Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


(2)

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

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

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

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

Calculations relating to the OECD/NEA/CSNI International Standard Problem No. 33 were carried out with the GRS code ATHLET.This problem was a natural circulation experiment with primary coolant inventory reduced stepwise. The experiment was conducted in the PACTEL facility in Lappeenranta (Finland), which is a 1/305 volumetrically scaled, full height three loop simulator of the Russian VVER-440 type reactor. The main events of the experiment could be shown and explained by the ATHLET calculations:

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

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

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

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

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

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

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

The possibilities to evaluate radioactive contaminated sites with knowledge-based methods are discussed on the basis of a knowledge-based evaluation system for non-radioactive sites. The discussion treats methodical and programming aspects.

A computer system is presented which will be an effective support for the Saxonian government offices responsible for the evaluation of contaminated sites and the decision concernig the kind of remediation. This system XUMA (German synonym for expert system on environmental hazards of contaminated sites) includes a knowledge base with the principal methods for handling contaminated sites. The main features of XUMA are:

Evaluation of contaminated sites,
Creation of analysis plans,
Assessment of contaminated sites,
Knowledge acquisition tool and
Explanation capability.
Furthermore XUMA's embedding into environmental IT-systems in Saxony is described.

A concept for the use of decision-analysis in planning local energy distribution systems is introduced. The concept is based on the coupling of multiple independent modules, what enables the finding of a solution optimum in cost and environmental compatibility by variation of boundary conditions and input parameters. The first modul is presented.

A knowlegde-based strategy for the evaluation of risks produced by contaminated sites is presented, which also gives a ranking for the temporal sequence of remediation. This strategy supports the responsible government offices. It is based on the Saxonian evaluation method for contaminated sites and is implemented in the computer programs XUMA and GEFA.

The influence of an external magnetic field on LMMHD two-phase flows in vertical rectangular ducts has been examined. The goal of the work is the construction of models being able to predict the average behaviour of the flow as well as being relatively easy to survey and to handle. Results regarding the slip ratio obtained from a bubbly flow model are compared with experimental data got from measurements at the mercury-air facility. In the case of an applied magnetic field discrepancies between model and experiment are obtained giving an indication of the imperfection of the present state of the model. The crucial point is the validation of the semiempirical closure laws involved in the LMMHD tow-phase flow models. In the present state of the experiments the influence of the void fraction on the apparent electrical conductivity of the two-phase flow has been investigated. The results obtained from the mercury-air facility of LEGI-IMG are located between the relations given by Maxwell and Petric & Lee, respectively.

Neutron embrittlement of reactor pressure vessel is a critical safety-related problem for VVER type reactors. For a better knowledge of this problem an irradiation programme was carried out in the VVER-2 reactor in Rheinsberg from 1984 - 89. With the programme the procedure and methods for the calculation of the transition temperature shift should be examined, the irradiation-induced change of fracture toughness should be determined and the influence of postirradiation annealing had to be investigated. 33 heats of both basic and weld material from low alloyed Cr-Mo-V and Cr-Mo-Ni steels were tested. The neutron fluence amounted to (1.5-79) x 1018 n/cm² (E>1MeV). In the unirradiated state the VVER material shows satisfying properties of strength and toughness and is comparable with the performance of ASTM type steels. The shift of the transition temperature is not always correctly predicted by means of the normally applied trend curves.

The dependence of the mechanical properties on the depth position in unirra- diated state and after irradiation up to neutron fluences of approximately. 5 x 1018 and 70 x 1018 cm-2 (E > 0.5 MeV) is tested on a forging made of VVER 440 reactor pressure vessel steel 15CrMoV. Specimens taken from a sub-surface region shows a higher strength and a lower transition temperature than ones from 1/4 - 3/4 of the wall thickness. Increased irradiation reduces these differences. The testing of specimes from the 1/4 depth position within the surveillance programme, as normally demanded by monitoring rules for nuclear power plants, results in a conservative safety assessment against brittle fracture even in the case of EOL fluence. By taking into account fluence attenuation, the flux effect etc., the toughness increases over the wall thickness from the inside to the outside after a longer operating time of the RPV.

Thin layer studies at the material research goniometer of the ROBL-
CRG beamline (ESRF Grenoble)

F. Eichhorn, W.Matz, F.Prokert, M. Betzl, P. Reichel, N. Schell

Forschungszentrum Rossendorf,
Institute of Ion Beam Physics and Materials Research,
P.O.B. 510119, D - 01314 Dresden, Germany

The Forschungszentrum Rossendorf installed a collaborating research
group (CRG) beamline at the European Synchrotron Radiation Facility
(ESRF) in Grenoble. The main parts of the Rossendorf beamline (ROBL)
are the beam conditioning optics, a radiochemistry end-station for
the study of radioactive materials by X-ray absorption spectroscopy
and a materials research end-station mainly intended for structural
studies of solids and melts by diffractometry and reflectometry.
The synchrotron X-ray beam is monochromatised and focused by a
successive reflection and diffraction at a first mirror, a double-
crystal mono-chromator and a second mirror. The whole possible
energy range extends from 5 to 35 keV with an resolution Delta-E/E = 1E-4 - 1E-5. The beam divergence can be controlled by bending the second
crystal and the second mirror.
A six-circle goniometer is installed for materials research studies.
Two parallel circles (for the sample and the detector) each with
horizontal and vertical axes allow experiments in both scattering
planes. The sample can be adjusted by two additional axes. The
minimum angular step of all circles is 0.0001°. The sample position
can be equipped with an x-y-z slide. Of special interest to study
are structures in thin near-surface regions of solids as this is the
typical modification region for samples treated by ion beam
techniques.
A survey about the experiments done so far will be given. As
examples of thin layer problems studied at this goniometer, in
detail it will be reported on phase transition studies of N
ionimplanted Ti-6Al-4V alloys in the paper of F. Berberich (this
school) and here on ...

