Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Due to their strong ability for complex and colloid formation, humic acids influence the speciation and consequently the migration behavior of actinide ions in the environment. In order to perform a trustworthy risk assessment for the conception of future nuclear waste repositories as well as for the remediation of former uranium mining and milling areas, reliable thermodynamic data on the interaction of uranium with humic acids under geogenic conditions are necessary.
The U(VI) complexation by humic acids was already the subject of a number of previous investigations. However, these studies were predominately performed in the acidic pH range, were the hydrolysis of the uranyl ion can be neglected. Only few studies exist on the interaction of U(VI) with humic acids under neutral pH conditions where ternary U(VI) humate complexes are formed.
In the present study we investigate the complexation of U(VI) by purified Aldrich humic acid at pH 7 under exclusion of CO2 ([HA]: 2 mg/L; [U]: 1·10-6-1·10-5 M, I: 0.1 M NaClO4). Under the studied experimental conditions and in absence of humic acid, U(VI) occurs in form of the following species: UO2OH+, UO2(OH)2(aq), (UO2)3(OH)5+, (UO2)4(OH)7+. The speciation is dominated by 62-73 % of (UO2)3(OH)5+. Based on this speciation, the formation of ternary uranyl hydroxy humate complexes is assumed. For determination of the U(VI) and humic acid speciation in solution we apply the conventional time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrafast pulses, respectively. For identification and quantification of the U(VI) species in solution, fluorescence spectra were measured for the relevant U(VI) hydrolysis species. The experimental data are evaluated applying the metal ion charge neutralization model [1], which describes the metal ion complexation by humic acids.

[1] Kim, J.I., Czerwinski, K.R.: Complexation of Metal Ions with Humic Acids: Metal Ion Charge Neutralization Model. Radiochim. Acta 73, 5 (1996).

Humic acids (HA) comprise an important part of natural organic materials. By the formation of soluble complexes with radionuclides, HA can affect the transport of these contaminants. Therefore, the understanding of the impact of HA on the actinide migration in geologic environments is essential for a reliable safety assessment of nuclear waste disposal sites. In the present study we investigated the influence of HA on the U(VI) sorption onto kaolinite. Kaolinite represents a well-defined model substance for clay-rich host formations.
Batch experiments were combined with EXAFS spectroscopy to obtain molecular-level information on the interaction of U(VI) with HA (14C-labeled) and kaolinite (KGa-1b) in natural systems.
From our batch experiments it is known that the sorption of U(VI) on kaolinite is influenced by experimental conditions such as pH, U(VI) concentration, CO2 and HA presence. U(VI) sorption increases with pH up to pH 7.5, then it decreases. In the absence of CO2, no decrease is observed. In the presence of CO2 HA effects U(VI) adsorption onto kaolinite over the entire pH range. At pH < 5 the presence of HA enhances the U(VI) uptake relative to the HA-free system because the adsorbed HA forms additional binding sites for U(VI). In the pH range between pH 5 and pH 8.5 the U(VI) sorption decreases in the presence of HA due to desorption of HA from the kaolinite surface resulting in the formation of dissolved U(VI)-HA complexes. At pH > 8.5 uranium sorption increases again relative to the HA-free system.
Previously, EXAFS spectroscopy was applied to study the structure of the U(VI) adsorbed on kaolinite [1], but no EXAFS was measured in the system U(VI)-HA-kaolinite. Therefore, we performed EXAFS measurements with U(VI)-HA-kaolinite sorbats in order to characterize the surface complexes of U(VI) in the presence of HA. Results of the spectroscopic measurements are interpreted and compared with the EXAFS results in the binary system without HA to obtain the information on the influence of HA on the near-neighbor surrounding of U(VI) in the kaolinite surface complexes.

[1] Amayri et al.: EXAFS - Untersuchungen zur U(VI) - Sorption an Kaolinit, presentation on BMWA Project Meeting, Saarbrücken, May 2004.

An electrochemical cell was developed for in situ investigations of radioactive materials using X-ray absorption spectroscopy. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell had to be gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement in order to avoid any gas release.

Microbes are widely distributed in nature and they can strongly influence the migration of actinides in the environment. Microorganisms in concentrations of 1x103 to 5x106 cells ml-1 were estimated by Pedersen et al. in the aquifer system of the Äspö Hard Rock Laboratory (Äspö HRL) in Sweden. The number of sulfate-reducing bacteria (SRB) was between 101 to 2x104 cells ml-1. We investigated the interaction of the SRB Desulfovibrio äspöensis, DSM 10631T, with plutonium. The 242Pu was provided as a mixture of ca. 46% Pu(VI) and ca. 34% Pu(IV)-polymer. Interactions between bacteria and plutonium in mixed oxidation states were not yet intensively investigated.
In this study, accumulation experiments were performed in order to obtain information about the amount of the Pu bound by bacteria in dependence on the contact time and the [Pu]initial at pH 5. We used liquid-liquid-extractions and absorption spectroscopy to determine the Pu speciation. In agreement with the results obtained with U(VI) [2] and Np(V), we found a strong dependence of the amount of accumulated Pu with [Pu]initial. Based on our results and taking into consideration the findings of Panak et al. [3], we developed a model describing the interaction of Pu(VI) and Pu(IV)-polymers with D. äspöensis. In a first step, the Pu(VI) and Pu(IV)-polymers are bound to the biomass. The Pu(VI) is reduced to Pu(V) due to the activity of the cells within the first 24 h of contact time. Most of the formed Pu(V) dissolves due to the weak complexing properties. The dissolved Pu(V) disproportionates to Pu(IV) and Pu(VI) which are then interacting with functional groups of the cell surface structure. Indications were found also for a penetration of Pu species inside the bacterial cells.

[1] Pedersen, K.: Microbial processes in radioactive waste disposal. SKB Technical Report TR-00-04 (2000).
[2] Moll, H.; Merroun, M.; Stumpf, Th.; Geipel, G.; Selenska-Pobell, S.; Hennig, C.; Roßberg, A.; Bernhard, G.: Interaction of Desulfovibrio äspöensis with Actinides, presented at the MIGRATION’03, Gyeongju, Korea (2003).
[3] Panak, P. J.; Nitsche, H.: Radiochim. Acta 89, 499 (2001).

This work was funded by the BMWi under contract number: 02E9491.

Naturally occurring aquatic humic substances (humic and fulvic acids) are known to effect the speciation and thus, the migration behavior of actinide contaminants in environmental systems due to their complexing and redox properties and their ability to form colloids. Therefore, to understand and predict the mobility of actinides in natural aquifer systems, amongst others, information on their redox stability in the presence of humic substances is necessary.
In the present work, the time dependence of the reduction of Np(V) to Np(IV) by humic substances of varying functionality has been studied under anaerobic conditions between pH 3.5 and pH 9. Synthetic humic acids with pronounced redox functionality (type Cat-Gly and Hyd-Glu) [1] were studied in comparison to natural humic substances (Aldrich humic acid, Kranichsee fulvic acid). For Np speciation in solution liquid-liquid extraction, laser-induced photoacoustic spectroscopy (LIPAS), NIR absorption spectroscopy, and ultrafiltration were applied. In comparison to the natural humic substances, the synthetic humic acids lead to a much stronger reduction of Np(V) to Np(IV) [2]. The Np(IV) formed in the course of the experiments is stabilized as Np(IV) humate. The tetravalent oxidation state remained constant for several months.
The redox capacities of the synthetic humic acids, which are significantly higher than those of the natural humic substances, can be attributed to their higher phenolic/acidic OH group contents compared to natural humic substances. The dominating role of phenolic/acidic OH groups for the reduction of Np(V) by humic substances could be verified applying a synthetic humic acid with blocked phenolic/acidic OH groups (type Hyd-Glu-PB). Furthermore, the influence of NO3- on the Np(V) reduction by humic substances was studied.
The results have shown that by application of the synthetic humic acids with distinct redox functionalities actinides can be stabilized in lower oxidation states, e.g. in complexation and sorption studies.

[1] Sachs, S., Schmeide, K., Brendler, V., Krepelová, A., Mibus, J., Geipel, G., Heise, K.H., Bernhard, G.: Investigation of the Complexation and the Migration of Actinides and Non-radioactive Substances with Humic Acids under Geogenic Conditions. Complexation of Humic Acids with Actinides in the Oxidation State IV Th, U, Np. FZR-399, Wissenschaftlich-Technische Berichte, Forschungszentrum Rossendorf, Dresden 2004.
[2] Schmeide, K., Geipel, G., Bernhard, G.: Study of the Neptunium(V) Reduction by Various Natural and Synthetic Humic Substances. In: FZKA 7070, Wissenschaftliche Berichte (G. Buckau, ed.). Forschungszentrum Karlsruhe, Karlsruhe 2005, 19-31.

The diffusion of humic acid (HA) in Georgia kaolinite KGa-1B was studied. The compacted clay plug was conditioned with a 0.01 M NaClO4 + 1 mM NaN3 solution at pH 5.2. The effective porosity ε and the effective diffusion coefficient De of water were determined using tritiated water (HTO). A synthetic 14C-labeled HA type M42 with a concentration of 11.0 mg/L and a specific activity of (17.0 ± 0.5) MBq/g was used as tracer. We applied a steady-state through-diffusion technique with constant gradient. The particle size distribution of HA was determined by ultrafiltration.

The migration of HA in compacted clay is governed by diffusion. However, compared to an ionic tracer some characteristics are observed. The De values found for HA (2·10^13 to 2·10^12 m^2/s) are about two to three orders of magnitude lower than that of HTO. Likewise the rock capacity factor α(HA) amounts to only 10 % to 50 % of ε. The spatial extension of the humic colloids constricts their mobility in the narrow pore space thus increasing the tortuosity of the diffusion path and decreasing the pore volume accessible for HA. This phenomenon is referred to as size exclusion effect. In [1] a significant adsorption of HA on KGa-1B was found (Kd = 680 ml/g at pH 5.2) which would result in a value for α above unity. Obviously, the size exclusion dominates the HA migration.
The particle size distributions of the high and the low concentration reservoir differ significantly. The mean particle size shifts from about 50 kD in the high to less than 1 kD in the low concentration reservoir. Only small particles are able to pass the pore system. This is in agreement with the HA distribution in the clay plug where most of the tracer was found at the high concentration boundary.

Brain imaging techniques have provided substantial insight into the pathophysiology of hepatic encephalopathy (HE). Magnetic resonance imaging gave hint to the fact that there is an increased deposition of manganese especially in the basal ganglia. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) showed that the preference of the basal ganglia might be due to differences in regional cerebral blood flow and an additional redistribution of blood flow from the cortex to subcortical regions in cirrhotics. PET studies using ammonia as tracer showed that the cerebral metabolism of ammonia and the permeability of the blood brain barrier for ammonia is increased in cirrhotic patients compared to healthy controls. The regional ammonia supply is in accordance with the regional blood flow. In accordance with these findings fluorodesoxyglucose-PET-studies of the brain in cirrhotics showed characteristic alterations of glucose utilisation in the patients with a relative decrease of the glucose utilisation of the cingulate gyrus, the frontomedial, frontolateral, and parieto-occipital cortex, while the glucose utilisation of the basal ganglia, the hippocampus, and the cerebellum was relatively increased. These findings fit well with the clinical characteristics of early stages of HE such as deficits in attention, visuo-spatial orientation, visuo-constructive abilities, motor speed, and accuracy.

