Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

In the report the boundary conditions and the resulting technical possibilities are described for the construction of a technical system for remote monitoring of the nuclear power plant Zaporosh`ye, unit 5, available for the supervision by the state regulatory body. The general structure of the system and especially different technical solutions for the remote data transfer are discussed in more detail.

In der Arbeit wird experimentell und theoretisch die Frage behandelt, wie ein externes longitudinales Magnetfeld die Stabilität des Zylinder-Nachlaufs (Karmansche Wirbelstraße) beeinflußt. Die Messungen wurden am Quecksilber-Versuchsstand des IMG Grenoble durchgeführt. Die Unterdrückung der Wirbel-straße wurde vom theoretischen Modell vorhergesagt und im Experiment verifiziert. Überraschend wurde sowohl vom Modell als auch im Experiment die Tendenz zu langwelligen Störungen gefunden, die bei wachsendem Magnetfeld immer ausgeprägter werden.

In order to improve operational surveillance of a WWER-1000 unit of the Ukrainian nuclear power plant Zaporozh`ye a technical monitoring system has been specified. The system shall enable the state regulatory and supervisory bodies to survey the unit operation independently of operators, to assess its safety status, and to impose appopriate conditions. Based on the definition of safety functions and control tasks 49 different technological parameters are investigated and selected for monitoring. Technical specifications of these parameters at NPP Zaporozh`ye and derived alerts by crossing operational threshold values of single parameters and/or parameter combinations are described in the report.

In order to improve operational surveillance of a WWER-1000 unit of the Ukrainian nuclear power plant Saporoshje a technical monitoring system has been specified. The system shall enable the state regulatory and supervisory bodies to survey the unit operation independently of operators, to assess its safety status, and to impose appropriate conditions. By its up-to-date configuration the system provides early indication of any operational incident and emission of radioactive materials connected. Based on the system an immediate warning in emergency situations is possible as well as an effective emergency management. For this purpose 49 operational parameters of the unit, 18 radiological parameters of the unit and the plant site and 6 meteorological parameters are monitored. The costs of establishing the technical system in its minimal size are estimated to about 1.3 Million DM (without expenses for installation of the system and of the data networks). Additionally about 650 000 DM are required for most necessary backfitting of measuring channels. Including another unit into the monitoring system implies further costs of about 200 000 DM.

Two improved impact testing facilities are used for the dynamic fracture toughness evaluation of precracked Charpy V-notch specimens. The methods of single specimen acoustic emission and crack mouth opening displacement testing are assumed to indicate the initiation points of stable crack growth. Thus, the dynamic ductile initiation J integral JId can be derived. It was shown that the toughness JId of the heat-resistant steel 10CrMo9.10 cannot be approximated by the J value at the maximum of the load deflection curve.

The unidirectional flow of an electrically conducting fluid around a cylinder of arbitrary electrical conductivity, which is driven by the interaction of a homogeneous electric current with a homogeneous magnetic field and the resulting force on the cylinder are calculated numerically without any approximation in a large range of parameters. Asymptotic solutions are derived for the case of very strong and very weak magnetic fields respectively. A comparison with experimental results on insulating and highly conducting cylinders leads to a partial agreement although inertial forces are not taken into account in the model. Finally, confinement effects are considered leading to a better agreement between theory and experiment.

Within the frame of the PHDR reactor safety research programme a large series of emergency core cooling injection tests was performed. The tests aimed at the study of the flow structure in the main circulation pipe and the heat exchange between the injected subcooled water and the saturated steam originating from the reactor, a KONVOI type PWR. They were carried out at the COCO facility (COntact COndensation). The paper deals with the results from hot leg injection tests obtained by the needle shaped conductivity probes developed in Rossendorf. Eight probes were placed at different positions around the injection nozzle. In KONVOI PWRs a special feature is used for the injection, the so called "Hutze", which is a cylindrical half-shell welded to the bottom of the circulation pipe and directing the water towards the reactor vessel against the steam flow. The probes provided very clearly readable data about the flow structure in a high time resolution. The flow regime was characterized in the cases of stratified flow (counter-current and co-current), complete flow revers and intermittent flow revers with plug formation. Additionally, in several cases the flow velocity was measured by means of cross correlation techniques.