After a short review about the state of art of spectrum adjustment for reactor pressure vessel dosimetry and their realization in Rossendorf plans for future developments are described. The most important outstanding problem is the calculation of covariances of the theoretical input spectra.
As example for an advanced spectrum adjustment some preliminary results of a reevaluation of 1984/85 irradiation experiments in Rheinsberg were presented.
Suggestions are made for common projects in the frame of the WGRD, VVER and EWGRD, especially the development and maintenance of a common reactordosimetric database for VVER type reactors and the organization of benchmark exercises for calculations of detector cross sections and spectrum covariances.

A general survey was given about the problems and growing possibilities of the Monte-Carlo method applied to particle transport.
In particular the following items were considered:

• the mathematical foundations of Monte Carlo methods
• analog games
• nonanalog games and the possibility to obtain zero variance
• equation for the variance in the analog and nonanalog case, meaning of impor tance function
• danger of miscalculation connected with nonanalog games
• "Weight Window Method" and analytical investigations to improve this method
• alternative methods to decrease the statistical errors
• possibilities to calculate optimum weights

Information was given about the Rossendorf system of Monte Carlo codes including measures for variance reduction with respect to the calculation of fluences at irradiation points within the Rheinsberg reactor. It was shown that by the used methods it was possible to obtain results with low statistical errors and therefore Monte Carlo methods are well suited for the determination of neutron fluences if applied to that part of the problem, where transport calculations are needed. The sensitivity of the obtained results against the used group sets of neutron data was considerably reduced by improving the calculation of scattering at hydrogen isotope, which is very important for this kind of calculation.

Problems of the calculation of neutron fluences for reactor pressure vessel embrittlement determination were discussed. For the example of the calculation of neutron fluences of irradiated specimens within the Rheinsberg reactor (time period 1984-1988) it was shown, for which parts of the problem Monte Carlo methods can be very well applicated.
Some special measures were discussed, which are used for the own Monte Carlo codes (system TRAMO), especially the improved "Weight Window Method" and a proper calculation of the needed weights. Further the preparation of all needed data to take into account the history for each irradiation period was described and the influence of different neutron group data and the different handling of anisotropy of elastic scattering was considered.

During abnormal core barrel motion of a VVER-440 type reactor significant phase relations and coherences between incore and excore neutron noise signals were observed. For the explanation of the phenomena a numerical algorithm based on the non-linear equations of motion of a double pendulum was developed. In order to confirm the numerical results qualitatively additional experiments at a small set-up modelling the control elements were performed. The typical signal patterns observed at the VVER-440 could be shown to originate from mechanical impacts between the control elements and the neighbouring fuel cassettes.

A set of technetium(V) mixed-ligand complexes was synthesized with different protonation constants pK_a, brought about by substitution. They were characterized regarding their lipophilicity and compared to the corresponding rhenium(V) complexes. Partition coefficients P, determined by reversed phase HPLC and the octanol shake flask method, were higher for the technetium than for the analogous rhenium species. Investigations were performed to assess the influence of the physicochemical molecule parameters on the biological behaviour of these compounds. The state of ionisation of the molecules had a significant influence on brain uptake in vivo. Less uptake was found for compounds with pK_a values around 9.5, which are fully protonated at physiological pH, than for those with pK_a values around 7.5, which are ionised to only about 50% at pH 7.4. transport through cells was studied with an in vitro blood-brain barrier (BBB) model, based on the human umbilical cord cell line ECV304. The resulting in vitro permeation curves agree with the in vivo results obtained in mice and rats with short incubation times (up to 30 min).

Während der anomalen Kernbehälterbewegung bei einem Reaktor vom Typ WWER-440 wurden signifikante Phasen- und Kohärenzbeziehungen zwischen dem Excore- und dem Incoreneutronenrauschen beobachtet. Für die Erklärung der Phänomene wurde ein numerischer Algorithmus entwickelt, der auf den nichtlinearen Bewegungsgleichungen eines Doppelpendels beruht. Zur qualitativen Verifizierung der numerischen Resultate wurden außerdem Experimente an einem kleinen physischen Modell der Regelelemente durchgeführt. Es konnte nachgewiesen werden, daß die am WWER-440 beobachteten typischen Signalmuster von mechanischen Anschlagvorgängen zwischen Regelelementen und benachbarten Brennstoffkassetten herrühren.

