Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Die ungarische Versuchsanlage PMK-2 ist ein im Volumenmaßstab 1:2070 skaliertes Modell einer Reaktoranlage vom Typ WWER-440. Das Experiment „1%-Leck im kalten Strang" ist die Wiederholung eines Experiments von 1990 mit erweiterter
Instrumentierung - insbesondere Nadelsonden aus dem FZ Rossendorf. Das Leck befindet sich am oberen Teil des Ringspalts und hat einen Durchmesser von 1 mm. Für das Experiment wird angenommen, daß zur Notkühlung nur das Hochdrucknotkühlsystem (HPIS) verfügbar ist. Im Forschungszentrum Rossendorf wurden Nachrechnungen zu dem vorgestellten Experiment mit dem Code ATHLET Mod1.1 Cycle A durchgeführt. Wie der Vergleich von Rechnung und Experiment zeigt, werden alle Phänomene des Experiments in der Rechnung gut wiedergegeben. Insbesondere konnten die beobachteten Instabilitäten im Naturumlauf sehr gut modelliert werden.

The existence of Main Isolating Valves (MIV) in the hot leg and the cold leg of each primary circuit loop is a special feature of WWER­440 type reactors. MIV's availability permits the disconnection of any loop during the work of all others, for example, in the case of leaks. The connection of a previous disconnected loop is a potential way for inducing a boron dilution accident, when infringements of rules and failure of technical systems occur. By combining the use of the codes SiTAP and DYN3D, more realistic boundary conditions were obtained than in previous investigations, were a plug of water with diluted boron concentration was supposed to travel through the core while keeping the other boundary conditions constant.

The considered test was a break on the upper plenum with different modes of emergency core cooling. The reference case was the non-availability of emergency cooling. Injecting the emergency coolant into the cold leg, no increasing of rod cladding temperatures was observed, but natural circulation instabilities occurred. Injecting the cooling into the hot leg, the cooling situation was getting worse. Due to the injected cold emergency coolant, the fluid density in the discharge volume was enhanced and the break mass flow increased. The observed events in the test were reproduced by the code with good agreement

Die Entwicklung supramolekularer Rezeptoren zur selektiven Komplexbildung von Anionen, Kationen und Neutralmolekülen ist von großem Interesse im Hinblick auf Anwendungen in der Analytik, Medizin und Technik. Die besondere Rolle der supramolekularen Chemie resultiert dabei aus der grundlegenden Überlegung, in biologischen Systemen genutzte Wirksysteme einer hochselektiven Erkennung und Bindung von Spezies sowie ihres Transportes mit Hilfe komplexer organisierter molekularer Funktionseinheiten auf die Lösung praxisrelevanter Probleme zu übertragen.
Möglichkeiten der selektiven Bindung und des Phasentransfers werden am Beispiel von ditopen Guanidiniumverbindungen für Oxoanionen sowie makrobi- bzw. -tricyclischer Carbonsäuren für Erdalkali-Ionen diskutiert.

This Paper proposes a set of 3-dimensional benchmark rod ejection problems for a VVER reactor, based on the wellknown NEACRP PWR rod-ejection problems defined by Siemens/KWU. Predictions for these benchmarks deriving using three hexagonal-z nodal transient codes, the PANTER code of Nuclear Electric, the HEXTIME code of Siemens/KWU and the DYN3D code of FZ-Rossendorf are presented and compared.

The paper presented concerns a comparative analysis of the third three­dimensional dynamic benchmark of AER by using different options of the DYN3D code developed in the RC Rossendorf. The benchmark was defined as a control rod ejection accident in a VVER­440 core without reactor scram including the whole core thermal hydraulics. For the basic analysis with the help of DYN3D, some modifications of the code were made to meet the specifications of the benchmark (thermal properties of fuel and cladding, heat transfer in the gas gap, DNBR­correlation, hydrau lic model) as close as possible (case A). An additional analysis was carried out by using the standard version of DYN3D without any modifications. The conditions of the benchmark were approa ched only via input data (case B). In the first part of the paper, a description of the thermohy draulic model of DYN3D is given. Specific aspects concerning the modelling of the benchmark conditions are outlined. In the second part, a c!
omparative analysis of the results obtained by different DYN3D options is given. In addition to the demonstration of the applicability of the DYN3D code for solving the problem without any modifications, the goal of the investigations was to get a feeling for the sensitivity of the results with respect to ther mohydraulic modelling. The global parameters like reactivity, nuclear power, power to coolant and total mass flow rate were obtained with good agreement between the cases A and B. However, differences occur in detailled parameters, especially for the hot channel, where heat transfer crisis occurs.

The coupling of advanced thermohydraulic codes with 3-dimensional neutron kinetic codes corresponds to the effort to replace conservative estimations by best estimate calculations. In the past advanced thermohydraulic codes and detailed core models were devoloped in most cases separatly. But it is often nesessary to consider the feedback between the coolant circuits and space dependent neutron kinetics. Examples for such cases are boron dilution accidents or inadverdant connection of a loop filled with cold water.
ATHLET is an advanced thermohydraulic code, developed by the German Gesellschaft fr Anlagen- und Reaktorsicherheit (GRS). Up to now only point kinetics and 1-dimensional neutron kinetics have been included. The DYN3D code, developed in the Research Centre Rossendorf (FZR) for the improvement of the simulation of reactivity initiated accidents in VVER-type reactors comprises 3- dimensional neutron kinetics, models for the thermohydraulics of the core including heat transfer from the fuel to the coolant, a fuel rod behavior model and a mixing model for the lower plenum.