BACKGROUND AND PURPOSE: Hypoxia of clonogenic tumor cells is a major reason for radioresistance and hence local failure in radiotherapy. The objective of the present study was to test the efficacy of the hypoxic cell sensitizer isometronidazole (ISO) during fractionated irradiation in two different human squamous cell carcinomas. MATERIAL AND METHODS: Local control was evaluated for FaDu (radiobiological hypoxic fraction [rHF] 7%) and GL tumors (rHF 0.1%) after single-dose (SD) irradiation under ambient conditions and after 30 fractions within 6 weeks (30 f/6 w). ISO was applied 60 min before SD irradiation at a concentration of 100 mg/kg body weight (b.w.) or 750 mg/kg b.w. in both tumors. During fractionated irradiation, ISO was applied daily 60 min before each fraction (100 mg/kg b.w., in FaDu also 750 mg/kg b.w.). RESULTS: 100 mg/kg b. w. ISO did not improve local control after SD irradiation or 30 f/6 w in both tumor models. Application of 750 mg/kg b. w. ISO significantly decreased the SD-TCD(50) in FaDu tumors (dose-modifying factor [DMF] = 1.2; p = 0.01) but not in the better oxygenated GL tumor. ISO at 750 mg/kg b.w. also significantly improved local control of FaDu tumors after 30 fractions in 6 weeks (DMF = 1.2; p = 0.01), indicating that hypoxic clonogenic cells in FaDu tumors are not only present before start of irradiation but also limit the efficacy of treatment during a fractionated course of radiotherapy. CONCLUSION: ISO at a concentration of 750 mg/kg b.w. shows an efficacy as a hypoxic cell sensitizer in severely hypoxic FaDu tumors but not in less hypoxic GL tumors. This supports the principle of hypoxic cell sensitization and improvement of local control of hypoxic tumors by nitroimidazole derivatives. However, doses of 750 mg/kg b. w. before each fraction may be difficult to achieve in the clinical situation. This, in light of the fact that other well-tolerable hypoxic cell sensitizers such as nimorazole with clinically proven efficacy at daily oral doses of < 3 g are available, limits the potential usefulness of ISO for radiation oncology.

The Stille reaction with 4-[(18)F]fluoroiodobenzene as a novel approach for the synthesis of radiotracers for monitoring COX-2 expression by means of PET has been developed. Optimized reaction conditions were elaborated by screening of various catalyst systems and solvents. By using optimized reaction conditions (18)F-labelled COX-2 inhibitors [(18)F]- and [(18)F]- could be obtained in radiochemical yields of up to 94% and 68%, respectively, based upon 4-[(18)F]fluoroiodobenzene.

Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 ((18)F) by conjugation with N-succinimidyl-4-[(18)F]fluorobenzoate ([(18)F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [(18)F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [(18)F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo.

Surface chemistry during wet chemical etching in alkaline KOH solution and dry etching in SF6/O2 plasma of high dose Ga+ implanted Si has been investigated by means of secondary ion mass spectroscopy (SIMS) and x-ray induced photoelectron spectroscopy (XPS). During wet chemical etching in a KOH/H2O solution a thin layer of GaOx of < 1 nm thickness is formed, which has been investigated more in detail by angle-resolved XPS.. In the case of dry reactive ion etching the surface chemistry is quite different. In this case a more enhanced oxidation of Ga takes place due to the high reactivity of atomic oxygen from the SF6/O2 plasma. SIMS results show that during RIE a Ga rich surface layer forms and therefore an enhanced Ga oxidation takes place leading to a thicker GaOx layer compared to wet chemical treatment. XPS depth profiling points at a stoichiometry of nearly completely oxidized Ga (Ga2O3) layer free from Si with a thickness of about 5 ... 10 nm. The etch rate lowering in Ga+ as- implanted silicon is ascribed to the formation of gallium oxide at the Si surface during the etch processes.

B-C-N thin films of a wide composition range were deposited by reactive d.c. magnetron sputtering of targets with different B/C ratio in an Ar/N2 atmosphere. The bonding characteristics of these amorphous films were investigated by Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy. The results of both characterisation methods indicate that real ternary compounds in which all three elements are bound to each other are only formed when at least one element has a low concentration in the film (and therefore could be considered as an impurity). Otherwise the deposited material tends to a phase separation into binary compounds and single phases.

Low resistance spin-dependent tunnel junctions are investigated for read-head applications due to their large tunneling magnetoresistance effect and low junction resistance-area product. Typical full junction structures can be Ta 70Å/NiFe 70Å/MnIr 80Å/CoFe 35Å/Hf(x)Al(y)O(z) t/CoFe 35Å/NiFe 40Å/Ta 30Å, with t around 10 Å, annealed to temperatures up to 250ºC. We analysed simpler structures with RBS experiments at a grazing angle of incidence in order to study the junction only. Heavy ion- and He-ERDA experiments were also done. The composition of the HfAlO barrier is determined, showing that a slightly substoichiometric oxide is formed. On annealing at 240ºC, the interfaces of the barrier become sharper. TEM results confirm that the barrier is continuous after annealing. This is related to an increase in the tunnel magnetoresistance signal from 4% to 13.5% after annealing.

A study of the mixing of a deborated slug during start-up of the first coolant pump in VVER-1000 type reactors was performed with the commercial CFD package CFX-5.7 using experimental results of the 1:5 scaled test facility. The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor CFX-5 and contains 2.5 Mio. tetrahedral elements. The CAD geometry and the grid model include the inlet nozzles, the downcomer incl. spacer elements and the lower plenum with the elliptical sieve plate and internals. Parts of the complicated lower plenum structures were modeled with the porous media approach in CFX-5, which uses directed resistance coefficients.

The output of the Best Practice Guidelines for optimizing the numerical studies of boron dilution transients in different reactor types was used in the numerical simulation. The discretisation scheme in time was set to second order Euler and in space to High Resolution. The SST turbulence model was taken.

The modeled deborated slug first arrives at the core inlet of the reactor pressure vessel in the neighboring areas at the outer case of the starting loop. Later the slug is almost homogenously distributed over the core inlet plane. The minimum averaged deboration value in the experiment and the CFD calculation is in good agreement when using a constant wall temperature (72%). The existing time offset in the numerical calculation could not been clarified.

In this work, junctions with reduced Hf coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (110) texture that can be the origin of lower Hf and coercivity when compared with CoFe. Junctions processed down to 2x4 um2 with 40Å thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R x A ~400 Ohm um2), Hc of ~10 Oe and Hf of ~2 Oe. CoFe-based junctions (R x A ~500W Ohm um2) have lower TMR (~35%) and larger Hf (~5-6 Oe) and Hc (~12-14 Oe). Local chemical composition analysis of the cross section indicated Fe-O segregation without Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones.

A PtMn/NiFe exchange bias system with an exchange bias field of 180 Oe was magnetically patterned by means of a low fluence focused ion beam. A 1 µm wide stripe pattern with the long axis (1000 µm) oriented parallel to the exchange bias field direction has been irradiated by 2x10¹⁴ Ga⁺/cm². In the irradiated area the coercivity is reduced and the exchange bias field vanishes, while in the nominally non-irradi-ated region between the irradiated stripes the exchange bias field is reduced to approximately 35 Oe. This reduction is attributed to the magnetic coupling of the irradiated stripes to their intervening non-irradiated regions. Magnetic domain imaging by means of Kerr microscopy and magnetic force microscopy support this interpretation.

To improve the performance of critical part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments mixing PIII and ion nitriding processes. A combination of high pressure (4 x 10(1)Pa), moderate temperature (up to 450degreesC) glow discharge nitriding with low pressure (8 x 10(-2)Pa) and low DC bias voltage ion nitriding (or DC PIII) was implemented. Depending on the particular conditions of the treatment and the depth probed, mixed phases of gamma(N) and epsilon were measured in the treated SS304 steel sample. This near surface modification resulted in an improved hardness (up to a factor of 2.7 x) of the sample which could also enhance its wear properties. Surface modification of T16Al4V alloy and SS304 steel by a combination of PIII and subsequent ion nitriding was investigated as well. Nitrogen ions were implanted into the specimens at 15 keV and then ion nitrided at ! low pressure (7 x 10(-2)Pa) with a bias of -800 V. Compared to the untreated samples, the hardness of Ti6Al4V alloy and the steels could be improved significantly. AES results indicated high retained doses in both samples, confirming the high efficiency of this hybrid process.

An apparatus for laser-induced breakdown detection (LIBD) was established, which is aimed at in-situ detection of aquatic colloids of a particle size down to < 50 nm and a particle concentration down to the ppt range. LIBD is based on the generation of dielectric breakdown events on individual colloid particles by pulses of a focused laser (cf. [1]). A diode pumped Nd:YAG laser is used as light source and is operated at maximum power for stability reasons. The pulse energy is controlled by a combination of two Fresnel rhombs and a calcite polarizer. The beam is focused into a quartz cell containing the particle suspension to be analyzed. The breakdown events are simultaneously observed by a CCD camera and by piezoelectric detectors.

Polystyrene latex standards of different particle size were diluted with de-ionized water (Membrapure) to mass concentrations of the ppt and ppb range. These solutions were used for the calibration of the LIBD system.

Two particle systems of environmental relevance were studied by LIBD.
First, a nearly particle-free spring water of a small stream was investigated. Photon correlation spectroscopy, an alternative technique of particle detection, was too insensitive to find particles in this water. Both the raw sample of this stream water and centrifugates/filtrates of the water could be successfully investigated and consistent results were provided by LIBD. Second, uranium(IV) colloids were generated in a glove box (N2 atmosphere) by cathodic reduction of uranium(VI) followed by the successive increase of the pH by coulometric titration. The formation of these colloids was traced by LIBD.

[1] Walther, C., Bitea, C., Hauser, W., Kim, J.I. and Scherbaum, F.J.
Laser Induced Breakdown Detection for the Assessment of Colloid Mediated Radionuclide Migration. Nucl. Instr. and Meth. B 195 (2002) 374-388

Feasibility study of wrist watched based radiation survey meter

Mechanische und optische Anforderungen an die Cavity des FEL

A start-up procedure for natural-circulation Boiling Water Reactors is illustrated. The procedure, developed in order to avoid flashing-induced instabilities at low pressures and low powers, does not require any additional system. The reactor vessel is pressurized while steam is produced outside the core and riser sections. In this way, the firsts stage of the pressurization takes place with the reactor operating in single-phase natural-circulation conditions, thus without occurrence of flashing-induced flow oscillations. At the same time, a smooth steam production and pressurization of the system is achieved. A simple analytical model is applied to the ESBWR of General Electric to have a first impression on the order of magnitude of the parameters involved and to verify whether the start-up of the reactor can be achieved in reasonable times. The feasibility of the procedure is then studied in details by means of the ATHLET code (Lerchi and Austregesilo, 2003), developed by GRS (Germany). This code has been successfully qualified against low-pressure flashing-induced instabilities within the framework of the EU project NACUSP

Colloids can either stimulate or retard the transport of actinides. Environmental colloids are formed by a variety of mechanisms. The most important one is the precipitation of secondary phases. There have already been several publications on colloid generation within water bod-ies due to chemical reactions after the mixing of waters of different chemical composition or after access of air. Much less information exists about a different mechanism of colloid for-mation in the nature – the direct production of secondary mineral colloids at the water-rock interface by the weathering of rock material.

The formation of colloids during the weathering of ground phyllite from an abandoned ura-nium mine and the sorption of uranium(VI) onto these colloids were studied. Centrifugation and ultrafiltration were applied. A method to differentiate between the primary mineral col-loids of the phyllite and the precipitated secondary mineral colloids was developed.

Significant amounts of colloids of the 101 to 102 nm size class were found in the suspension of ground phyllite after weathering times of 87 h to 792 h. Considerable fractions (up to 10 mg/L) of these 101 to 102 nm colloids consisted of secondary minerals. The following compo-sition of the freshly precipitated colloids is to be expected: Ferihydrite, aluminosilicates, amorphous Al(OH)3, gibbsite, possibly iron silicates, possibly iron-alumino silicates. It should be emphasized that a significant fraction of the secondary mineral colloids was composed of iron(III) compounds which is of relevance for the sorption behaviour of these colloids. A more detailed mineralogical characterization of the colloids is underway. The 101 to 102 nm secondary mineral colloids were relatively stable and remained in colloidal suspension over longer periods of time.

The direct formation of secondary mineral colloids at the mineral-water interface by the weathering of rock material is an alternative to the well-known mechanism of colloid forma-tion by the mixture of different water bodies or by aeration of a water body. This direct mechanism of colloid production occurs during the weathering of freshly crushed rock in the unsaturated zone as for instance crushed rock in mine dumps. Colloids produced by this mechanism can influence the transport of actinides since they have a large specific surface area and a high sorption affinity for heavy metals. This was demonstrated for uranium(VI).

Information on molecular speciation provides a basis for the reliable assessment of actinide migration in the environment. We use several methods for the separation of colloids from liquids (e.g. ultracentrifugation, ultrafiltration) in combination with spectroscopic techniques (EXAFS, ATR-FTIR, Mössbauer) and modeling of surface complexation reactions. This enables us to investigate the speciation of colloid-borne uranium in waters occurring in or escaping from abandoned uranium mines during the remediation process. Mine flooding was simulated on a 100 L scale by mixing acid mine water of elevated U concentration with oxic, near-neutral groundwater until pH~5.5 was reached. The freshly formed colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, silica, and carbon compounds. EXAFS analysis at the U-LIII absorption edge suggested a bidentate surface complex of UO22+ on FeO6 octahedra, but two minor backscattering contributions in close vicinity to the absorber remained unexplained. Since only Al could be excluded as backscattering atom, we studied U sorption on Fh at pH 5.5 in presence and in absence of sulfate, silicate, and atmospheric CO2 to clarify the bond structure.

