Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

LOCA experiments are characterized by a more or less rapid primary pressure decrease in the early phase of the transient. After
pump coast down natural circulation becomes the dominant decay heat removal mechanism. After leak initiation boiling in the
reactor core leads to formation of two-phase flow conditions in the primary circuit. At these conditions different types of
two-phase flow instabilities can appear. The instabilities play an important role in the behaviour of the primary circuit, because the
instabilities can disturb the decay heat removal from the reactor core.

At the PMK-2 test facility natural circulation instabilities could be detected in 3 different experiments: a 1% cold leg break, a 1%
cold leg break with primary bleed and a surge line break.

With the help of the presented calculations it could be shown, that ATHLET is able to calculate the accident behaviour in a good
agreement with the experimental data. All significant phenomena, such as hot and cold leg loop seal clearing, stagnation of the
natural circulation, phase and mass separation along the facility and especially the natural circulation instabilities are calculated
very well. In some cases the ATHLET calculation provide the more detailed information required to clarify the complex
processes connected with the different kinds of instabilities.

Verschiedene Methoden zur Ermittlung der STC-Leistung von Photovoltaik-Generatoren aus gemessenen Kennlinien werden vorgestellt und diskutiert. Dabei handelt es sich um Varianten einer ursprünglich auf Blässer zurückgehenden Methode. In nahezu allen untersuchten Fällen wurden Generatorminderleistungen bis zu 25%, in Einzelfällen sogar mehr, festgestellt. Die erzielten Ergebnisse haben Konsequenzen auf die Bewertung von Erträgen von PV-Anlagen.

Collecting measurement data of NPP transients will be of key importance for the validation of coupled thermohydraulics / neutron kinetics codes. The transient data should cover relevant effects caused by the interaction between 3D neutron kinetics and thermohydraulics. Data will be collected for both VVER types (VVER­440 and VVER­1000).

Um sich ein besseres Bild über die Strömungsvorgänge im Downcomer und im unteren Plenum eines Druckwasserreaktors machen zu können, wurde mit einem CFD-Code (CFX 4.1) die Strömung unter möglichst realen Randbedingungen nachgerechnet. Hierfür wurden uns freundlicherweise Meßdaten des Anfahrvorganges der Hauptkühlmittelpumpe des DWR Konvoi zur Verfügung gestellt. Die Nachrechnung realer Anfahrvorgänge des DWR Konvoi mit Hilfe von IBS-Meßdaten zeigten eine relativ gute Durchmischung des Kühlmittels im unteren Plenum. Interessant war es festzustellen, daß das Geschwindigkeitsmaximum im unteren Downcomerbereich wie ein Halbkreis um den angefahrenen Stutzen liegt. Unterhalb dieses Stutzens ist die Geschwindigkeit vermindert.

The radiation embrittlement of the reactor pressure vessel is highly safety-relevant for VVER-type pressure vessels. The sensitivity against radiation embrittlement depends on the chemical composition of the pressure vessel steel. Using an irradiation experiment at surveillance positions in two Russian VVER 440-type reactors the effects of copper, phosphorus and nickel on the radiation embrittlement should be investigated. For that, eight mock-up alloys were selected. Their chemical composition varied between 0.015 and 0.42 % Cu, 0.002 and 0.039 % P, 0.01 and 1.98 % Ni, 0.09 and 0.37 % Si, and 0.35 and 0.49 % Mn. Charpy-V impact tests and tensile tests were performed with specimens machined from these alloys. The specimens were tested in the as-received state, in the irradiated state (fluence: 1x10¹⁹ and 8x10¹⁹ /cm² [E>0.5 MeV]) an in the post-irradiation annealed state. In the as-received state, the alloys have a ferritic microstructure. Apart from Cu, the alloyed elements are solved in the matrix.
Irradiation produces strong hardening and embrittlement. The effect increases with the Cu and P content. Ni causes an additional embrittlement. It is independent on the Ni concentration within the range of 1.1 to 2 % Ni and results in a shift of the ductile-brittle transition temperature of about 120 °C after a fluence of 1x10¹⁹ /cm² by a flux of 4x10¹¹ /cm²s. The shift does not depend on the Cu or P content. Furthermore the upper shelf energy is especially reduced by the Ni-rich alloys. For very low content of Cu and P these relations are not valid. The irradiation effect can be eliminated by annealing at 475 °C /100 h. For high content of Cu or P the recovery is incomplete, it remains a residue of 20 to 25 % of the irradiation effect. Ni has no influence on the recovery.
Comparing the results of this study with the ones of the surveillance programmes of the VVER 440-type reactors, the alloys with low Ni content show the same irradiation behaviour as the weld metal. For the Ni rich alloys such well-walidated references are missing.
The experiment is part of an extended research programme. It supposed to continue in order to gain information about the synergistic effects of these elements.

