Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Experiments were performed to investigate heating up processes of fluids in storage tanks under the influence of an external heat source. Several tests were carried out both with heating from the bottom and with heating from the side walls. The test tank was equipped with thermocouples for measuring the temperature distribution and with needle probes for measuring of the local void fraction.
Calculations were performed using the CFD-code CFX-4. The simulation comprises two phase flow, subcooled boiling at the heated wall and steam release at the tank surface. The paper presents comparisons of measured and calculated temperatures and void fractions. CFX-4 simulations using the implemented boiling model reproduce and explain the observed physical phenomena. Convergence problems occurred with higher vapour volume fractions.

Magnesium and aluminum were alloyed by implantation with iron ions. The implantation energy was 200 keV while the ion doses ranged over several decades from 1x1015 up to 9x1017 cm-2. In this way highly disordered alloyed layers with up to 90 at.% iron were obtained [1]. To study possible ordering, stabilization and redistribution processes samples were annealed in vacuum at subsequently increasing temperatures up to 600 °C for aluminum and up to 400 °C for magnesium. The annealing process was observed by conversion electron Mössbauer spectroscopy, Auger electron depth profiling, and X-ray diffraction. In the case of the Fe-Al system different iron aluminides are formed. In the case of the Fe-Mg system (insoluble with each other), a-iron is precipitated in small clusters in the final state.

Air-water flow at ambient conditions in a vertical pipe with an inner diameter of 51.2mm is investigated. An electrode wire-mesh sensor enables the measurement of the phase distribution with a very high resolution in space and in time. Local bubble size distributions are calculated from the data. The measurements were done in different distances from the gas injection device. As a result the development of bubble size distributions as well as the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe.

The state-of-the-art of structural integrity assessment of reactor pressure vessels (RPV) uses universal and experimentally verified reference fracture toughness curves. These curves are constructed as the lower boundary to an available plain strain fracture toughness, KIC, database.
Recent industry attention has been focussed on the direct use of measured fracture toughness properties in the RPV integrity assessment. The Master Curve Concept (MC)is a new methodology to characterise the fracture toughness in the transition region. The MC methodology provides a reference temperature, T0, that directly relates the reference toughness curve to the measured fracture toughness values.
The utilities and licensing authorities establish short and long-range objectives in implementing MC technology. The short range objective is to develop an alternative method of indexing the universal plain strain fracture toughness curves using measured fracture toughness T0 instead of the existing drop weight and Charpy-based methodology. The long range objective is to implement a statistically defined MC as an alternative fracture toughness curve in place of the KIC lower bound curves.
The paper introduces the state-of-the-art and future trend of the RPV integrity assessment in Germany. In the second part the MC approach is demonstrated for Russian WWER-type RPV steels.

A wire-mesh sensor, which is based on local conductivity measurement, has been applied to studies on the characteristics of bubböe flow in a rectangular channel (20 x 100 mm²). Special design of the sensor allowed the measurement of the local instantaneous true gas velocity besides the measurement of the local instantaneous void fraction. A review of an already published method for true gas velocity measurement under consideration of the uncertainty caused by limitations in the sampling frequency is presented. A cluster-algorithm is proposed for the evaluation of bubble size distribution and volume flow reconstruction. The validity of this algorithm for spatial field reconstruction was benchmarked by theoretical considerations as well as comparison of the calculated with alternatively measured data. Good agreement was stated. The achieved information was used to obtain plots showing the bubble/slug velocity (up to the second statistical momentum) depending on the spherical-equivalent bubble diameter. This information was measured inside a transient bubble flow with void fraction of up to 20 %. Occurring phenomena are explained by presented Fourier spectra of the cross-sectional averaged void fraction and the gas volume flow.

We consider inverse problems in MHD that are related to the reconstruction of velocity fields from external measurements of electromagnetic fields. Possible applications are contactless flow measurements in metallurgical and crystal growth facilities as well as velocity reconstructions for cosmic and laboratory hydromagnetic dynamos. In the case of small magnetic Reynolds numbers it is necessary to apply external magnetic field and to measure the flow induced electromagnetic fields. Analytical results concernig the uniqueness problem of velocity reconstruction and the need for regularization are discussed. First results for inverse dynamo theory, i.e. the region of high magnetic Reynolds number, are also presented.

Scanning electron microscopy, atomic force microscopy and XRD analyses were performed for the study of the influence of the substrate temperature during deposition on the surface structuring and phase formation on thin metallic double layers. Thin layers of Au, Cr, Al and Cr were deposited at 150 and 300 °C on 30-nm Cu layers evaporated on (100) wafer Si substrates. Possible applications of such layers are Raman active surfaces and model layers for diffusion experiments. The topographical investigation revealed an increase with temperature of surface structuring that is related to the formation of intermetallic and oxide phases. At 150 °C deposition temperature, the average roughness of the films was determined to 2 – 3 nm and the surfaces appeared smooth. In agreement with previous ion beam analysis measurements, a significant surface roughness occurred at 300 °C depending on the type of the metallic films. The lowest average surface roughness value was measured for the Al/Cu/Si system (Ra = 14.1 nm). About double the roughness was measured for the Au/Cu/Si and Cr/Cu/Si layer systems. In contrast, single Cu layers a high value of Ra = 93.0 nm was determined. The combined analyses showed that the formation of intermetallic phases, such as AlCu and CuAl2, reduces a surface roughening. However, the formation of oxide phases, such as CuO2, increase the average surface roughness.

The evolution of copper rich clusters and vacancy clusters in the neutron irradiated VVEER steels is investigated beginning at the nucleation stage. For this, typical VVER-type reactor conditions are considered. Cluster dynamics approach is used for calculation of the size distribution function, mean radius, number density of copper precipitates and the concentration of free Cu-atoms in dependence on the irradiation time. The results for time of one year are compared with the results of small angle neutron experiments which were carried out at specimens irradiated at surveillance position of VVER reactors.

The Ultrasound Doppler Velocimetry (UDV) is a non-intrusive technique to measure velocities of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. But, in case of hot metallic melts the user is confronted with a number of specific problems: First of all the application of the ultrasonic transducers is usually restricted to maximum temperatures of 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.
The feasibility of velocity profile measurements by UDV has already been demonstrated for low temperature liquid metals as mercury [1] and gallium [2]. Now, first successful measurements in liquid sodium at 150°C are published [3]. We will present mean profiles of a flow in a rectangular exposed to an external, transverse magnetic field. To demonstrate the capability of UDV the transformation of a well-known turbulent, piston-like profile to a M-shaped velocity profile with growing magnetic field strength was observed. The significance of artefacts such as caused the existence of reflecting interfaces in the measuring domain will be discussed.
An integrated ultrasonic sensor with acoustic wave guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can be applied at maximum temperatures up to 400°C, but an extension up to 800°C can reasonably be expected.. In this presentation we show some experimental results obtained in a PbBi bubbly flow at 250...300°C. Ar bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. Mean values of the liquid as well as the bubble velocity were extracted from the data and will be presented as function of the gas flow rate.

[1] Y. Takeda: Measurement of velocity profile of mercury flow by ultrasound Doppler shift method. Nucl. Techn. 79 (1987), 120-124
[2] D. Brito, H.-C. Nataf, P. Cardin, J. Aubert, J.-P. Masson: Ultrasonic Doppler velocimetry in liquid gallium. Exp. Fluids 31 (2001) 6, 653-663
[3] S. Eckert, G.Gerbeth: Velocity measurements in liquid sodium by means of Ultrasound Doppler Velocimetry. accepted for publication in Exp. Fluids (2002)

During the last decades the Ultrasound Doppler Velocimetry (UDV) became a very powerful tool to measure the velocity structure of liquid flows. Because of the ability to work in opaque fluids and to deliver complete velocity profiles in real time it becomes very attractive for liquid metal applications. But, in case of hot metallic melts the user is confronted with a number of specific problems: First of all, the application of the ultrasonic transducers is usually restricted to maximum temperatures of 150°C. The transmission of a sufficient amount of ultrasonic energy from the transducer to the fluid has to be guaranteed. Here, the acoustic coupling and the wetting conditions have to be considered as important issues. Moreover, the flow has to be seeded with reflecting particles to obtain Doppler signals from the fluid.
The feasibility of velocity profile measurements by UDV has already been demonstrated for low temperature liquid metals as mercury [1] and gallium [2]. Now, first successful measurements in liquid sodium at 150°C are published [3]. We will present mean profiles of a sodium flow in a rectangular duct exposed to an external, transverse magnetic field. To demonstrate the capability of UDV the transformation of a well-known turbulent, piston-like profile to a M-shaped velocity profile with growing magnetic field strength was observed. The significance of artefacts such as caused by the existence of reflecting interfaces in the measuring domain will be discussed.
An integrated ultrasonic sensor with acoustic wave guide has been developed to overcome the limitation of ultrasonic transducers to temperatures lower than 200°C. This sensor can presently be applied at maximum temperatures up to 400°C, but an extension up to 800°C can reasonably be expected. In this presentation we show some experimental results obtained in PbBi bubbly flows at temperatures up to 350°C. Ar bubbles were injected through a single orifice in a cylindrical container filled with stagnant PbBi. Velocity profiles were measured in the bubble plume. Mean values of the liquid as well as the bubble velocity were extracted from the data and will be presented as function of the gas flow rate.
Velocity profiles of a single-phase PbBi flow in a tube were successfully obtained at the KALLA laboratory of FZK. By means of the integrated sensor stable velocity signals could be received over a period of about 72 hours at temperatures between 180°C and 350°C.

[1] Y. Takeda: Measurement of velocity profile of mercury flow by ultrasound Doppler shift method. Nucl. Techn. 79 (1987), 120-124
[2] D. Brito, H.-C. Nataf, P. Cardin, J. Aubert, J.-P. Masson: Ultrasonic Doppler velocimetry in liquid gallium. Exp. Fluids 31 (2001) 6, 653-663
[3] S. Eckert, G.Gerbeth: Velocity measurements in liquid sodium by means of Ultrasound Doppler Velocimetry. accepted for publication in Exp. Fluids (2002)

The contribution of quantum shape fluctuations to inertial properties of rotating nuclei has been analysed within the self-consistent one-dimensional cranking oscillator model. It is numerically proven that for even-even nuclei the dynamical moment of inertia calculated in mean field approximation in the intrinsic frame is equivalent to the
Thouless-Valatin moment of inertia. If the contribution of the quantum fluctuations
to the total energy is taken into account, the dynamical moment of inertia differs from the Thouless-Valatin value.

The test A of the test series performed at the UM2x4 loop test facility for the International Standard Problem ISP-43 was calculated with the CFD Code CFX-4.3. The results of the calculation show qualitatively good agreement with the experimental data. The structure of the flow field and the form of the propagating temperature perturbation front are well modeled by the CFD code. However, deviations occur at local positions. Comparative calculations with and without taking into account buoyancy have shown, that buoyancy effects are noticeable, but the mixing is mainly momentum controlled.

Beam dumps are installed at the experimental areas of the ELBE facility. Their purpose is to absorb the primary electron beam and the secondary radiation. The beam dump consists of a purified graphite core inside a water cooled stainless steel vessel. The radiation shield surrounding the beam dump will be designed individually for each experimental area. In this context, dose rate calculations were carried out to estimate the dose rate source term around the stainless steel vessel of the beam dump. Detailed Monte Carlo simulations were carried out using the code FLUKA. The energy dependent photon and neutron fluences and the equivalent dose rates were obtained near the surface of the cylindrical steel vessel for a beam current of 1 mA and energies of 20 MeV and 50 MeV.