The paper presents the results of small-break loss-of-coolant tests carried out at the test facility ISB-VVER located in Elektrogorsk, Russia. Presently, it is the only operating integral model of the Sovjet type VVER-1000 reactor suitable for thermalhydraulic investigations. A small leak in the upper plenum of the reactor vessel was chosen for the test scenario. Different emergency core cooling (ECC) injection modes were applied and compared. It was show that the best results of ECC injection are obtained by a combined injection into both hot and cold leg. It is possible to maintain a reliable core cooling even without an injection by the safety injection tanks, which were assumed to be not available. The tests provided data suitable for code verification. Applied needle shaped void fraction probes delivered detailed information about the two-phase flow in the primary circuit.

Es wird die Struktur eines technischen Computersystems zur betrieblichen Überwachung der Zuverlässigkeit und Sicherheit ukrainischer KKW durch die staatlichen Aufsichtsbehörden beschrieben. Nach Auffassung der Autoren führt der Aufbau eines solchen Überwachungssystems, unabhängig von den Kontrollsystemen des Betreibers, zu einer schnellen, signifikanten und kostengünstigen Sicherheitserhöhung beim Betrieb der Reaktoranlagen vom Typ WWER-1000.

Es wird ein Ultraschall-Laufzeit-Bewegungsverfahren vorgestellt, mit dem der duktile Rißfortschritt in 3-Punkt-Biegeproben kleiner Abmessungen gemessen werden kann. Das Verfahren erfüllt die Genauigkeitsanforderungen nach DIN 54120 und arbeitet quasikontinuierlich.

The 4-[¹⁸F]fluorobenzoyl compounds of Neurotensin(8-13) (NT(8-13)) as well as [Arg⁸pseudo(CH₂NH)Arg⁹]NT(8-13) were obtained by reaction of N-succinimidyl 4-[¹⁸F]fluorobenzoate ([¹⁸F]SFB) with these peptides in aqueous buffered solutions at pH 8.3 in r.c.y. of up to 43 % (related to [¹⁸F]SFB; decay-corrected) within 80 min (including HPLC purification). This is the first example for the specific radiolabelling of the alpha-amino group at the N-terminal arginine unit of peptides using [¹⁸F]SFB.

Bei Druckentlastungsexperimenten mit Ethanol an einem Versuchsreaktor von 105 l Volumeninhalt der Hoechst AG wurden nadelförmige Leitfähigkeitssonden zur Messung von Dampfgehalt, Gasgeschwindigkeit und Blasengröße eingesetzt. Es wurden insgesamt 5 Sonden im oberen Bereich des Reaktors auf verschiedenen Höhenmarken eingebaut. Hiervon dienten 4 Einpunktsonden ausschließlich der Dampfgehaltsmessung. Die Spitze der Sonde steht in Kontakt mit der elektrisch leitenden Flüssigkeit. Durch Versorgung mit einer kleinen Gleichspannung wird ein Strom hervorgerufen, der unterbrochen wird, wenn die Sondenspitze sich in einer Dampfblase befindet. Der Gasgehalt des zweiphasigen Gemisches wird aus der Integration der Kontaktzeit mit der Gasphase bezogen auf die gesamte Meßzeit berechnet. Bei einer weiteren Sonde handelte es sich um eine Zweipunktsonde, die zusätzlich die Bestimmung der Geschwindigkeit der Dampfblasen erlaubt. Dies geschieht durch Auswertung der Zeit, die zwischen dem Eintreffen der Blasen an deren vorderer Elektrode und dem Umschließen der hinteren Elektrode verstreicht. Mit dem bekannten axialen Abstand der zwei Elektroden wird hieraus die Geschwindigkeit berechnet. Durch Kombination der Geschwindigkeitsinformation mit der Dauer des Blasenkontakts wurden Blasengrößen bestimmt. Es konnte gezeigt werden, daß Leitfähigkeitssonden trotz des geringen elektrischen Leitwerts von Ethanol benutzt werden können. Es wurden insgesamt 4 Versuche mit einem Anfangsdruck von maximal 0,98 MPa durchgeführt. Bei der Druckentlastung kam es zum Aufsieden des Behälterinhalts und zum Auftreten eines Zweiphasengemischs. Durch das Anwachsen des Dampfgehalts an der Entlastungsöffnung kommt es zur Beschleunigung des Druckabbaus, woraufhin der Dampfgehalt an den Sondenpositionen zunimmt. Die Sonden registrieren schließlich infolge der Verringerung des Behälterinhalts nacheinander den Durchgang Gemischspiegels. Mit Hilfe der Zweipunktsonde wurden Blasengrößen bestimmt. Durch den zufälligen Charakter der Berührung Blase - Sonde werden Sehnenlängen der Blasen und damit deren Größe bestimmt. Die Meßwerte lassen den Schluß zu, daß eine heterogene Blasenströmung mit einem hohen Anteil von Großblasen vorgelegen hat. Mit dem eindimensionalen Rechenmodell BLDN konnten nach Implementierung eines Stoffdatensatzes für Ethanol die gemessenen Gasgehaltsverläufe gut reproduziert werden.