In 1985 abnormal core barrel motion had occured at unit 2 of the Greifswald NPP indicated by extremly large neutron noise. Amplitudes of up to 4mm were estimated from the external neutron noise signals.
The coherence and phase relations between excore and incore neutron noise signals exhibited typical features from which it could be concluded that even the control elements were forced to vibrations by the moving core barrel.
To obtain principal understanding about these phenomena and to draw conclusions for the surveillance of the excore and incore neutron signals, experimental and numerical investigations were performed. An experimental set-up was constructed providing all necessary displacement signals via HALL probes. This physical model, being a double pendulum with an annular channel surrounding the lower pendulum, can be operated in a linear mode (small excitation amplitudes) as well as in a non-linear mode (larger amplitudes which cause impacts between channel and lower pendulum).
The numerical simulation algorithm is based on a mechanical system consisting of linear elements (inertia, dampers, springs) and non-linear elements (gaps). In this way impacts between control element and neighbouring fuel cassettes which are strongly non-linear events can be modeled. After simulating the time series, which is possible for any detector position at the control element or at the set-up respectively, transfer functions, coherences, phase relations etc. can be computed.
It could be shown that the typical linear phase shifts between excore and incore neutron noise signals are due to impacts between the control elements and the neighbouring fuel cassettes. The obtained results can be used to establish a sensitive detection procedure for control element vibrations induced by abnormal core barrel motion.

Es wurde ein Ultraschallverfahren zur Rißlängenmessung während des Dreipunktbiegeversuchs entwickelt, das auf der Beugung von Ultraschallwellen an der Rißspitze beruht. Die Information über Rißlänge und Rißfortschritt wird aus der Laufzeit der gebeugten Ultraschallwellen gewonnen. Das vorgestellte Verfahren ist das einzige der bisher bekannten Ultraschallverfahren, das an einer so kleinen Probenform erfolgreich angewendet wurde.

Für die Wohnsiedlung Rossendorf wurde ein Meßsystem zur Erfassung der Wärmeflüsse für Heizung und Warmwaser entworfen, realisiert und erprobt. Zum Einsatz kam ein industrielles Meßsystem mit Prozeßrechner der Firma Johnson Controls. Durch Testmessungen wurde der Nachweis der Funktionsfähigkeit der Anlage erbracht. Als kritisch erwies sich die genaue Bestimmung der Wärme- bzw. Volumenströme.

Re/Tc labelled nucleobases and nucleosides are developed and characterized in connection with cell uptake studies on cultured normal and tumour cells [1,2]. Stable Re and Tc complexes of nucleic acid components have been prepared where uracil derivatives are either involved in a mercaptoacetyl glycine (MAG) SN₃ coordination sphere or are part of "3+1" mixed-ligand complexes. Furthermore a prelabelling method has been successfully used for coupling the nucleic acid components to a performed Re/Tc complex.
Uptake of such complexes into proliferating cultured normal and tumour cells and their crude cytosolic and nuclear fractions, including postincubation effects and the influence of the metabolic state of the cells, has been observed.

Für ein im Bau befindliches konventionelles Heizsystem auf Erdgasbasis wurden technische Varianten einer einzubindenden Solaranlage untersucht. Dabei stand die optimale Nutzung und Verteilung der von der Solaranlage zu liefernden Wärme im Vordergrund. Als ausschlaggebend erwiesen sich die Berücksichtigung unterschiedlicher Temperaturniveaus der verschiedenen untersuchten Abnehmer (Wohngebiet, Schule). Für 2 Varianten erfolgte eine Systemauslegung und eine Abschätzung der zu erwartenden solaren Gewinne.

Im Rahmen der wissenschaftlich-technischen Zusammenarbeit zwischen Deutschland und Rußland und einem Koordinierten Forschungsprogramm der IAEA wird das Bestrahlungsverhalten russischer und westlicher Reaktordruckbehälter(RDB)stähle untersucht. Im unbestrahlten Ausgangszustand weisen die Chargen des Grundwerkstoffes 15Ch2MFA des russischen Druckwassereaktors WWER-440 eine große Streuung in den im Charpy-V Test ermittelten Übergangstemperaturen und Hochlageenergien auf. Eine geringe Streuung in diesen Kennwerten haben die untersuchten Chargen des Grundwerkstoffes 15Ch2NMFA(A) des russischen Druckwasserreaktors WWER-1000. Die ermittelten Übergangstemperaturen liegen niedriger als bei den ASTM RDB-Stählen A533B Cl. 1 und ASTM A508 Cl. 3. Die J-Integralwerte für technische (J0,2)- und physikalische Rißinitiierung der untersuchten RDB-Stähle und der dazugehörigen Schweißgüter wurden mit den Hochlageenergien aus dem Charpy-V Test und den Streckgrenzen des Zugversuches korreliert.

A German/Russian irradiation programme was performed in the high flux irradiation channels of the PWR VVER-2 Rheinsberg from 1984 to 1987. Within the programme Charpy-V-, COD-, 0,5-CT-, X-CT- and 1-CT specimens of reactor pressure vessel (RPV) steels 15Kh2MFA and 15Kh2NMFA(A) and RPV weld metal 10KhMFT, 10Kh2MFA(U) and 10KhNMA(A) were irradiated. These materials are used in the pressurized water reactor of Russian type VVER-440 and VVER-1000. The irradiation of one series of experiments took one year. In this paper the unirradiated initial state of the material is characterized. The mechanical properties measured at different temperatures include instrumented Charpy-V notch- and quasistatic fracture toughness data. Furthermore the neutronfluence of the specimens were calculated in dependence of the position in the high flux irradiation channels of the PWR VVER-2 Rheinsberg.