EXAFS showed the unknown backscattering contributions in all the sorption samples regardless of the presence or absence of the tested components. Contrary to structural models proposed in the literature, bidentately complexed carbonate ligands do not explain our experimental EXAFS data. But ATR-IR spectra showed that U-carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. We propose a new structural model including exclusively Fe, H, and O atoms in which the bidentately bound UO22+ is oriented in a way that yields a distance of ~2.9 Å to the O atom of an adjacent, edge-shared FeO6 octahedron. This model predicts a second Fe shell at ~4.35 Å which tightly fits the experimental data.

In summary, uranium may form different sorption complexes with colloidal ferric hydroxides: a binary bidentate uranyl complex with modified orientation, and ternary U-carbonato complexes with monodentate linkage of the carbonate ligand. The affinity of carbonate and uranyl to form such complexed surface species will increase when sorption sites with high affinity, as provided by colloidal Fh, are present.

The renewed interest on MSR systems has stimulated the development of computational tools assigned for analysis and simulation of MSR systems. The code system is a tool developed at Forschungszentrum Rossendorf for the analysis of burn-up behavior and transient simulation of Molten Salt Reactors. The computing method is based on the coupling between the well-known Monte Carlo transport code MCNP-4C2 and the burn-up code ORIGEN 2.1. In the second part the contribution shows applications of the system DYN3D-MSR dynamics code for Molten Salt Reactors, which is based on FZR two groups diffusion code DYN3D designed for dynamics calculation of light water reactors.

This contribution shows some applications of code HELIOS at Research Center Rossendorf. These are: A cell assembly models of the European Pressurized Water Reactor (EPR), including burnup calculations, with HELIOS Version 1.6, and applications of a typical pressurized water reactors of the type KONVOI with HELIOS Version 1.6 & 1.7 and comparisons with the lattice transport and burnup code CASMO 4. The second part gives remarks what can be done better in future codes.

The MHD activities at FZR are summarized. Main focus is put on applied MHD projects like in crystal growth, metal casting, electromagnetic levitation or metal fibre extraction. For basic research activities, the dynamo project and the studies on seawater flow control are presented.

The basic idea of tailored magnetic field solutions is outlined, and examples from crystal growth and metallurgical applications are given for this approach. The importance of a combined approach is pointed out consisting of numerical simulations and cold liquid metal model experiments.

Um die künftigen Redoxbedingungen, die durch den natürlichen Holzabbau in gefluteten Gruben entstehen, zu charakterisieren, wurde das Wasser eines Hochmoors im Erzgebirge untersucht. Das Redoxpotential im Moorwasser, gemessen mit einer Platinelektrode, sank von der Oberfläche bis in einen Meter Tiefe von etwa 600 mV auf -100 mV. Aus der Tiefenwasseranalyse und der Untersuchung des Sumpfgases, das aus dem Grund extrahiert wurde, errechnete sich ein Redoxpotential von -119  5 mV. Charakteristisch für das stark reduzierende Milieu ist das Auftreten von Methan und Schwefelwasserstoff im Sumpfgas. Aus der Kenntnis dieses Zustands kann für die künftige Situation in der gefluteten Grube die Schlussfolgerung gezogen werden, dass Uran(VI) und Arsen(V) im Laufe der Zeit reduziert werden und als Uran(IV)-Hydroxid und Arsen(III)-Sulfid ausgeschieden werden. Auf diese Weise findet ein natürlicher Reinigungsprozess im Grubenwasser statt.

To characterize the future redox milieu caused by natural degradation of wood in flooded uranium mines the aquifer of a highland bog ground was studied as a natural analogue site. Going from the surface to a depth of one meter in the bog water the redox potential measured with a platinum electrode changes from about 600 mV to -100 mV. From the depth-water analyses and analyses of bog gas extracted from the ground an Eh value of -119  5 mV could be calculated. Methane and hydrogen sulfide were found in the gas characterizing the strongly reducing condition in the bog ground. From that the conclusion for the future mine situation can be drawn that uranium(VI) and arsenic(V) will be reduced and precipitated as U(OH)4 and As2S3. In that way decontamination of the mine water takes place as a consequence of a natural attenuation process.

We determined Sb speciation in 9 soil samples from 6 Swiss shooting ranges using Sb K-edge EXAFS spectroscopy and advanced statistical data analysis methods (ITFA). Despite the high variability in Geology, pH (3.1 - 7.5) and Sb concentrations (1000 - 17000 mg/kg), we found only two species: metallic Sb(0) and Sb(V) forming inner-sphere sorption complexes on Fe oxide surfaces. The relative amount of Sb(0) ranged from 0 to 75 %, the relative amount of Sb(V) ranged from 25 to 100 %. Distribution between the two species was not explained by any of the measured variables. No evidence for Sb(III) was found in the bulk samples. To the best of our knowledge this is the first quantitative determination of the chemical Sb forms in bulk soil samples.

Electroluminescence with power efficiencies larger than 0.1 % is observed from silicon pn diodes prepared by boron implantation. The implanted boron concentration is above the solubility limit for the post-implantation annealing temperature leading to the formation of boron clusters during annealing. The electroluminescence from electron-hole pairs exhibits an anomalous increase in the total intensity with increasing temperature. This behavior is explained by the thermal release of carriers trapped at local potential minima related to the boron clusters.

The flow field in the pressure vessel of a PWR is of turbulent nature. Statistical fluctuations occurring under quasi-stationary and transient flow conditions influence the mixing of coolant with different quality. It can be assumed, that the resulting boron concentrations and coolant temperatures at the inlet of the fuel assemblies are influenced by these fluctuations, too. Experiments at the ROCOM test facility for a hypothetical boron dilution event following the inadvertent start-up of the first main coolant pump were carried out with the goal to provide boundary conditions for core calculations. The core behaviour is simulated with the reactor dynamic code DYN3D. The influence of statistical fluctuations of the coolant and its consequences are investigated. Several simulations are performed with different core boundary conditions based on average values, a single measurement and values which are the boundaries of given confidence intervals of the measurements. Considering the different simulations the influence of the turbulent fluctuations on the reactor power and its distribution cannot be neglected. It can be important for similar transients, if safety parameters are close to the given limits.

Cone-beam type X-ray CT is a potential mehtod to measure three-dimensional phase-distribution in vessels. An example for that is the measurement of gas profiles in stirred chemical reactors. Such data is highly valuable for the assessment and evaluation of chemical processes, for optimisation of the reactor and stirrer design, and for evaluation of computational fluid dynamics codes used to model the fluid flow and heat transer in reactive systems. However, there are considerable difficulties for accurate quantitative measurements, for instance of average gas fraction in a fluid, due to beam hardening and radiation scattering effects. In a theoretical and experimental work we have investigated the non-linear effect of both physical phenomena and developed a suitable measurement setup as well as calibration and software correction methods to achieve a highly accurate void fraction measurement with X-ray cone-beam tomography.

A new ion beam facility for slow highly charged ions is presented that will provide low and medium energetic highly charged ions. An Electron Cyclotron Resonance (ECR) ion source delivers high currents of low and medium charged ions whereas very highly charged ions at lower ion currents are supplied by an Electron Beam Ion Trap(EBIT). The new ion beam facility will provide an experimental environment for basic research in atomic and solid state physics, as well as applied research in areas such as surface engineering, nanostructuring and nanobiotechnology.

In the interaction of highly charged ions with solid surfaces a main interest lies in the study of the dissipation channels for the potential energy. A large amount of information about secondary electron emission and X-ray emission has been collected in the past, enlightening the physics of the relaxation process of HCIs at surfaces. Calculating the amount of energy, which is dissipated into these channels only 10% to 15% is obtained. Less information is available about the absolute amount of the potential energy, which is deposited into the surface. In view of possible applications of HCIs for surface modifications the knowledge of this amount is essential.
In order to study the energy retention of the potential energy of HCIs into solid surfaces, we apply a calorimetric approach [1]. The ions (charge state q=2 .. 8) are extracted from an ECR ion source with 5 kV and decelerated to final kinetic energies down to 60 eV x q after beam transport and charge state separation. By using a liquid-nitrogen cooled calorimetric setup the retention of the total energy, kinetic and potential, is determined via the temperature increase during the bombardment. Measuring the energy retention at kinetic energies from 200 – 60 eV and extrapolating to 0 eV kinetic energy the separated potential energy is obtained. The experiments were done on clean Cu, Si, and SiO2 surfaces.
Here, we present a comparative study of the relative retention coefficients of the potential energy for the metallic, semiconductor, and insulator surfaces. In addition, measurements of the secondary electron yield are taken into consideration for a detailed picture of the energy dissipation channels.
[1] U. Kentsch, G. Zschornack, H. Tyrroff, and W. Möller, Phys. Rev. Lett. 87, 105504 (2001)

The secondary electrons emitted during the interaction of highly charged ions with solid surfaces carry detailed information about the complex interaction mechanism. In the past, the study of the secondary electrons emitted from the interaction with metal surfaces revealed the fascinating dynamics of the hol-low atoms formed above and below the surface. However, in the case of the interaction with insulating surfaces there is still some controversy whether the relaxation dynamics is the same as for metals. In addition, the microscopic and macroscopic charging of the insulating surfaces, which constitutes an im-portant part of the interaction mechanisms, makes these studies difficult.
Here, we report on the emission of electrons from Ne9+ interacting with thin SiO2 films. The typical LMM and KLL Auger electrons resulting from the last steps in the neutralisation process are observed on top of a broad secondary electron background. The mean peak positions of the Auger electrons are shifted to lower energies compared to the Auger electrons from metal sur-faces. Two mechanisms will be discussed for the interpretation of this obser-vation: the macroscopic charging of the SiO2 surface and a weaker screening of the ions in the SiO2 film.

Es werden Substanzen vorgeschlagen, die radioaktive Metalle mit hoher Stabilität binden und deren Metallkonjugate nach Applikation in den Körper metabolisch stabil sind, außerdem ein Verfahren zur Herstellung der Substanzen

Es wird eine Blitzlampenspiegelanordnung vorgestellt, die eine homogene und schnelle Erwärmung von Halleitersubstraten bei unwesentlich höheren Anlagenkosten ermöglicht.

Various magnetic properties like the saturation magnetization, the Curie temperature, the coercivity and the magnetic damping behavior can easily be modified by means of ion irradiation and implantation. In combination with focused ion beam techniques even a pure magnetic patterning without changing the surface topography becomes feasible. A magnetic domain pattern can be imprinted by using ion irradiation in an applied magnetic field. Thus doping of magnetic materials opens a route to a new class of artificial magnetic materials with adjustable magnetic properties.
Here, as an example, we report on the tailoring of the magnetic properties of Permalloy (20 nm Ni81Fe19) by means of 30 keV Cr implantation. Due to the doping the Curie temperature of the Permalloy film decreases with the implantation fluence and drops below room temperature at an averaged Cr concentration of about 7 at-%. Also the saturation magnetization and the uniaxial anisotropy decrease. However the magnetic damping behavior of Cr implanted Permalloy films is strongly enhanced which is due to a combination of structural changes and alloying effects in the thin film. In order to clarify the basic mechanism for the enhancement the chemical and structural contributions to the magnetic damping parameter are separated by a comparison to results of 30 keV Ni implantation.