Das Programm BLDN (BLow-DowN) basiert auf einem eindimensionalen Strömungsmodell zur Beschreibung der axialen Dampfgehaltsverteilung in einem stehenden zylindrischen Druckbehälter bei einem Abblasevorgang unter Beschränkung auf eine Komponente. Zur Beschreibung der axialen Dampfgehaltsverteilung werden für Dampf und Flüssigkeit die gemeinsamen Massen- und Energieerhaltungsgleichungen gelöst. Es wird von thermodynamischem Gleichgewicht ausgegangen. Die zum Abschluß des Systems notwendige Phasendriftbeziehung wird in Form einer Phasendifferenzgeschwindigkeit als Funktion vom Dampfgehalt und den Stoffwerten verwendet. Mit Hilfe dieser Beziehung werden die Geschwindigkeiten beider Phasen gekoppelt. Der Impuls des Strömungsmediums wird vernachlässigt. Die Impulsgleichungen bleiben deshalb unberücksichtigt. Im Druckgefäß wird lediglich ein hydrostatisches Druckprofil berechnet, mit dessen Hilfe die Meßwerte von Differenzdruckgebern simuliert werden können. Die Anwendbarkeit des Modells ist wegen der fehlenden Impulsgleichungen auf kleine Lecks beschränkt. Der trägheitsbedingte Druckimpuls, der auf die Differenzdruckgeber in den ersten Zehntelsekunden des Aufsiedens wirkt, wird nicht nachgebildet. Die Verbindung zwischen Leckmassenstrom und Druckabfallgeschwindigkeit wird durch integrale Massen- und Energiebilanzen hergestellt, die über den gesamten Behälter gebildet werden. Je nach Option wird der Druckabfall aus dem Leckmassenstrom (BLDN) oder umgekehrt (BLDN_PV) berechnet. Der Wärmestrom, der von den Behälterwänden infolge des Absinkens der Fluidtemperatur während des Druckentlastungsvorgangs ausgeht, wird mit einer Wärmeübergangszahl für gesättigtes Sieden berechnet. Die momentane Temperatur an der Behälterinnenwand wird durch analytische Lösung der Wärmeleitungsgleichung in der Wand bestimmt. Der Verlauf des Massenhöhenstands (collapsed level) wird durch Integration des Leckmassenstroms bestimmt. Der Gemischspiegel wird unter Vorgabe des jeweiligen Massenhöhenstands aus der axialen Dampfgehaltsverteilung ermittelt. Bei der Berechnung des Dampfgehalts am Leckort wird die Lage des Gemischspiegels und die Höhe der Sprudelschicht (Schaumzone) berücksichtigt. Letztere bildet sich am Übergang von der Blasenströmung zum Dampfraum heraus.

Die Analyse von Ultraschall-Transmissionssignalen zeigte, daß eine laufende Identifikation des Stromungszustandes in Rohrleitungen durch einen Aufbau von Relationen zwischen den physikalischen Parametern einer Zweiphasenströmung und den charakteristischen Mustern gemessener Signale möglich ist. Auf dieser Grundlage werden Ergebnisse eines Systems, welches aus einer Ultraschall-Meßeinheit, einer Datenbankeinheit und einer Mustererkennungseinheit besteht, vorgestellt. Dieses System liefert am Ausgang vier Parameter: einen Identifikator fur die Strömungsform, die separaten Volumenströme der flüssigen und der gasformigen Phase und den abgeleiteten Gasgehalt. Der Parametersatz dient als einer von mehreren Eingabensätzen fur das übergeordnete Überwachungs- oder Diagnosesystem. Die mit diesem System erzielten Erkennungsraten liegen zwischen 87 % und 94%.

Druckentlastungsexperimente der TU Hamburg/Harburg von überkritischem CO₂ aus einem Druckbehälter werden vorgestellt. Dabei wurden mit einer Gamma-Durchstrahlung axiale Dampfgehaltsprofile im System CO₂-flüssig und CO₂-gasförmig sowie Druck- und Temperaturverläufe gemessen. Die Experimente, insbesondere die lokalen Gasgehalte, können durch das Programm BLDN des FZR mit Erfolg nachgerechnet werden, wobei verschiedene Driftansätze auf ihre Anwendbarkeit auf CO₂ hin überprüft wurden.

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 first four Greifswald reactor units belong to the WWER 440/230 reactor family and they are the only ones permanently shut-down. The status of the WWER 440 units as concerns the plant specific material data is shortly described in the paper. The lack of material data is a real problem of the 230 model reactors and the high lead factor in the surveillance irradiations of the more modern 213 units is an essential uncertainty in the safety assessment of the units. In addition most aof the 230 units have been and some of the 213 units will be annealed. Greifswald units are fully representative WWER 440 units and they represent irradiated, irradiated-annealed and irradiated-annealed-reirradiated material conditions. In this paper a basic material research programme is proposed, which can greatly support the operating WWER units.

In the present paper the stability of the time-dependent, three-dimensional, incompressible flow around a circular cylinder exposed to an external magnetic field is investigated numerically. We perform a linear 3d stability analysis of the 2d flow being either steady or quasiperiodic as known from previous work. By monitoring the time evolution of the integral energy of the 3d disturbances in the computational domain we decide whether the flow is globally unstable or stable. The results are compared and validated with recent results for the purely hydrodynamic problem. We restrict the analysis to a magnetic field being aligned with the oncoming flow. For this case we numerically confirm the general result of Hunt that in the (Re, N)-plane parameter regions above the 2d-neutral stability curve exist where the flow is 3d-unstable but 2d stable (steady) because the magnetic field acts in a different way on 2d and 3d instabilities.