Anhand von Beispielen wurden elastische low blow's und deren komplexes akustisches Verhalten an einer ungekerbten hochfesten Stahlprobe unter Ausschluß von plastischer Deformation und Rißbildung diskutiert. Störsignale, die durch verschiedene Prozesse generiert werden, sollen somit besser verstanden und letztlich von Nutzsignal separiert werden. Die Korrelation der gemessenen Störsignale zu charakteristischen Ereignissen, wie Reibungsquellen und mechanischer Kontakt, gelang noch nicht. Deshalb wird eine zusätzliche AE-Instrumentierung von Probe und Widerlager in Betrach gezogen, die bei der Störquelleninterpretation hilfreich sein wird.

A new nodal method HEXNEM2 for hexagonal geometry is described. The method is based on a two-dimensional expansion of the intranodal fluxes. Polynomials up to the second order and exponential functions are used in each group. By this method the singular terms occurring in the transverse integration methods are avoided. Side averaged and corner point values of fluxes and currents are used for the coupling of nodes. A calculation scheme for the outgoing partial currents at the sides and similar expressions for the corners from given incoming values are used in the inner iteration which gives a fast running scheme. The method is tested against 2-dimensional hexagonal benchmark problems for the VVER-type reactors. The results show that the multiplication factor and nodal powers are predicted accurately. A considerable improvement can be shown of the results for the VVER-1000 benchmarks compared with the method developed previously for the code DYN3D and the simpler method HEXNEM1.

The pulsed fast reactor IBR.2, Dubna, is at present the most powerful pulsed neutron source used for condensed matter research. The neutron pulses are generated periodically by reactivity modulation, which is accomplished by a rotating two-reflector system. The neutron physics which has been involved in the development of various reflectors is analysed with respect to the neutron pulse length. Two new reflectors are proposed.

A review on R&D activities of the FZR group in the field of Liquid Metal MHD is given in this lecture. Special attention is paid to sodium related experiences (facility, experimental programme, measuring techniques) being of interest for the Breeder development. In particular, first tests of a contactless gas phase detection system are presented. This system was developed by RWTH Aachen and FZR, and tested for the first time at FZR. It allows a detection of small, even single gas bubbles independent of their acoustic activity.

A review on R&D activities of the FZR group in the field of Liquid Metal MHD is given in this lecture. Particular emphasis is put on the measurements and theoretical results with respect to heat&mass transfer in anisotropic MHD turbelence. Corresponding models, experimental set-ups, and measuring techniques are described. Two-phase flow measurements are presented obtained at the FZR sodium facility. The prospects of cylindrical turbulence promoters are discussed.

Control of melt motions is important for most of the crystal growth technologies in order to improve the crystal quality and the yield. There were several attempts in the past to use steady magnetic fields for a damping of instabilities. Much more possibilities for flow control exist if unsteady magnetic fields are used, preferably in combination with steady fields. This new active melt control is attractive for industrial use. Principal mechanisms of this type of flow control are presented in this lecture, particularly adressed to the needs of the Si-Cz-technology. The research project is developed together with the institute of physics Riga and Wacker Chemitronics Ltd. Burghausen

Up to now there are only few investigations on the microstructural change of VVER-type reactor pressure vessel steels after neutron irradiation. Consequently, the understanding of the mechanism of neutron embrittlement is not physically but only empirically based. Apart from the modern methods of high resolution analytical electron microscopy the small angle scattering with neutrons and X-rays enables experiments to gain information on size, volume fraction and composition or structure of nanometer-scale precipitates as they are typical for irradiation-induced ones. First experiments with these techniques have shown the irradiation-induced microstructural changes significantly differ from the changes which were found in ASTM-type steels. For continuing such investigations a programme of joint Russian-German investigation is suggested.

Irradiation-induced precipitates are the cause for neutron embrittlement of reactor pressure vessel steels. It can be shown that for the VVER-type steel 15Kh2MFA the shift in the ductile-brittle transition temperature depends nearly linearly on the volume fraction of these precipitates.
The nature of the irradiation-induced precipitates has been investigated at the steel 15Kh2MFA. This steel differes from ASTM-type A503 and 533 steels mainly in its content of the carbide forming elements chromium, molybdenum and vanadium.
Small angle neutron scattering (SANS) experiments using the SANS-2 facility at the FRG-1 reactor in Geesthacht (Germany) were employed in the past. SANS gives information about size and volume fraction of the precipitates, but hardly about the chemical composition.
In order to prove and to characterize the nature of the irradiation-induced precipi- tates anomalous small angle X-ray scattering (ASAXS) has been carried out at the JUSIFA facility of Hamburg synchrotron laboratory HASYLAB (Germany) at present. By the method of contrast variation, it is also possible to get information on the chemical composition.
ASAXS experiments with contrast variation at energies near the vanadium-K -absorption-edge reveal the content of vanadium within the irradiation-induced precipitates. The scattering density of the precipitates is lower than the scattering density of the iron matrix. The chemical shift of the vanadium K -absorption-edge shows that vanadium does not precipitate in an elementary state. Assuming, the precipitates are vanadium carbide these results can be explained. The results are in accordance with those of SANS experiments and former positron annihilation spectroscopy experiments.