Two mechanisms are proposed for the theoretical description of the dilational viscoelasticity on a liquid surface. Possible relaxations of the temperature and electric charges induced due to the passage of the transverse-longitudinal surface waves are discussed. The dilational viscosity of the liquid metal surface can be realistically estimated from the charge oscillations model.

Usually the action of steady magnetic fields on electrically conducting flows is a damping one. But several examples exist where additional instabilities are due to the magnetic field influence. Such examples will be listed up based on a classification of the various MHD actions. The physical reason for these phenomena and possible applications will be discussed.

The application of an external magnetic field to the flow of any electrically conducting fluid can drastically change the flow characteristics, particularly for highly conducting fluids like liquid metals or semiconductor melts. If the magnetic field is steady there is the general expection that the magnetic field influence is a damping one: suppression of instabilities, turbulence damping up to relaminarization, suppression of vortex shedding, etc. Indeed, several metallurgical applications of magnetic fields are based on the assumption that this action always consists of a strong damping. The primary action of a steady magnetic field is an anisotropic redistribution of vorticity. If this results in flow damping depends strongly on the question how the induced electric currents can close in the liquid volume. In the present lecture we give some examples from our research projects in the field where a destabi-lizing action of a steady magnetic field was found, even resulting in a serious increase of turbulence intensity for increasing magnetic field. First example is a simple liquid metal duct flow. Experimental results will be presented showing that by a suitable promotion of vorticity parallel to the magnetic field lines the turbulence intensity (and correspondingly the heat & mass transfer) is increased by factors 4 to 10 compared to both the non-magnetic case and the case without turbulence promoters. The turbulence intensity can even increase with growing distance from the turbulence promoter. A physical interpretation will be given. Second example is the standard hydrodynamic problem of a flow around a circular cylinder. 2-D and 3-D numerical simulations will be presented showing clearly the suppression of the Karman vortex street due to the magnetic field influence, but also the destabilizing magnetic field action: 3-D instability is found for Re=180, a Reynolds-number where the pure hydrodynamic flow is known to be 3-D stable. Due to the magnetic field action the Squire Theorem is no more valid and, indeed, 3-D instability is found at parameters where the flow is 2-D stable. Physical interpretation and comparison with experimental results will be given. Further examples for a destabilizing magnetic field action will be briefly mentioned: flows driven by thermoelectricity, steady magnetic field influence on an inductively stirred melt. These experimental results will mainly be shown by video sequences.

In order to predict type and amount of defects created by keV ions under realistic implantation conditions a combination of computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations is proposed. Time-ordered BCA simulations are applied to ballistic processes with characteristic energies above several 10 eV. Athermal, rapid thermal, and thermally activated processes with lower characteristic energies are treated by MD simulations. They yield the as-implanted defect state formed several 10 ps after ion impact. The MD calculations are performed in cells which are much smaller than the entire volume of the collision cascade of an incident ion but much larger than the distance between nearest neighbour atoms in the lattice. The as-implanted damage produced by a single ion in a certain cell is found to be completely determined by the nuclear energy deposition of the ion into the cell. Therefore, the MD calculations need to be performed
only in one cell for different values of nuclear energy deposition, and statistical considerations based on BCA simulations can be employed to obtain the depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) created on average per incident ion.
The novel simulation method is applied to investigate the damage morphology produced by 15 keV B, 30 keV P, and 15 keV As implants.