Die Beschreibung der Strömungsfelder in Blasensäulen ist Grundlage für die Bestimmung der Stoff und Wärmetransportvorgänge. Dabei steht die Untersuchung der instationären Zirkulationsbewegung der flüssigen Phase im Mittelpunkt, die mit Hilfe spektraler Verfahren berechnet wird. Das Modell wird für ein zweidimensionales rechteckiges Gebiet in kartesischen Koordinaten (Strömungsbox) aufgestellt. Hierbei wird die nichtlineare Wirbeltransportgleichung durch den spektralen Ansatz für free-slip Randbedingungen gelöst, der die Wirbeltransportgleichung in ein System von gekoppelten, nichtlinearen gewöhnlichen Differentialgleichungen umwandelt, die die zeitliche Entwicklung der Fourier-Koeffizienten a_n,m(t) und damit die Evolution der einzelnen Wirbelmoden beschreiben. Die nichtlinearen Terme werden durch explizite Berechnung der Konvolutionssummen gemäß dem traditionellen Galerkin-Verfahren ermittelt. Für die diskrete Phase wird angenommen, daß das Gas durch eine bestimmte Anzahl von Düsen im Boden der Säule eingespeist wird. Es werden Blasen mit konstantem Durchmesser angenommen, die diskret modelliert werden, d.h. ihre momentanen Koordinaten werden durch Partikeltracking ermittelt. Die Momentangeschwindigkeit einer Blase ergibt sich aus der Vektorsumme der Geschwindigkeit der Flüssigkeit am Ort der Blase und der Relativgeschwindigkeit der Blase als Folge des lokalen Druckgradienten. Die Blasenkoaleszenz wird nicht berücksichtigt. Die Blasen verlassen das Strömungsgebiet bei Erreichen des oberen Randes. Es wird angenommen, daß jede einzelne Blase eine Kraftwirkung auf die Flüssigkeit verursacht, die in der Wirbeltransportgleichung im Volumenkraftterm berücksichtigt wird. Hierbei wird näherungsweise eine Dirac-Funktion angenommen, deren Stärke der Auftriebskraft entspricht. Die Kraftwirkungen aller Blasen im Strömungsgebiet werden addiert. Rechenergebnisse für eine rechteckige Strömungsbox mit Gaseinspeiusung über eine oder mehrere im Boden angeordnete Kanülen zeigen die Anregung von Wirbeln, die zu einer Deformation der Blasentrajektorie führen. Dabei treten typische typische instationäre Zirkulationszellen auf. Wichtig ist, daß die spektralen Verfahren auch bei Begrenzung auf wenige Moden in der prinzipiell Lage sind, großräumige Zirkulationszellen in der Blasensäule zu beschreiben. Klassische Verfahren erfordern demgegenüber stets eine feine räumliche Nodalisierung. Hieraus folgt, daß mit spektralen Verfahren grundlegende Erkenntnisse bei Anwendung von Wenigmodenmodellen mit geringem Rechenaufwand erzielt werden können.

The AER benchmark problem defined by L. Korpas et al. for the calculation of VVER­440 control rod worth was solved by using the code DYN3D in 1994. The KAB MAGRU library, generated by the NESSEL code was used then as a source of macroscopic group data. Now DYN3D calculations have been repeated with a new group data library created in EGP Prague by the KASSETA code. Burnup calculations have been carried out for the cycles 4 to 7 of Paks­2 NPP. The critical boron concentrations as a function of time, calculated with both data libraries, were compared to the values measured in the progress of the cycles. The results are in good agreement. The comparison of the fuel­element averaged burnup values after calculating 4 full cycles shows a maximum deviation of about 2 percent between the two data libraries. Concerning the control rod efficiencies the relative deviation is higher. This is due to relatively great differences in the macroscopic group data produced for the control rod!
s by NESSEL and KASSETA. The deviations between results calculated by the same code with different group data indicate that using different data libraries by the AER benchmark participants may be a main reason for the high differences between their results.

The preliminary results of the activation measurements and calculations in the different points of the irradiation facility KORPUS are shortly described and analyzed. The tasks of these investigations are the dosimetry characterization of the facility and creation of the international dosimetry benchmark.

A series of three-dimensional hexagonal dynamic benchmark problems have been defined during 1992 - 1994 in the international VVER cooperation forum AER. All three problems are asymetric control rod ejections from low power level in a realistic VVER-440 core with fuel of three different enrichments and given nuclear data. However, the complexity of the models needed in the benchmark solutions is continuosly increased beginning from pure reactor kinetics and extending to real core thermal hydraulics modelling with a hot channel and DNB effects. Solutions calculated by six organizations with five different mostly nodal codes are included. Agreement of neutron kinetics results is very good. More differneces are induced by thermal hydraulics modelling.

The capability of neuronal networks and fuzzy pattern classification is compared using measuring data that originate from experiments on leakage detection. The classification procedures are to localize simulated acoustically active leaks and to determine the leak rate. Different types of neural networks are needed to perform these two tasks. Alternatively fuzzy classifiers can be applied. Concerning the generalization capability, i.e. the recognition of positions and leak rates that could not be trained, neural networks clearly superior over fuzzy classification.

The new version DYN3DR of the code DYN3D/M2, initially designed for hexagonal-z
core analysis, has been developed for reactor cores with rectangular fuel assemblies.
The neutronic part of the two code versions can be used for steady-state and transient
calculations of reactor cores. The neutron kinetics in both versions is based on the
solution of the two group neutron diffusion equation by nodal methods being different
for hexagonal and rectangular geometry. The thermal-hydraulic module FLOCAL
simulating the two phase flow of coolant and the fuel rod hehaviour is used in both
versions. The accuracy of DYN3DR is demonstrated by comparisons with rod ejection
benchmarks for a PWR with rectangular fuel assemblies. The two phase flow model of
FLOCAL also allows the simulation of BWR transients. Results for the transient BWR
benchmark initiated by increase of inlet subcooling are shown.

The neutron kinetic part is parallelized for running on SUN workstations with several
processors. The speedup for steady state neutronic calculations is presented.

The coupling of advanced thermohydraulic codes with 3-dimensional neutron kinetic codes corresponds to the effort to replace conservative estimations by best estimate calculations. ATHLET is an advanced thermohydraulic code, developed by the German "Gesellschaft für Anlagen- und Reaktorsicherheit" (GRS). The DYN3D code, developed at Forschungszentrum Rossendorf (FZR) for the simulation of reactivity initiated accidents in nuclear reactors with hexagonal and Cartesian fuel element cross section geometry comprises 3-dimensional neutron kinetics, models for the thermohydraulics of the core and the thermomechanical fuel rod behaviour.