The overall approach comprises the pure calculation part, the gamma spectrometric analyses of fluence monitors and the comparison of theoretical and experimental results using the spectrum adjustment procedure. Monte Carlo methods were used to perform the transport calculations. By application of special measures of variance reduction the statistical errors could be reduced so much that accurate 3-dimensional Monte Carlo methods could be generally used in reasonable calculation time. The uncertainties of the results due to the use of different group values of neutron cross sections were assessed by testing different group sets. In that way it could be shown that the kind of group data is of minor influence.

Es werden Erfahrungen der auf diesem Gebiet tätigen Mitarbeiter in Rossendorf bei der Berechnung und Messung von Neutronenfluenzen sowie bei der Anwendung der Spektrumsjustierung dargelegt. An Hand dieser Erfahrungen wird auf noch offene Probleme eingegangen, die insbesondere bei neutronendosimetrischen Problemen zum Reaktor WWER-1000 auftreten. Es werden Möglichkeiten zur Bewältigung dieser Probleme diskutiert und auf eigene Vorstellungen eingegangen. Insbesondere wird betont, daß man mit Hilfe moderner Verfahren der Varianzreduktion die genaue 3-dimensionale Monte-Carlo Methode als Standardverfahren für die Transportrechnungen anwenden kann.

The thermalhydraulic behaviour of a PWR during beyond-design-basis accident scenarios is important for the verification and optimisation of accident management measures and code development. Analyses require integral experiments, such as PKL III at Siemens / KWU, which simulates a 1300 MWe KWU-design PWR with scaling factor of 1:145.
The paper presents PKL III results obtained by needle shaped conductivity probes developed in the Forschungszentrum Rossendorf [1]. The probes provided local void fractions and particle frequences within an averaging period of 2s. This time resolution is sufficient to characterize slow transients. A special flow pattern map developed for the probes enabled the calculation of the length of an average bubble. The measured information was used to determine the changing flow regimes.
At first, a secondary side feed-and-bleed procedure was investigated. Two probes were installed in the feed water line close to the steam generators. A depressurization of the secondary side caused flashing of the feed water and discharge of two-phase flow. A comparison of the measured void fraction with the density reading of a radiation densitometer installed next to the probes shows good agreement. The experimentally found flow regimes are also consistent with expected trends from flow regime maps developed by other researchers (e.g. [2]). Both show slug flow at the beginning of the secondary-side depressurization.
In the second experiment, a primary-side feed-and-bleed following steam generator tube rupture, four probes were installed at one location in the vertical part of the pressurizer surge-line, but at different radial positions. Another set of probes was installed in the horizontal pressurizer bleed-line. Two of them were used for time-of-flight measurements providing velocity values directly. Flow regimes such as stratified flow in the horizontal tube or annular flow in the vertical tube were found during the depressurization.

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

The state-of art of ultrasonic two-phase flow measurements is characterised by a number of different approaches commonly based on the identification and characterisation of individual voids (bubbles, plugs etc.) applying the techniques of ultrasonic testing. The recorded individual events are integrated to extract parameters as void fraction or volume flow rates. The main limitation of these methods arises from the complicated structure of two-phase flow at higher void fractions which leads to multiple diffractions of the sound beam. The measurement is therefore limited to low void fractions or a simple flow structure.
The main idea of the present work was to overcome these limitations by means of pattern recognition. An ultrasonic beam crossing the two-phase flow is modulated by the changing structure of the voids passing by and therefore the through-transmission signal must contain information about the parameters of the two-phase flow even if information about individual flow effects cannot be derived. Therefore it was supposed that a pattern recognition algorithm trained with signals obtained at known conditions is able to identify the set of the flow parameters (flow rates, void fraction etc.) in an unknown situation.

The pulsed fast reactor IBR-2, Dubna, is at present the most powerful pulsed neutron source used for condensed matter research. The neutron pulses are generated periodically by reactivity modulation, which is accomplished by a rotating two-reflector system. The neutron physics which has been involved in the development of various reflectors is analysed with respect to the neutron pulse length. Two new reflectors are proposed.

In the Research Center Rossendorf post test calculations of the SPE4 were performed using the thermohydraulic code ATHLET. The SPE-4 experiment was a small break loss of coolant accident in the cold leg with unavailable high pressure injection system. For the prevention of core damage the secondary side bleed and feed was used. The experiment was performed at the Hungarian PMK-2 test facility, modelling the Paks VVER-440 reactor. In the calulations different nodalizations were tested for modelling the hydroaccumulators and the horizontal steam generator. Deviations between calculation and experiment were observed especially in the primary pressure decay and consequently in the behaviour of accumulator injection. It was found, that the prediction of observed core dry out depends on the correct calculation of the low pressure injection setpoint.