Maintaining the integrity of the reactor pressure vessel (RPV) is of highest safety priority. The task is not trivial because the material is exposed to operation conditions that change the material properties and consequently reduce the safety margins. In the common view, this concerns above all the effects of neutron irradiation, which causes a reduction of the toughness. It is state-of-the-art to monitor the effect by an in-service surveillance programme. Recently, there are results that further environmental degradation effects could be of significance. Primarily the influence of gamma radiation and the irradiation-induced hydrogen embrittlement could also affect the material behaviour. Gamma rays produce a high rate of surviving point defects, which can accelerate ageing embrittlement. Hydrogen reduces the fracture toughness of RPV steels. Enhanced uptake of hydrogen can locally occur due to the radiolysis of water in water-starved condition existing in gaps or cracks. Irradiation defects can trap hydrogen and, thus, the hydrogen concentration can increase additionally. Several results are shown and the consequences for the RPV safety assessment and the embrittlement monitoring are discussed.

Es wurde die Eignung von [1-11-C]-Acetat zur quantitativen Perfusionsbestimmung in der myokardialen PET untersucht. Bestimmt wurde zum einen die Flußabhängigkeit der Acetatextraktion anhand eines Vergleichs mit dem derzeitigen Standardtracer 13-NH3, zum anderen wurde die statische Güte der mit beiden Tracern abgeleiteten Perfusionswerte untersucht.

Investigations concerning the "n+1" concept for the preparation of mixed-ligand technetium and rhenium complexes are briefly summarized. Chemical extensions were made with the aim to get less lipophilic and more stable chelates and involve the search of new precursor molecules, alternative types of tridentate ligands and new synthetic routes. N.c.a. preparation of "3+1" complexes can be done either by ligand exchange at Tc gluconate or in one step starting from pertechnetate. Aspects of reactivity are briefly discussed, particularly the reaction with glutathione in vivo. "n+1" complexes were preferably used for the design of receptor-binding tracers showing that the "3+1" unit seems to be well-suited to be adapted to receptor-affine anchor groups.

In this report is described the theoretical and experimental determination of all needed parameters for the neutron exposure of the different specimens that were irradiated in the Rheinsberg reactor within the period from 1984 until 1988 to obtain data for neutron embrittlement studies.
The methodical approach is represented, possible sources of errors are discussed and all the needed results are collected. The work can be divided into a pure calculation part, into the description of the extraction of the monitors and their gamma spectrometric analysis and into the discussion of the spectrum adjustment procedure which combines experimental and theoretical results. Therefore, this representation deals not only with this special task but gives also a survey about the methodical approach and the state of art in Rossendorf for the general problem of determination of neutron fluences, because the developed methods are generally applicable and not limited to the special problem of neutron embrittlement. Different problems with respect of neutron fluences exist also in Germany.
The calculation of fluences is based on an accurate description of the history of the reactor for all irradiation periods, i.e. the time and space dependence of burn up, power and fisson sources. This information was given for a time and space grid of all fuel elements.
For the calculation of the fluences were not used time dependent fluxes, but at first integral sources of fission neutrons are calculated for different fissionable isotopes. Using these given integral source distributions the fluences were calculated and the results from the different fissionable source were composed. For the improvement of the comparison between experimental and theoretical results a special method was used calculating special integral sources for the given detector, because each detector according to its decay notes another integral source resp. flux distribution, which has to be theoretically corrected.
The basis of all transport calculations was the Monte Carlo method in a special problem adjusted kind. Special procedures were developed and successfully applicated for the reduction of statistical errors. Therefore, also for single specimens results with small statistical errors were obtained. It is remarkable that this accurate method which allows a realistic 3-dimensional description of the system reactor-surroundings could be applied with reasonable calculation times for the great number of needed calculations.
To reduce the uncertainties connected by using of group cross sections some calculations with different group sets are performed. It could be shown, that for the Russian ABBN-78 group data (10 groups within the relevant energy range) and the group data on the base of JEF-1 (123 energy groups) a very good agreement could be realized. Also the application of the known code MCNP with a further independent data base gave the same results within the statistical errors. Furthermore we have used for tests the newest Russian group data MULTIK-90, which we have obtained from the Phys. Energetic Institute Obninsk.
Besides the standard CT1-, Charpy- and tension-specimens were irradiated CTX-, CT05- and CT5-specimens, too. The usual positions of these irradiations were the so-called Target channels. For some cases the Irradiation or Surveillance channels have been used, too.
The experimental determination of the neutron fluences was performed by the gamma spectrometric analysis of the used activation detectors. For the Russian detectors the elements Fe, Cu and Nb were used. For some measurements detectors from Rossendorf were applied. The contents of these detectors are Ti, Fe, Ni, Co, Cu, and Ag. Additionally 103Rh was used, too.
All the methods for the analysis of experiments have been enlarged and improved, because many difficulties beginning with the extraction of detectors and their bad consistency had to be overcome. An essential problem was the est ...