The reactor core model DYN3D was coupled with ATHLET according to two basically different strategies. The first way of coupling uses only the neutron kinetics part of DYN3D (internal coupling). In the second way, the whole core is cut out from the ATHLET plant model and is completely described by DYN3D (external coupling). In this case the values of pressure, mass flow rate, enthalpy and boron acid concentration at the bottom and at the top of the core have to be transferred between the codes. This way of coupling is efficiently supported by the General Control and Simulation Module (GCSM) of ATHLET. Almost no changes of the single programs are necessary.

For plausibility test of the code coupling, comparative calculations between point kinetics, internal and external coupling were performed for different hypothetical accident scenarios. First results of the analysis of a main steam line break scenario for a VVER-440 type reactor by the help of ATHLET-DYN3D are presented. The effect of different assumptions for the coolant mixing in downcomer and lower plenum of the reactor has been investigated.

Two heats of reactor pressure vessel steel type A533-B-1 differing in their Cu content (0.07 and 0.14 wt.-%) were irradiated to a fluence of 1x1018 neutrons/cm2 at temperatures of 60, 121, and 288 °C, respectively. Their microstructure has been studied by SANS, SAXS, and PAS in the as-irradiated and post-irradiation annealed stages and compared to the behaviour of unirradiated material and the results are discussed.

The knowledge about properties of the anisotropic turbulence in liquid metal flows exposed to an external magnetic field is essential for several technological applications such as the concept of a selfcooled liquid metal blanket for thermonuclear fusion reactors, but also of basic interest for turbulence research. Flow parameters like pressure drop and heat transfer rate are essentially determined by the interaction between the external magnetic field and the liquid metal flow. Several experimental studies revealed that the application of a magnetic field leads not exclusively to a suppression of the turbulent perturbations. Velocity fluctuations remain and demonstrate a distinct anisotropy of the MHD turbulence showing a tendency to become two-dimensional. The properties of the local transport of heat or mass are strongly governed by the anisotropic character of the flow. In this context a number of questions arises regarding the origin, the decay time or the size of the turbulent elements. A typical feature of the two-dimensional turbulence is that the energy becomes concentrated in organised large scale fluctuations. This fact ensures an intensive heat transfer on longer distances. Because of the anisotropy of the electromagnetic dissipation term vortices will be scarcely damped over long distances if their axes are aligned with the magnetic field lines. For practical applications it is important to identify possibilities to promote the formation of such quasi-two-dimensional vortices in order to control the heat or mass transfer rate of the flow. It is well-known that the mentioned perturbations can be generated by rather specific means, for example, mechanical inserts or electrical currents between definitely arranged electrodes, etc.. In this paper we force the turbulence intensity by mechanical means employing a grid of cylindrical bars or flat stripes. Due to the favourable material properties of the used liquid sodium we are able to extend the measurements into the region of high interaction parameters. In this way the obtained results complement the already existing knowledge about the two-dimensional MHD turbulence.

In order to improve the operational surveillance of a VVER-1000 unit of the Ukrainian nuclear power plant Zaporosh'ye a technical monitoring system has been specified and installed during the last three years.
The technical system enables the operator and supervisory body to monitor the core and the unit continuously during normal and off-normal conditions, to assess the safety status of core and unit, and to impose appropriate measures. The system provides an early indication of any operational incident and of emissions of radioactive materials. Based on the system an immediate warning in emergency situations is possible as well as an effective emergency management. For this purpose 49 different safety related operational parameters of the core and unit - e.g.: neutron flux, pressure - primary and secondary circuit, fuel rod outlet water temperature, boron concentration - primary circuit and so on -, 18 radiological parameters of the unit and the plant side and 6 meteorological parameters are automatically monitored and evaluated.
The system was put into operation at the end of 1995. It is now working under test conditions.
The paper presents the technical solution of the system and the evaluation principles. Additionally the paper gives a short overview about the results obtained during the test operation of the system.

A technical system to improve the operational monitoring of the Zaporozh'ye NPP as a tool for the supervisory authority is presented. The system is mainly directed to monitoring the operational data for early detection of, and information about, anomalous events and gives input data for source term estimation. Additionally, radiological data from the site and the environment as well as meteorological data are integrated in the system for pollution transport calculations. Thus the system's information is well suited to becoming a data source for RODOS system.

The present work is aimed at the investigation of two-phase flow in vertical pipes. Even under these very simple boundary conditions, strong 3D effects are observed. The distribution of the gas phase over the cross section varies significantly between the different flow patterns, which are known for the vertical two-phase flow. The paper presents a new device for measuring the void distribution with a high resolution (242 mea-suring points in a cross section area, measuring frequency approx. 1 kHz). This high resolution allows the calculation of local and averaged void fractions, a flow pattern visualization and the determination of bubble size distributions. Bubble flow appears with void center and boundary maximum distribution. The bubble size distribution allows the classification of the transition from homogeneous to inhomogeneous bubble flow and bubble to slug flow. These criteria are compared with selected empirical or theoretical flow pattern maps. The measurements are also used to assess the capability and the accuracy of the code CFX-4.2. The 3D calculations were still only successful for bubble flow, while the experiments were carried out in a wide range of superficial velocities, including other flow patterns like plug or churn turbulent flow.

The Siemens AG is developing the new innovative boiling water reactor concept SWR1000. New features are the passive safety systems (e.g. emergency condensers, building condensers, passive pressure pulse transmitters, gravity-driven core flooding lines).

For the experimental investigation of the emergency condenser effectiveness, the NOKO test facility has been constructed at the Forschungszentrum Jülich in cooperation with Siemens. This test facility has an operating pressure of 10 MPa and a maximum power of 4 MW for steam production. The emergency condenser bundle consists of eight tubes and is fabricated with planned geometry and material of the SWR1000. In more than 200 experiments, the emergency condenser power was determined as a function of pressure, water level and concentration of noncondensables in the pressure vessel as well of pressure, water level and temperature in the condenser.