Eine Methode zur Erkennung und Ortung von Lecks an Druckanlagen komplizierter 3-dimensionaler Topologie ist entwickelt worden. Sie basiert auf der Merkmalsextraktion aus dem leckinduzierten Körper- und Luftschall und wendet neuronale Netze zur Mustererkennung an. Die zum Anlernen der neuronalen Netze notwendigen Schallmuster werden mit Hilfe von simulierten Lecks an einer Originalstruktur erzeugt. Als Merkmale zur Charakterisierung des Leckortes werden Kohärenzwerte zwischen hochfrequenten Mikrofonsignalen und RMS-Werte von Schallemissionssensoren angewendet. Die Methode ist sogar einsatzfähig, wenn die Leckortung auf der Basis von Laufzeit- oder Dämpfungsdifferenzen versagt. Die Methode wird prototypisch für einen russischen WWER-Druckwasserreaktor entwickelt. Die Anwendung neuronaler Netze ermöglicht eine Adaption der Leckortungsmethode an Druckanlagen unterschiedlicher Topologie.

A reactivity initiated transient caused by entering a plug of water with reduced boron concentration into the core during incorrect loop startup in a VVER-440/W-213 reactor is analyzed . Due to the asymmetric distribution of the boron dilution, significant space-dependent effects are expected. That requires the use of a three-dimensional reactor core model. The analysis was carried out with the help of the code DYN3D/M2 developed for investigations on reactivity initiated accidents in thermal reactors with hexagonal fuel elements. A semi-analytical model adjusted to experimental data on coolant mixing in VVER-440 type reactors is used for the estimation of boron concentration distribution at core inlet. For comparisons, the two limiting cases, ideal mixing and no mixing, are investigated.

The coupling of Re- and ^99mTc-MAG₃ complexes with amines and nucleobases was carried out with good yields using O-(benzotriazol-1-yl-)N,N,N',N'-tetramethyl-
uronium-tetrafluoroborate (TBTU), and base in polar aprotic solvents (NMP, DMF, DMSO). The one step reaction followed by simple gel chromatography makes the method well appropriate for preparations at the low no-carrier-added level of technetium-99m.

A series of rhenium "n+1" mixed-ligand, thioether-carbonyl and organometallic complexes of 21-substituted progesterone have been synthesized. The conjugates contain the rhenium metal at several oxidation states, being +5, +3 and +1. The complexes were used in a competitive receptor-binding assay (rat-uterus, 0°C) to determine their binding to the progesterone receptor. The best affinity of 9% (RU 5020=100%) was obtained with a "3+1" mixed-ligand complex, containing a NMe group as the central donor atom in the tridentate ligand part.

Mercaptoacetyl glycine (MAG₁) (1) forms, in the presence of appropriate monodentate ligands, tridentate/monodentate (3+1) coordinated complexes with Tc(V) and Re(V). Exchange of the chlorine by monodentate ligands in [MO(MAG₁)Cl]^- (2) gives access to new mixed-ligand complexes [MO(MAG₁)(XR)] (3) . Some representatives have been prepared and characterized by elemental analysis, ir and uv spectroscopy and EXAFS. Thiobenzoate as monodentate ligand gives the complex (4) that, after debenzoylation, reacts with halogen containing compounds under displacement of the halogen by a [MO(SNO)S] moiety.

Organic derivatives (2) of 6-methyl-8alpha-amino-ergoline 1 and derived complexes of rhenium (3,5) and technetium (4) have been prepared and evaluated with regard to their affinity to the dopamine D₂ receptor. The molecular structure of the rhenium complex 3 was determined. The affinity of the benzoyl derivative 2b is comparable with that of terguride (IC₅₀ values 2.7 for 2b vs. 4.8 nMol), while the affinities of the related Tc and Re complexes are in the range from 54 to 165 nMol.

Structural investigations on rhenium and technetium peptide complexes have been carried out using X-ray absorption spectroscopy (EXAFS) and capillary electrophoresis. Small cysteine containing peptides with altered amino acid sequences were used as model systems to study the metal complexation behaviour. By means of capillary electrophoresis, complex species existing over the pH range could be identified as well as protonable groups in these complexes. EXAFS measurements in solution delivered information about the complex coordination spheres. The metal complexation modes and complex stoichiometries of directly labelled metal complexes of large biologically active peptides could be elucidated.