Usually the assessment of the irradiation sensitivity and annealing behavior of reactor pressure vessel (RPV) steels is performed by means of destructive test methods, mainly impact and tension tests. In this paper a new kind of search for an efficient temperature-time regime for postirradiation thermal heat treatment is presented using nondestructive test methods like positron annihilation (Doppler broadening parameter S) and hardness (Vickers hardness HV 10).
Samples of Cr-Mo-V RPV steels (Soviet type 15Kh2MFA) were irradiated to different fluence levels of fast neutrons at temperatures T < 156 °C in a test reactor (base metal) and T = 265 °C in a pressurized water reactor (base as well as weld metal). From isochronal and isothermal annealing curves of HV 10 and S, favorable temperature-time regimes for each type of irradiated material were estimated. The data obtained from tension and impact tests indicate that sufficiently large recoveries took place by application of these regimes.
The new approach presented is especially useful in such cases where only the smallest amounts of irradiated materials are available-a case often met for RPV surveillance specimens.

By the installation of more than 400 modern solar thermal collector plants with a summarized collector area of about 3000 m2 a remarkable entry in the thermal use of solar energy was reached in Saxonia in 1992. Simultaneously a network of little enterprises came into existence, which now work actively in the field of energy and environmental techniques. This development was essentially supported by the Saxonian promotion programme of rational use and application of renewable sources of energy.

Recent results on the study of a liquid metal flow around an insulating cylinder with constant aligned magnetic field are presented. From the experimental point of view, a special type of differential pressure transducer using strain gauges is described. The results obtained with mercury as liquid metal are presented for an interaction parameter N ranging from O to approximately 8. The stabilizing effect of the magnetic field on the boundary layer separation is shown. Pressure distribution around the cylinder as well as the overall pressure drag coefficient CD are given for different values of N. The last section presents analytical calculations of the flow distribution of an inviscid fluid when N << 1. The theoretical results are in good agreement with these experimental results.

A literature review on thermoacoustic engines (TAEs), with particular emphasis on liquid metal MHD TAEs is presented. The main aim of this paper is to draw the attention and the interest of the international MHD community to these new developments since it has only been discussed in the literature on acoustics.
TAEs provide a new way to convert heat to mechanical energy, or more strictly speaking, to acoustic power. They have an efficiency comparable to existing techniques but with the possibility of increasing reliability because there are no moving parts. TAEs utilize heat flow from a high-temperature source to a low-temperature sink to generate acoustic power in the form of high-amplitude sound waves in liquid sodium. Since acoustic power is inconvenient in most situations, a power transducer is required to convert acoustic power into an electric one. Though there are a number of converter mechanisms, the magnetohydrodynamic one is particularly suited for sound waves in liquid metals. A magnetic field perpendicular to the direction of sound propagation is applied to the center of the resonator, in which the sound has been generated. There are electrodes in the sodium that form an electric current path perpendicular to both magnetic field and sound velocity.

This study briefly summarizes the activities of the Rossendorf group in the field of liquid metal MHD. It shows in which way the present investigations on basic problems in liquid metal MHD followed from the fast-breeder research. Special interest is focussed on liquid metal two-phase flow and MHD flow around obstacles, as well as the laminar-turbulent transition in two-dimensional MHD flows. Most of the investigations are theoretical, but partly connected to experiments performed in Riga, Latvia or Grenoble, France. Own experiments at a sodium loop are described. Finally, the most promising directions of future research are presented.

Theoretical and experimental results of MHD drag coefficients are summarized. Special attention is paid to Stokes flow, where a typical error has been found in the literature. This situation is clarified here, and correct results are presented. Numerical calculations are performed for the MHD Stokes flow around a cylinder in a transverse magnetic field, yielding qualitative agreement for the drag with both measurement as well as a rough asymptotic analysis. The MHD drag coefficient of the cylinder in a transverse magnetic field increases proportionally to M . lnM if M >> 1 (where M is the Hartmann number). Finally, the deflection of a rising bubble in a liquid metal is determined if the direction of the magnetic field is inclined relative to the vertical line.

The flow around a circular cylinder is considered for the following particular configuration: The fluid is electrically conducting and the whole system is inside an external magnetic field. This magnetohydrodynamic (MHD) flow is of interest for various applications but also for basic fluiddynamic research.
As an introduction to typical MHD effects a simple model system is considered: Fluid flow parallel to the cylinder axis. It allows an analytical solution of the combined system of Navier-Stokes- and Maxwell-equations. The results clearly show the development of the typical shear-layers resulting from the electromagnetic and viscous forces: Boundary layer at the cylinder surface, tangential layers at the cylinder poles, deep core and outer core of the wake.
Analytical and experimental results will be summarized concerning the more interesting standard geometry of a flow perpendicular to the cylinder axis.
The experimental results include turbulence intensities and the induced magnetic field at different locations in the up- and downstream wakes, as well as the pressure at the cylinder surface.

In 1992 in the new Federal States of Germany the renewing of district heating plants was supported by the gouvernment. Plants for heat generation, and heat transport and distribution and customer installations were included in the renewing. In Saxonia an amount of approximately 80 million DM could be devided among the applicants. With regard to the enormous uncovered demand the gouvernment decided to continue the program from 1993 up to 1995. Based on the experiences with the 1992 promotion program some hints can be given to the user of the new program.

