktivierungsdetektor eingesetzt.
Durch das umfangreiche Datenmaterial sind axiale und radiale Neutronenflußverläufe bestimmt und es gelingt ein eindeutiger Bezug von Meßwert zur Bestrahlungsprobe.

Seit Anfang der 70er Jahre sind an WWER-440-Reaktoren mehrfach anomale Schwingungen von Einbauten des RDB beobachtet worden, die teilweise zu Komponentenschäden führten.
Daher wurden speziell für den WWER-Typ zugeschnittene Diagnoseverfahren entwickelt, die auf der Korrelationsanalyse von Schwankungsanteilen des Neutronenflusses (incore und excore) und von nichtnuklearen Signalen wie Körperschall, Druckfluktuation und Beschleunigungen beruhen.
Um eine wirklich sensitive Fehlerfrüherkennung zu erreichen, wird ein theoretisches Schwingungsmodell auf der Basis Finiter Elemente (FE) entwickelt. Dieses Modell gestattet die Interpretation von gemessenen Schwingungssignalen in dem Sinne, daß die gemessenen Resonanzpeaks den Eigenschwingungen des gekoppelten mechanischen Systems zugeordnet werden können.
Darüber hinaus werden Sensitivitätsstudien durchgeführt, die die Veränderungen des Schwingungsverhaltens bei mechanischen Komponentenschäden verdeutlichen.

Modelling the mechanical vibrations of pressurized water reactor internals the fluid-structure-interaction is to be taken into account. Especially at VVER-440 reactors there is a strong influence of the fluid due to the specific geometry. The intention of the presentation is to provide a solution of the continuity and the Navier-Stokes equations for the special case of a narrow annular gap geometry considering the fluid friction.
To obtain an analytical solution for these coupled 3D partial differential equations further assumptions and simplifications must be made:

• the width of the annular gap is small compared with the diameter,
• displacements of the mechanical structure are small compared with the gap width
• the fluid flow velocity components are independent on the radius.

Due to the low geodetic height differences and the presence of loop seals in VVER-reactors, the behaviour of natural circulation is an important safety feature. The experiment to the OECD/NEA/CSNI International Standard Problem No. 33 was dedicated to the investigation of this phenomenon. During the test, defined quantities of primary coolant waere drained, while the facility was operated at 10% of nominal power and without pumps. The test was stopped with increasing temperatures of the fuel rod simulator.
In RC Rossendorf pre- and posttest calculations were performed by the code ATHLET, which was developed by the "Gesellschaft für Anlagen- und Reaktorsicherheit".
The main events of the experiment could be predicted, shown and explained by the ATHLET calculations:

• After draining of about 20% of the primary inventory, the mass flow in the loops stagnates. Simultaneously, the primary pressure increases and the pressurizer is partly refilled.
• In later periods the mass flow through the three loops is nonequally distributed, which could be reproduced by the ATHLET calculations at least qualitatively.

In the Research Centre Rossendorf pre- and posttest calculations to the OECD/NEA/CSNI International Standard Problem No. 33 were carried out with the GRS code ATHLET. This Problem was a natural circulation experiment with stepwise reduced primary coolant inventory. In the ATHLET calculations after a drainage of about 50% of the primary inventory cyclic oscillations of the mass flows and the void fractions were observed. These are found in the experimental results also. A simple analytical model was developed to distinguish physically caused oscillations from numerically caused ones. The oscillations observed could be interpreted as density wave instability in the local recirculation loop core- bypass.

An incorrect startup of a pump in an isolated loop containing a plug of diluted absorber can initiate a reactivity accident in a VVER-440. It is assumed that the main gate valve is opened after starting the main coolant pump. When the plug enters the core, it gives rise to a positive reactivity. An asymmetric distribution of diluted water in the core is expected which requires a 3-dimensional analysis for a more correct description of this accident.
The code DYN3D/M2 developed for investigations of reactivity initiated accidents in thermal reactors with hexagonal fuel elements is used for analysis. A model describing the mixing of water from the different loops in the lower plenum of a VVER-440 reactor gives the boron concentration at the inlet of each fuel element. The two limiting cases, ideal mixing and no mixing, are investigated for comparisons.

The starting point of these investigations is the performed irradiation program for the Rheinsberg reactor for 3 different reactor periods during 1984 to 1988. In this program a great number of steel specimens were irradiated at different positions. Additionally a certain number of activation monitors were installed. For the planned mechanical proof of these specimens information of the irradiation condition of all specimens are needed. Therefore we have to calculate the neutron fluences at the different irradiation points for all relevant reactor periods. A spectrum adjustment is used to proof and correct calculational results taking into account measurement results.

A cobalt-neodymium liquid alloy ion source for applications in focused ion beam devices was developed and investigated. The performance and the main parameters of the ion source are presented.

Im Institut für Sicherheitsforschung des Forschungszentrums Rossendorf wurde ein Photovoltaik-Experimentierfeld in Betrieb genommen. Die Anlage, die der Durchführung von wissenschaftlichen Begleituntersuchungen zum Bund-Länder-1000-Dächer-Programm dient, besteht aus 3 Teilfeldern. Ein Strahlungsmeßfeld dient der Erfassung meteorologischer Parameter und der Bestimmung der Energieproduktion unterschiedlich geneigter und ausgerichteter Module. Eine netzgekoppelte Referenzanlage erlaubt die Untersuchung der Energieflüsse und Verlustquellen. Im Modulfeld werden der effektive Wirkungsgrad bzw. die Energieproduktion von derzeit 13 unterschiedlichen Modulen in Abhängigkeit von Einstrahlung und Temperatur gemessen. Zur Durchführung der Messungen und Datenauswertung wurden spezielle Hard- und Softwarelösungen entwickelt.