Für eine gute Bildqualität bei gleichzeitig möglichst niedriger Strahlenbelastung für den Patienten ist es bei PET-Untersuchungen erforderlich, die Aktivität möglichst genau auf die Spritzen aufzuziehen. Dabei kommt es zu einer kaum vermeidbaren deutlichen Strahlenbelastung der Hände und insbesondere der Finger. Dies ist die Folge der nicht ganz einfachen Handhabung der Spritzen beim Füllen. Es ist fast unmöglich, die gewünschte Dosis - trotz Berechnung - beim ersten Mal genau aufzuziehen. Dadurch ist die Hand immer wieder in unmittelbarer Nähe der Aktivität, was letztlich die hohe Strahlenbelastung der Hand bedingt. Um diese Strahlenbelastung beim Abfüllen zu vermindern, sind neben den bereits bestehenden Strahlenschutzmaßnahmen, wie z. B. der Bleiburg mit Bleiglassichtfenster und dem mit Blei abgeschirmten Aufbewahrungsgefäß für das mit Aktivität gefüllte Vial, weitere hinzugekommen.
So werden bei größeren Mengen benötigter Aktivität (bei mehr als 3 Patienten) zwei Abfüllungen aus der Radiochemie angefordert, wobei die zweite Abfüllung erst dann in das Labor geholt wird, wenn die erste Abfüllung aufgebraucht ist. Weiterhin wird beim Aufziehen der Spritzen mit einer Zange, zum Halten der Spritze, sowie einer Pinzette, zum Halten und Fixieren der Kanüle, gearbeitet. Beide Maßnahmen dienen zur Vergrößerung des Abstandes von der Aktivität. Zur Registrierung der Strahlendosis wurde jeweils ein Fingerring pro Hand, eine Filmdosimeter und ein elektronisches Dosimeter getragen.
Es wird die mit den zusätzlichen Strahlenschutzmaßnahmen erreichte Verminderung der Strahlenbelastung der Hände vorgestellt, sowie die Bedeutung in Beziehung zur maximal zulässigen jährlichen Strahlendosis gewertet.

The synthesis of N-(MAG1)-histamine and the preparation of its Tc and Re complexes are reported. As proven by spectroscopic methods, HPLC investigations and by X-ray structure analysis, N-(MAG1)-histamine forms stable, neutral and square pyramidal 1:1 coordination compounds with MO3*-cores of Tc and Re. The preparation of the isostructural 99mTcO(V)-N-(MAG1)-histamine complex has been achieved with 80-95% radiochemical yield.

Objectives: In the past a series of I-123 labeled N-(dialkylaminoalkyl)benzamides have been successfully applied to image human melanoma metastases. This prompted the development of Tc-99m complexes which should mimic the biological characteristics of these benzamide derivates.
Methods: Four N-(2-diethylaminoethyl)benzamide derivatives have been synthesized comprising the following phenyl substituents for Tc-99m complexation: 4-(Bz-S-Ac-Gly-Gly-NH) 1, 3-(NH2)-4-(Bz-S-Ac-Gly-NH) 2, 3-(Bz-S-Ac-NH)-4-(Bz-S-Ac-NH) 3, and 4-HS 4. The Tc-99m complexes were obtained by treating ligands 1-3 at 100°C for 10 minutes with Tc-99m pertechnetate, tartaric acid and stannous chloride as a reducing agend. Complex 4 was formed accordingly in the presence of N-methyl-3-azapentan-1,5-dithiol at 50°C. Biodistribution time-course studies were performed using C57B1/6 mice with subcutaneous B16 murine melanoma.
Results: The highest melanoma uptake was obtained with complex 1(3.42 and 4.48 %ID/G at 1 and 6 hr pi, respectively). The melanoma affinity decreased in the order 1>>4>2>>3.The melanoma uptake corresponded proportional with the blood values. Thus bioavailability of the Tc-complexes in the blood seemed to control melanoma uptake. A similar dependency was observed with radioiodinated benzamides.
Conclusion: Among the compounds tested so far complex 1 proved to exhibit high melanoma affinity and deserves further investigations as a melanoma seeking radiopharmaceutical.

In the last years contaminated sites have become a relevant problem in the Federal Republic of Germany because there exist a large number of these sites. That's why in Germany more intensive efforts are undertaken in order to start necessary remediations. Basic initial conditions for an effective execution of these works are on the one side a systematic registration of these sites and on the other side the creation of a uniform evaluation capability for the assessment of environmental hazards.

Regarding this background the Research Centre Rossendorf (FZR) together with Nuclear Engineering and Analytics, Inc. Rossendorf apply and modify the computer code system XUMA (German synonym for expert system on environmental hazards of contaminated sites) which is a joint project of the Institute for Applied Information Science of the Karlsruhe Nuclear Research Centre and the State Institute for Environmental Protection of Baden-Württemberg. XUMA is a knowledge based computer system, which shall support the staff of the responsible governmental offices in the uniform evaluation of the hazard potential, the preparation of analysis plans, and the assessment of contaminated sites and mines.

To enable the registration and evaluation of contaminated sites at engineering offices FZR developes an interface program which can be generated automatically from the knowledge base of the expert system XUMA. This interface program can be executed at each IBM-compatible PC without any additional runtime environment.

An extensive irradiation programme was performed in the Rheinsberg VVER-2 reactor from 1984 to 1988. The programm comprised 25 different heats from base or weld metal of VVER-440- and 1000-type reactor pressure vessel steels using specimens of variant geometry (CT, COD, tension, Charpy-V). Mainly, it focused on validating of the safety assessment procedure and on determining of fracture mechanics parameters in their dependence of fluence and thermal annealing.
At present the investigation of the irradiated specimen is still outstanding. In the unirradiated state all VVER-type steels investigated show good toughness and strength properties and are comparable with A 533 class 1 and A 508 class 3 steels. The scattering between the different heats of same materials is partly large and does not correlate with the chemical composition or the heat treatment. The results of irradiated specimens up to now do not always confirm the values which are obtained on the base of the valid safety assessment procedure in a conserva- tive wise. That supports the urgency to extend the data base for irradiated VVER-type pressure vessel steels.