A comparative study of the oxidation behaviour of ZrNb1 and Zircaloy-4 was carried out in a steam atmosphere in the temperature range from 700-1100 °C. ZrNb1 and Zircaloy-4 are oxidizing approximately according to similar oxidation kinetics. The oxidation rate of ZrNb1 is somewhat lower. It can be described by the equation m = 0.4873 t exp(-10261/T). However, remarkable differences are observed in respect to morphology of the oxide and the O-stabilized -layer, hydrogen uptake, and both the fraction and distribution of the oxygen dissolved in the metal. Above all the rapid drop in ductility by exposure to steam is of significance under safety aspects. Differences in the thermodynamic conditions for equilibrium of the ternary systems Zr-0-Nb and Zr-0-Sn may provide an appropriate explanation of these differences.

The paper gives results of the contribution of Research Center Rossendorf to the IAEA Coordinated Research Programme "Optimizing of Reactor Pressure Vessel Surveillance Programmes and Their Analysis - Phase 3". The report includes information about material and specimen fabrication, the irradiation conditions, and the test methods. For the unirradiated state impact energy-temperature curves, dynamic J integrals for cleavage fracture, quasistatic crack resistance curves, and crack initiation J integral values are given.

The irradiation programme Rheinsberg serves to investigate the neutron embrittlement of VVER type reactor pressure vessel steel. Within this programme Charpy-V (partly with fatigue crack and side grooved), CT- and tensile specimes of 24 different heats from VVER 440 type and VVER 1000 type reactor pressure vessel steel (basic or weld material) were irradiated in the high flux channels of the VVER-2 Rheinsberg from 1984 - 88. The testing and evaluation of the irradiated specimen will be done within the framework of bilateral scientific-technical cooperation between Russia and Germany. The report gives a systematic review of all material data existing for the unirradiated initial state. Results of Charpy- V-impact tests and quasistatic 3-point-bending tests are discussed in detail.

The ordinary coherence function 2( ) defined by
Sxy( ) 2
2( ) = (1)
Sxx( ) * Syy( )

is of squared type with a positive bias depending on the number N of accumulated estimations. If the analyzed signals x(t), y(t) as well as the correlated contribution inside x(t), y(t) are normally distributed the power spectral densities Sxx, Syy are 2-distributed. Then the product as well as the quotient in equ. 1 are not of a classical distribution type and the determination of the concrete type becomes difficult.
Therefore the bias and the corresponding standard deviation are investigated experimentally using uncorrelated normally distributed white noise. The result shows for estimation numbers N > 5, that the bias of 2 corresponds to the amount of 1/N. The belonging positive standard deviation
sigma ( OVERLINE { gamma SUP 2 } (f SUB i)) ~ = ~ SQRT { { Sum from { i = 1} TO M { ( OVERLINE { gamma SUP 2 } (f SUB i) ~ - ~ OVERLINE { gamma SUP 2 } ) } SUP 2 } OVER {M -1 } }


(2)

for N > 5 t is in the same order of magnitude as the bias itself. That means: For the evaluation of coherences a confidence band of +(4...5) * should be used to select values of significant statistical accuracy. Only for these selected values one can be sure, that the phase values belonging the same frequency point are useful for system identification.

The contents is largely covered by a the extended contribution to this annual report.

The maximum permissible time step size is an input parameter of the ATHLET code. In the ATHLET input data description a value of 5 s is recommended for this parameter. For first tests of the coupling of the ATHLET code with the 3D neutron kinetic code DYN3D test calculations with a simplified VVER-440 data set were carried out. The results were compared with ATHLET calculations with point kinetics. The influence of the maximum permissible time step size on the results of these calculations with point kinetics is discussed for two test cases. In the first case the time points for opening and closing of safety valves are shifted for maximum permissible time steps greater than 0.5 s. In the second case there is an oscillation of power for maximum time steps of 2 s, which is removed by a maximum time step size of 0.5 s. These examples show, that the recommended value for the maximum permissible time step size is not suitable for all problems.

Neutronic problems connected with the design of a compact 14MeV neutron source for fusion material research based on a plasma mirror are treated. In particular it has been demonstrated, that further construction efforts are necessary to comply with the established radiation limits for the magnetic system. Further it is not possible to raise the useful high energy flux by arranging reflectors. If one of the source areas of the machine is equipped with a moderator, a thermal neutron source with a flux of about 5·1014 n cm-2 s-1 can be achieved.