Owing to its large magneto-crystalline anisotropy energy, L1_0 ordered tetragonal FePt is among the most intensively discussed materials when it comes to pushing the superparamagnetic limit towards minimum particle sizes for future ultra-high density magnetic data storage media. Depending on the preparation technique, however, the formation of the L10 thermodynamic equilibrium phase is often impeded by either a lack of thermodynamic driving forces or a lack of diffusivity.
Recently it has been shown that gas phase prepared FePt nanoparticles can exhibit a very narrow size distribution with a mean diameter of roughly 6 nm. Together with a packing density of 2.8 x 10^12 particles / cm^2 a potential data storage density of 18 Tbit / inch^2 could be achieved. Unfortunately these particles are superparamagnetic at room temperature due to their multiply twinned icosahedral structure. Therefore it is of essential importance to transform these nanoparticles into the favourable L10 phase in a post-deposition treatment.
In the present study, post-deposition 5 keV He irradiation has been employed in order to perform the phase transformation of such gas phase prepared FePt nanoparticles. Structural characterization of the samples was carried out by means of High Resolution Transmission Electron Microscopy (HRTEM). After ion irradiation the previously multiply twinned icosahedral particles have transformed mostly into the single crystalline fcc structure. However, no indication for the chemically ordered L10 phase is found. This might be due to the fact that either the particles investigated are already smaller than a critical particle size below which the L10 phase is no longer the thermodynamic equilibrium phase in FePt, or kinetic aspects may be of increasing importance at these length scales.

Im Rahmen des Planfeststellungsverfahrens für die Stilllegung des ERAM wurden standortspezifische Sorptions- und Löslichkeitsexperimente durchgeführt, um die potentielle Rückhaltung von Radionukliden belastbar in einer Sicherheitsanalyse berücksichtigen zu können. An ausgewählten Verschließmaterialien (Salzbeton und Magnesiabinder) des Endlagers für radioaktive Abfälle Morsleben (ERAM) für die Radionuklide Uran und Kohlenstoff-14 (als Carbonat) sowie am Grauen Salzton für die Radionuklide Plutonium, Americium, Uran, Radium und Kohlenstoff (als [¹⁴C]-Carbonat) wurden belastbare Sorptionsdaten aus Sorptionsexperimenten ermittelt, die für Modellrechnungen zur Ausbreitung von Radionukliden im Nah- und Fernbereich des ERAM verwendet werden können.
Als flüssige Phase für die Sorptionsexperimente wurden zwei endlagertypische gesättigte Salzlösungen eingesetzt: Lösung 1, eine quinäre Salzlösung, und Lösung 3, die hauptsächlich Natriumchlorid enthält.
Zusätzlich zur Sorption der Radionuklide wurden die Löslichkeiten der Radionuklide in den mit dem jeweiligen Bodenkörper konditionierten Salzlösungen bestimmt.

Beta decays of _94,96Ag and ₁₀₃Sn nuclei into Proton Channels have been studied in the recent experiments at the GSI-ISOL facility

Release of reactive (phosphate-like) phosphorus (P) from fresh water sediments represents a significant internal P source for many lakes.
Hypolimnetic P release occurs under reducing conditions that cause reductive dissolution of ferric hydroxide (Fe(OH)3). This hypolimnetic P release may be naturally low or artificially reduced by sediment with naturally high or artificially elevated concentrations of aluminum hydroxide (Al(OH)3). We present field and laboratory data for a common extraction analysis of sediments from 43 lakes differing in trophic status, pH regime, climate, and P loading. The results indicate that a simple sequential extraction of sediment may be a useful predictor of sediment’s ability to release P. Sequential extractions of sediment P, Al, and Fe using water (H2O), bicarbonate-dithionite (BD), and NaOH (at
25°C) showed that negligible amounts of P would be released from lake sediments during hypolimnetic anoxia if either: (1) the molar AlNaOH~25:FeBD ratio is >3, or (2) the molar AlNaOH~25:P(H2O+BD) ratio is >25. These ratios can be used as operational targets for estimation of sediment P release potential and Al dosing of P-rich sediment to prevent hypolimnetic P release under anoxic conditions.

The common concept of heavy metal migration in the hydrosphere differentiates between solid and liquid phase, considered as immobile and mobile. Colloidal phases are often neglected, which may have the following consequences on environmental hazard prognosis (Zänker et al. 2003):

a) The contaminant is regarded as mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
b) The contaminant is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
c) Only if the contaminant is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
This study is focused on the incidence of colloids and their binding of toxic metals in streams of the Erzgebirge (Germany), a low mountain region which strongly suffered in the past from mining activities, e.g. uranium mining, and from acid rain loads exceeding the buffering reaction by weathering. Mildly acidic conditions (pH 5-6.5), which may occur in the runoff from dumps or arise on the reversal from stronger acidification (Ulrich and Meybohm 2005), or by mixing of waters with different loads of protons and metals, favor the generation of colloids by hydrolysis of iron (Fe) and aluminum (Al) or by dissolution of clay minerals and precipitation of secondary ferric oxides.
Based on samples from the confluence of two forest streams in the Erzgebirge, 27Al MAS NMR spectroscopy showed that Al-rich colloids contain distinct Al(O)4 centers similar to the -Keggin polyoxocation AlO4Al12(OH)24(H2O)127+(aq) [Al13] (left Fig.). These colloids form via aggregation of the Al13 nanoclusters (Furrer et al. 2002) and bear a high surface density of functional groups capable of accumulating heavy metal cations.
Fe-rich colloids (right Fig.), which often consist of metastable ferrihydrite, exhibit similar properties. Such colloids form when acidic seepage (e.g. from a uranium mine or dump) mixes with near-neutral surface water. Uranium (U), which is soluble under strongly acidic (UO22+) and alkaline (uranyl carbo-nate complexes) conditions, will be scavenged and immobilized by colloids which aggregate and settle in the slightly acidic pH region. On the other hand, contaminants that are usually immobile (As, Cu, Pb), can be mobilized by colloids. The molecular structure of some sorption complexes derived from EXAFS and ATR FT-IR spectroscopy is discussed.

References
Furrer, G., Phillips, B.L., Ulrich, K.-U., Pöthig, R. and Casey, W.H. (2002) The origin of aluminum flocs in polluted streams. Science 297, 2245-2247.
Ulrich, K.-U. and Meybohm, A. (2005) Reservoir ecosystems recover from atmospheric acidification: I. Trends of chemical reversal. ACID RAIN 2005, Conference Proceedings, 000.
Zänker, W., Richter, W., Hüttig, G. (2003) Scavenging and immobilization of trace contaminants by colloids in the waters of abandoned ore mines. Coll. Surf. A 217, 21-31.

Most of the atmospherically acidified drinking-water reservoirs in the Erzgebirge (Germany, southern Saxony) responded more rapidly to the strong reduction of oxidized sulfur and nitrogen emissions than surface waters from other siliceous mountain ranges in Germany (Ulrich and Meybohm 2005). The substantial decrease of proton concentration and toxic forms of aluminum provided a basis for the recovery of sensitive aquatic organisms. Three of four reservoirs which were monitored over a decade showed significantly (p<0.01) falling trends of chlorophyll a and phytoplankton biovolume, mainly due to the decline of dinophyceae. Biovolumes of diatoms and picoplankton slightly increased in the Werda and Muldenberg Reservoir. The zooplankton biocoenosis was dominated by rotifers and small phyllopods, the genus Daphnia was still lacking.
Since 1999 and 2002, small perch (Perca fluviatilis) and sunbleak (Leucaspius delineatus) occurred in the Muldenberg and Werda Reservoir, respectively. The zooplanktivorous sunbleak population showed an extremely high fluctuation of abundance (1,000 67,000 individuals per hectare) and biomass (1 29 kg ha-1, Fig.). Even a population crash due to increased natural mortality happened. The fish individuals revealed a very low factor of corpulence, which indicates limited energy supply and high intraspecific competition on food resources (i.e. on zooplankton, Fig.). Severe top-down control may further delay the recovery of bigger zooplankton species (e.g. Daphnia) and consecutive planktonic groups of the food web. Introduction of predatory fishes could help to control zooplanktivorous fish populations and to prevent mass mortality.

References
Ulrich, K.-U. and Meybohm, A. (2005) Reservoir ecosystems recover from atmospheric acidification: I. Trends of chemical reversal. ACID RAIN 2005, Conference Proceedings, 000.

In Saxony, about two million people are supplied with drinking-water from reservoirs, of which 16 suffered from atmospheric acidification. After the German reunification, the waterworks were modernized and adjusted on the treatment of acidic soft waters. But the emissions of oxidized sulfur (SO2) and nitrogen (NOx) compounds strongly declined within the 1990s. Whereas lakes of the Bohemian Mountains responded rapidly by chemical reversal from acidification (Kopáček et al., 2002), siliceous low mountain ranges in Germany showed a delayed or even no response (Alewell et al., 2001).
This paper presents major trends of chemical water composition monitored for 11 years in 7 acidified drinking water reservoirs and 22 tributaries of the Erzgebirge (Germany), and statistically evaluated by the Seasonal Kendall Test. About 85% of these surface waters showed significantly (p<0.05) declining concentrations of protons (-76%), nitrate ( 55%), sulfate (-26%), and reactive aluminum (Al, 104% on average). The strong decrease of toxic forms of Al provided a basis for recovery of sensitive aquatic organisms like fish (Meybohm and Ulrich, 2005).
Dependent on each initial acidification stage which differed, the study waters shifted one or two stages towards neutrality within a decade, thereby passing through a transitional stage of seasonally (episodically) fluctuating pH regime as illustrated by the Figure. The concentrations of dissolved organic carbon, ammonium, chloride, calcium, magnesium, manganese, and iron showed no trend in 60-75% of the investigated waters. But four reservoirs showed rising trends of iron, probably due to increased microbial activity in the sediment favoring anoxic release of ferrous iron.
The rapid chemical response of the study waters is attributed to the very high level and thus intense reduction of industrial SO2 and NOx emissions, which declined by 99% and 82% in southern Saxony between 1993 and 1999. Deposition rates of protons and sulfate decreased by a factor of ~3, but total N deposition remained almost constant. Soil protection liming, which was performed as a measure of forest remediation, contributed positively to the chemical reversal in about 20% of the surface waters, in particular of those where the cumulative dolomite supply on the total drainage area exceeded 7 t ha-1.

References
Alewell, C., Armbruster, M., Bittersohl, J., Evans, C.D., Meesenburg, H., Moritz, K. and Prechtel, A. (2001) Are there signs of acidification reversal in freshwaters of the low mountain ranges in Germany? Hydrol. Earth System Sci. 5(3), 367-378.
Kopáček, J., Stuchlík, E., Veselý, J., Schaumburg, J., Anderson, I., Fott, J., Hejzlar, J. and Vrba, J. (2002) Hysteresis in reversal of Central European mountain lakes from atmospheric acidification. Water Air Soil Pollut.: Focus 2, 91-114.
Meybohm, A. and Ulrich, K.-U. (2005) Reservoir ecosystems recover from atmospheric acidification: II. Signs of biological recovery. ACID RAIN 2005, Conference Proceedings, 000.

Die Nutzung biologischer Strukturen für die Nanotechnologie ist auf Grund der Größe vieler wichtiger Biomoleküle ein naheliegender Ansatz. S-Layer (engl.: surface layer) sind als äußerste parakristalline Proteinschicht bei vielen Bakterien und Archaea zu finden. Die Untereinheiten dieser Schichten, Protein- oder Glykoproteinmonomere, haben die Fähigkeit zur Selbstorganisation als monomolekulare gitterartige Schicht und eignen sich deshalb bestens zur Funktionalisierung von Oberflächen und zur Herstellung von Ultrafiltrationsmembranen. Einige S-Layer von bakteriellen Isolaten aus Schwermetall- und Radionuklid-belasteten Umgebungen haben außerdem die Eigenschaft, bestimmte Metalle zu binden und können deshalb zur Herstellung von Nanostrukturen, Metallclustern definierter Größe oder als selektive Bindungsmatrix in Filter zur Reinigung kontaminierter Wässer eingesetzt werden.

It is shown that the α²-dynamo of Magnetohydrodynamics, the hydrodynamic Squire equation as well as an interpolation model of PT-symmetric Quantum Mechanics are closely related as spectral problems in Krein spaces. For the α²-dynamo and the PT-symmetric model the strong similarities are demonstrated with the help of a 2×2 operator matrix representation, whereas the Squire equation is re-interpreted as a rescaled and Wick-rotated PT-symmetric problem. Based on recent results on the Squire equation the spectrum of the PT-symmetric interpolation model is analyzed in detail and the Herbst limit is described as spectral singularity.