Post test calculations of NOKO experiments were performed with an improved version of ATHLET. To calculate the heat transfer coefficients during condensation in horizontal tubes it was necessary to develop the module KONWAR and to implement it in ATHLET. KONWAR is based on the flow regime map of Tandon and includes several semiempirical correlations for the determination of the heat transfer coefficients. The comparison bet-ween calculations and experiments shows good agreement.

Am 29. Oktober 1998 veranstaltete die Ortssektion Sachsen der Kerntechnischen Gesellschaft e.V. an der TU Dresden ein Seminar zum Thema "Experimentelle Untersuchungen zur Wirksamkeit passiver Komponenten für den SWR1000". Diese Thematik erhielt u. a. durch das von Siemens beantragte standortunabhänige Prüfverfahren (vgl. atw 43 (1998), Nr. 10, S. 650) sowie der am 5. November in Königswinter durchgeführten KTG-Tagung "SWR1000 - ein zukunftsweisendes Reaktorkonzept" eine besondere Aktualität. In dem derzeit von der Siemens AG entwickelten innovativen Siedewasserreaktor SWR1000 werden zur Erhöhung der Sicherheit und der Wirtschaftlichkeit aktive Sicherheitssysteme weitestgehend durch passive ersetzt oder mit diesen kombiniert. Hierzu zählen die nachfolgend im Detail beschriebenen Systeme Notkondensator, Gebäudekondensator sowie Passiver Impulsgeber.

The condensation in horizontal tubes plays an important role e.g. for the determination of the operation mode of horizontal steam generators of VVER reactors or passive safety systems for the next generation of nuclear power plants. Two different approaches (HOTKON and KONWAR) for modeling this process have been undertaken by For-schungszentrum Jülich (FZJ) and University for Applied Sciences Zittau/Görlitz (HTWS) and implemented into the 1D-thermohydraulic code ATHLET, which is developed by the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS) mbH for the analysis of anticipated and abnormal transients in light water reactors. Although the improvements of the condensation models are developed for different applications (VVER steam generators - emergency condenser of the SWR1000) with strongly different operation conditions (e.g. the temperature difference over the tube wall in HORUS is up to 30 K and in NOKO up to 250 K, the heat flux density in HORUS is up to 40 kW/m² and in NOKO up to 1 GW/m²) both models are now compared and assessed by Forschungszentrum Rossendorf e.V. Therefore post test calculations of selected HORUS experiments were performed with ATHLET/KONWAR. It can be seen that the calculations with the extension KONWAR as well as HOTKON improve significantly the agreement between computational and experimental data.

Free surfaces of liquid gallium and mercury were studied by light scattering from thermally exited capillary waves. Great precautions were taken to prepare an oxide-free liquid metal surface inside a small evacuated container. Experimental results are shown in the form of q dependencies of the wave peak frequency wo and the damping constant ?. The observed damping constants of capillary waves differ greatly from those predicted by the classical theoretical treatment of Hg and Ga surfaces as those of simple liquids. This effect is explained in terms of the presence of a surface layer of highly correlated atoms accompanying the liquid-vapor transition. Viscoelastic properties of surface layer are extracted from the fit of experimental spectra with a theoretical form utilizing a well known phenomenological model. Results of the fit demonstrate that the surface viscosity appears to be negative. This implies that the widely used phenomenological model should be replaced by another one incorporating the Maxwell viscoelastic model. Special point has been made on studying the temperature dependence of the wave peak frequency at the free and oxidized Hg surface. This dependence emphasizes negative derivative of the surface tension d?/d? linked with the spatial distribution of free electrons being much
stronger temperature dependent than local surface ordering recently revealed at the mercury-vapor interface. In contrast, ?o(?) dependence collected at the Hg-HgO interface displayed two principally different tendencies: it increased steadily on the Hg surface covered with an oxide monolayer but was nearly constant at the surface covered with a polymolecular film of HgO. This behavior is discussed in the framework
of various theoretical models.

The report deals with the results of ATHLET post-test calculations for an experiment at the Hungarian integral test facility PMK-2. The experiment „pressurizer surge line break" was carried out within the PHARE 4.2.6b project. The primary objective of this test was to provid data for the phenomena associated with a pressurizer surge line break transient. The post-test analyses were performed with ATHLET mod1.1 Cycle C by the Forschungszentrum Rossendorf (FZR) and with ATHLET mod1.1 Cycle D by the Atomic Research Institute Budapest (KFKI) and the Gesellschaft für Anlagen- und Reaktorsicherheit (GRS).

Perinatal hypoxic-ischemic cerebral injury is a major determinant of neurologic morbidity and mortality in the neonatal period and later in childhood. There is evidence that the dopaminergic system is sensitive to asphyxia. However, the respective enzyme activities have not yet been measured in the living neonatal brain. In this study, we hav used F18-labeled 6-fluoro-L-3,4-dihydroxyphenylalanine (FDOPA) together with positron-emission tomography l(PET) to estimate the activity of the aromatic amino acid decarboxylase (AADC), the ultimate enzyme in the synthesis of dopamine (DA), in the brain of newborn piglets. Simultaneously, the cerebral blood flow (CBF) was measured with colored microspheres. Asphyxia elicited an up to threefold increase of the CBF. Despite this, the blood-brdain transfer of FDOPA as well as the clearance rate constants from brain were unchanged. However, the synthesis rate of FDA from FDOPA was significantly increased in frontal cortex, striatum, and midbrain. The increase of the AADC activity and the decrease of monoamine oxidase activity may contribute to the increase of extracellular DA during asphyxia which is expected to be involved in severe disturbances of neuronal metabolism, e.g., by generating free radicals.