Aluminum carbide precipitates are formed after Al ion implantation with dose 3x10¹⁷ cm^-2 at 500°C into single crystalline 6H SiC. The aluminum carbide (Al₄C₃) precipitates are in epitaxial relation with 6H-SiC matrix, having the following orientation relation, [0001]6H-SiC//[11-20]Al₄C₃ and [11-20]6H-SiC//[11-20]Al₄C₃ , as transmission electron microscopy reveals. The aluminum carbide appears around the maximum of the Al depth distribution. Si precipitates were also detected in the same zone.

In Analogie zum Pilotprojekt für den 5. Block vom KKW Saporoshje - WWER-1000/W-320 - wurde für die beiden WWER-440/W-213 Blöcke vom KKW Rovno eine verbesserte betriebliche Überwachung eingerichtet. Dazu werden dem Vor-Ort-Inspektor am KKW Standort und der Aufsichtsbehörde in Kiew einmal pro Minute 55 aktuelle sicherheitsrelevante Parameter pro Block und 7 standortspezifische Parameter zur Erfassung und Bewertung mittels moderner technischer Mittel on-line zur Verfügung gestellt. Die zur Ausstattung des Arbeitsplatzes des Vor-Ort-Inspektors unbedingt benötigten Ausrüstungen wurden unter Berücksichtigung der aktuellen Anforderungen des KKW Rovno spezifiziert, beschafft und der ukrainischen Seite unentgeltlich überlassen. Bei Funktionstests Ende 1998/Anfang 1999 wurden Datensätze aus dem lokalen Rechnernetz des KKW Rovno fehlerfrei nach Kiew übertragen und auf einem Rechner im Informations- und Krisenzentrum in Form von Tabellen, Grafiken und Schemata dargestellt.

Das vor zwei Jahren im KKW Saporoshje in Betrieb genommene System zur verbesserten betrieblichen Überwachung wurde an die Kiewer Zentrale der ukrainischen Aufsichtsbehörde angeschlossen. Dazu wurden die für den Anschluß und die Ausstattung dieser Zentrale in der ersten Ausbaustufe unbedingt erforderlichen technischen Mittel einvernehmlich spezifiziert, in Deutschland beschafft, im notwendigen Umfang erprobt, in die Ukraine überführt und dem Partner am Einsatzort unentgeltlich überlassen. Bei der Erprobung des Informationstransfers aus dem KKW Saporoshje in die Kiewer Zentrale wurde nachgewiesen, daß die von der ukrainischen Behörde gemietete Standleitung die notwendigen technischen Anforderungen erfüllt. Bei Funktionstests Mitte Januar 1998 wurden On-line-Daten aus dem Saporoger System der verbesserten betrieblichen Überwachung fehlerfrei nach Kiew übertragen.
Ferner sind der ukrainischen Seite zum Anschluß des KKW Rovno an die Kiewer Zentrale die gleichen technischen Mittel zur Verfügung gestellt worden.

The presented work aimed at the experimental determination of rapidly changing void fraction distributions. The main idea was to apply arrays of needle shaped conductivity probes to a transient two-phase flow. The goal was to provide a time resolution in the range of tenth of a second. For a first application, a bubble column was investigated. The transient process was initiated by sudden changes of the flow rate of the injected gas (air). The experimental setup consisted in a vertical cylindrical column with an inner diameter of 0.24 m and a height of 2 m. In the bottom of the column a special injection plate was installed. About 200 steel cannulae served as injection nozzles. The injection nozzles were divided into two groups, which were fed from separate air distribution chambers. Both groups were equally distributed over the cross section of the column. This measure allowed to double or to halve the air flow rate without effecting the diameter of the generated bubbles, when the air supply of one of the distribution chambers is switched on and off. For the purpose of gas fraction measurement, 8 single wire probes were mounted on a movable probe comb. The diameter of the sensitive tip was 0.2 mm. The tran-sient void fraction distribution was measured on elevations of 0.4, 0.8 and 1.2 m. The transient process was initiated repeatedly by opening and closing the magnetic valve of the air supply system. After the changes, the air flow was kept constant for intervals of 10 s. The signals of the 8 void fraction probes were recorded and averaged over periods of 0.2 s for each realisation of the transient process. The data acquisition process was synchronised with the control of the magnetic valve. Afterwards, the obtained void fraction courses were superimposed. By repeating the transition process more than 400 times, an effective measuring time of at least 80 s for each void fraction value was achieved. The rapid change of the gas fraction pofiles and the gas fraction wave propagating through the column was measured.

Subsequent studies have identified many scenarios which can lead to reactivity excursions due to boron dilution. The comparative study, presented in this paper, deals with the so-called "restart of the first reactor coolant pump" scenario and its reactor-dynamic consequences for the both VVER reactor types - VVER-440 and VVER-1000.
The transient simulations have been performed using the three-dimensional core dynamics code DYN3D. The DYN3D modeling features, including recent developments, as well as the cross-section generation methodology, involved in these calculations, are described. The analyzed accident scenario is outlined together with the assumptions made. The results of core response in this boron dilution accident for both VVER reactors have been compared within ranges, determined by the two reactivity values of interest: the criticaly limit and the reactivity initiated accident (RIA) limit.