Bubble Columns are widely used in the process industry and their scale-up from laboratory scale units to industrial units have been a subject of extensive study. The void fraction distribution in the bubble column is affected by the column size, superficial velocity of the dispersed phase, height of the liquid column, size of the gas bubbles, flow regime, sparger design and geometry of the bubble column. The void fraction distribution in turn affects the interfacial momentum transfer in the bubble column. The void fraction distribution in a rectangular bubble column 10cm wide and 2 cm deep, has been measured using Wire-Mesh Tomography. Experiments were performed in an air-water system with the column operating in the dispersed bubbly flow regime. The experiments also serve the purpose of studying the performance of wire-mesh sensors in batch flows. A ‘wall peak’ has been observed in the measured void fraction profiles, for the higher gas flow rates. This ‘wall peak’ seems to be unique as this distribution has not previously been reported in bubble column literature. Low gas flow rates yielded the conventional ‘center peak’ void profile. The effect of column height and superficial gas velocity on the void distribution has been investigated. Wire-mesh Tomography also facilitates the measurement of bubble size distribution in the column. This paper presents the measurement principle and the experimental results for a wide range of superficial gas velocities.

The objective of the ECORA project is the evaluation of computational fluid dynamics (CFD) software for reactor safety applications, resulting in best practice guidelines (BPG) for an efficient use of CFD for reactor safety problems. The project schedule is as follows: (i) establishment of BPGs for use of CFD codes, for judgement of CFD calculations and for assessment of experimental data; (ii) assessment of CFD simulations for three-dimensional flows in LWR primary systems and containments; (iii) quality-controlled CFD simulations for selected UPTF and SETH PANDA test cases; and (iv) demonstration of CFD code customisation for PTS analysis by implementation and validation of improved turbulence and two-phase flow models. The project started in October 2001 and is for a period of 36 months. The project consortium consists of 12 partners combining thermal-hydraulic experts, code developers, safety experts and engineers from nuclear industry and research organizations. At mid-term, the following results were achieved: (i) BPGs are available for simulations of reactor safety relevant flows. These BPGs have found interest in the European projects FLOMIX-R, ASTAR and ITEM; (ii) important flow phenomena for PTS and containment flows have been identified; (iii) experimental data featuring these phenomena have been selected and described in a standardised manner suitable for simulation with CFD methods; (iii) surveys of existing CFD calculations and experimental data for containment and primary loop flows have been performed and documented; (iv) first results for simulations of PTS-relevant single-phase and two-phase flow cases are available.
Documentation is available via the internet at http://domino.grs.de/ecora/ecora.nsf. The models developed within the project are implemented in industrial and commercial CFD software packages and are therefore accessible by industry and research institutions.

Microbial diversity was studied in water samples collected at depths of 290 to 324 m from the Siberian deep-well radioactive disposal site S15 near the Russian city of Tomsk. For this molecular and cultivation approaches were applied. The biomass from the samples was concentrated via consequent filtration on filters with pore sizes of 1.2, 0.45, and 0.22 µm. For one of the samples 16S rDNA bacterial and archaea clone libraries were constructed from the total DNA (S15A) recovered from the biomass collected on the three filters. For another parallel sample two bacterial clone libraries S15B and S15D were generated from the DNA extracted individually from 0.45 and 0.22 µm filters, respectively. The analysis of the libraries demonstrated that the estimation of the diversity strongly depends on the way of collecting the biomass. About 65% of the clones in the S15A bacterial library were affiliated to ß-proteobacterial Dechlorosoma species. The rest of the clones represent very diverse bacterial groups. In the S15B library the Dechlorosoma sp. represented 30% of the total number of clones. This result indicates a possible dominance of Dechlorosoma sp. in the S15 samples [1]. Another 20% of the clones from the S15B library were affiliated with a low identity to a novel cyanobacteria-related lineage. Sequences representing the same “cyanobacteria-like” group were also found in the 0.22 µm library. However, populations of Cytophagales were the most predominant in the latter library and represented about 55% of the clones.
In addition, Euryarchaeota and Crenarchaeota 16S rDNA sequences were identified in the S15A total DNA as well. Most of them were affiliated to 16S rRNA genes of not jet cultured archaeons, found in different metal-rich habitats.

Autotrophic microorganisms were retrieved in the S15 samples by using primer pairs specific for the form I [2,3] and form II [4] of RubisCO gene. Some of the identified sequences from the form I were affiliated with RubisCO genes of Proteobacteria, which were related to those identified previously in the same samples via the 16S rDNA approach. Interesting is also the result that more than 80% of the form I sequences were affiliated with the RubisCO genes of different species from the β-subclass of Proteobacteria. The 16S rDNA approach indicated a dominance of β-proteobacterial species in the same samples as well. The retrieved form II sequences were affiliated with α-proteobacterial RubisCO genes.

Several oligotrophic bacteria were isolated under aerobic conditions from the 0.22 µm filter. They were related to -Proteobacterial and to Actinobacterial species. Three of the isolates, affiliated to Microbacterium oxydans possess microdiverse 16S rDNA stretches. The ability of these isolates to tolerate and sorb uranium and other heavy metals was studied. The results demonstrated that the resistance to and binding of heavy metals are strain-specific for these isolates.

Acknowledgements
This work was partly supported by grant FIKW-CT-2000-00105 (BORIS) from the European Community. We thank A. Zubkov, E. Zaharova, E. Kamenev and A. Rybalchenko for the supplying of the S15 samples.

References
[1] M. Nedelkova, G. Radeva and S. Selenska-Pobell. (2005) In: Underground Injection Science and Technology, Elsevier Science, (in press).
[2] A. Alfreider, C. Vogt, D. Hoffmann and W. Babel. Microbial Ecology 45 (2003), p. 17-328
[3] K. Nanba, G.M. King and K. Dunfield. Appl. Environ. Microbiology 70 (2004), p. 2245-2253
[4] H. Elsaied and T. Naganuma. Appl. Environ. Microbiology 67 (2001), p. 1751-1765

Uranium ores are very common in several regions of Germany, e.g. Saxony, Thuringia and Bavaria. Weathering and ore mining are processes which result in mobilization of uranium. So far only a general radiation dose limit for drinking water exists in Germany but no limit value for uranium itself. The latter is a radioactive and also toxic element and therefore discussions have raised to adopt a limit value for uranium in Germany. Against this background the development of novel strategies for cleaning uranium contaminated water became an increasingly interesting subject. In the past the Bacillus sphaericus strain JG-A12, recovered from the uranium mining waste pile “Haberland” nearby the town of Johanngeorgenstadt, was demonstrated to bind selectively several heavy metals including uranium [1]. Molecular and structural analyses of the uranium complexes formed by the cells, spores and the surface layer (S-layer) protein of B. sphaericus JG-A12 via extended X-ray absorption fine structure (EXAFS) spectroscopy identified carboxyl and phosphate groups as binding sites for uranium [2]. Moreover sol-gel techniques were used for immobilization of B. sphaericus JG-A12 cells in a porous silicate matrix. [4, 5]. The obtained biological ceramic (biocer) is particularly suitable for the use as selective filter material for the immobilization of uranium from polluted industrial waters.

This work is aimed to investigate the capability of biocers containing B. sphaericus JG-A12 cells to remove uranium from contaminated drinking water. For the experiments four different tap water samples supplemented with 30 µg uranium per liter and one Hungarian mineral water with a uranium content of 142 µg uranium per liter were selected. Uranium sorption by the biocer showed the removal of over 99% of dissolved uranium from the tap water samples. In the case of the heavy metal containing and highly saline mineral water 86% of uranium and 76% of zinc were immobilized.

In order to improve the uranium binding capacity of the biocers, the uranium sorption by B. sphaericus JG-A12 cells was tested depending on the amount of phosphorus present in the growth medium. Highest binding capacities were achieved with biomass grown in phosphate rich media, containing at least 1.4 mM phosphorus. In contrast, the binding capacity was remarkably lower with biomass grown in phosphate limited medium. Furthermore uranium binding of the isolated and purified S-layer of B. sphaericus JG-A12 was investigated. Interestingly, the S-layer of B. sphaericus JG-A12 possesses even at low concentration of uranium higher affinity to uranium than the S-layer protein of its closest relative B. sphaericus NCTC 9602 or the reference protein bovine serum albumine. Recent analyses of the S-layer genes of B. sphaericus JG-A12 [6] allow to perform in future genetic modifications of the cell surface of B. sphaericus JG-A12. This displays a further possibility to enhance the capacity and the selectivity of the uranium binding by the next generation of biocers.

Acknowledgement
This work was founded through Project DFG SE 671/7-2 from the German Research Community (DFG) and trough EC grant GRD1-2001-40424. We thank R. Getzlaff and I. Plumeier (GBF Braunschweig) for their assistence and U. Soltmann (GMBU, Dresden) for the preparation of the biocer.

References
[1] S. Selenska-Pobell et al. 1999. FEMS Microbiology Ecology 29, 59-67
[2] J. Raff et al. 2004. In: R.B. Wanty and R.R. Seal II. Water-Rock Interaction. 1, 697-701
[4] J.Raff et al. 2003. Chemistry of Materials 15, 240-244
[5] U. Soltmann et al. 2003. Journal of Sol-Gel Science and Technology 26, 1209-1212
[6] K. Pollmann et al. (in preparation)

An experimental study with respect to the influence of a rotating magnetic field (RMF) on the unidirectional solidification of Pb-Sn alloys is reported. The magnitude of the bulk flow in the melt generated by the RMF varies with the magnetic Taylor number Ta. The forced convection causes distinct modifications of the temperature and concentration field such as a reduction of the temperature gradient ahead of the solidification front. Without electromagnetic stirring the alloy solidifies solely in form of dendrites aligned parallel to the heat flow direction. In contrast, a transition from a columnar to an equiaxed growth (CET) is observed if the solidifying ingot is exposed to an RMF. The position of the CET is shifted towards the bottom of the casting by increasing the Ta number. The CET was found to occur for a cooling rate of about 0.4 K/s and temperature gradients in the range between 0.6 and 1.0 K/mm

In processes involving electrically conducting liquids, the application of an external magnetic field offers efficient opportunities for a contactless flow control and fluid handling. However, for a well-aimed optimisation of the flow structure local information about flow quantities like velocity, pressure, temperature, concentration or void fraction are necessary. In case of liquid metals the choice of a suitable measuring technique is a crucial problem, because the user is confronted not only with the opaqueness but also with high temperatures as well as a strong chemical reactivity of the fluid against many materials. Therefore, measuring techniques well-known from ordinary hydrodynamics generally fail for liquid metal applications. As a consequence, no commercial measuring systems are available for liquid metal applications.
During the last years experimental activities of FZR were focussed on the development and qualification of techniques to measure the velocity in liquid metal flows. Various liquid metal model experiments with various liquid melts at different temperatures have been performed to test and evaluate local sensors as well as integral methods.

Measurements of the cross sectional distribution of gas fraction and bubble size distributions were conducted in a vertical pipe with an inner diameter of 51.2 mm and a length of about 3 m for air/water bubbly and slug flow. The use of a wire-mesh sensor allows a high resolution of the gas fraction data in space as well as in time. From these data time averaged values for the two-dimensional gas fraction profiles decomposed according to a large number of bubble size classes were calculated. This allows to extract data for the radial gas fraction profiles for a given range of bubble sizes as well as data for local bubble size distributions. The structure of the flow is characterized by these data. The measurements were done for up to 10 different inlet lengths and for about 100 combinations of gas and liquid volume flow rates. The data are very useful for the development and validation of meso-scale models for the forces acting on a bubble in a shear field of the liquid flow and models for bubble coalescence and break-up. Such models are necessary for the qualification of CFD codes for the simulation of bubbly flows.

Hydrogen solubility has been studied in hydrogenated amorphous silicon (a-Si:H) prepared by plasma-enhanced chemical vapour deposition with hydrogen-diluted silane. Post-hydrogenation experiments have been carried out using hydrogen plasma and hydrogen ion implantation. Thermal annealing and silicon ion implantation have been used to change the defect density in the amorphous silicon network. Hydrogen concentration has been established by means of nuclear reaction analysis and infrared spectroscopy. It has been shown that the hydrogen solubility in a-Si:H is strongly related to the density of the hydrogen trapping sites in the silicon network and the value of the solubility limit is determined by the material structure and consequently by the a-Si:H preparation conditions. The ratio between the hydrogen concentration and its solubility limit has been discussed in the context of the light-induced degradation of a-Si:H.