Besides plutonium, the long-lived isotopes of americium and curium play a crucial role for long-term performance assessment of nuclear waste repositories. In order to predict the mobilization and retardation of these nuclides, it is necessary to know the structures of the inorganic and organic actinide species that are involved in the process of migration. Thereby, the characterization of the Am3+ and Cm3+ aquo ions forms the base for further investigations.
In the literature only few measurements can be found of co-ordination numbers of trivalent actinides in aqueous solutions. By using UV/Vis spectroscopy, a co-ordination number of 9 was calculated for Am3+ aq [1]. The complexation behavior of curium is often investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) [2,3]. In analogy to trivalent lanthanides, a co-ordination number of nine is assumed for Cm3+aq. An extended X-ray absorption fine structure (EXAFS) spectroscopy investigations of Am3+ and of Cm3+ in 0.25 M HCl obtained co-ordination numbers of 10.3(0.3) and 10.2(0.3), respectively [4].
In order to determine a reliable reference value for the co-ordination number of Cm3+ and Am3+ aquo ions, the samples used in our EXAFS measurements were prepared in non-complexing 1.0 M perchloric acid. High actinide concentrations (1 x 10-3 mol/L) were used in order to achieve low-noise EXAFS spectra, which enable a precise determination of bond lengths and co-ordination numbers of the Am3+ and Cm3+ aquo ions.
The experiments were performed at the Rossendorf beamline (ROBL) at the ESRF in Grenoble [5]. The radiochemistry experimental station at ROBL has been designed to perform X-ray absorption fine structure (XAFS) spectroscopy of solid and liquid non-sealed radioactive samples [6]. EXAFS spectra were collected in transmission mode at the americium LIII edge at 18504 eV (E0=18520 eV) and at the curium LIII-edge at 18970 eV (E0=18990 eV), respectively. Zr and Nb metal foils were measured and the first inflection point of the X-ray absorption spectra (Zr K edge at 17998 eV, Nb K edge at 18986 eV) were used for energy calibration. EXAFS data treatment and fit were done using the EXAFSPAK program package [7]. Parameters for the backscattering phase and amplitude, the mean free path, and the reduction factor were calculated using the FEFF8 code [8]. Since no suitable Am or Cm reference compound was available for the measurements, the EXAFS spectra were fitted with constant S02 equal to 0.9 and 1.0. Two different sets of atomic clusters were taken as the basis for the phase and amplitude calculations. On the one hand the solid state structure of the curium dioxides was used [9] with a co-ordination number of eight and on the other hand the structure of the tetraaquatrinitratoeuropium(III)-dihydrate [10]. This compound shows the curium-homologous lanthanide Eu3+ as central atom, which is surrounded by ten oxygen atoms. Both clusters lead to nearly the same results. Dirac-Fock potentials were used for the core of the central atoms in the FEFF calculations. The EXAFS spectra of the Am3+ and Cm3+ aquo ions using the Eu cluster [10] are shown in figure 1. One shell is uniquely defined in both cases. The corresponding EXAFS structural parameters are collocated in table 1.
Figure 1. Raw Am3+ (upper graph) and Cm3+ (lower graph) LIII-edge k3-weighted EXAFS spectra and corresponding Fourier transforms. (Solid line - experiment; dashed
line - theoretical fit.)

Table 1. EXAFS structural parameters for the Am3+ and Cm3+ aquo ions. The standard deviations as estimated by EXAFSPAK are given in parenthesis.
Sample Shell N (S02=0.9) N (S02=1.0) R [Å] s2·103 [Å2] ?E [eV]
Am3+ Am-O 10.4(0.3) 9.3(0.3) 2.47(0.02) 9.3(0.3) -12.6(0.3)
Cm3+ Cm-O 9.3(0.3) 8.4(0.3) 2.46(0.02) 7.5(0.4) -22.3(0.4)

The measured bond distances, R±0.02 Å, are the same for the Am3+ and Cm3+ aquo ions and agree with the results of [4]. The co-ordination number, N±1, is somewhat higher for ...

Results on the growth of GaAs by the vertical gradient freeze (VGF) technique with a rotating magnetic field (RMF) are presented. The experiments were aimed at influencing the heat flux at the liquid-solid interface in a predefined way to reduce its bending. Si doped crystals with a diameter of two inch were grown. Variation of the heat flux is directly evaluated from dopant striations artificially produced by means of pulses of the RMF itself. The results are compared with those obtained by global modelling of the furnace as well as by analytical and numerical treatment of the melt flow. The concave deflection of the interface is found to decrease considerably under forced convection and at certain aspect ratio a wavy shape is observed. The RMF induced redistribution of axial thermal gradients resulting in a temporary variation of the growth rate that becomes lower in the outer region of the melt and higher in the central part is measured directly. The experimental results agree well with the numerical
computations.

A focused ion beam system is applied to investigate the dose dependence of the shape of Ge channeling implantation profiles in Si and SiC at two very different dose rates (1011 and 1018 cm-2 s-1), and for implantation temperatures between room temperature and 580 0C. The competing influence of dose rate and temperature observed is explained in terms of intracascade defect relaxation. For the different implantation temperatures, the time scale for defect reduction is estimated. The results obtained for Si are compared with those for SiC.

Nucleation of dislocation loop at the crack tip in a material subjected to uniaxial loading is investigated. Analytical expression for the total energy of rectangular dislocation loop at the crack tip is found. Depencence of the nucleation energy barrier on dislocation loop shape and stress intensity factor at the crack tip is determined. It is established that the energetic barrier for nucleation of dislocation loop strongly depends on the stress intensity factor. Nucleation of dislocation loop is very sensitive to stress field modifiers (forest dislocations, precipitates, clusters of point defects, etc.) in the crack tip vicinity.

The densification of SiO2 on silicon towards the interface, as already concluded in a recent work, is confirmed to exist in thinner oxides obtained by etching, and in a native oxide, too. Furthermore, an annihilation state is revealed in the thermally grown and etched, as well as a native, oxide which must resemble low quartz in its structure. A lower limit d = (2.2 +- 0.1) nm of the thickness of the interface layer resembling low quartz in its structure can be estimated. A variety of the state-of-the-art theoretical calculations to aid the experimental findings is summarized. It is discussed why the presented results corroborate the model of quasi-epitaxial oxide growth and pseudo-polymorphic relaxation of the grown oxide.

The hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower head of a Light Water Reactor (LWR) leads to the question about the behaviour of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
Scaled coupled melt pool convection and vessel creep failure experiments are being performed in the FOREVER program at the Royal Institute of Technology, Stockholm. These experiments are simulating the lower head of a pressurized reactor vessel under the thermal load of a melt pool with internal heat sources. Due to the multi axial creep deformation of the three-dimensional vessel with a highly non-uniform temperature field these experiments offer an excellent opportunity to validate numerical creep models. A Finite Element model is developed and using the Computational Fluid Dynamic module, the melt pool convection is simulated and the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a new creep modelling procedure. Additionally, the material damage is evaluated considering the creep deformation as well as the prompt plasticity.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. After analysing the calculations, it seems to be advantageous to introduce a vessel support which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

Heating up experiments at the secondary pools side of the NOKO test facility were performed, to investigate mixed convection phenomena. The NOKO test facility was designed to investigate the heat transfer capability of an emergency condenser and was operated in the Research Centre Jülich.
In the Forschungszentrum Rossendorf the heating up tests were analyzed by CFD-simulations using the AEA-Technology code CFX-4. Applying the Boussinesq approximation the simulation of the heating up process is possible, at least qualitatively. Using the laminar approach, temperature oscillations caused by plumes could be simulated.
A further test series performed at Forschungszentrum Rossendorf deals with the investigation of transient boiling. Heating up a 10 l water tank from the side walls, the temperatures and the void fractions at different locations in the tank were measured. CFX-4 simulations using the implemented boiling model reproduce and explain the observed phenomena. Convergence problems occurred with higher vapor volume fractions.

Cosmic magnetic fields, including the fields of planets, stars and galaxies, are believed to be caused by dynamo action in moving electrically conducting fluids. While theory and numerics of hydromagnetic dynamos have flourished during the last decades, an experimental validation of the effect was missing until recently. We sketch the long history towards a working laboratory dynamo. We report on the first successful experiments at the sodium facilities in Riga and Karlsruhe, and on other experiments which are carried out or planned at various places in the world.

Ein online Monitoring-System für die Prozessführung eines komplexen heterogenen Hydrierprozesses in einer Produktionsanlage der Degussa AG wird beschrieben. Es arbeitet mit gekoppelten Stoff- und Wärmebilanzen, die adaptive Modellkomponenten zur Anpassung an die jeweilige Zielanlage nutzen. Aus dem zeitlichen Verlauf der Bilanzen wird auf den aktuellen Prozesszustand geschlossen, der durch die Konzentrationsverteilung von Ausgangs-, Zwischen- und Endprodukten charakterisiert wird. Die Industrieerprobung des Monitoring-Systems erfolgte im Rahmen eines entwickelten Batch-Informations-Management-Systems, das in die vorhandene Prozessleittechnik einer Mehrzweckanlage eingebaut wurde. Ergebnisse der Prototyp-Erprobung während einer Hydrierungs-Produktionskampagne werden vorgestellt.

Calorimetric and in situ Fourier Transform Infrared (FTIR) spectroscopic studies to monitor the unpredictable initiation of a strongly exothermic Grignard reaction and to determine their thermokinetic parameters are represented. Instead of operating under reflux conditions which are commonly used to control the Grignard formation, the calorimetric measurements were carried out in a closed jacketed stainless steel pressure reactor. This novel technique has some advantages. For example, a more accurate determination of the molar reaction enthalpy is possible, the increase of the reactor temperature and pressure can also be used to monitor the initiation process of the Grignard formation, and the dosage of the pure organic halide into a closed reactor vessel leads to a predictable and reproducible induction time. Thus, this technique might contribute to reduce the hazardous potentials of Grignard reactions.

The effect of radiation embrittlement has high safety significance for Russian VVER reactor pressure vessel steels. Heats of base and weld metal of the as received state, irradiated state and post-irradiation annealed state were investigated by SANS to get insights about the microstructural features caused by neutron irradiation.
The SANS intensities increase in the momentum transfer range between 0.8 and 3 nm-1 for all material compositions in the irradiated states. The size distribution function of the irradiation-induced defects has a pronounced maximum at 1 nm in radius. Their volume content varies between 0.1 and 0.7 vol.% dependent on material composition and increase with the neutron fluence. The comparison of nuclear and magnetic scattering indicate that the defects differ in their composition. Thermal annealing reduces volume fraction of irradiation defects.

Neutron irradiation leads to a number of phenomena that have been extensively studied. Stoller from Oak Ridge National Laboratory (USA) suggested to describe the real damage structure of VVER RPV steels by a composite model with point defect clusters and Cu-rich clusters. The kinetics theory has been applied in our investigations to clarify the relevance of this model for VVER reactor pressure vessel (RPV) steel. Kinetics theory has to take into account the nucleation, deterministic and coarsening stages. In accordance with experimental data the preferable attention is given to the vacancy clusters.