The Gas Dynamic Trap (GDT) of the Budker Institute Novosibirsk is an axisymmetrical plasma mirror device with a mirror ration in the range of 12.5-100. It confines a cold and dense target plasma in a collisional regime and a minority of fast ions in a kinetic regime. The target plasma flows out of the central chamber into external MHD-stabilizers where the curvature of the magnetic field lines is favourable with respect to stability against curvature driven MHD flute modes. The research programme of the GDT facility is focused on the generation of the plasma physical data base that is necessary for the GDT based neutron source project proposed by the Budker Institute. The paper reports on the recent upgrade of the neutral beam injection system and on the new plasma parameters achieved by that.

ZIEL DER STUDIE: Die Transplantatvaskulopathie (TVP) stellt eine häufige Komplikation im Verlauf nach Herztransplantation dar. Mit der konventionellen Perfusions-Szintigraphie kann diese diffuse Veränderung des koronaren Gefäßbettes nicht zuverlässig erkannt werden. Daher wurde in dieser Untersuchung die regionale myokardiale Perfusion und die koronare Flußreserve mit der ¹³N-NH₃ PET gemessen und mit den Ergebnissen der Koronarangiographie sowie dem intrakoronaren Ultraschall (IVUS) verglichen.
ZUSAMMENFASSUNG UND ERGEBNISSE: Bei Patienten ohne signifikante TVP (angiographisch/IVUS) betrug die Koronarreserve im Mittel 3,0±0,8. Weiterhin fand sich im Vergleich hierzu keine signifikante Verminderung der Flußreserve (2,7±0,8), wenn bei unauffälligem koronarangiographischen Befund nur mit dem IVUS eine <40%ige Stenose nachweisbar war. Bei Patienten mit einer >50%igen koronarangiographischen Stenose kam es zu einer deutlichen Einschränkung der induzierbaren Konarreserve (1,3±0,4;p<0,05). Der minimale koronare Widerstand korrelierte mit dem Stenosegrad, aber nicht mit der Zeit nach der Transplantation. Bei Patienten mit stark erhöhtem koronaren Widerstand fanden sich in der Nachbeobachtungszeit signifikant vermehrte ernste kardiale Ergebnisse.

Within the framework of the German 1000-Roofs-PV Programme a total of 2056 grid-connected PV systems with a total output of 5,3 MWp were installed on the roofs of private houses. All systems were subjected to a five years measurement programme, 100 systems selected on a statistical basis were equipped with a special measuring system. Besides these long term activities specific work has been carried out on the analysis for low energy yields, the inspection of PV-plants, sociological questions and architectural aspects. All work has been carried out in joint co-operation between Franhofer ISE Freiburg, FZ Rossendorf, ISFH Emmerthal, IST Energietechnik Augsburg, JRC Ispra (Italy), TÜV Rheinland Köln, Umweltinstitut Leipzig and WIP München.

Für die sicherheitstechnische Bewertung und ökonomische Betriebsführung von exothermen Semibatch- und Batch-Reaktoren hat die Simulation von Störungen eine entscheidende Bedeutung erlangt. In einem Laborreaktor mit zusätzlich ausgerüsteter Meßlanze werden Störungen bei der säurekatalysierten Essigsäureanhydrid-Methanol-Veresterung untersucht und die gemessenen Temperatur- und Druckverläufe mit den Ergebnissen von Simulationsrechnungen verglichen. Am Beispiel von Rührerfehlern wird gezeigt, daß gegenwärtig auf experimentelle Störungssimulationen zumindest in Laborreaktoren noch nicht verzichtet werden kann.