The production of K+-mesons in pA (A = D: Q Cu, Ag, Au) collisions has been investigated at the COoler SYnchrotroii COSY-Julich for beam energies T-p = 1.0-2.3 GeV. Double differential inclusive p C cross-sections at forward angles theta(K+) < 12&DEG; as well as the target mass dependence of the K+ momentum spectra have been measured with the ANKE spectrometer. Far below the free NN threshold at T-NN = 1.58 GeV the spectra reveal a high degree of collectivity in the target nucleus. From the target mass dependence of the cross-sections at higher energies, the repulsive in-medium potential of the K+--mesons can be deduced. Using pN cross-section parameterisations from the literature and our measured pD data we derive a cross-section ratio σ(pn --> K+X)/sigma(pp --> K+X) similar to (3-4).

The QCD sum rule approach to in-medium modifications of the omega meson in nuclear matter is reviewed with emphasis of its relation to 4-quark condensates and chiral symmetry restoration. Possible implications of the CB-TAPS experiment for the reaction gamma A -> A' omega (-> pi⁰ gamma) are sketched and the particularly important role of di-electron probes, accessible with HADES, is highlighted. A brief update of a parametrization of the previous dilepton and photon probes from CERES and WA98 of heavy-ion collisions at CERN-SPS energies is presented.

The time-dependent flux over the fission barrier of an excited nucleus under the influence of dissipation is investigated. Characteristic features of the evolution of the amplitude of the probability distribution and the velocity profile at the fission barrier are derived. Analytical results are compared to numerical Langevin calculations and used to develop a new analytical approximation to the solution of the Fokker¿Planck equation for the time-dependent fission-decay width. This approximation is
shown to be more realistic than previously proposed descriptions, which were widely used in the past.

Forty years of uranium mining in the German state of Saxony have left a legacy of uranium-contaminated pits, waste piles, mine tailings and surrounding soils. Since 1963, and more extensively since 1989, contaminated sites were covered in order to protect people and environment. Little is known on the further fate of uranium at these buried sites. Therefore, we investigated two mine tailing samples from hydrochloric-acid ore-extraction, which were buried for 30 years under several meters of mine and communal waste.
The two samples were collected at depths of 5 m (sample 1) and 12 m (sample 2) below the surface. Due to the neutralizing influence of the waste cover, the upper sample 1 had a pH of 8, while the lower sample 2 had a pH of 4. Both samples were retrieved from oxic redox conditions. Chemical extractions showed that U is predominantly water soluble and/or ion exchangeable in sample 1, while U is predominantly bound in weakly soluble solid phases in sample 2. To further identify the uranium species, we applied a combination of Synchrotron-based methods, namely Extended X-ray Absorption Fine-Structure (EXAFS) spectroscopy of bulk samples, micro X-Ray Diffraction (µ-XRD) and micro X-Ray Fluorescence (µ-XRF) spectroscopy. In sample 1, uranium predominates homogeneously distributed at concentrations in the mg/kg range in aggregates with a diameter of tens to hundreds of µm. The aggregates consist of layer silicates (muscovite, kaolinite, illite), jarosite and gypsum. Chemical extractability, EXAFS, µ-XRD, and µ-XRF strongly suggest that U(VI) is adsorbed on edge sites of the layer silicates. In sample 2, U is heterogeneously distributed among single crystals and small aggregates with very high U concentrations (g/kg) and variable elemental composition. Besides the matrix minerals muscovite, kaolinite, illite and quartz, we identified pitchblende and coffinite, and found evidence for other uranyl hydroxide and vanadate solids. In addition, a smaller amount of uranium seems to be adsorbed to mineral surfaces as in sample 1.
The results suggest that a substantial amount of uranium remained in the buried tailings as relatively mobile, adsorbed U(VI) species. No clear evidence for secondary uranium mineral precipitates was found.

Silizium ist zwar die Basis für nahezu die gesamte Mikroelektronik, die Integration mit optischer Funktionalität ist jedoch nur eingeschränkt möglich, da Silizium als indirekter Halbleiter ein schlechter Lichtemitter ist. Andere optoelektronische Komponenten, wie Dektektoren, Modulatoren oder Wellenleiter können aus Silizium hergestellt werden, ein Siliziumlaser hat sich bisher aber allen Realisierungsversuchen widersetzt. In den letzten Jahren hat es jedoch rasante Fortschritte bei der Effizienz Silizium-basierter Lichtemitter gegeben, sogar optischer Gewinn (gain) wurde berichtet. Ich möchte diese Entwicklung zusammenfassen und dann unsere Unterschungen an Bor-implantierten Si pn Dioden und an mit seltenen Erd-Ionen implantierte MOS-Strukturen präsentieren, deren Effizienzen schon nahe zum anwendungsrelevanten Bereich kommen.

Chrombeschichtung von Baustahl mittels Ionenstrahlbehandlung

The evolution of reactive gas uptake at the target surface has been investigated by real-time in situ diagnostics during magnetron sputtering. Using a planar circular dc magnetron for reactive sputter deposition of TiN from a Ti target in an argon/nitrogen gas mixture, the target uptake of nitrogen was determined at varying gas flows of nitrogen using the 14N(d,)12C nuclear reaction, directly demonstrating the target "poisoning" effect. The expected hysteresis behavior at increasing/decreasing nitrogen gas flow is confirmed. Within the precision of the measurement, the nitrogen content remains unaltered after switching off the magnetron, indicating the absence of a significant mobile fraction of nitrogen in the target. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen. This is quantitatively reproduced by TRIDYN collisional computer simulations.

Bulk nickel samples, produced by electrodeposition, resulting in different initial structure properties, were experimentally studied by X-ray diffraction, as well as by scanning and transmission electron microscopy. Attempts are made to correlate the mechanical behaviour during cyclic plastic deformation with the response of the microstructure. A special effort is made to examine the influence of grain size and internal stresses on the deformation processes.

Combined external Ion Beam Analysis (IBA) measurements, consisting of Proton Induced X-ray Emission–Proton Induced Gamma-ray Emission–Rutherford Back-Scattering (PIXE-PIGE-RBS) have been performed on several obsidian fragments with archaeological significance at the Rossendorf tandem accelerator using a 3.85 MeV proton beam. A comparison was made between these external IBA results and the ones previously obtained on the same obsidian samples using Laser Ablation–Inductively Coupled Plasma–Mass Spectrometry (LA-ICP-MS). The purpose of the study was to assess the potentiality of external IBA for provenance studies on archaeological obsidian, especially as a non-destructive alternative to the LA-ICP-MS method. As an example, the source attribution of an archaeological obsidian fragment from Transylvania to Tokay Mountains/Slovakian range flow is discussed.

Structural modifications of solid Si (0 0 1) targets exposed to the XUV TESLA free lectron laser radiation were studied. The samples were irradiated with the photon energy centered at 14 eV, in short pulses of only 80 fs and of peak power up to 1 GW. The FEL beam was focused on sample surfaces to microspots of size 10–100m. The energy density in the spots varied from below the ablation threshold up to far above this threshold. The structural modifications induced with the irradiation were studied by AFM, Nomarski contrast microscopy and by X-ray diffraction methods. A variety of morphological structures created in the damaged areas was found. The maps of the X-ray diffracted intensity distribution recorded around chosen spots on the Si surface made it possible to probe the damage distribution range around the spots. The observed features are related to the FEL irradiation fluencies applied.

EDXRF analysis with subsequent multivariate data analysis proves useful for the determination of the authenticity of iridescent glass artifacts. Thus, clusters of the glass groups investigated were formed which can be associated with the glass manufacturers. By means of ion beam analysis with the external proton beam the producing technology of iridescent glass objects of the Art Nouveau glass manufacturer Loetz/Austria with so-called Papillon pattern was characterised in a non-destructive way. Due to the simultaneous application of PIXE and RBS the glass structure including a sequence of glass layers covered with a SnO2-layer of approximately 50 nm thickness on the surface could be described.

The dispersion of bubbles in a vertical two-phase flow is studied experimentally by means of wire-mesh sensors and high-speed video camera. The first technique is applied to a 200 mm pipe with flow patterns ranging from bubbly to slug/churn flow. The latter technique is instead applied to a rectangular bubble columns at low void-fractions. The experimental results are compared with numerical investigations.

For the investigation of air/water stratified flow, a horizontal channel with rectangular cross-section was build at Forschungszentrum Rossendorf. The channel allows the investigation of air/water co- and counter-current flows under atmospheric pressure, especially the slug behaviour.
Optical measurements were performed with a high-speed video camera, and were complemented by simultaneous dynamic pressure measurements. Further, an interface capture technique was developed and possible applications (e.g. plot of the time dependent water level in a cross-section, recognition of the slug position) presented.

During last decades magnetohydrodynamic (MHD) effects have attracted growing interest because of its potential impact on numerous industrial technologies. In processes involving electrically conducting liquids, the application of an external magnetic field offers efficient opportunities for a contactless flow control and fluid handling. However, for a well-aimed optimisation of the flow structure local information about flow quantities like velocity, pressure, temperature, concentration or void fraction is necessary. In case of liquid metals the choice of a suitable measuring technique is a crucial problem, because the user is confronted with the problems of opaque fluids, high temperatures as well as a strong chemical reactivity of the fluid against many materials. Therefore, measuring techniques well-known from ordinary hydrodynamics generally fail for liquid metal applications. As a consequence, no commercial measuring systems are available for liquid metal applications.
We present a summary of our R&D activities on velocity measuring techniques for liquid metal flows. Various model experiments with various liquid melts at different temperatures have been performed to test and evaluate local sensors as well as integral methods.
A mechano-optical probe was developed which has to be positioned directly inside the liquid metal flow. The measuring principle is based on the separation of a direct mechanical interaction between flow and sensor tip and the optical acquisition and processing of the signal. The insensitivity of the system to electrical noise and external magnetic fields can be considered as an important advantage. Until now, the sensor has been tested in metallic melts up to temperatures of about 450 °C, but an extension up to 800°C should be straightforward. The ultrasound Doppler velocimetry (UDV) represents a powerful tool since it delivers a full velocity profile along the ultrasonic beam. It can operate with a direct contact to the melt, but also through a channel wall. To overcome the thermal restriction of the ultrasonic transducers an acoustic wave guide has been used. The acoustic wave guide and the piezoelectric element are combined in form of an integrated sensor. This approach allowed the first successful application of the ultrasound Doppler technique in liquid metals at temperatures above 200°C. The feasibility of this integrated sensor concept was demonstrated in experiments in metallic melts as sodium, PbBi, CuSn or aluminium.
In some applications even a coarse knowledge of the flow topology and the direction of the main eddies would be of high value. We study the possibility of velocity reconstruction in electrically conducting fluids from external measurements of induced magnetic fields. The method is based on the fact that an external magnetic field is deformed by the motion of the fluid. Applying the primary magnetic field in two different directions and measuring the related induced magnetic fields at an array of Hall probes, the three-dimensional velocity field can be reconstructed. Besides some theoretical basics, we present experimental results of a demonstration experiment.

The mould filling process of aluminum investment casting consists basically of the flow in a U-bend showing a high pouring velocity at the beginning and decreasing velocity values during the course of the process. The high velocities during the starting phase are supposed to cause distinct problems like bubble or inclusion entrapment. Several types of filters are already in use for the purpose of inclusion filtering but velocity reduction, too.
We present results on the design and application of a DC magnetic field to control the pouring velocity. Numerical calculations were performed to simulate the filling process and the effect of the magnetic field. The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. 3d transient calculations using the commercial finite- element code FIDAP (FLUENT Inc.) were carried out for a simplified model system as well as for the real aluminum casting unit. The term for the electromagnetic force was implemented into the code via a user defined subroutine, and an additional equation for the electrical potential was solved. End effects due to the limited size of the magnet poles were taken into account. In that way, results from three-dimensional transient simulations of the filling process were obtained.
Parallel to the simulations model experiments have been performed using the low melting eutectic InGaSn. The casting unit was modelled by a plexiglas model. The ultrasonic Doppler velocimetry was applied to carry out detailed velocity measurements in the model. Such measurements delivered the basis to validate the numerical calculations. A comparison between numerical and experimental results showed an excellent agreement, allowing scaling up the simulations to the realistic aluminium casting process.
Real tests have been performed at an industrial investment caster with molten aluminium. The primary action of the magnetic field, i.e. the reduction of the velocity peaks at the beginning of the process, was clearly shown. In a second set of experiments the amplitude of the DC field was tuned during the process. At the beginning the maximum braking force was applied, whereas the field strength was reduced with increasing fluid level in the casting unit. In this regime, a clear reduction of the peak velocities is obtained without a significant prolongation of the overall filling time.