A wire-mesh sensor developed by the Forschungszentrum Rossendorf produces sequences of instantaneous gas fraction distributions in a cross section at a rate of up to 10 000 frames per second and a spatial resolution of about 2-3 mm. This sensor was applied to an upwards air-liquid flow in a vertical pipe of 51.2 mm diameter. After a brief introduction of the functioning of the sensor, the paper presents results obtained in a at vertical pipe operated with an air-water mixture. Two wiremesh sensors with a measuring matrix of 24x24 points (resolution 2 mm) were placed in a small axial distance behind each other. They were used to study the flow structure in the transition region from bubble to slug flow at an imaging frequency of 2 500 Hz. The two available measuring planes allowed to obtain velocity profiles of the gaseous phase. A sensor with 16x16 points (resolution 3 mm) was applied to visualize the transition from bubbly via churn turbulent to annular flow with 10 000 frames per second. In the churn flow region, periodic plug-like structures were found. In the annular flow the sensor is able to resolve wispy structures.

The response of the reactor core to a reactivity perturbation caused by a decrease of the boron concentration or a decrease of temperature in one loop of the primary circuit strongly depends on the degree of mixing with the undisturbed loops. In case of an emergency core cooling (ECC) injection, the flow field can be additionally dominated by gravity effects, because the density difference between ECC water and coolant inventory is significant. The streak formation may cause thermal loads on the reactor pressure vessel wall (PTS).

In order to study coolant mixing inside the reactor pressure vessel in the flow path beginning from the inlet nozzles and ending at the core entrance the test facility ROCOM (Rossendorf Coolant Mixing Model) was built and operated during the last three years. The facility represents a German KONVOI type PWR (1300 MWel) in a scale of 1:5. ROCOM is equipped with four fully functioning loops. The circulation pumps are driven by motors with computer controlled frequency transformers. In this way, a wide variety of flow rate regimes, such as four-loop operation, operation with pumps off, simulated natural circulation modes and flow rate ramps can be realized.
In case of the experiments on ECC injection, the higher density of the injected water was simulated by adding sugar (glucose).
The evolution of the spatial distribution of the deborated coolant respectively the ECC water was measured by tracering with sodium chloride solution. Conductivity distributions were measured by electrode mesh sensors, one close to the reactor inlet nozzle (16x16 measuring points), two sensors in the upper and lower part of the downcomer (2D grids of 4 radial and 64 angular measuring positions) and one sensor at the core entrance (inlets of each of 193 fuel elements). The maximum measuring frequency is 200 Hz. The results allow the visualizations of the measured distributions at the sensor positions. In case of running main circulation pumps, the coolant from the affected loop arrives in a sector at the azimuthal position of the corresponding inlet nozzle. But on contrary to the extreme assumption of a sharp sector, the slopes of the sector are smooth and the maximum disturbance is about 70-80 % of the disturbance at the reactor inlet. Pump start-up scenarios as well as asymmetric natural circulation in one of the four loops are connected with a different picture. In this case, the water with a decreased boron concentration arrives at the core entrance at the side opposite to the azimuthal position of the inlet nozzle, in which the flow starts.
The injection of ECC water with a higher density is accompanied with the appearance of a streak of cold water streaming downwards in the downcomer. Experiments at ROCOM were carried out to identify the transition from momentum driven flow in the downcomer to a density driven regime (critical Froude number). The relative density difference was varied between 0 and 10 % and the loop flow rate between 0 and 15 % of the nominal. In case of momentum controlled flow (high Froude numbers) the ECC water reaches the core inlet first on the side opposite to the azimuthal position of the affected loop. If the density difference is large (low Froude numbers) the ECC water falls down almost in a straight line and reaches the core inlet at the azimuth of the inlet nozzle.
Parallel to the experimental work, CFD calculations were performed. Good results were achieved with the code CFX-4.2. Nozzle region, downcomer and lower plenum were discretized in a mesh of about 400 000 nodes. The calculations well reflect both shape and amplitude of the distributions at the core entrance, if a k-eps turbulence model is used. The code validation benefits from the detailed information delivered by the mesh sensors. Furthermore, a simplified mathematical model was developed to generalize experimental results using some linear properties of the transport equation for the temperature respectively the bo...

The paper presents a wire-mesh sensor for high-speed visualisation of transient gas fraction distributions in two-phase flows. It is based on the measurement of the local instantaneous conductivity of the two-phase mixture. The maximum time resolution of the device is 10 000 frames per second. The sensor consists of two electrode grids with 16 electrodes each. This results in 16 x 16 sensitive points, which are equally distributed over the cross section. The sensor was used to measure gas fraction and velocity profiles, bubble size distributions and their evolution along the flow path in a vertical upwards gas-liquid flow.

We analyze the centrality dependence of thermal parameters describing hadron multiplicities, hadron spectra and dilepton
spectra in heavy-ion collisions at SPS and RHIC energies.

QCD sum rules are evaluated at finite nucleon densities and temperatures to determine the change of pole mass parameters for the lightest vector mesons rho, omega and phi in a strongly interacting medium at conditions relevant for the starting experiments at HADES.
The role of the four-quark condensate is highlighted.
A few estimates (within a fire ball model and BUU calculations) of dilepton spectra in heavy-ion collisions at 1 AGeV are presented.

The prognostic value of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) in the assessment of post-treatment residual masses in patients with Hodgkin's disease (HD) or non-Hodgkin's lymphomas (NHL) was evaluated. We prospectively studies 58 patients with HD (n = 43) or NHL (n = 15) who had post-therapeutic complete remission with residual masses (CRu) indicated by computerized tomography. Analysis of 62 residual locations by FDG-PET was performed separately for HD and NHL. Patients with a PET-positive residual mass [standardized uptake value (SUV) > 3] had a recurrence rate of 62^.5% (5/8 patients), whereas patients with PET-negative residual mass (SUV -< 3^.0) showed a recurrence rate of 4% (2/50 patients, P = 0^.004). A positive FDG-PET study correlated with a significantly poorer progression-free survival (P < 0^.00001). No recurrence occurred in any of the 39 HD patients with negative PET scan (negative predictive value, 100%). Four out of four NHL patients with a positive PET study relapsed (positive predictive value, 100%).
In conclusion, FDG-PET is a suitable non-invasive method with a high degree of accuracy in the prediction of early recurrence in lymphoma patients with CRu.

Embrittlement of nuclear reactor materials is regarded as one of the most important problems in radiation physics. One of the widespread approaches relates the embrittlement of bcc materials (ferritic/martensitic steels, vanadium alloys etc.) to impurities that can precipitate under irradiation. Fracture of iron as wll as modern structural materials occurs through crack nucleation and growth. Precipitation can affect crack growth directly via elastic interaction and indirectly through locking the dislocation motion. The primary topic of the research is the effect of obstacles for dislocation motion on the plastic zone formation, the crack blunting and shielding. Features of the plastic zone (size, dislocation density etc.) are investigated. Reduction of stress intensity factor vs. size, volume fraction and distribution of precipitates is evaluated. Dependence of embrittlement of structural reactor materials on the concentration of precipitates is established.

Das Verhalten des Reaktordruckbehälters bei Kernschmelzstörfällen ist von hoher sicherheitstechnischer Bedeutung für die Beherrschung derartiger Störfälle. An der Königlichen Technischen Hochschule Stockholm werden dazu EU-geförderte Simulationsexperimente (FOREVER) durchgeführt. Der untere Teil eines 1:10 skalierten Druckbehälters wird mit einer oxidischen, ca. 1200 °C heißen Schmelze und mit Innendruck belastet. Die dabei auftretenden Temperaturen und Dehnungen werden in Abhängigkeit von der Zeit während des Experimentes gemessen. Metallografische Untersuchungen nach Abschluss des Experimentes geben zusätzliche Informationen über die aufgetretenen Belastungen. In Abhängigkeit von der axialen und radialen Position lassen sich eine Reihe typischer Strukturen nachweisen, wie Oxidschichten, Reaktionszonen mit der Kernschmelze, Entkohlungszonen, bainitische Zonen oder Bereiche mit ferritisch-perlitischem Zeilengefüge. Von besonderem Aussagewert ist die räumliche Verteilung der Kriechporen. Glühexperimente an den Proben mit unbeeinflussten Ausgangsgefüge liefern eine Vergleichsgefügereihe. Auf diese Weise können die Maximaltemperaturen ebenso wie die axialen und radialen Temperaturgradienten abgeschätzt werden. Die metallografischen Befunde bestätigen die FEM-Vorausrechnungen der Experimente.

A two-step screening method is described to identify regularly arranged surface layers (S layers) on Gram-positive bacterial strains. A non-destructive release of S-layer sheets is achieved by enzymatic hydrolysis of the underlying peptidoglycan using lysozyme. The existence of regular S layers is then directly confirmed by scanning force microscopy or transmission electron microscopy. This method requires a minimal amount of bacterial cells and may be used as a 'quick test' for demonstrating the presence of S layers.

The crosslinked polyurethaneurea films based on polyoxitetramethylenglycol and polyoxipropyleneglycol with toluenediisocyanate and 3,3'-dichlor,4,4'-diaminediphenylmethane were synthesised in a solution where the solvent evaporates during the polymerisation. FT-Raman and FTIR spectra were analysed and intermo-lecular force constants of hydrogen bonds were calculated. On the base of intensity of the Raman and IR line of spectra which reflects hydrogen bond formation, the optimal structure of hydrogen bonds and the conformations of macromolecules of polyure-thaneurea were observed for the solvent ethylacetate.

TixAl1-x thin films were deposited on stainless steel substrates using plasma immersion ion implantation and deposition (PIIIAD). A cathodic arc was employed as a source of metallic ions from Ti0.5Al0.5 targets and the arc plasma was guided by a curved magnetic field filter. The resultant thin films were analysed using Auger electron spectroscopy (AES) and X-ray diffraction techniques. A dynamic profile simulation code, TRIDYN, based on binary collision approximation was applied to understand the Ti and Al profiles in the deposited thin film. The results indicate that the film composition and phase formation depends on the applied bias, duty cycle and off time energy of the bombarding ions. The results also indicate that in PIIIAD conditions, the assumption of time averaged dc bias is improper to describe pulsed biasing, with deposition, resputtering and ion implantation all occuring simultaneously.

Bacteria in polluted environments are adapted to the toxic compounds present there
and often possess effective detoxification strategies. For this reason they are
very prospective for development of in situ bioremediation processes. In former
experiments a selective binding by cells and spores of Bacillus sphaericus
JG-A12 of U, Cu, Pb, Al and Cd from drain waters of uranium mining wastes was
demonstrated. The strain JG-A12 was recovered from the uranium mining waste pile
"Haberland" near the town of Johanngeorgenstadt. B. sphaericus JG-A12 possesses
a surface layer (S-layer). The latter differs significantly at its N-terminal
domain from all other S-layers studied up to date. Cells, spores and purified
S-layer protein fraction of this strain were used for construction of biological
sol-gel ceramics (biocers). Metal-binding kinetics of cells, spores, purified
S-layer fraction and the corresponding biological ceramics were measured. The
biosorption of uranium and copper by the corresponding biocomposites was strongly
influenced by the way of the biocer preparation The highest metal binding capacity
possess biocers with embedded vegetative cells. Larger amounts of uranium and
copper were accumulated by biocers which were prepared by freeze drying or using
penetration reagents like sorbit. Desorption of the bound metals and regeneration
of the biological ceramics was achieved using aqueous citric acid.