Calculations relating 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 primary coolant inventory reduced stepwise. The experiment was conducted in the PACTEL facility in Lappeenranta (Finland), which is a 1/305 volumetrically scaled, full height three loop simulator of the Russian VVER-440 type reactor. The main events of the experiment could be shown and explained by the ATHLET calculations:

• After the second draining the mass flow in the loops stagnates. Simultaneously, the primary pressure increases and the pressurizer is partly refilled.
• In the periods after the third drain step the mass flow through the three loops is nonequally distributed, which could be reproduced by the ATHLET calculations at least qualitatively.

A method for detecting and localizing leaks at complicated three-dimensional topologies by measuring the leak induced structure-borne and airborne sound and by applying pattern recognition procedures is being developed. The sound patterns necessary to train fuzzy logic classifiers and neural networks are generated with simulated leaks at the original structure. As features for characterizing the occurrence and the location of a leak, coherence values between high-frequency microphone signals and RMS-values of acoustic emission sensors are used. The method is even applicable when localization based on propagation time differences or sound attenuation differences fail.

A reactivity initiated transient caused by entering a water plug with diluted boron concentration into the core during incorrect loop startup in a VVER-440/W-213 reactor is analyzed with the help of the code DYN3D/M2. The water with diluted boron concentration from the one loop is mixed with the water of the other loops before the core inlet. The results for the transient are influenced by three different mixing models that were investigated:

• ideal mixing: the boron concentration at all inlets of fuel assemblies is uniformly distributed,
• no mixing: the boron perturbation occurs only in the fuel elements of the sector belonging to the considered loop,
• mixing model: estimation of boron dilution at the core inlet by superposition of reference distributions, defined experimentally or pre-calculated by a simplified analytical model.

The first kinetic benchmark of AER was defined for comparison of different 3-dimensional kinetic codes developed for the hexagonal geometry of fuel assemblies in a VVER-reactor. The transient was assumed to be caused by ejection of nonsymetric control rod in a VVER-440 reactor. Feedback effects were neglected. The positive reactivity insertion not leading to prompt criticality results in a slower power increase and was compensated by insertion of shutdown rods.
The benchmark problem No. 2 discussed on the meeting of working group D in Budapest 1993 consists also of a control rod ejection accident in a VVER-440. The initial configuration is similar to benchmark No. 1. A nonsymetric control rod with a worth of 2 ßeff is ejected at hot zero power (HZP). The Doppler effect being the main feedback effect for this type of transients is the only feedback and is taken into account by an adiabatic model of fuel temperature. Therefore it is possible to calculate this type of transient with codes which do not contain a complete thermohydraulic model.
As in problem No. 1, the nuclear data are given to exclude at this step of comparison the effects caused by different nuclear data. A sharp and high power peak connected with large deformations of flux shape is expected to give a serious test for codes and methods of calculation.
The problem, the input data and the expected results which will be used for comparisons are specified.

Reactivity initiated accidents (RIA) have to be analyzed for safety assessment of nuclear reactors. The presented 3-dimensional core simulator DYN3D/M2 describes the space dependent effects of reactivity perturbations caused by control rod motions or local changes of coolant temperature and boron concentration. The safety margin can be determined more precisely by use of 3-D models than with simpler methods as point model or one-dimensional kinetics. A nodal expansion method (NEM) for hexagonal geometry of VVER fuel elements was developed to reduce the numerical effort of 3-dimensional neutron kinetics. The changes of thermohydraulic parameters as fuel and coolant temperatures, coolant density and poisoning are determined with the help of the thermo-hydraulic model FLOCAL included in the code. The feedback effects derived from the influence of the thermohydraulic parameters on the neutron physical constants. Applying DYN3D to safety calculations of reactivity transients, the code was validated by comparing its essential parts with benchmarks, other codes and experiments. An accident caused by the ejection of a single control rod in a VVER-440 reactor was analyzed. The results show a very high power peak in the neighbourhood of the ejected rod. Runs with time step control indicate that the computer time can be reduced in comparison to fixed time step. Simulations with a smaller number of coolant channels were investigated for coupling the core model with codes simulating the whole coolant system of a nuclear power plant.

The dispersion of small gas bubbles in a vertical upwards liquid metal two phase flow is investigated theoretically as well as experimentally. Local void fraction measurements are presented for a vertical sodium-argon flow with and without external magnetic field. The dispersion of an initially narrow void distribution shows this behaviour clearly: There is an overall focussing effect of the magnetic field on the void distribution, but the dispersion of gas bubbles is much more suppressed parallel to the field than perpendicular to it.
The bubble transport is modelled by a simple diffusion equation. The model takes into account that bubbles represent no passive tracer of the flow field but have an own dynamics due to their relative velocity to the liquid phase. The experimental results will be analyzed in terms of the corresponding diffusion coefficients.