Abstract. The paramagnetic rhenium (II) thionitrosyl compounds trans-[Re(NS)Cl3(MePh2P)2] and trans-[Re(NS)Br3(Me2PhP)2] are characterized by crystal structure diffraction and EPR spectroscopy. Trans-[Re(NS)Cl3(MePh2P)2] is formed during the reduction of (a) [ReNCl2(MePh2P)3] with disulphur dichloride (S2Cl2) or (b) of mer-[ReCl3(MePh2P)3] with trithiazyl chloride ((NSCl)3). Trans-[Re(NS)Br3(Me2PhP)2-] is the final product of the ligand exchange reaction of mer-[Re(NS)Cl2(Me2PhP)3-] with bromine whereby the metal occurred to be simultaneusly oxidized.
The crystal structure analyses show for trans-[Re(NS)Cl3(MePh2P)2] (monoclinic, C2/c, a = 13.831 (3) C, b = 13.970 (1) C, c = 14.682 (2) C, b = 95.33 (1), Z = 4) and trans-[Re(NS)Br3(Me2PhP)2-] (monoclinic, C2/c, a = 33.292 (5) C, b = 8.697 (1) C, c = 17.495 (3) C, b = 115.65 (1), Z = 8) linear co-ordinated NS ligands (Re - N - S - angles 180° and 174.8°). The metal atom is octahedrally co-ordinated with the phosphine ligands in trans position to each other.
X-band and Q-band EPR spectra of the rhenium (II) thionitrosyl complexes (5d5 "low-spin" configuration, S = 1/2) are detected in the temperature range 295 ³ T ³ 130 K. They are characterized by well resolved 185,187Re hyperfine patterns.
The hyperfine parameters are used to get information about the spin-density distribution of the unpaired electron in the complexes under study.

Keywords: Thionitrosyl compounds, Rhenium complexes, EPR spectroscopy, X-ray structure

Doses from 2 x 10¹⁵cm^-2 to 2 x 10¹⁷cm^-2 of ⁵⁷Fe ions were implanted with 40 keV into n-type Si(111) at 350°C. The iron concentration profiles reach peak maximum concentrations from 0.3 at.% for the lowest dose up to about 34 at.%. For the highest dose a plateau-like profile is formed due to the effect of sputtering. The phase formation of the iron disilicides was studied by ⁵⁷Fe conversion electron Mössbauer spectroscopy. Depending on the implanted dose two different regions of phase formation are found. For doses £ 1 x 10¹⁶cm^-2 only the metastable g-FeSi₂ is present whereas at values ³ 2 x 10¹⁶cm^-2 a mixture of a- and b-FeSi₂ is formed. The phase composition in this second region is dose dependent and with increasing iron content an enlarged fraction of the b-phase is found. At the highest dose of 2 x 10¹⁷cm^-2 mostly b-FeSi₂ and no a-FeSi₂ is present. But additionally to the b-FeSi₂ a second component occurs in the Mössbauer spectrum which is observed for the first time. With respect to the iron concentration this subspectrum could be attributed to a new metastable state of the mono silicide. Different annealings of the as-implanted samples at 900°C and 1150°C lead to the formation of the pure b- and a-FeSi₂, respectively. Additionally to the measurements of the concentration profiles investigations of the lateral element distributions in the layers were performed with scanning Auger electron microscopy. It can be concluded that during the annealing at 1150°C precipitates of the a-FeSi₂ grow in the Si matrix.

Es wird ein Überblick über den Entwicklungsstand und die Anwendung von Computercodes mit Kopplung von thermohydraulischen Anlagenmodellen von Kernkraftwerken und 3D Neutronenkinetik gegeben. Insbesondere wird auf die Ankopplung von Neutronenkinetikmoduln an den Thermohydraulikcode ATHLET eingegangen. Es werden Arbeiten zur Validierung der Codekomplexe durch Nachrechnung von transienten Prozessen in Kernkraftwerken und internationale Programmvergleiche beschrieben. Die Anwendung von ATHLET mit gekoppelter 3D Neutronenkinetik für Störfallanalysen wird an 2 Beispielen demonstriert. Mit den gekoppelten Programmsystemen sind erstmals konsistente Störfallanalysen ohne zusätzliche konservative Annahmen möglich. Entwicklungsbedarf besteht noch bei der Berücksichtigung von 3D Temperatur- und Borkonzentrationsverteilungen innerhalb des Reaktors,
die den hypothetischen Störfallablauf wesentlich beeinflussen können.

A possibility for the determination of velocity fields in conducting fluids is presented. Applying a magnetic field from outside, electric and magnetic fields are induced by the fluid motion. These fields can be measured at the walls and outside the fluid volume respectively. The inverse problem of reconstructing the velocity from the measured electric and magnetic fields is solved using Tikhonov regularization.

The mono oxo rhenium(V) complexes of cysteine and cysteine methyl ester were synthesised via ligand exchange reaction starting from rhenium gluconate. Unexpectedly, the obtained oxo Re(V) complex with cysteine methyl ester was partially saponified. Both complexes were fully characterised by common analytical techniques in their solid state. Thus, an octahedral complex structure with 2(NH2,S) coordination in the equatorial plane and one carboxyl group bound trans to the oxo group is proven for both compounds by X-ray diffraction. Furthermore, the existence of a dioxo species at higher pH was proven for the first time with this type of ligands by determing the nearest coordination sphere of the rhenium centre in solution at a pH of 12 using extended x-ray absorption fine structure spectroscopy (EXAFS).

The diastereoselective synthesis of 6-aroyl-3,5-diarylspiro[cyclohexa-2,4-diene-1,2´-indolines] 4 possessing three stereocenters from 2,4,6-triaryl-pyrylium perchlorates 1 and chiral methyleneindolines 3, generated in situ by deprotonation of the corresponding 3H-indolium perchlorates 2, in the presence of triethylamine/acetic acid in ethanol by a 2,5-[C4+C2] pyrylium ring transformation is reported. Structure elucidation is performed by X-ray structure determinations of the spiro[cyclohexadiene-indolines] 4a, 4p and 4t. The influence of various substituents at C-3 of the methyleneindolines 3 on the stereochemistry of the transformation, mechanistic details as well as spectroscopic data of the products 4 are discussed.