Bacillus sphaericus strain JG-A12 was isolated from the uranium mining waste
pile "Haberland" near the town of Johanngeorgenstadt. Vegetative cells and spores
of this strain accumulate selectively large amounts of U, Cu, Pb, Al and Cd from the
highly polluted drain waters of this uranium waste. Interestingly, the strain
JG-A12 possess a surface layer protein (S-layer) with a novel structure. The ability
of B. sphaericus to interact with heavy metals and its geographic origin make
it a good candidate for preparation of bacteria-based ceramics (biocers) for in
situ bioremediation of uranium mining waste pile waters. Biocers were prepared by
dispersing vegetative cells, spores and purified S-layer protein fraction of B.
sphaericus JG-A12 in aqueous silica nano-sols, gelling and drying. Different types
of ceramics were prepared by using air or freeze drying and adding water soluble
compounds as sorbit. Variations in porosity and structure of the biocers were
examined using scanning electron microscopy. The sorption and desorption of uranium
and copper by these biocomposites were investigated and visualised by EDX analysis.
Highest binding capacity demonstrate biocers with embedded Bacillus cells. For
reusing the biocers sorbed uranium and copper can be completely removed from them
by washing with aqueous citric acid.

During the long period of uranium mining and production in Saxony, large amounts of ores were treated and leached. Waste piles and waste waters from those procedures with high concentrations of heavy metals and radionuclides still remain in this part of Germany. For further use of the mentioned areas, they have to be cleaned. For this purpose, bacteria recovered from the contaminated sites are very prospective, because developing detoxification strategies as binding or reduction of heavy metals and radionuclides, they are well adapted to the complex and toxic conditions in the wastes. Bacillus sphaericus JG-A12 was recovered form the uranium mining waste pile "Haberland" near the town of Johanngeorgenstadt. Vegetative cells and spores of this strain accumulate selectively and reversible large amounts of U, Cu, Pb, Cd and Al. Interestingly, B. sphaericus JG-A12 possesses a paracrystalline surface layer protein (S-layer) as outermost component of its cell wall. Compared to the known S-layers of the other B. sphaericus strains, the N-terminal domain of B. sphaericus JG-A12 S-layer possesses a novel primary structure. Cells, spores and stabilized S-layer sheets were embedded by sol-gel techniques in xerogels. The sorption and desorption of uranium and copper by the free biocomponents and the biocomposite material were investigated using EDX analysis.

Bacillus sphaericus JG-A12 was isolated from the uranium mining waste pile "Haberland" near the town of Johanngeorgenstadt, Saxony, Germany. The drain water and the soil at this site are highly contaminated with heavy metals and radionuclides. Sorption experiments with vegetative cells and spores of B. sphaericus JG-A12 demonstrate specific and reversible accumulation of U, Cu, Pb, Al and Cd from the drain water of the waste. The latter makes this bacteria an interesting candidate for the development of in situ bioremediation processes based on biological ceramics (biocers). In addition, B. sphaericus JG-A12 possesses a surface layer (S-layer) which differs at its N-terminal domain (220 amino acid residues) significantly from all other S-layers studied up to date. In this study vegetative cells, spores and stabilized S-layer sheets were immobilized in the SiO2 matrix by dispersing in aqueous silica nanosols, gelling and drying. Variations in the porosity and structure of the biocers were achieved by different drying methods or adding water soluble compounds as sorbitol. The time dependence of the uranium sorption and desorption by the free biocomponents and biocomposites was investigated. Localization of the bound metals and a characterization of the metal complexes formed at the biocer were carried out using scanning electron microscopy and EDX.

Low resistivity ( < 0.1 Ohm cm), p-type SiC layers can be produced by the combination of high dose Al ion beam doping and ion beam induced crystallization. The implanted SiC layers have a nanocrystalline structure consisting of randomly oriented grains of mainly 3C-SiC. The electrical properties of the doped layers were investigated by sheet resistance and Hall measurements in dependence on temperature. In comparison with the standard doping process the hole concentration is enhanced by more than one order of magnitude.

Scaled coupled melt pool convection and vessel creep failure experiments are being performed in the FOREVER program at the Royal Institute of Technology, Stockholm. These experiments are simulating the lower head of a pressurized reactor vessel under the thermal load of a melt pool with internal heat sources. Due to the multi axial creep deformation of the three-dimensional vessel with a highly non-uniform temperature field these experiments offer an excellent opportunity to validate numerical creep models. A Finite Element model is developed and using the Computational Fluid Dynamic module, the melt pool convection is simulated and the temperature field within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a new creep modeling procedure. Additionally, the material damage is evaluated considering the creep deformation as well as the prompt plasticity.
After post-test calculations for the FOREVER-C2 experiment, pre-test calculations for the forthcoming experiments are performed. Taking into account both - experimental and numerical results - gives a good opportunity to improve the simulation and understanding of real accident scenarios. After analyzing the calculations, it seems to be advantageous to introduce a vessel support, which can unburden the vessel from a part of the mechanical load and, therefore, avoid the vessel failure or at least prolong the time to failure. This can be a possible accident mitigation strategy. Additionally, it is possible to install an absolutely passive automatic control device to initiate the flooding of the reactor pit to ensure external vessel cooling in the event of a core melt down.

Positron Doppler-broadening spectoscopy was used to examine a series of neutron-irradiated model alloys and 73W-weld steel. The composition of the model alloys was systematically varied in the amounts of copper, nickel and phosphorus. The 73W-weld steel contains 0.31 % copper and 0.60 % nickel. The samples were examined in the non-irradiated and neutron-irradiated states, as well as after successive isochronal anneals at temperatures ranging from 200 °C to 600 °C.
By comparing the Doppler-broadening spectroscopy W-parameters measured in pure metals with those measured in the materials in this study, we were able to draw inferences as to the nature of the irradiation-induced defects that cause hardening and embrittlement. The results indicate that the damage is a combination of irradiation-induced metallic precipitates and vacancy-type defect clusters.

kein Abstract

Microorganisms have a potential to affect the mobility and overall environmental behaviour of uranium through solubility and speciation changes, biosorption, bioaccumulation or other transformations. Recently, three eco-types of A. ferrooxidans were recovered from different sites and depths of two uranium mining waste piles. These natural A. ferrooxidans isolates interact with uranium and tolerate this radionuclide in a type-specific way. In this study, we used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared Spectroscopy (IRS), Time-resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) analysis to conduct atomic and molecular scale studies on U(VI) interaction with the three eco-types of A. ferrooxidans. On the basis of the combined information from the above mentioned methods we conclude that the uranium is bound by A. ferrooxidans cells mainly in a form of organic uranyl phosphate complexes. Moreover, the largest part of the uranium accumulated by A. ferrooxidans cells is located within the extracellular polysaccharides. Additionally, some part of the uranium was found on the cell walls. A limited amount of the metal enters the cells and is than detoxified through sequestration by intracellular polyphosphate bodies.

Uranium and other actinides may be present initially as soluble or insoluble forms in nature and, after disposal, they may be converted from one to the other form by microorganisms. Under appropriate conditions, actinides can be mobilized or immobilized by direct (enzymatic) or indirect (nonenzymatic) microbial actions. These include: (i) oxidation-reduction reactions, (ii) changes in pH and Eh, (iii) chelation, or production of specific sequestering agents, (iv) formation of stable minerals, (v) biodegradation of actinides-organic complexes, and (vi) biosorption by microbial biomass and biopolymers. In this work, we investigated uranium sorption efficiency of different bacterial strains isolated from uranium mining wastes such as Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans Pseudomonas stutzeri and Pseudomonas migulae, and also of some reference strains under various conditions (pH, amount of biomass, temperature). In addition, from desorption studies we obtained information about the kind of interaction (sorption, surface complexation, or uptake) and the binding strength. In order to conduct atomic and molecular scale studies on U(VI) interaction with these bacteria, we used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Infrared Spectroscopy (IRS), Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS) analysis. Transmission electron microscope (TEM) was used for imaging the location of uranium accumulated by the bacterial cells, and for determining the active binding sites of the examined different types of biomass, and consequently to elucidate the possible mechanism of uranium accumulation. Electron-dispersive X-ray (EDX) analysis allowed to perform an elemental analysis of the uranium accumulates.

In order to apply the protective effect of Cl doping on the high temperature oxidation resistance of TiAl alloys for complicated shaped parts, plasma immersion ion implantation (PI3) of chlorine into technical TiAl alloys was investigated. A specialized PI3 apparatus was optimized for the strongly etching electronegative Cl plasma. Plasma diagnostics was performed using a Langmuir probe. In order to sustain a sufficient dense plasma, different RF- antenna configurations are discussed and the resulting densities are compared. The influence of plasma pulsing on the surface interaction of Cl during the process is evaluated.
Different commercial alloys were implanted and tested. The resulting depth profiles of the modified surface layer are investigated using depth profiling with Auger electron spec-troscopy (AES). After implantation, the Cl is located close to the surface. Oxidation tests at 900°C in air for 100 h showed a strong reduction of the oxidation, which is comparable to conventional beam line im-plantations of Cl. The effect is rather independent of the alloy composition and therefore interesting for application.
ing depth profiles of Cl are investigated using depth profiling with Auger electron spectroscopy (AES). After treatment, the Cl is located close to the surface. The retained dose depends mainly on the temperature during implantation, which is controlled by the repetition rate of the pulses. Oxidation tests at 900°C in air for 100 h showed a strong reduction of the oxidation, which are comparable to conventional beam line im-plantations of Cl. The effect is rather independent of the alloy composition and therefore interesting for ap-plication.

Radioactive wastes are classified as high-level wastes (spent fuel etc.), transuranic wastes (wastes from spent fuel reprocessing, nuclear weapons), and low- and intermediate-level wastes which are generated from a variety of activities, for instance, uranium mining. The presence of uranium in these wastes, is a major concern because of its potential to migrate from the waste repositories and piles and to long-term contaminate the environment. Therefore, it is becoming increasingly clear that such polluted sites will require a long-term stewardship in addition to remediation. Effective remediation and stewardship will require a better understanding of the environmental chemistry of uranium. Results of experimental investigations of uranium accumulation and studies of microbial ecology in uranium-rich environments strongly imply that microorganisms play significant role in uranium mobilization and immobilization. Biological processes for uranium immobilization in particular, include biosorption, bioaccumulation, precipitation, and biomineralization. In this work, we investigated the uranium sorption efficiency of different bacterial strains isolated from uranium mining wastes such as Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Pseudomonas stutzeri, Pseudomonas migulae and the corresponding reference strains under various conditions (pH, amount of biomass, temperature). The ability of the above mentioned microorganisms to tolerate uranium and some other heavy metals was studied as well.

Over 40 years, the intensive uranium mining and milling in the Southeast of Germany (Saxony and Thuringia) has caused environmental pollution in this region. Therefore, it is becoming increasingly clear that such contaminated sites will require a long-term stewardship in addition to remediation. Effective remediation and stewardship will require a better understanding of uranium environmental chemistry. Microbial cells are known to reduce, oxidize, biosorb, bioaccumulate, and bioprecipitate uranium and other actinides. Recently, three different eco-types of A. ferrooxidans were recovered from different sites and depths of two uranium mining wastes. The strains of these three types possess different capability to accumulate and tolerate uranium. In this study, we used a combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Time-resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), Transmission Electron Microscopy (TEM) and Energy-Dispersive X-ray (EDX) analysis to conduct atomic and molecular scale studies on U(VI) interactions with the three eco-types of A. ferrooxidans. On the basis of the combined information obtained by the above mentioned methods we conclude that the uranium is bound by the cells of the three A. ferrooxidans types in a form of organic uranyl phosphate complexes, which differ in their strength.