TOPFLOW stands for Transient TwO Phase FLOW. The new thermal-fluiddynamic test facility of FZR was built for generic and applied studies of transient two phase flow phenom-ena in power and process industries. It is used as experimental basis to develop and validate three-dimensional CFD, in particular for an application to safety relevant flow simulations in the field of nuclear reactor safety. The work is carried out in a close and very fruitful coopera-tion with the code developer ANSYS-CFX. Object of the experimental studies is a gas-liquid two-phase flow. In the field of nuclear technology, the introduction of CFD is connected with high expectations concerning the quality of the predictions compared to the established one-dimensional thermal hydraulic analyses, since CFD allows to substitute geometry-dependent empirical closure relations by more physically justified closure laws that are formulated on the scale of the structures of the gas-liquid interface. In this way, modelling becomes much more independent from geometrical and thermodynamic boundary conditions and the scale-up to the real reactor scale becomes more reliable than in case of traditional thermal hydraulic codes.

TOPFLOW is not a dedicated integral test modelling a specific reactor type. It was rather de-signed as a multi-purpose facility for different single-effect experiments. This offers numer-ous possibilities for experiments to study basic two-phase flow phenomena as well as to per-form applied research for the industries. The latter includes, for instance, investigations of innovative and passive safety systems for nuclear reactors, like the emergency condenser for boiling water reactors, a model of which is a major component of TOPFLOW. A carefully designed instrumentation including advanced two-phase flow sensors of own development delivers experimental data of high quality, that reflect the addressed phenomena and processes in the necessary detail.

An important role plays the availability of measuring information from wire-mesh sensors with a high spatial resolution of 3 mm, which deliver sequences of complete two-dimensional gas fraction distributions from the entire cross section of both pipes DN50 and DN200 with a frame rate of 2500 Hz. These sensors were upgraded to operational parameters of 280 °C and 65 bar. First results on void profiles and bubble size distributions as well as the evolution of the flow structure along a vertical pipe obtained in this parameter range will be presented.

Another new method used at TOPFLOW is the strategy to install a test facility inside a tank pressurized with air of up to 50 bar and operate if in pressure equilibrium with the inner at-mosphere of the tank. The advantages can be summarised as follows: (1) the test facility itself can have strange shapes that are unfeasible for pressurised components, (2) the manufacture of the test itself will be cheap, since no pressure carrying components are needed, (3) thin walls make it easy to apply instrumentation, for instance optical measurements through glass walls or temperature field measurements by directing an infrared camera to a thin metal wall, (4) no expensive and time consuming licensing procedures are necessary, because the test is housed in the tank designed for the maximum overpressure.

Bacteria can interact in different ways with uranium. Therefore, they play a major role in biogeochemical cycling of this element. Natural bacterial communities were studied of several different soil samples collected from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). The 16S rDNA retrieval showed that the communities were predominated by members of -Proteobacteria and Holophaga/ Acidobacterium. In order to analyse the influence of U(VI) on the natural bacterial community structure, one of the studied soil samples, containing originally 40 mg/kg U, was supplemented with nearly 60 mg/kg U(VI) as uranyl nitrate. After four weeks of incubation, selective sequential extractions revealed, that most of the added U(VI) was weakly complexed, hence remained bioavailable. The predominant bacterial populations were shifted from -Proteobacteria and Holophaga/Acidobacterium to Pseudomonas sp., Arthrobacter sp. and Geobacter sp.. Column experiments are in progress in our laboratory, which will help to improve our understanding of the influence of U(VI) on the natural bacterial community. The influence of aeration was also studied on the changes of the bacterial community structure induced by the addition of U(VI).

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt, Germany. The cells of this strain are capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters. It was demonstrated that this strain is enveloped by a surface layer protein (S-layer) which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different kind of molecules and also nucleation sites for formation of metal nanoclusters like Pd, for example. In this study we demonstrate that the cells of B. sphaericus JG-A12 and their purified and recrystallized S-layer are capable to bind effectively Au(III) from salt solutions. Moreover, in the presence of reducing agents such as molecular H2, Au(III) is reduced to metallic nanoclusters. Reduced gold nanoclusters were regularly distributed and sized according to the pores of the protein lattice. The metallic nature of the clusters was confirmed by different techniques such as EXAFS, XANES, UV-Vis spectroscopy and by X-ray powder diffraction. The size of the gold nanoparticles was estimated to be about 10 Å. Changes in functional groups in the cells and S-layer due to gold binding were observed by FT-IR microscopy. The cellular localization of the deposited Au(III) and of the gold nanoclusters was defined using transmission electron microscopy (TEM) and environmental scanning electron microscopy (ESEM). The results demonstrated that B. sphaericus JG-A12 might be used to prepare gold nanoparticles that can be tailor-made for particular applications.

Bacteria have evolved several different mechanisms to tolerate uranium or to use U(VI) as terminal electron acceptor in anaerobic respiration. Because of this, bacteria play a major role in geomicrobiological cycling of uranium and can be used for the bioremediation of uranium-contaminated sites. In this work natural bacterial communities were investigated by the use of 16S rDNA retrievals in several soil samples from the uranium mining waste pile Haberland near the town of Johanngeorgenstadt (Saxony, Germany). Inductively coupled plasma mass spectrometry (ICP-MS) and selective sequential extraction (SSE) analysis were used for the geochemical characterization of the soil samples. The 16S rDNA analysis showed that the natural bacterial communities were predominated by -Proteobacteria and Acidobacteria. SSE analysis demonstrated that the uranium was weakly complexed and bound by Mn(hydr)oxides or Fe(hydr)oxides. The soil samples contain in addition to uranium also other heavy metals like arsenic for example. In order to understand how U(VI) influences the structure of natural bacterial community, one of the studied samples with the lowest indigenous amount of U was supplemented with 60 mg/kg U(VI) in form of uranyl nitrate. After four weeks of incubation, SSE analysis and 16S rDNA retrieval were done in parallel. The SSE analysis demonstrated that most of the supplemented uranium was weakly complexed and remained probably bioavailable. The 16S rDNA retrieval showed that populations of Pseudomonas, Arthrobacter and Geobacter were stimulated by the addition of U(VI) to the soil sample. For more profound understanding of the influence of U(VI) on natural bacterial community, column experiments are running in our laboratory.

The sorption complexes of uranium to colloidal ferrihydrite (Fh) were investigated by EXAFS and ATR FT-IR spectroscopy in mildly acidic solution (pH 5.5) in presence and in absence of atmospheric CO2. EXAFS has shown that sulfate, silicate, and carbonate are not involved as ligands bidentately bound onto the adsorbed U. Hence a new surface bond structure of U on hydrous ferric oxides is proposed which tightly fits the experimental EXAFS data. However, ATR FT-IR spectra suggest ternary uranyl carbonato surface complexes under these conditions open to the atmosphere. The conflicting spectroscopic results can be harmonized by proposing a monodentate linkage of the carbonate ligands.

Various developments of velocity measuring techniques, their test in different liquid metals, and applications in hot melts are reported. A Mechano-Optical Probe (MOP) performing local measurements up to temperatures of about 700°C has been developed and successfully tested. The Ultrasound Doppler Velocimetry (UDV) can be considered as another attractive technique to get velocity data from opaque flows. To extend the application range to higher temperatures and to abrasive liquids a new integrated ultrasonic sensor with an acoustic wave guide has been designed. First successful measurements in a CuSn melt of about 620°C and in liquid Al of about 750°C were carried out. A fully contactless investigation of the mean velocity field is possible by magnetic tomography. Local measurements of the induced magnetic field and the application of inverse reconstruction techniques allow an analysis of the flow structure. A first demonstration experiment showing the feasibility of this approach for the reconstruction of the three-dimensional mean velocity structure is presented.

iIon irradiation induced interface mixing was used to generate silicon nanoclusters at the SiO2-Si interface of metal-oxide-semiconductor (MOS) structures aiming at electronic memory applications. No particular processing issues have been encountered during integration of this technique in standard submicronic C-MOS technology. The memory properties of the fabricated structures as a function of the Si+-irradiation dose and post-irradiation temperature and time have been examined through electrical measurements of capacitors and transistors. Low-voltage operating devices that can endure more than 106 programming/erasing cycles have been successfully achieved. While excellent device uniformity and reproducibility have been observed over 6-inch wafers, more research is still required to improve charge retention and ensure the standard 10-year retention time needed for true non-volatile memory applications.

The remediation of contaminated areas and facilities of the former uranium mining and milling in Saxony and Thuringia (Germany) requires detailed knowledge on the uranium migration in natural aquifer systems. Humic acids (HA), polyelectrolytic organic macromolecules, are of importance for the mobilization of radiotoxic and toxic metals in the environment due to their ability for complex and colloid formation. In addition, HA are characterized by redox properties that can influence the oxidation state of metal ions which effects their speciation and consequently their migration behavior.

In order to improve the knowledge on the interaction between HA and uranium we characterized the redox properties of different HA (Eh values, Fe(III) redox capacities) and studied the stability of the oxidation state of U(VI) in presence of HA on a time-scale of several weeks. We obtained a spectroscopic proof for the reduction of U(VI) to U(IV) by HA with pronounced redox functionalities applying laser-induced photoacoustic spectroscopy.

This demonstrates a possible relevance of HA for the migration of tetravalent actinides. Therefore, we investigated the transport behavior of the redox couple U(IV)/U(VI) in presence of HA in quartz sand by column experiments. Retardation factors and eluate recoveries were determined. We found that HA influences the transport of both, U(IV) and U(VI). In presence of HA both redox species migrate nearly as fast as the groundwater flow. In case of U(VI) HA exhibits a significant mobilizing effect. There are strong indications for a similar impact on the U(IV) transport.

The ability of hydroxyapatite Ca10(OH)2(PO4)6 (HAP) to immobilize metal ions, particularly lanthanides and actinides, is well known. The long-term stability of this fixation is proven by natural analogue studies. Thus, HAP is a potential filling material in engineered barriers in abandoned mining areas as well as in the near-field of underground repositories for nuclear and toxic waste.
The interaction of U(VI) with HAP was studied in batch and unsaturated column experiments and by time-resolved laser-induced fluorescence spectroscopy (TRLFS). We investigated a seepage water from Schlema (Saxony) with a Uranium concentration of 10-5 M and a syn-thetic HAP packed in a matrix of purified quartz sand.
The batch sorption experiments show 100 % adsorption of UO22+. The break-through curves measured in the column experiments with continuous pulse injection yield a retardation factor Rf = 33.2 ± 1.5 compared to the conservative tracer tritiated water. This value corresponds to the strong adsorption behavior. An elution of the column with ten pore volumes of a uranium-free solution revealed a distinct tailing and a uranium recovery near unity. Thus, the sorption process proved reversible. The TRLFS measurements facilitate a differentiation of uranium bound to the HAP surfaces and to the quartz matrix. Furthermore, the surface speciation of uranium could be identified. Finally, a numerical model using the reactive transport code Crunch describes the transport behavior of uranium.

Natural aquatic and terrestrial environments exert large variations in redox state due to oxygen diffusion on one hand and microbial processes on the other hand. Actinides with their large number of oxidation states are especially susceptible to these redox changes, forming different aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell, which allows to study the structure and speciation of aqueous actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. Due to the specific safety requirements for handling of radioactive materials the electrochemical cell is gas tight. The spectro-electrochemical cell comprises two safety compartments and a special electrode arrangement. First U LIII-edge X-ray absorption spectra have been obtained from aqueous solutions of U(VI) and U(IV) in high concentrated chloride solutions.

Dokumentation zu einem IDL-basierten Steuerprogramm für die Prozesssteuerung einer MBE-Anlage

The small punch test (SPT) is a suitable miniaturized test method to determine the actual and local material state in structural components under operating conditions. A combined experimental-numerical approach is presented to identify material parameters of plastic deformation and ductile damage behaviour from the SPT. Neural networks (NN) are generated and trained by finite element simulations to obtain the relation between a load displacement curve of the SPT and the matching material parameters. These parameters, identified from the SPT, are validated by reference values determined from smooth and notched tensile specimens. Next, the same parameters are used to simulate the ductile crack growth in fracture specimens by means of finite elements. This way, even fracture thoughness data J_Ic of the materials could be successfully predicted. These findings substantiate the feasibility to gain comprehensive material characteristics from the SPT and their transferibility to quantify the ductile failure of strucural components.