A dual beam experiment has been set up combining real-time depth profiling and low-energy ion implantation in order to study the kinetics of ion nitriding. The choice of low energy ion implantation allows precise and independent control of the important ion nitriding parameters ion energy, ion current density, temperature and residual gas composition. Real-time depth profiling is achieved by Elastic Recoil Detection (ERD) using an angle resolving ionization chamber telescope detector. A large solid angle (5.4 msr) allows a fast data acquisition and hence real-time depth profiling with a time resolution of about 30 s combined with a depth resolution of about 10 nm. The capabilities of the setup and its limitations will be discussed. Measurements revealing the role of mechanisms relevant for the nitriding transport during ion nitriding of stainless steel i.e. diffusion, sputtering, absorption of oxygen from the residual gas will be presented.

A boron dilution scenario caused by the connection of a previously disconnected primary circuit loop in a Russian WWER­440 type reactor is considered. The scenario is specific for this reactor type because of the existence of Main Isolating Valves in the loops. The additional failure of safety systems during the connection procedure was assumed. The analysis was carried out by the combined use of SiTAP and DYN3D. By the help of the fast running plant simulator code SiTAP several modifications of the scenario were considered. The scenario with the most dangerous consequences was identified and has been analysed using the three­dimensional core model DYN3D including a coolant mixing model for the lower plenum. The boundary conditions for the DYN3D analysis were obtained from SiTAP calculation. Comparing the results of both codes, a similar behaviour of the mean reactor parameters can be observed, but in the 3D analysis local exceeding of safety relevant parameters was obtained. Thus, the point kinetics model is not conservative, but by using SiTAP more realistic time­dependent boundary conditions for the 3D model could be provided than in previous analyses. The strong consequences of the considered scenario suggest the nessecity of additional measures for preventing this type of accidents.

A brief information about the 7th Symposium of Atomic Energy Research held in
Hoernitz near Zittau (Germany) in September 23-26, 1997, is given. Atomic
Energy Research (AER) is an internatiol association of 23 nuclear power plants,
organisations for scientific-technical support of nuclear authorities and
research institutions from 8 countries on the physics and nuclear safety of
Russian VVER type reactors. At the symposium, about 70 papers were contributed
in sessions on neutron transport methods, core design and reactor operation,
core monitoring, reactor dynamics and reactor safety, waste management and
criticality safety, thermo- and fluid-dynamics.

Das kritische J-Integral J_i ist als Zähigkeitsparameter zur Beschreibung der Einleitung des stabilen Rißwachstums (Initiierung) geeignet. Bei erhöhter Belastungsgeschwindigkeit erweist es sich jedoch als schwierig, die Initiierung zu detektieren und einem Punkt auf der Kraft-Durchbiegungs-Kurve zuzuordnen. In dieser Arbeit wird dieser Punkt mittels Schallemission (SE) bestimmt. Die Versuchstechnik zur Ermittlung von J_i umfaßt ein Pendelschlagwerk mit hammerfinnenintegrierter Sonde zur schlagartigen und eine servohydraulische Prüfmaschine mit zusätzlicher Probeninstrumentierung zur dynamischen Belastung von ermüdungsangerissenen Kleinproben in ISO-V-Geometrie.
Es können verschiedene Arten von SE-Signalen beobachtet werden. Ein Signal korrespondiert mit der Rißinitiierung. Der Nachweis für die Initiierung bei Auftreten dieses Signals wird mit unterschiedlichen Mehrprobentechniken geführt.

Im Institut für Sicherheitsforschung des FZR werden verschiedene Meßverfahren für Zweiphasenströmungen entwickelt. Die Arbeiten sind in der Abteilung Störfallanalyse angesiedelt. Der Ausgangspunkt war die Notwendigkeit von lokalen Dampfgehaltsmessungen bei thermohydraulischen Experimenten zur Kernreaktorsicherheit. Deshalb sind alle Aktivitäten bisher auf die Untersuchung von Flüssigkeits-Gas- bzw. Flüssigkeits-Dampfgemische gerichtet gewesen. Das erste, speziell für den Einsatz bei Störfallsimulationen an sog. integralen Primärkreismodellen von Kernreaktoren mit Druckwasserreaktor entwickelte Meßverfahren waren nadelförmige Leitfähigkeitssonden. Mittlerweile hat sich das Profil hinsichtlich der Zweiphasenmeßtechnik deutlich erweitert. Zu den seit einigen Jahren erfolgreich bei verschiedensten sicherheitstechnischen Experimenten eingesetzten Leitfähigkeitssonden kamen Verfahren, die auf Ultraschall, Positronenemittern und Video-Bildverarbeitungsmethoden beruhen. Was die Leitfähigkeitsmessung betrifft, so wurde in der letzten Zeit ein Gittersensor entwickelt, der eine zeitlich hochauflösende Visualisierung der Strömung in Rohrleitungen ermöglicht. Mit dem Sensors wurde die Kavitation hinter einer Schnellschlußklappe visualisiert, die sich am Anfang einer ca. 200 m langen Rohrleitung befindet. Die Tests fanden an einer Versuchsanlage des Instituts für Umwelt-, Sicherheits- und Energietechnik (UMSICHT) in Oberhausen statt. Über die Methoden hinaus, zu denen eigene Entwicklungsarbeit betrieben wird, werden auch die Kapazitätstomographie (Process Tomography Ltd. Manchester), die Laser-Doppler-Anemometrie, gekoppelt mit einem Laser-Doppler-Partikel-Analysator (LDA/LDPA, Polytech, Aero-metrics) und natürlich die hydrostatische Dichtemessung für Zweiphasenmessungen angewendet.