Die Synthese von SiC-Kristalliten durch Implantation von Kohlenstoff in Silizium ist kein einstufiger Prozess. Die Implantation bewirkt eine elastische Deformation der Si-Matrix und die Bildung von SiC-Partikeln in Abhängigkeit von der Ionenfluenz und den thermischen Bedingungen während der Implantation und des Anlassprozesses.
Das Wachstum der SiC-Kristallte in der Si-Matrix wurde mit unterschiedlichen Röntgentechniken wie Diffraktometrie zur Phasenidentifizierung, hochauflösender Diffraktometrie, Texturmessungen, grazing incidence diffraction, reciprocal space map an der Rossendorfer Beamline (ROBL) und hochauflösender Elektronenmikroskopie untersucht.
Es wurde gefunden, dass in einer vergrabenen Schicht 3C-SiC Kristallite gebildet werden. Nach ihrer Orientierung zur Si-Matrix können diese in drei Gruppen eingeteilt werden: mit (i) regelloser Orientierung wie in einem Pulvermaterial, (ii) Fasertextur mit der Oberflächennormale als Faserachse und (iii) perfekter kristallographischer Ausrichtung der kubischen Kristallachsen SiC<100> || Si<100>.
Eine thermische Behandlung begünstigt das Wachstum von hochorientiertem Material: dabei ist eine höhere Implantationstemperatur effektiver als ein nachfolgender Anlassprozess selbst bei höherer Temperatur.

The structure and the elemental depth distributions of Y1Ba2Cu3O7-d (YBCO) and La0.7Sr0.3MnO3 (LSMO) were examined by q-2q XRD, and by 1.7 MeV 4He+ Rutherford Backscattering Spectrometry (RBS) in random and channeling geometry. The YBCO layers were magnetron sputtered, with the varying parameters oxygen pressure and annealing time. The layers have high crystalline quality and an almost sharp interface with the substrate as revealed by the analysis. It is shown that the oxygen content influences considerably not only the superconducting behavior, but also the lattice parameters and the cmin parameter (the minimum yield which is the ratio of aligned to random Rutherford backscattering spectra). We have found by high-precision RBS simulation, that independent on the film quality, a disordered interface region of 20 to 30 nm is present in all structures. As a complementary study we have performed also AES depth profiling.

The paper deals with structural, morphological and electrical investigations of thin AlN films obtained by two techniques. The first one consists in rapid thermal annealing of aluminium evaporated onto Si (100) at 600, 800 and 1000oC in NH3 atmosphere for times in the range of 15-180 sec. The other part of the structures was obtained by broad energy range ion bombardment (BERIB) of aluminium by doses ranging from 1.5x1017 cm-2 to 6x1017 cm-2. This technique, to our knowledge was not previously described in the literature. The ion implantation was carried out with two species - nitrogen atoms with energies from 50, 30, and 20 keV and nitrogen ions with energies from 50 and 30 keV. These energy spectra were chosen in order to ensure continued and wide nitride layer of thickness at least of 150 nm. The simulations of the implanted constituent distributions were estimated by the code SRIM. The both implanted series were consequently annealed at 800 and 1000oC for times ranging from 30 to 90 sec. Four-point electrical measurements, scanning electron microscopy, SEM, X-ray diffraction and Rutherford Backscattering Spectrometry (RBS) have been used to characterize the layers.

The development of novel devices for optical communication and integrated sensor applications is mainly focused on their possible integration into dedicated integrated circuits. The main problem concerning integrated optical systems in silicon technology has always been the formation of an highly efficient silicon-based light emitter which is a key feature to make a real step into the world of integrated optoelectronics.
One of the most promising approaches to form such a silicon based light emitter is ion beam synthesis. In this paper we will report our recent progress in extracting blue-violet (~400 nm) electroluminescence (EL) from an ion beam synthesized Ge-rich silicon dioxide layer. The power efficiency of the EL was as high as 0.5 % which is one of the best values ever reported for Si - based light emission. The lifetime of the EL-device can reach several hours without special precautions of stabilizing the EL-active layer against ion or other contamination. Moreover, results are reported dedicated to the investigation of the excitation mechanism of this strong EL.

Si-based light emitters will be a key element of future optoelectronics. One of the most promising approaches is Ge-implantation into thin SiO2 films on crystalline Si. This system exhibits a strong violet electroluminescence with a power efficiency up to 0.5 % [L. Rebohle et al., J. Electrochem. Soc.: Electrochem. and Solid State Lett. 7 G57 (2001)], but the mechanism of electrical excitation is not yet fully understood. In this paper the electrical excitation of the luminescence centers is investigated by means of electrical and electroluminescence transient measurements. It is found that the most probable way to excite luminescence centers is the impact excitation by hot electrons. Whereas the injection is explained by trap assisted tunneling of electrons from the substrate into the oxide, the electrons will be transported via traps or in the SiO2 conduction band. Furthermore, the electroluminescence rise and decay time is estimated to be of the order of 100 microsec.

In this paper we report on recent results obtained from flash lamp annealing (FLA) for the formation of ultra-shallow junctions. Si (100) wafers were implanted at ultra-low energy (500eV) with boron to a fluence of 1015 ions/cm2. FLA was carried out at temperatures of 1100 and 1200°C with a soak time of 20ms. For comparison conventional rapid thermal annealing (RTA) was performed at 1100°C and 1200°C. The boron diffusion and the dopant activation were investigated by secondary ion mass spectroscopy (SIMS) and spreading resistance profiling (SRP). The activated doses after FLA were as high as 20% of the implanted dose and confined in a layer of 60 nm. The sheet resistances were comparable to those after RTA treatment.

A reference material has been produced which can be used for the calibration of surface - and near-surface analytical methods.

Energy spectra of protons channeling along the (0001) axis of several SiC polytype crystals, (namely 4H, 6H, 15R, 21R) in the energy region Ep=1.7-2.5 MeV, in the backscattering geometry, were taken and analyzed. Computer simulations based on the assumption that the dechanneling of protons follows an exponential law are in very good agreement with the measured spectra. The obtained results for the two crucial channeling parameters, ?, the mean channeling distance, and, a, the ratio of the stopping powers in the aligned and random mode are compared for the different structures and an attempt is made to explain the occuring similarities as well as the differences, in order to evaluate the use of SiC polytypes as substrates in implantations and thin film depositions. An attempt is also made to correlate the results from the present work to the ones obtained in the past for simpler crystallographic structures, namely Si <100> and Si <111>, as well as more complex ones, such as SiO2 (c-axis).

Phase transformations in implanted iron may strongly depend on the sample thickness. The effect essentially relies on lower impurity concentration required for given phase transformation in thin films when compared with thick layers or bulk samples.

In the present work, composite AgSiO2 thin coatings, containing metal nanoparticles, were prepared on glass substrates by the sol-gel route. The coatings were thermally treated in oxidative and reductive conditions up to 500oC for metal nanoparticle formation. The coating structure and the nanoparticle formation were studied by Atomic Force Microscopy (AFM) and Rutherford Backscattering Spectroscopy (RBS) techniques. In the case of RBS, 1.4 MeV 4He+ ions were used for all samples, and low energy 16O and 12C ions in selected ones (Heavy Ion RBS), in order to improve the depth resolution for the profiling of the metal component. The antibacterial activity against Escherichia Coli is examined by antibacterial-drop test. The coatings exhibited a high antibacterial activity, which was enhanced with the increase of the metal concentration and was reduced with the increase of the particle size of the metal nanoparticles. The possible correlation between the layer interdiffusion after the thermal treatment and the antibacterial activity is examined and analyzed. Although further studies are required, RBS and HIRBS seem to be excellent tools for the quality control in the production of sol-gel thin coatings.

The need of the experimental support for validation of the computational tools to be applied to analyze the mixing of diluted slugs has been recognized in various countries. The test series for the International Standard Problem ISP-43 provides a platform for experiences to be applied to the simulation of a well-defined test series. Test A of the UM2x4 loop test facility was calculated with the CFD Code CFX-4.3. The results show qualitatively good agreement with the experimental data. The structure of the flow field and the form of the propagating temperature perturbation front are well modeled by the CFD code. However, deviations occur at local positions. Comparative calculations with and without taking into account buoyancy have shown, that buoyancy effects are noticeable, but the mixing is mainly momentum controlled.

Am Institut fuer Sicherheitsforschung des Forschungszentrums Rossendorf e.V. wird die Mehrzweck-Thermohydraulikversuchsanlage TOPFLOW zur Untersuchung stationaerer und transienter Phaenomene in Zweiphasenstroemungen sowie zur Entwicklung und Validierung der in Computational Fluid-Dynamic Codes enthaltenen Modelle aufgebaut. Im Detail sind Experimente zu den Themen

• transiente zweiphasige Stroemungen in vertikalen, horizontalen und beliebig geneigten Rohrleitungen sowie in reaktortypischen Geometrien,
• Sieden in grossen Behaeltern und Wasserpools,
• Erprobung passiver Komponenten und Sicherheitssysteme

• Kondensation in horizontalen Rohren in Ab- und Anwesenheit von nichtkondensierbaren Gasen.

Nanometer-sized SiC precipitates were in-situ synthesized in Si by simultaneous implantation of two ion beams, of C+ and Si+ ions. The results of simultaneous dual beam implantation were compared with those of sequential dual beam ion implantation and of single beam C+ ion implantation. Remarkable differences were observed regarding the content and the crystal perfection of SiC precipitates as well as the defect structure of the Si substrate. The SiC precipitation during dual beam synthesis was found to depend on the ion energy of the second beam and on the implantation mode, simultaneous or sequential. For suitable implantation conditions the simultaneous dual beam synthesis can improve the in-situ SiC formation in comparison to the single beam synthesis. A higher density of the SiC precipitates with better crystal perfection was observed whereas their size was not changed. The second ion beam enables to shift the dynamic equilibrium of constructive and destructive processes for the SiC formation.
A model is proposed assuming that SiC precipitation preferentially proceeds in regions with vacancy defects. The implantation process itself creates vacancy-dominated and also interstitial-dominated regions. The balance of the local point defect composition is shifted under the second ion beam. In this way the conditions for SiC precipitation can be modified.

Unusual metastable paramagnetic phases have been observed in Fe-Cr thin films fabricated by pulsed laser deposition. In the present paper, X-ray diffraction and Mössbauer spectroscopy have been applied to follow the structural and magnetic phase transformation in these alloys induced by ion irradiation. The projected range of the chosen implantation energies of 40 keV for Cr and 25 keV for Ne lies in the center of the about 40 nm thick films. It has been found that the critical dose for the transformation to the more stable body-centered cubic (b.c.c.) structure depends on the initial phase of the film and the ion mass. The initial body-centered tetragonal phase which forms in the alloys with low Cr content (~30 at.%) can be completely transformed in the b.c.c. phase already by a dose of 5x1015 Cr/cm2 whereas the primitive orthorombic phase at roughly equiatomic Fe-Cr alloys is about 4 times more resistant against ion bombardment. One needs to apply a five times higher Ne-ion dose to induce the same transformation as by the Cr bombardment. The observed effects are discussed comparing the radiation damage caused by the different ions and the grade of affinity of the initial phase to the b.c.c. one.