The Rossendorf Focused Ion Beam IMSA-100 was used for writing implantation of cobalt (E = 30 keV Co+ and 60 keV Co++; D = 0.5...5x1017 cm-2) at room temperature to form CoSi2 microstructures on silicon by ion beam synthesis. For that aim two types of Liquid Alloy Ion Sourses (LAIS) were developed. As implanted and annealed (600°C for 60 min and 1000°C for 30 min in N2 atmosphere) silicide structures were analysed by SEM, EDX and electrical measurments.

The behaviour of radiation induced carbon related defects in high resistivity silicon detectors has been investigated. The defects were introduced by alpha-particle irradiation and the measurements were carried out by the DLTS-technique. The unusual defect behaviour consists in low temperature anealing, including self annealing at room temperature, of the interstitial carbon C_i with a simultaneous increase of the (C_i-O_i)-complex concentration. The kinetic parameters of the process have been determined from the increase of the C_i-centre concentration versus time. Tho annealing velocities have been observed, which ar due to different heat treatments during the detector fabrication process.

The time-dependent drag force on a spherical drop is analyzed for the linear limit of small Reynolds numbers. There is an error in the literature on the generalization of the known Basset memory kernel of a rigid sphere to the case of a drop. Correct results are presented here. A new overshooting effect is found if thermocapillarity is driving the drop motion rather than gravity.

A theoretical analysis of liquid drop unsteady migration under microgravity conditions is presented, for the case of an interfacial tension gradient on the drop surface generated by a uniform temperature gradient in the surrounding liquid. The effect of buoyancy due to a residual gravity vector aligned parallel to the temperature gradient is included. The relevant equations are solved in the creeping flow limit where in the convective transport of momentum as well as that of the energy is neglected, i.e. at low Reynolds and Marangoni numbers. The flow and the temperature field within and around the drop are obtained after transforming the results from the Laplace domain, in which they are derived, to the time domain. The time transient behaviour of the migration speed depends strongly on the choice of the initial flow and temperature fields.

After a brief discussion of the meaning of diffraction pole figures due to polycrystals the main sources of statistical and physical errors in quantitative texture analysis are analysed. The essential influence of the microcopical architecture (lattice perfection of the crystallites, grain sice and orientation distribution) of the sample material on the results of texture analysis is demonstraded. Possibilities of an estimation of errors by computer simulation or of correction by applying of useful correction methods are pointed out.

Modelling the mechanical vibrations of pressurized water reactor internals the fluid-structure-interaction is to be taken into account. Especially at VVER-440 reactors there is a strong influence of the fluid due to the specific geometry. The intention of the presentation is to provide a solution of the continuity and the Navier-Stokes equations for the special case of a narrow annular gap geometry considering the fluid friction.
To obtain an analytical solution for these coupled 3D partial differential equations further assumptions and simplifications must be made:

• the width of the annular gap is small compared with the diameter,
• displacements of the mechanical structure are small compared with the gap width
• the fluid flow velocity components are independent on the radius.

Methods of acoustic leak monitoring are of great practical interest for the safety of pressure vessels and pipe lines not only at the primary circuit of nuclear power plants. In this report some aspects of acoustic leak localization at complicated three-dimensional topologies for the case of leakage monitoring at the reactor vessel head of a VVER-440 are discussed.
An acoustic method based on pattern recognition is being developed. During the learning phase, the localization classifier is trained with sound patterns that are generated with simulated leaks at all locations endangered by leak. After training unknown leak positions can be recognized through comparison with the training patterns.
The sound patterns of the simulated leaks are simultaneously detected with an AE-sensor array and with high frequency microphones measuring structureborne sound and airborne noise, respectively.
The initial results show the used classifiers principally to be capable of detecting and locating leaks, but they also show that further investigations are necessary to develop a reliable method.

The recent safety analysis investigations of the VVER type reactors require the use of three-dimensional hexagonal kinetic codes. For this purpose the codes KIKO3D and DYN3D were developed in the Atomic Research Institute Budapest and in the Research Center Rossendorf, respectively. The kinetic codes have to be validated before being used for safety assessments. A benchmark problem is defined, as the first step of the validation procedure of hexagonal kinetic programs.
The problem describes a rod ejection transient in a VVER-type geometry, where the worth of the ejected rod is just below the prompt critical value. The initial power is near to zero and the power rise is not too large. Therefore, the transient can be treated without feedback based on given the time-dependence of the cross sections and geometry.
KIKO3D results are presented, i.e the solution of time dependent nodal equations by the Improved Quasistatic (IQS) Method. The time dependence of the integrated power and the reactivity are compared with the adiabatic results. These results are also compared with the results of two different DYN3D calculations carried out in Rossendorf and in Berlin.

The design of an achromatic mass separator which consists of two ExB filters, a stigmator, and the separation aperture is descibed. The optical properties of the ExB filters are derived. The influence of the designd mass are shown.