A wire-mesh tomograph for gas-liquid two-phase flows is presented. It is based on the measurement of the conductivity distribution over the cross section of the flow. Two planes of wire grids are placed into the flow in a short distance from each other. The angle between the wires of both grids is 90 °. The conductivity is measured at all cross points of the wires of the two planes. An imaging rate of 1000 frames per second was achieved, the measured data is directly transformed into local volumetric gas fractions without image reconstruction efforts. The minimal conductivity of the liquid necessary for applying the sensor is very low. Pure water (s » 0.5 µS/cm) can be measured without any problems. Up to now, the 2 x 16 wire mesh sensor was tested in a vertical air-water flow.

2-D and 3-D instabilities in the wake of a circular cylinder placed in an electrically
conducting fluid and subjected to a constant magnetic field aligned with the freestream are investigated numerically. Increasing magnetic fields suppress 2-D instability
(vortex shedding), whereas 3-D instabilities are influenced in a more complex way. In the presence of a magnetic field, 3-D instability has been detected below the 2-D stability threshold. This can lead to a reversal of the order of instabilities, i.e. 3-D instability appears at lower Re than 2-D instability.

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.
The results of the analysis of a main steam line break scenario for a VVER-440 type reactor by the help of DYN3D-ATHLET are presented. The effect of different assumptions for the coolant mixing in downcomer and lower plenum of the reactor has been investigated.

The relationship between regional parenchymal cerebral blood volume (CBV), regional cerebral blood flow (CBF) and the calculated mean transit time (MTT) was investigated in 14 newborn piglets. The effects of combined hypoxic hypoxia (p_aO₂ = 32 ± 5 mm Hg) and hypercapnia ((p_aCO₂ = 68 ± 5 mm Hg) were measured in seven animals. Remaining animals served as the control group. During baseline conditions the highest CBF and CVB values were found in the lower brainstem and cerebellum, whereas white matter exhibited the lowest values (p<0.05). MTT was prolonged within the cerebral cortex (2.34 ± 0.42 s^-1) compared with the thalamic MTT (1.53 ± 0,38 s^-1) (p<0.05). Under moderate hypoxia/hypercapnia, a CBF increase to the forebrain (p<0.05) resulted in an elevated brain oxygen delivery (p<0.05) and so CMRO₂ remained unchanged. Moreover, a moderate increase of CBV and a marked shortening of MTT occurred (p<0.05). The CBV increase was higher in structures with lowest baseline values, i.e., thalamus (66% increase) and white matter (62% increase) (p<0.05). MTT was between 22% of baseline in the lower brainstem and 49% in white matter (p<0.05). We conclude that under normoxic and normocapnic conditions the newborn piglets exhibit a comparatively enlarged intraparenchymal CBV. Moderate hypoxia and hypercapnia induced a marked increase in cerebral blood flow which appears to be caused by an increased perfusion velocity, expressed by a strongly reduced mean transit time and by a concomitant CBV increase.

This paper presents a neural-network approach to early identifying dangerous states in chemical semibatch reactors. Data sets which were supplied both from a process simulator and from measurements in a laboratory reactor were used to train and test neural networks and a fuzzy pattern classifier for different normal and faulty states. Three-layer perceptron networks were found to be best suited for classifying different normal and abnormal process states. Even multiple fault states can be recognized by the perceptron network correctly.