The ever increasing demands for high precision machining and increased cutting performance, in terms of cutting speed and lifetime, require wear resistant tools of large dimensional accuracy that have very sharp cutting edges. All these requirements can not be fulfilled by the classic PVD and CVD technologies because they result in rather thick overlay coatings.
In this report, first experiments are presented on a hybride plasma immersed ion implantation process (PIII) for depositing thin TiN coatings on hardened and annealed high speed steel or cemented carbides. The layers were produced using a dc-cathodic arc source with a titanium cathode and a nitrogen feed gas. As the cathodic arc generates additional to the metal plasma, a large amount of liquid metal droplets, the plasma was guided to the samples through a 900 magnetic bending field avoiding the deposition of droplets on the samples. The obtained layer thickness was below 1 µm for deposition times of 2 min.
To improve the adhesion of the deposited layers on the substrate materials, sputter cleaning by energetic ions was used during the initial phase of the process. Negative high voltage pulses in the range from zero to 5 kV have been applied to the samples during the deposition. The effect of the energy of these ions on the coating structure was also investigated by SEM, TEM and XRD. Mechanical and functional properties were investigated by hardness measurements and fretting wear tests respectively. Finally cutting performance tests of PIII-treated drills were performed, revealing that a 0.8µm thick TiN PIII-coating increased the lifetime of the drills by a factor of 2.5.

Tiefenselektive Phasenanalyse der a-FeSi2-Bildung nach Beschuß von ß-FeSi2 mittels DCEMS, XPS und AES

Improvement of Tribological Properties of Ti6Al4V by Nitrogen Plasma Immersion Ion Implantation

Nitrogen Plasma Ion Implantation of Al5052 Alloy

Iron silicides are of growing interest because of their interesting properties in reference to potential applications in thermoelectrics, photovoltaics and optoelectronics. For phase analysis by Mössbauer spectroscopy on bulk material or on thin layers, the knowledge of their hyperfine parameters is necessary.
In the present study, the Mössbauer spectra of single crystals of various silicides e-FeSi, ß-FeSi2 and a-FeSi2 are collected by conversion electron Mössbauer spectroscopy at room temperature. Measurements were performed at different angles between the propagation direction of the exciting g-radiation and the crystal axis of the single crystals.
The Mössbauer spectrum of the monosilicide consists of two lines while those of the disilicides consist of four lines. In the latter two cases, an unambiguous assignment of the lines to two quadrupole doublets could be performed. The hyperfine parameters including the signs of the quadrupole splittings are determined with high accuracy. Moreover, the direction of the main axis of the electric field gradient in regard to the crystal orientation was determined.
The results are compared with those obtained at powder or thin layer samples in the past. Differences and coincidences are discussed.

Spin-density enhancement in the presurface zone of chromium

Depth analysis of buried iron disilicide formation by Fe ion implantation into Si was performed by DCEMS.

In the Western Erzgebirge in Germany the abandoned uranium mines are mostly related to the rock phyllite. Currently, many of these mines are being flooded. The flood water is contaminated with uranium and penetrates the phyllite through cracks and fissures. The contact of the flood water with the rock leads to dissolution processes. One of the major components in this phyllite is an iron-rich chlorite. Chlorites are 2:1 sheet silicates, with an octahedral sheet sandwiched between two tetrahedral sheets. In contact with water chlorites tend to dissolve leading to a loss of octahedral layer cations, i.e. Al3+ with Mg2+, Fe2+ and Fe3+ substitutions. During the dissolution the chlorites are progressively degenerating to vermiculite and secondary iron minerals. In previous studies these secondary iron minerals have been determined as a poorly-crystalline iron oxide hydroxide, like ferrihydrite, which has a significant influence on the uranium migration behavior.
In flow-through experiments the kinetics of the U(VI) uptake on chlorite were studied to show the sorption behavior of U(VI) during the dissolution of chlorite within the phyllite of the abandoned uranium mines. These flow-through experiments were carried out under oxic conditions and at room temperature, using a NaClO4-solution with an ionic strength of 0.1 M and a pH of 7. An UO2(ClO4)2 solution was added to reach an initial U(VI) concentration of 1*10-6 M. The dissolution rates calculated for Al, Mg and Si are decreasing during the first hours of the experiment. Due to the precipitation of iron oxide hydroxides in a pH-range > 5 the released Fe cations have not been determined in the reacted solution. The dissolution rate of Fe is for this reason remaining low during the experiment. The formed secondary iron minerals are responsible for the remarkable high uptake of U(VI) on chlorite. In the first 24 h period of the experiment 72 % of the totally uranium was sorbed. In the following hours the relative amount of the sorbed uranium decreases, since most of available sorption sites of the chlorite and of the secondarily formed iron oxide hydroxides were already occupied. Additional sorption of U(VI) out of solution on the solid chlorite during the flow-through experiment is therefore decreasing. Conclusively, the chlorite within the phyllite is retarding under oxic conditions most of the U(VI) during the flooding, due to the dissolution of chlorite and the subsequent precipitation of iron oxide hydroxides.

Batch and column experiments were carried out to study the dissolution of gypsum by water under saturated and unsaturated conditions. The experimental results were verified by calculations. Comparing the dissolution in batch and column experiments, which were performed with a water flow velocity of 0.015 cm/h, one has to conclude that under unsaturated conditions only the
very small portion of 2.2 percent of the grain surface is chemically reactive. Experiments and calculation show that the gypsum release in the column is mainly determined by the flow velocity.

Mine waste dumps and industrial tailings often emit toxic substances like sulfuric acid, heavy metals, or radionuclides over seepage discharge. An important parameter to characterize these transfer processes is the mean residence time tm of the infiltration water usually determined from tritium measurements. Conventional models assume a constant reservoir size (aquifer thickness) and to a great extent stationary hydraulics.
Emerging dumps, in contrast, exhibit a more or less continuously increasing thickness during deposition. The infiltration water is partly or even completely consumed to build up a static reservoir of adhesive water in the initial dry pores. The water percolation begins not until the field capacity is reached. This deceleration depends on deposit rates, recharge rates and cap-illary capacity and increases the portion of older components in the effluent waters compared to model assumptions.
In a case study a time series of effluent waters from a mining dump of Kupferschiefer mining in the south-eastern Harz-foreland was analyzed for ³H. The interpretation using the linear model revealed contradictions between residence time of infiltration waters and life span of the dump.
For the case of the linear model a proposal is made to modify the residence time distribution function. The

Almost all risk assessment studies related to uranium mining and milling legacies rely on the wide-spread but simplistic KD concept of distribution coefficients, which subsumes all relevant physico-chemical phenomena into only one parameter. To overcome the resulting limitations, more realistic chemical speciation patterns are needed, including complex formation, heterogeneous phase equilibria and surface complexation. Following this strategy, the paper presents a digitized version of a thermodynamic sorption database as required for the parametrization of Surface Complexation Models (SCM). It is mineral-specific and hence also suitable for additive models of more complex solid phases such as rocks or soils. All major electrostatic variants of SCM are integrated. Also the concept of strong and weak binding sites, and the 1-pK approach is applicable. Surface species include ternary ones.
Data records comprise of mineral properties, specific surface areas, surface binding site concentrations and protolysis constants, sorption ligand information, and surface complexation reactions, all coupled to an extensive bibliography. Based on them, a detailed picture about the distribution of actinide SCM data amongst minerals, SCM subtypes and ligands is presented. Derived from that and focused on uranium, critical data gaps are identified, existing parameter sets are evaluated, and consistency tests are performed. Final goal is the establishment of recommended reference data sets.
Only few of the surface complexes proposed in the literature (mostly resulting just from best-fit considerations) are actually validated by spectroscopic evidence. If such information is available it is stored in the database and used for data evaluation.
Originally implemented as a stand-alone relational database under MS Access on a PC, the database RES³T (Rossendorf Expert System for Surface and Sorption Thermodynamics) is now connected to the WWW and accessible through common web browser interfaces.

The chemical characterization of the radionuclide species is essential for a reliable assessment of the migration of radionuclides and heavy metals into the geological and biological environment on the load pathway soil - plant - animal - human. Only a few is known about the speciation of uranium in plants. Therefore we investigate the change of speciation during the transfer of uranium from initial solution into plant.
Various plants (lupins, dandelion e.g.) were grown in an agricultural test field and in the laboratory on contaminated soils (up to concentration of 1g U/kg soil) and as hydroponics in the uranium containing solutions (uranium concentration: 10-5 M - 10-2 M, pH: 3 - 8). For the study of the chemical speciation in the initial solution (pore water and hydroponic solution) and in plant samples we use the Time-Resolved Laser-Induced Fluorescence Spectroscopy, the X-Ray-Absorption Spectroscopy and the Scanning Electron Microscopy. Differences between the uranium speciation in the initial solutions and the speciation in the plant could be detected spectroscopically. The chemical speciation of the uranium seems to be identical in the roots, shoot axes and leaves. It is independent of the growing conditions (soil culture or hydroponic) and the type of the plant. Spectroscopic results show the formation of uranyl phosphato complexes as the main species in plants.

The formation of Fe-colloids resulting from the chemical weathering of chlorite (Mg5.5Al2.48Fe2+3.02Fe3+0.94)(Si5.33Al2.66)O20 was studied in batch experiments. The chemistry of the detected colloids was determined by SEM/EDS measurements on separated agglomerated colloids fixed on filter membranes. The results show that the Fe-colloids exist as aqueous colloids as well as sorbed colloids forming iron coatings on the chlorite platelets. It was also observed that the newly-formed Fe-colloids are preferentially attached to the {hk0} edge surfaces and only to a minor extent as isolated Fe-colloids to the {001} basal plane surfaces. The average surface coverage of sorbed Fe-colloids on the {hk0} edge surfaces was found to be 0,276 žm2 of sorbed Fe-colloids per 1 žm2 of {hk0} chlorite surface, i.e. 27,6 % of the {hk0} surfaces is covered with adsorbed Fe-colloids. This value is significantly higher than the surface coverage found on the {001} basal plane surfaces. Here, the average surface coverage of Fe-colloids on the {001} basal plane surfaces was determined to be 0,030 žm2 of sorbed Fe-colloids per 1 žm2 of {001} chlorite surface, i.e. 3,0 % of the {001} surface area is covered with sorbed Fe-colloids. This shows that there are nine times more Fe-colloids adsorbed onto the edge surfaces than on the basal plane surfaces.
The detected colloids were, based on their chemistry, their spherical character and small particles sizes, identified as ferrihydrite. In addition, Mössbauer spectroscopy measurements were used to quantify the increase of ferric iron which formed during the batch experiment. This detected increase in ferric iron in the chlorite from 14.0 to 15.3 % š 1% was attributed to the formation of ferrihydrite.
The assumption that the edge surfaces of sheet silicates show a much higher affinity for adsorption reactions was so far not conclusively proven. However, the results of this study clearly show that colloid adsorption on the sheet silicate chlorite preferentially takes place on the {hk0} edge surfaces indicating that the edge surfaces of sheet silicates are by far more reactive in regard to sorption reactions than the distinctively less reactive {001} basal plane surfaces. In addition, the influence of Fe-phases as weathering products on sorption processes in nature is discussed.

Es ist ein Zeichen einer guten Sicherheitskultur, wenn Hersteller, Betreiber und Gutachter gleichermassen das Sicherheitsniveau von Kernkraftwerken stetig anheben wollen. Derzeit bietet sich die Gelegenheit, ueber fruehere, aktuelle und zukuenftige Konzepte nachzudenken. Ziel ist es, zukuenftige Anlagen zu optimieren, durch Systemvereinfachungen die Uebersichtlichkeit zu erhoehen und somit ihre Zuverlaessigkeit zu verbessern. Ferner sollen Effektivitaet und Wirtschaftlichkeit gesteigert werden. Hierzu wird seit Mitte der 90er Jahre an verschiedenen Stellen weltweit die Effektivitaet und das Betriebsverhalten passiver Sicherheitssysteme untersucht.
Im Beitrag wird auf die Geschichte des NOKO-Versuchsstandes zurueckgeblickt. Ferner werden ausgewaehlte Hoehpunkte der experimentellen Untersuchungen (u. a. der experimentelle Nachweis der thermohydraulischen Wirksamkeit des Notkondensators, des Gebaeudekondensators sowie des passiven Impulsgebers) beschrieben.