In the course of our investigations into mixed ligand systems containing thiol residues, we have examined, among others, the reactions of bidentate aminethiols with monodentate thiols, as well as tridentate/monodentate mixed ligand systems in the presence of ReOCl3(PPh3)2. Mixed ligand complexes of the general type "2+1+1" and "3+1" have been isolated. Surprisingly, in our synthetic attempts to clarify the mechanism of such reactions, we revceived two unexpected cis-dioxorhenium(V) P,S,N-coordinated complexes, where the aminethiol acts as a bidentate ligand over the Re(V) precursor. The two novel complexes of the general formula ReO2[R2NCH2CH2S][PPh3] where NR2=NEt2 (Complex 1) and NR2=N(CH2CH2)2C(OCH2)2 (Complex 2) are presented below. Both complexes have been characterized by elemental analysis and spectroscopic methods. Crystallographic studies show that the coordination geometry around rhenium is trigonal bipyramidal with the two cis-oxo groups and the sulfur atom of the ligand occupying the basal plane, while the nitrogen of the ligand and the phosphorus occupy the apical positions.

In the REBEKA-test facility of the Karlsruhe Research Centre (FZK) temperature-transient single-rod creep burst tests on Zirconium-Niobium 1 (ZrNb1) cladding tubes of Russian VVER reactors have been performed under conditions simulating a loss-of-coolant accident (LOCA). For the time being the test results obtained allow a comparison of the burst behaviour of ZrNb1- and Zircaloy-4 (Zry4) cladding tubes. The burst temperature and burst strains, respectively as influenced by the burst pressure, burst temperature and heating rate exhibit in the phase transformation temperatures which are up to 100 K lower for ZrNb1 compared to Zry4. For a reliable description of the ZrNb1 cladding behaviour in a LOCA further experimental and theoretical research work is needed.

A joint Russian/German irradiation experiment was performed at the pressurized water reactor VVER 2 of the Rheinsberg NPP (Germany). The experiment comprises about 800 Charpy V-notch, SENB and CT specimens made from 24 different heats of Russian type RPV base and weld metals.
Comprehensive calculations of the neutron fluence were carried out. A multigroup Monte Carlo method allows the calculation of the neutron fluence of each specimen or of different points within a large specimen under consideration of the details of the geometric arrangement. As the calculations shown the neutron fluence considerably varies over the cross section of an irradiation rig. Therefore, influence of the flux gradients on testing of Charpy V-notch and CT-specimens is evaluated.
Methods taking into account a fluence correction of the measured absorbed energies are presented and discussed

The report deals with results of ATHLET calculations for the Hungarian test facility PMK-2. The test facilty is a 1:2070 scaled
down model of a VVER-440 reactor. The calculated experiments includes a „inadvertent opening of the pressurizer safety valve"
and a „pressurizer surge line break". Both experiments were carried out within the PHARE 4.2.6b project. For the calculations
the code ATHLET mod1.1 Cycle C was used. The results of the calculations were compared with the experimental data.

Membranzellen für elektrochemische Reaktionen unter Bildung gasförmiger Produkte (z. B. Chlor, Sauerstoff, Wasserstoff) unterscheiden sich von herkömmlichen Blasensäulenreaktoren durch die Bildung feiner Gasbläschen an der festen Oberfläche der Elektroden und durch eine Begasung der Flüssigkeit über die gesamte Zellenhöhe. Gegenüber reinem Wasser bewirken Zusätze von anorganischen Elektrolyten mit kleinen Anionen eine Behinderung der Koaleszenz der Gasblasen. Zur Untersuchung der Zweiphasenströmung in einer solchen Anordnung wurde eine Nachbildung der Elektrodenreaktion mit Gasentwicklung durch die katalytische Zersetzung von Wasserstoffperoxid an Platin realisiert. Als Blasensäule dient ein Plexiglasrohr mit einem Innendurchmesser von 52 mm. Zentrisch im Rohr ist der Katalysator, ein mit Platin beschichtetes Titanrohr, angeordnet. Der volumetrische Gasgehalt der Dispersion wird mittels über die Säulenhöhe angeordneten Differenzdruckaufnehmer gemessen. Die Volumenstromdichte an Gas steigt linear mit der Säulenhöhe an. Bei kleinen Gasbelastungen (Gasvolumentrom pro aktive Katalysatorfläche) und geringen Eintrittskonzentrationen des Wasserstoffperoxids bildet sich erwartungsgemäß eine homogene Blasenströmung heraus. Ab einem Gasgehalt von ca. 20% gewinnt die Schwarmbehinderung an Einfluß auf die Blasenströmung. Der Gasgehalt der Dispersion wächst überproportional an. Nehmen Gasbelastung und Anfangskonzentration des Wasserstoffperoxids größere Werte an, geht die Blasenströmung in eine Schaumzone über. Im untersuchten Lastbereich erstreckt sich der Schaum bis zu ca. 68% des Reaktionsvolumens. Unabhängig von der örtlichen Volumenstromdichte an Gas werden hier über mehrere hintereinander geschaltete Meßvolumina gleiche Gasgehaltswerte gemessen, d.h. der Zuwachs an eingetragenem Gas wird durch das Anwachsen der mittleren Aufstiegsgeschwindigkeit des Blasenschwarms infolge von Koaleszenz kompensiert. Hinsichtlich seiner Stabilität kann der Schaum als kurzlebig charakterisiert werden. Es wurden Schaumzerfallszeiten im Bereich von 40 Sekunden gemessen.