This paper presents a neural network approach to the identification and diagnosis of dangerous states in chemical batch reactors. The efficiency of this approach has been proven when monitoring an exothermic chemical process, i.e. the esterification between acetic anhydride and methanol. For training and for testing the state classifiers, data sets delivered both from a process simulator and measurements in a laboratory reactor were used. The classification behaviour of neural networks is compared with fuzzy pattern classification. Results show that perceptron networks might be successfully applied as an additional supervision method to support the operator in making decisions under critical situations.

The reconstruction of neutron flux density and thermal power density inside the hexagonal cassette of VVER type is described in this paper. The method of succesive smooting combined with folloing analytical solution was used for the detailed pointwise evaluation of neutron fluxes and thermal power densities diestributions in the cassette interior. The program module RECON based on the above mentioned method is presented in the next part of this paper. The results generated by the 3-dimensional reactor dynamic code DYN3D are used as input data for this subprogram. RECON can be used for methodical off-line investigation or to be implemented into the code DYN3D. This implementation is demonstrated at the end of paper.

The reconstruction of neutron flux density and thermal power density inside the hexagonal cassette of VVER type is described. The method of successive smooting combined with following analytical solution was used for the detailed pointwise evaluation of neutron fluxes and thermal power densities distributions in the cassette interior. The program module RECON based on the above mentioned method is presented. Results generated by the 3-dimensional reactor dynamic code DYN3D are used as input data for this subprogram. RECON can be used for methodical off-line investigation or to be implemented into the code DYN3D. This implementation is demonstrated.

Hervorgerufen durch plötzliche Änderungen der Strömungsgeschwindigkeit treten in Rohrleitungssystemen Druckwellen ("Druckstöße") auf, die wesentlich höher sein können als die im stationären Betrieb vorliegenden Fluiddrücke. Diese sich mit hoher Geschwindigkeit von etwa 900-1500 m/s längs der Rohrleitung ausbreitenden Druckwellen entstehen hauptsächlich durch schnell ausgeführte Regelungs- und Stelleingriffe oder durch Störungen des bestimmungsgemäßen Betriebs. Im Rahmen eines BMBF-geförderten Vorhabens werden experimentelle Untersuchungen an zwei ca. 225 m langen, mit Hoch- und Tiefpunkten ausgestatteten Rohrleitungsschleifen der Nennweiten DN50 und DN100 durchgeführt. Die untersuchten Strömungsgeschwindigkeiten betragen 0,5 bis 5,0 m/s, wobei unterschiedliche Versuchsfluide zum Einsatz kommen. Während der Versuche werden Druckspitzen bis 80 bar, Dampfanteile und lokale Kraftspitzen bis zu 80 kN in hoher zeitlicher Auflösung vermessen. Das Versuchsprogramm umfaßt: Vermessung von Kavitationserscheinungen ("Kavitationsschläge") beim Öffnen und Schließen von Stell-, Regel- und Sicherheitsarmaturen, Einströmen kompressibler und inkompressibler Medien in leere und teilgefüllte Rohrleitungen bei unterschiedlichen Antriebsdrücken bis 40 bar, Ermittlung dynamischer Lagerlasten beim Auftreten von Druckstößen, Kavitationsschlägen und oszillierenden Strömungen (Gas/Flüssigkeitspfopfen). Die Ergebnisse der experimentellen Untersuchungen werden mit Programmen zur Simulation transienter Strömungsvorgänge in Rohrleitungssystemen verglichen (FLOWMASTER, SIR-3S, FLUSTRIN, WANDA, PIPENET, INROS, MONA). Es werden Aussagen zur Genauigkeit der einzelnen Programme und der hierfür erforderlichen Modelltiefe getroffen. Insbesondere werden die Aussagegenauigkeit der implementierten Kavitationsmodelle und die Notwendigkeit einer Berücksichtigung von Fluid-Struktur-Wechselwirkungen für die Planung und den Betrieb verahrenstechnischer Anlagen geprüft.

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 reduced it.