The ferric oxide schwertmannite is commonly formed in acid mine drainage waters (pH-range from 2.8 to 4.5) in the presence of high sulfate concentrations. Because of its large specific surface area its may influence the migration of uranium(VI) by sorption processes. The aim of this study were structural informations for uranium(VI) surface complexes given by Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy. We include Goethite in our investigations as a reference to compare and interpret the schwertmannite data.

Samples for EXAFS analysis were prepared under N₂ atmosphere using 200 mg of schwertmannite or goethite with initial uranium(VI) concentrations of 1x10^-5 (pH 6.5) to 5x10^-5 M (pH 4.2). The ionic strength was adjusted using 0.01 M Na₂SO₄ or NaClO₄ respectively. EXAFS spectra were recorded at room temperature in fluorescence mode at the Rossendorf beamline (ROBL) at the ESRF in Grenoble. The measured EXAFS oscillations were fitted using EXAFSPAK procedure. The theoretical phase shifts and backscattering amplitudes were calculated with FEFF8.

All distances of the equatorial oxygens are about 2.37 Å. These are significantly shorter than typical values of 2.41 Å for the aquatic UO₂ ²⁺ ion, which indicates strong interactions. An iron backscatterer is clearly found for uranium(VI) sorbed onto goethite at pH 4.2 and 6.5 in sulfate-rich solution as well as for schwertmannite at pH 4.2 in perchloric solution. Such a uranium - iron distance indicates a bidentate inner sphere complexation. In contrast, the EXAFS of uranium(VI) sorbed onto schwertmannite at pH 4.2 in sulfate-rich solutions shows only a sulfur backscatterer at a distance of 3.66 Å, indicating the formation of a ternary surface complex.

Tetrahedral amorphous carbon (ta-C) is an amorphous form of carbon with a high content of sp3 bonded atoms, which can be deposited as thin films by energetic carbon ions or neutral atoms. As-grown ta-C films possess a high level of intrinsic compressive stresses (~10 GPa) inhibiting the use of this very promising material. The stress is due to a specific growth mechanism (subplantation), resulting from a competition between the densification of subsurface layers by incoming ions and the thermally activated diffusion of subplanted atoms to the surface. In agreement with experiment, we demonstrate using atomic scale simulation that low-temperature annealing can induce a considerable stress reduction in as-grown ta-C with minor
changes in its atomic structure and density. Simulating annealing by means of empirical molecular-dynamics with the interatomic Brenner potential for carbon and realistic boundary conditions, the dependence of the residual stress on the annealing temperature was investigated. It is found that a complete stress relief in ta-C is not accompanied by a change in the short-range order. The average atomic coordination remains nearly constant up to 1400 K. The stress relaxation mechanism discussed involves only structural optimization within the sp3 bonded constituent of ta-C and does not require clustering of sp2 bonded atoms.

The uptake of heavy metals into plants is commonly quantified by the soil-plant transfer factor. Up to now little is known about the chemical speciation of actinides in plants. To compare the obtained spectroscopic data of uranium complexes in plants with model compounds, we investigate the complexation of uranium with relevant bioligands of various functionalities. A very important class of ligands are phosphate esters, which serve as phosphate group and energy transmitters as well as energy storage mediums in biological systems.
Therefore, in our study we present the results of uranium complexation with glucose-1-phosphate (G1P) obtained by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and potentiometric titration. The TRLFS-experiments were performed at a fixed uranyl concentration (10^-5 M) as a function of the ligand concentrations (10^-5 to 10^-3 M) in a pH range from 2 to 4.5. The potentiometric titrations were performed at fixed uranyl (10^-4 M) and ligand (10^-3 M) concentrations in a pH range from 3 to 10.
The TRLFS-measurements show a decrease in the fluorescence intensities with increasing ligand concentrations, and no shift of the emission bands. The TRLFS spectra indicate the presence of only one species with fluorescence properties. This species has a lifetime of 1.50 µs and was identified as the free uranyl ion. Therefore we conclude that the complexed uranyl glucose phosphate species shows no fluorescence.
From quantitative evaluation of the TRLFS spectra we conclude, that 1:1 uranyl glucose phosphate species UO₂(G1P) has formed. The complex formation constant was calculated to be log beta=5.60.
The results of the potentiometric titration show the same type of complex with a stability constant of log beta=5.37.

The influence of deposition conditions on the sp3 content, intrinsic stress, and elastic modulus in hard amorphous carbon (a-C) films was studied at the atomic scale. Simulation of ion beam deposition of carbon films was performed by the molecular-dynamics method with a modified analytical hydrocarbon potential of Brenner. Deposition of films with a thickness of up to 10 nm was computed for ion energies E = 10-80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and the intrinsic stress on substrate temperature was found to be in qualitative agreement with experiment. At low substrate temperatures and low ion energies, the sp3 fraction increases with ion energy, giving at E > 30 eV a highly sp3 bonded tetrahedral amorphous carbon (ta-C) with a high level of intrinsic compressive stress. This trend also remains at room emperature, however with lower values of sp3 content, whereas at T > 200 °C a transition to graphite-like a-C with dominating sp2 bonding was found.

A model of thermochemical polishing, namely the conversion of diamond into non-diamond carbon at elevated temperatures and the subsequent dissolution of the non-diamond carbon into a transition metal polishing plate is investigated. Equations of the conversion rate k1, the dissolution rate k2, the diffusion constant of carbon in steel D, and the concentration profile of carbon in steel N(x,t)are derived. The rate constants are calculated for four diamond films polished at varying temperatures. Elastic recoil detection analysis (ERDA) measured carbon depth profiles in steel agree well with theoretical calculations. However, the calculated value of D = 1,16 x 10-14 cm2/s is far below the value of D = 1,19 x 10-7 cm2/s for gamma-iron. The discrepancy between the two values is related to oxygen-enhanced segregation of carbon in the near surface region of steel and to the incorporation of elements which act as trap centers of carbon in steel.

The volatility of plutonium oxides in the O₂-H₂O_(g)/SiO_2(s) system has been studied by thermochromatography in the temperature range 1475 to 600 K. Oxides of uranium and neptunium have been studied for comparison. Oxide samples containing 10¹⁵ - 10¹⁶ actinide atoms were heated in the starting position of the thermochromatographic silica columns. Mixtures of helium, oxygen and water vapor were applied as reactive mobile gas phase. Resulting from thermochromatography the volatile actinide species are deposited in the column downstream, thus creating inner chromatograms along a temperature gradient. At the end of each experiment the actinide chromatograms were measured by alpha spectrometry.
Plutonium was found to be volatile in humid oxygen at temperatures above 1250 K. The Pu volatility is lower than that of uranium, but higher as one would expect for stable Pu(IV) which is nonvolatile under the applied experimental conditions. The Pu volatility is assigned to PuO₂(OH)_2(g). The experimental results give further evidence that water can oxidize plutonium dioxide.

This paper reports the synthesis, biological evaluation and in vitro autoradiography of a new technetium-99m radioligand with high affinity for the 5-HT_1A receptor. The neutral complex combines an N₂S₂ diamine dithiol (DADT) ligand as complexing moiety for oxotechnetium(V) and a 2-(1-piperazino)phenol via a 6-carbon alkyl chain, derived from desmethyl-WAY-100635 (DWAY). The complex displays an IC₅₀ value for the 5-HT_1A receptor of 1.29 nM against the selective 5-HT_1A agonist [³H]8-OH-DPAT, a moderate selectivity towards the alpha₁-adrenergic receptor (IC₅₀ of 8.1 nM against [³H]prazosin) and a good selectivity for the D₂ receptor (IC₅₀ of 192 nM against [³H]spiperone) and the 5-HT_2A receptor (IC₅₀ of 922 nM against [³H]ketanserin). Biodistribution studies in rats show an initial brain uptake of 0.65%±0.07% ID 2.5 min p.i. In vitro autoradiographic studies of the ^99mTc complex in rat brains indicate a strong specific accumulation of the radioactivity in 5-HT_1A receptor-rich brain regions.

The remediation of former uranium mining and milling sites of Saxony and Thuringia requires the purification of uranium contaminated seepage and mine waters. The separation of uranium(VI) from aqueous solution by calixarenes by means of solvent extraction is described in the literature (e.g., [1,2]). Calixarenes are macrocyclic molecules formed by 4, 6 or 8 parasubstituted phenolic units linked by methylene bridges ortho to the OH functions. Thus, molecules of various ring sizes are formed. The substitution of calix[6]arenes on the hydroxyl group by carboxylic and hydroxamic groups, respectively, leads to ligands that are able to bind uranium(VI) selectively.
The present work represents an innovative method for the separation of uranium(VI) from aqueous solution using uranophile calix[6]arenes that are fixed on textile substrates such as polyester fabric. For this, the calix[6]arenes are statistically functionalized by spacer groups (n-alkyl groups) that enable their fixation onto polyester fabric.
The complex formation of the textile bound calixarenes, e.g., carboxymethoxy-p-mono-nonyl-penta-tert-butyl-calix[6]arene, and their selectivity towards uranium(VI) ions is studied as a function of pH value, ionic strength and competing ions by means of batch experiments. Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is used to determine complex formation constants. The reaction mechanisms are discussed. As competing ions, Na⁺, Ca²⁺, Mg²⁺ and Fe³⁺ as well as SO₄ ^2- are studied, that occur typically in mine waters. Furthermore, the reversibility of the uranium binding is evaluated. The results are compared with those obtained for the corresponding non-fixed calixarenes [3].
The new technique for the remediation of uranium contaminated waters is also applicable for lower contamination levels ([UO₂ ²⁺] < 1x10^-6 M) and is especially suitable for smaller remediation objects. The applicability of this separation principle to further actinides is expected.

[1] Shinkai, S., Koreishi, H., Ueda, K., Arimura, T., Manabe, O.: Molecular Design of Calixarene-Based Uranophiles which Exhibit Remarkably High Stability and Selectivity. J. Am. Chem. Soc. 109, 6371 (1987).
[2] Nagasaki, T., Shinkai, S.: Synthesis and Solvent Extraction Studies of Novel Calixarene-based Uranophiles Bearing Hydroxamic Groups. J. Chem. Soc., Perkin Trans. 2 (7), 1063 (1991).
[3] Schmeide, K., Barz, B., Heise, K.H., Bernhard, G., Gloe, K.: Solvent Extraction of Uranium(VI) by Calix[6]arene. In: FZR-318, Annual Report 2000 (Th. Fanghänel, ed.). Forschungszentrum Rossendorf, Institute of Radiochemistry, Rossendorf 2001, p. 17.