Die Studie beinhaltet die Sichtung, Zusammenstellung und Bewertung der zur Bearbeitung sicherheitstechnischer Fragestellungen benötigten Daten für die Modellierung geochemischer Prozesse. Der Abschlussbericht basiert auf den im Rahmen dieses Projektes erstellten Zwischenberichten. Die nach Sichtung und, soweit möglich, kritischer Begutachtung ausgewählten Daten sind in einem separaten Anhang in tabellarischer Form zusammengestellt.

In photothermal beam deflection (PTBD) spectroscopy generating and detection of thermal waves occur generally in the sub-millimeter length scale. Therefore, PTBD provides spatial information about the surface of the sample and permits imaging and/or microspectrometry. Recent resulrs of PTBD experiments are presented with a high spatial resolution which is near the diffraction limit of the infrared pump beam.

Die auf dem “Master-Curve” (MC)-Konzept basierende ASTM-Prüfvorschrift E 1921 ist für die Ermittlung einer Referenztemperatur T0 homogener Stähle mit einer kubisch-raumzentrierten (ferritischer) Grundstruktur konzipiert. In der Realität sind große Schmiederinge, Grobbleche und insbesondere Schweißverbindungen makroskopisch oft nicht homogen. Aus diesem Grund wurden auf dem MC-Konzept basierende Verfahren entwickelt, mit denen sich Referenztemperaturen von inhomogenen Stähle ermitteln lassen. An russischen Reaktordruckbehälterstählen des Typs 15Kh2MFA werden J-Integral basierte Bruchzähigkeitswerte KJc beim Ein-satz von Spaltbruch gemessen und nach der Standard MC-Methode und den modifi-zierten Verfahren ausgewertet.
The Master Curve (MC) approach of defining reference transition temperature, T0, has been standardized in ASTM Standard Test Method E 1921. The basic MC approach for analysis of fracture test results is intended for macroscopically ho-mogeneous steels with a body centred (ferritic) structure only. In reality, the steels are seldom fully macroscopically homogeneous. In this paper, new comparatively simple extensions of the MC are applied on forgings of Russian reactor pressure vessel steel 15Kh2MFA. J-integral based fracture toughness values KJc measured at the onset of cleavage fracture were evaluated with the basic MC evaluation, the lower tail modification of the SINTAP procedure, a bimodal estimation and a maxi-mum likelihood estimation of the random inhomogeneity.

The successful quasi-particle model is compared with recent lattice data of the coefficients in the Taylor series expansion of
the excess pressure at finite temperature and baryon density. A chain of approximations, starting from QCD to arrive at the model expressions for the entropy density, is presented.

Non-invasive imaging of genes which are introduced into cells is a useful method for gene therapy monitoring. The labeling of acyclic purine and pyrimidine nucleoside derivatives with fluorine-18 required for the HSV-1 tk imaging approach with Positron Emission Tomography (PET) 18 is described. The methoxytritylated and tosylated precursors were radiolabeled using a K[¹⁸F]F/kryptofix 2.2.2^TM complex, followed by removal of the protecting groups under acidic conditions and HPLC purification. The radiochemical yields of the ¹⁸F-tracers amount to 5 - 15 % (decay corrected) after a synthesis time of 85 - 95 min, the radiochemical purity was > 98 % with an average specific activity of 19 GBq/μmol at the end of synthesis.

Molecular speciation is a prerequisite for reliable assessment of contaminant migration in the environment. We use sophisticated techniques for concentrating colloids (e.g. ultracentrifugation, ultrafiltration) in combination with Extended X-ray Absorption Fine Structure (EXAFS) and Attenuated Total Reflectance Infrared (ATR IR) spectroscopy to investigate the speciation of colloid-borne uranium in waters which occur in abandoned ore mines. Mine flooding was simulated in a 100 L scale by mixing acid mine water of elevated U concentration and near-neutral groundwater from an aquifer above the mine until pH~5.5 was reached. The generated colloids adsorbed 95% of the total uranium and consisted mainly of 2-line ferrihydrite (Fh) besides traces of aluminum, sulfur, sil-ica, and carbon compounds. EXAFS analysis at the U-LIII absorption edge suggested a bidentate surface complex of UO22+ on FeO6 octahedra, but two minor backscattering contributions in the vicinity of the absorber remained unexplained. Since only Al could be excluded as backscattering atom, we studied U sorption on Fh at pH 5.5 in presence and in absence of sulfate, silicate, and atmospheric CO2 to clarify the bond structure.

EXAFS showed the unknown backscattering contributions in all the sorption samples regardless of the presence or absence of the tested components. Contrary to structural models in the literature, bidentately complexed carbonate ligands cannot explain the results when using U concentrations around 0.1 mM. But ATR-IR spectra showed that U(VI) carbonato complexes must be involved in the sorption of uranyl on Fh. These results are not contradictory if the carbonate ligands were bound monodentately, which is currently being studied. Nevertheless, carbon cannot act as backscattering atom in carbonate-free samples prepared in N2 atmosphere. Monte-Carlo Target Transform Factor Analysis was employed to test if the EXAFS spectra could be fitted by a struc-ture including exclusively Fe, U, and O atoms. We propose a new model in which the bidentately bridged UO22+ is oriented in a way that yields a distance of ~2.9 Å to the O atom of an adjacent, edge-shared FeO6 octahedron. This model predicts a second Fe shell at ~4.35 Å which tightly fits the experimental data.

Summarizing, uranium may form different sorption complexes with colloidal Fh: a binary bidentate uranyl complex with modified orientation, and ternary U carbonato complexes with monodentate linkage of the carbonate ligands, depending on specific conditions.

The performance of the normalization method (NM) is evaluated and compared with the standard unloading-compliance method of fracture-toughness analysis for a broad spectrum of different materials and specimen geometries. The critical J-integral values based on the normalization method are summarized and compared with the results of unloading compliances tests. The results demonstrate the applicability of the normalization method for the J-R curve determination for a range of steels. The normalization method yields results, which deviate as much as 15 % from the values obtained with the unloading compliance method, and thus results of acceptable accuracy can e attained with this method.

This paper provides a summary of Master Curve fracture toughness test results on small surveillance-type single- edge bend (SE(B)) and one-inch thick compact tension (1T-CT) specimens of the IAEA reference reactor pressure vessel (RPV) steel JRQ and other national RPV steels from numerous laboratories throughout the world. The JRQ test blocks distributed to the different laboratories were mainly from test plate 6JRQ. The mean fracture toughness of the 6JRQ plate material generally can be described satisfactorily with the standard Master Curve method from ASTM E 1921-02. The mean T0 values shows in accordance with previous investigations that a bias of around 10 K exists between the T0 values of CT and SE(B) specimen types so that CT specimens give higher T0. The analyses of both JRQ and national RPV steels confirm that the procedures specified in ASTM E 1921-02, as well as the SINTAP procedure, are generally valid and applicable for characterizing RPV type steels and even steels showing distributed inhomogeneity.

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wird nachgereicht

wird nachgereicht

The capabilities and limitations of wavelet analysis are demonstrated for the illustrative case of two practial applications: investigation of magneto-tunneling signals and the extended x-ray absorption fine structure (EXAFS) of uranium. A brief introduction to wavelet analysis is given. The term "window size" of the mother wavelet function is defined; this concept underlies one of the ideas for a criterion of optimal choice of the mother wavelet function. The capabilities of a software package developed by the authors are demonstrated; this software was used for all the calculations done in the course of this study.

Extended Xray absorption fine structure data evaluation usually begins with the Fourier transform of the spectrum. We suggest the wavelet transform as a complement to the Fourier transform. While the Fourier transform analyzes the distances to the backscattering atoms, wavelet transform additionally reveals the wavenumber dependence of the scattering. Thus wavelet analysis can differentiate between heavier and lighter backscattering atoms, even if they are almost equidistant from the central atom. First the method of operation and the advantage of the wavelet analysis will be demonstrated by simple models. Then it is applied to the interpretation of extended Xray absorption fine structure spectra concerning the complexation of UraniumVI with the carboxylic groups acetic, formic, and glycolic acid. The wavelet transform analysis suggests clearly for the system Uraniumformic acid both, UU and UCC, structural elements. In contrast to the clear separation of different scattering paths by wavelet transform, Fourier transform analysis was not able to resolve the two different backscattering processes.

Surface Complexation Models (SCM) can describe sorption processes at the mineral-fluid interface on a scientific, quasi-thermodynamic basis. The effect of parameter uncertainty in blind predictions is illustrated by the example of Np(V) sorption onto hematite.
The Diffuse Double Layer (DDL) model was chosen as SCM submodel to keep the number of parameters at a minimum. From the surface species reported so far, =FeOH₂ ⁺, =FeO^-, =FeONpO₂, =FeONpO₂(HCO₃)₂ ^2-, =FeOHCO₂, and =FeOCO₂ ^- were selected with their normalized DDL reaction constants log K_n, taken from the RES³T database (Brendler et al., 2003).
The modeling was performed with the FITEQL code, version 3.2. The predictions were evaluated by comparison with the experimental results by Kohler et al. (1999), comprising of 52 data points for the Np(V) sorption at varied pH, ionic strength, solid/liquid ratio, Np content, and air P_CO2. When focusing on the conventional distribution coefficient K_D, the maximum deviation for all data subsets is less than one order of magnitude, a spreading considered to be reasonable in performance assessment applications.
Because the protolysis constants can not be varied independently, the point of zero charge (PZC) and delta pK were calculated based on experimental pK₁ and pK₂. Consequential we generated 20 independent pK data sets with the aid of Gaussian-distributed random numbers. None of these parameter sets did deliver unacceptable blind predictions for the distribution coefficients.
The formally large scatter of pK values as extracted from literature is actually not critical. Even the use of inconsistent values from other electrostatic models will yield similar results. For well-defined mineral systems, provided a suitable database is accessible, the SCM approach seems to be promising.
(References: Brendler V. et al. (2003), J. Cont. Hydrol., 61, 281-291.; Kohler M. et al. (1999), Radiochim. Acta, 85, 33-48.)

The relations linking structure, microhardness and adhesion were studied for ion-beam mixed tungsten layers deposited on the surface of high-speed steel. The 45 nm thick W layer were mixed with 340 keV Kr ions at temperatures ranging fro, RT up to 450°C. The increase of mixing temperature results in partial crystallization of the layers and the increase of the layer hardness. Substantial increase of layer adhesion has been observed in scratch tests for all mixed samples.

To gain a better understanding of the behavior of the reactor pres
sure vessel lower head in case of a core meltdown scenario in a light water reactor experiments have been conducted worldwide. Especially for experiments including a heated melt pool in the lower head like FOREVER (performed at the Royal Institute of Technology, Stockholm) it is necessary to model the melt pool convection and the temperature field within the vessel as well as creep and plasticity processes and the dislocation of the melt pool due to the expanding vessel.
Therefore a 2D Finite Element Model with 3 different sub models is developed based on the code ANSYS® Multiphysics. A thermal sub model includes planar and contact elements for conductive heat transfer. Additional surface elements are used to simulate convection and radiation from outer surface areas and a radiation matrix is used to account for internal radiative heat exchange. Normally a CFD-simulation would have been required for the natural convective heat transfer in the melt pool, but at very high internal Rayleigh numbers there is no turbulence model that correctly simulates the heat transfer. Therefore an Effective Conductivity Convectivity Model is implemented to simulate the heat transfer from the melt pool to its boundaries.
The resulting temperature field of the vessel wall is applied to the mechanical sub model of the vessel. To describe the visco-plastic deformation a numerical creep data base was developed where the creep strain rate is evaluated in dependence on the current total strain, temperature, and equivalent stress. For an evaluation of the failure times a damage model according to an approach of Lemaitre is applied. The third sub model uses hyperelasticity and contact elements to move the melt pool along with the creeping vessel wall.
In this paper the differences between the results of a simple coupled and a recursive coupled FE-simulation are highlighted. Due to the thermal expansion at the beginning and the accumulating creep strain later on the shape of the melt pool and of the vessel wall are changing. Despite the fact that these relative small geometrical changes take place relatively slowly over time, the effect on the temperature field is rather significant concerning the mechanical material behavior and the resulting failure time. Assuming the same loading conditions the change in the predicted failure time between the simple and the recursive coupled model is in the order of magnitude of the total failure time of the simple model. The comparison with results from the FOREVER-experiments shows that the recursive coupled model is closer to reality than the single step model.