As part of the programme implemented by the German Ministry of Environment, Nature Conservation and Reactor Safety to cooperate with the Central and Eastern European States and Commonwealth of Independent States in the area of nuclear safety, a technical system to improve operational monitoring has been designed, specified and established since 1992 as a pilot project by the Research Centre Rossendorf and the Technischer Überwachungsverein Rheinland with a significant contribution from the state scientific and technical centre of the Ukrainian supervisory authority in the Zaporozh'ye/Ukraine nuclear power plant.
The technical system complements existing operational checking and monitoring facilities by including modern means of information technology. It enables concentration on a continuous monitoring of the state of unit 5 in normal operation and in cases of anomalies or incidents so that when recognisable deviations from the regular plant operation occur, the Ukrainian supervisory authority can immediately inquire and if necessary impose conditions on the operator. The radiological and meteorological parameters at the nuclear power plant location are monitored to the extent necessary to assess the current radiation situation and to implement effective emergency management measures.
For this purpose
49 different safety related operational parameters of the core and unit
18 radiological parameters of the unit and the plant site and
6 meteorological parameters
are permanently and automatically recorded, monitored and evaluated.
Test operation of the technical system was commenced at the end of 1995.
Following the completion of the user software by the scientific and technical centre of the Ukrainian supervisory authority and the operator and the establishment of evidence of reliability under nuclear power plant conditions, the industrial testing phase of the system was started in the middle of 1996.
The poster gives an overview about the general cond ...

The neutron embrittlement problem of current pressure vessel reactors is of great safety and economic concern. It culminates in Russian VVER-type reactors. Compared with Western pressurized water reactors, the shorter distance to the core results in substantially higher neutron fluences for the pressure vessels. In the case of the VVER-1000, the increased content of nickel and the position of a weld at a height near to the maximum flux are additional, unfavorable pecularities. These circumstances caused the embrittlement problem of VVER pressure vessels to become the objective of many international research collaborations. The reactor dosimetry group of Forschungszentrum Rossendorf participated in the Interlaboratory Reactor Dosimetry Experiment Balakovo-3 with Monte Carlo fluence calculations, activation measurements and with spectrum adjustments. The paper describes the specific features of the methods applied, presents and discusses the results and draws conclusions with respect to further investigations.

A system of electric arc evaporators for fast Ti-coating has been installed inside the gas dynamic trap (GDT) of the Budker Institute Novosibirsk. In this way the vacuum conditions could be substantially improved and consequently the plasma parameters especially those of the fast ions remarkably increased. The fast ion lifetime raised up by more than one order of magnitude. Under the new conditions special experiments were carried out to study the neutral gas dynamics inside the GDT and to compare with numerical results which were obtained by means of the Monte Carlo code TUBE.

Cobalt disilicide layers were produced by 70 keV Co2+ focused ion beam implantation into Si(111) at temperatures of about 400°C and subsequent annealing. The CoSi2 layer quality depends on pixel dwell-time and subtrate temperature. Only properly chosen parameters result in a continuous layer. The dwell-time (1-250 µs) and substrate temperature (355-400°C) dependence was investigated by scanning electron microscopy, reflectivity measurements and Rutherford backscattering spectroscopy/channeling. The results show that the irradiation damage increases with dwell-time and decreases with temperature, indicating an interplay between the damage creation rate and the dynamic annealing rate. Already after implantation of less than a tenth part of the dose required for continuous layer formation, the quality of the resulting CoSi2 layer is predertermined.

Die Entwicklung und der aktuelle Stand der Nutzung erneuerbarer Energien in Sachsen wird referiert. Als besonders ausbaufähig - da an der Schwelle zur Wirtschaftlichkeit stehend - erweist sich die Windenergienutzung. Begrenzt sind danach die Ressourcen an Wasserkraft und Biomasse, deren Beitrag an einer künftigen Stromversorgung jeweils unter 2% liegen kann.

Anhand ausgewählter Ergebnisse wird der aktuelle Stand der Nutzung der Photovoltaik vorgestellt. Trotz einer Reihe bemerkenswerter technischer Fortschritte bei den Hauptkomponenten und einer Vielzahl errichteter Demonstrationsanlagen liegen die Kosten von Solarstrom noch einen Faktor 10 zu hoch. Deshalb besteht nach wie vor ein erheblicher Forschungsbedarf, um diese Technologie zur Marktreife zu bringen.