There is ample evidence from groundwaters, river waters, lakes or seawater that colloids influence the transport behavior of contaminants such as As, Pb, Cu, Zn, actinides, fission products, hydrophobic organics etc. Little efforts have been made to elucidate the role of colloids in mine waters. We studied mine waters of very different nature for their colloid-chemistry.
Very stable Fe(III) oxyhydroxy sulfate colloids were found in acid rock drainage (oxic acidic pore waters, pH < 3). The particle size was < 5 nm, the colloid concentration reached the g/l range. Mineralogically, the particles were a mixture of hydronium jarosite and schwertmannite. As and Pb showed a high tendency to adsorb onto these particles. Quite a different type of colloids was found in the oxic "bulk waters" of mines as for instance in tunnel waters (near-neutral pH). The particles were composed of oxyhydroxides of Fe(III) and Al, the particle size was 100 to 300 nm, the particle concentration was about 1 mg/l, the colloids were unstable, i.e. they tended to aggregate. Important colloid-borne contaminants were As, Cu, Zn, Pb, Po. Uranium(VI) adsorption is normally supressed due to the formation of uranyl carbonato complexes in such "bulk waters". The flooding of mines can be regarded as the dilution of acidic pore waters to form "bulk waters". Huge amounts of iron(III) particles with a size of 100 to 300 nm are formed under such conditions. The adsorption of trace elements rises drastically when the pH reaches the near-neutral region. Uranyl adsorption to the iron(III) particles is neither supressed by acidity nor by uranyl carbonate complexation in the pH region 4 to 6. Therefore most of the uranium(VI) is colloid-borne in waters of the transition type; scavenging, colloid aggregation and sedimentation can result in the immobilization of uranium in such waters ("natural attenuation").

Inorganic colloids in mine waters are able to influence trace heavy metal transport. In oxic waters they mainly result from the formation of oxyhydroxides and oxyhydroxy sulfates of Fe(III) and Al due to the oxidation of Fe2+ and the hydrolysis of Fe3+ and Al3+. However, the colloid inventories and the colloid properties depend on the mine wa-ter type. Acidic pore waters (pH < 3) contain large amounts (g/l range) of relatively stable ultrafine (< 5 nm) iron(III) oxyhydroxy sulfate particles which most probably consist of a mixture of hydronium jaro-site (HFe3(SO4)2(OH)6) and schwertmannite (Fe8O8(OH)6SO4). Arse-nic and lead tend to be adsorbed onto these colloids. Waters of higher pH (pH > 4) contain smaller amounts (mg/l range) of Fe- and Al-rich colloids of 100 to 300 nm that are unstable. They carry elements such as As, Pb, Zn, Cu, Po, Th, Ac. These trace heavy metals can be scavenged by the colloids and can be immobilized due to colloid coagulation and sedimentation ("natural attenuation"). In the pH range from 4 to 6 (flooding waters) also U(VI) is adsorbed onto the colloidal particles since their adsorption is neither prevented by high acidity nor by the formation of uranyl carbonato complexes. Also U(VI) can be scavenged and immobilized in this pH range. However, in "bulk wa-ters" of pH > 6 such as tunnel waters the adsorption of U(VI) to the colloids is normally prevented by carbonate complexation

The OECD Main Steam Line Break (MSLB) Benchmark was defined to validate the thermal-hydraulic system codes coupled with three-dimensional neutron kinetic codes. The reference problem is a MSLB in a pressurized water reactor (PWR) at end of cycle (EOC). The analyses were performed with the three-dimensional core model DYN3D, the thermal-hydraulic system code ATHLET and the coupled code DYN3D/ATHLET. The results of the DYN3D and ATHLET simulations based on the specification are compared with the results of other participants in the final OECD reports. The effect of the thermal-hydraulic nodalisation of the core, i.e. the number of coolant channels, and the influence of the coolant mixing inside the pressure vessel are studied in the paper. Calculations with a reduced number of coolant channels are performed often in coupled calculations for saving
computational time. Results of a 25-channel model were compared with the 177-channel calculation (1 channel/assembly). The results for global parameters like nuclear power show only small differences for the two models, however the prediction of local parameters such as maximum fuel temperatures requires a detailed thermal-hydraulic modeling. The effect of different coolant mixing within the reactor pressure vessel is investigated. It is shown that the influence of coolant mixing mitigates the accident
consequences when three-dimensional neutron kinetics is applied. In case of point kinetics, coolant mixing leads to an opposite effect. To profit from the three-dimensional core model, a realistic description of the coolant mixing in the coupled codes is a topic of further investigations.

Ex-vessel neutron dosimetry at NPP with VVER was used for validation of 3D absolute neutron fluence calculations. As second step of the VVER-1000 Balakovo-3 Ex-vessel Exercise, an analysis of calculational results has been performed. The reference experimental data - End-Of-Irradiation activities AEOI - were used as criteria of validation. The purpose of the research was to perform an intercomparison of independent calculational results and comparison with reference data of the full-scale VVER-1000 ex-vessel experiment. New and improved results of calculations analysed in the paper were run with codes and applied libraries DORT/BUGLE-96, DORT/EURLIB-6, DORT/ABBN-93 (and ABBN-93 modifications), TRAMO/ENDF/B-VI, MCNP/ENDF/B-VI. Calculated pure 3D or 3D synthesis multigroup neutron fluence rates in positions of experimental capsules provided by every calculator were used as basic calculational information. As first step of their comparative analysis a study was done of the used calculation input data prepared on the base of the same reactor information. For example, a difference of neutron source model details may be a reason of some discrepancy of results obtained by similar calculational procedures. Aspects of the influence of different dosimetry cross sections and local power history on the calculation of AEOI from calculated spectra were investigated. The analysed dosimetry cross section libraries were IRDF-90v2, JENDL-D99, RRDF-98 and ENDF/B-VI based BUGLE-96 responses. Final C/E values were based on AEOI. The C/E values for threshold dosimetry reactions 237Np(n,f), 93Nb(n,n'), 238U(n,f), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a), which are widely used in reactor pressure vessel dosimetry for fast neutron fluence evaluation, showed on the whole the expected agreement (better 20 %). It was found that the C/E data for the Balakovo-3 exercise in application to the 237Np(n,f) and 93Nb(n,n') reactions may be improved in case of using JENDL-D99 library. Another new aspect of the Balakovo-3 research is an analysis and intercomparison of calculational and experimental results for (n,g) dosimetry reactions. Different type (n,g) detectors were irradiated in cadmium. The obtained reaction rates characterize the distribution of epithermal neutrons. A comparison of the reaction rates, for example, for reactions 93Nb(n,g), 69Co(n,g) and 103Ag(n,g) in case of DORT/BUGLE-96 calculations has shown a coincidence of experiment and calculation data within ± 11 %. For one ex-vessel position where bare (n,g) detectors were irradiated thermal neutron parameters were evaluated and compared.

Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was used to study the properties of uranium complexes (emission spectra and fluorescence lifetimes) formed by the cells of the three recently described eco-types of Acidithiobacillus ferrooxidans. The results demonstrated that these complexes have different lifetimes which increase in the same order as the capability of the strains to accumulate uranium. The complexes built by the cells of the eco-type II were the strongest, whereas, those of the eco-types I and III were significantly weaker. The emission spectra of all A. ferrooxidans complexes were almost identical to those of the uranyl organic phosphate compounds. The latter funding was confirmed by infrared spectroscopic analysis.

Material of a mine waste dump of Kupferschiefer mining was investigated in column and equilibrium experiments in closed vessels over 64 days and 90 days, respectively. The de-ployed solids are composed of silicate phases, calcite, dolomite, gypsum, and a few percent of residual sulfides, already indicating a depletion of the karstifyable material and in particular a dedolomitization. The development of the solution composition at the columns outflow is characterized by a steady increase of alkalinity with a striking transient maximum, succeed-ing draw back and equilibration. In connection with an increasing mole fraction of magnesium in solution this phenomenon is interpreted as consequence of dedolomitization and depicted in abinary solubility diagram according to Lippmann (1980). In calcium rich pore waters (due to gypsum dissolution) dolomite dissolves incongruently precipitating calcite. Such compli-cated reaction paths are usually not identified by "crude" batch experiments. Moreover it could be shown that the formation of preferred flow paths may even affect the solution com-position in particular cases. In these experiments an estimation of transport parameters was not yet carried out, but is planned for the future to apply reactive transport codes for model-ing these processes.

The ability of transport codes ANISN, DORT, ROZ-6, MCNP and TRAMO, as well as nuclear data libraries BUGLE-96, ABBN-93, VITAMIN-B6 and ENDF/B-6 to deliver consistent gamma and neutron flux results was tested in calculation of an one-dimensional cylindrical model consisting of a homogeneous core and an outer zone with a single material. Model variants with H2O, Fe, Cr and Ni in the outer zones were investigated. The results are compared with MCNP-ENDF/B-6 results. Discrepancies are discussed. The specified test model is proposed as a computational benchmark for testing calculation codes and data libraries.

Radiation embrittlement of pressure vessel steel in mixed neutron-gamma fields is mostly determined by neutrons, but in some cases also by gamma-radiation. Depending on the reactor type, gamma radiation can influence evaluations of lead factors of surveillance specimens, effect the interpretation of results of irradiation experiments and finally, it can result in changed pressure vessel lifetime evaluations. This work aims to facilitate for some reactor types the evaluation of the importance of gamma radiation for embrittlement studies. Absolute neutron and gamma fluence spectra had been calculated for two core loading variants of the Russian PWR type VVER-1000, for a German PWR of Konvoi-Type and for a German BWR. Based on the calculated spectra several fluence integrals and radiation damage parameters were derived for the region of the midplane azimuthal flux maximum for different radial positions between the core and the biological shield, particularly, the inner and outer PV walls, the ¼ PV thickness and the surveillance positions. The relative contributions of gamma radiation to the sums of gamma and neutron contributions are of special interest. As damage parameters the displacements per atom of iron are given separately for neutrons and gammas as well as some rough estimations of the numbers of freely migrating defects. To get some notion about the uncertainty of the obtained dpa, the calculations were performed using different dpa cross section evaluations. Additionally, gamma produced dpa were calculated by means of the Monte Carlo code EGS.
Another parameter of practical interest for pressure vessel dosimetry, the contribution of photofission to the total number fissions, was calculated for the detector reactions 237Np(n,f) and 238U(n,f).
Most of the calculations were performed using a 3D synthesis of 2D/1D-flux distributions obtained by the DORT code with the BUGLE-96 library. To increase the reliability of the evaluations some of the calculations were repeated by different laboratories. For two reactors the influence of the group approximation on the calculation results was investigated by parallel calculations with the continuous energy Monte Carlo code MCNP using nuclear data from the library ENDF/B-VI.
The results were compared and the reasons of found discrepancies were discussed.

The Forschungszentrum Rossendorf (FZR) e.V. is building a new large-scale test facility for thermal hydraulic single effect tests, named TOPFLOW. The acronym stands for Transient Two Phase Flow Test Facility. It will mainly be used for the investigation of generic and applied steady state and transient two phase flow phenomena in power- and process industries. Main research activities are the investigation of:

· transient flow regimes in horizontal, vertical and inclined tubes,
· the dynamic behaviour of interphase areas in gas-liquid flows,
· critical mass flows and oscillations during depressurization of chemical reactors,
· natural convection in large pools with local heating,
· natural convection in parallel channels and feed pipes and
· condensation phenomena (e.g. in emergency and isolation condensers, WWER steam generators).
It is FZR strategy to use TOPFLOW as a central experimental basis for the nuclear competence centre, rejoining FZR, the Technical University of Dresden (TUD) and the University of Applied Sciences Zittau-Görlitz (HTW) and to offer it to working groups throughout Europe. They will be invited to come to Rossendorf with their ideas and to perform their experiments here making use of the parameters (power, water and steam mass flow, pressure range, measuring instrumentation) and the multipurpose character of the test facility.