Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A new way to fabricate submicron CoSi2 structures on Si wafers is presented. The method consists of a combination of focused ion beam (FIB) implantation of Co+ ions and subsequent flash lamp irradiation. With our FIB equipment IMSA-100 one- and two dimensional structures were implanted by writing with a 35 keV Co+ beam which was focused to a spot diameter of 200nm. However, for the porposed method the spot size is not the crucial dimension because the final structure size is controlled by a local melting and recrystallization process in the implanted regions. Here the structure size is determined by the amount of implanted atoms which can be concentrated by the local melting process into the submicron CoSi2 structures. The local melting is caused by heteronucleation at the Si wafer surface during the short period of superheating, which is obtained by intense flash lamp irradiation of 3 or 20 ms duration. Disintegration of implanted CoSi2 wires by precipitate formation during thermal annealing, which was reported by Liddle et al. (Mater. Res. Soc. Symp. Proc. 279 (1993) 881), can be avoided by this method. The CoSi2 structures were analysed by scanning electron microscopy (SEM) and energy dispersiv X-ray analysis (EDX). Dots and wires of about 200 nm diameter and width, respectively, have been fabricated during these first experiments, whilst smaller dimensions seem to be possible in future.

Die Ergebnisse des ersten zehn Betriebsmonate der Solaranlage Freital werden vorgestellt. Bei einem Kollektornutzungsgrad von 29% wurde ein Ertrag von 264 kWh/m² erreicht. Für das erste volle Betriebsjahr wird ein Wert von 327 kWh/m² erwartet. Mehr als 2/3 der erzeugten Solarwärme wurde in das Fernwärmenetz eingespeist, der Rest diente der Warmwasserbereitung einer Schule.

In this report is described the theoretical and experimental determination of all needed parameters for the neutron exposure of the different specimens that were irradiated in the Rheinsberg reactor within the period from 1984 until 1988 to obtain data for neutron embrittlement studies.
The methodical approach is represented, possible sources of errors are discussed and all the needed results are collected. The work can be divided into a pure calculation part, into the description of the extraction of the monitors and their gamma spectrometric analysis and into the discussion of the spectrum adjustment procedure which combines experimental and theoretical results. Therefore, this representation deals not only with this special task but gives also a survey about the methodical approach and the state of art in Rossendorf for the general problem of determination of neutron fluences, because the developed methods are generally applicable and not limited to the special problem of neutron embrittlement. Different problems with respect of neutron fluences exist also in Germany.
The calculation of fluences is based on an accurate description of the history of the reactor for all irradiation periods, i.e. the time and space dependence of burnup, power and fisson sources. This information was given for a time and space grid of all fuel elements.
For the calculation of the fluences were not used time dependent fluxes, but at first integral sources of fission neutrons are calculated for different fissionable isotopes. Using these given integral source distributions the fluences were calculated and the results from the different fissionable source were composed. For the improvement of the comparison between experimental and theoretical results a special method was used calculating special integral sources for the given detector, because each detector according to its decay notes another integral source resp. flux distribution, which has to be theoretically corrected.
The basis of all transport calculations was the Monte Carlo method in a special problem adjusted kind. Special procedures were developed and successfully applicated for the reduction of statistical errors. Therefore, also for single specimens results with small statistical errors were obtained. It is remarkable that this accurate method which allows a realistic 3-dimensional description of the system reactor-surroundings could be applied with reasonable calculation times for the great number of needed calculations.

The technical equipment required to improve the operational monitoring of the NPP Zaporozh'ye, Ukraine is represented. it includes two measuring lines for the upgrading of the operational measuring equipment and seven computer-engineering components for establishing an on-site NPP supervision and has been specified in accordance with NPP experts and specialists of the Ukrainian State Supervisory Authority. Furthermore, the results of practical tests are described to check the hard- and software suitability for the down loading of measuring data from an operational computer using an original SM-2M computer made in Russia and a simulator in the laboratory. To prove the exact function a special laboratory variant of the coupling receiver software was been developed. Conceptional proposals for the algorithmic realization of the on-site monitoring of the NPP Zaporozh'ye conclude this report.

A finite-element-model describing the mechanical vibrations of the whole VVER-440 primary circuit is being developed to support the early detection of mechanical component faults. A special fluid-structure-element was developed to consider the reaction forces of the fluid in the downcomer upon the moving core barrel and the rector pressure vessel. It was derived from an approximated analytical 2D-solution of the coupled system of 3D fluid equations and the structural equations of motions. By means of the vibration model all eigenfrequencies up to 30 Hz and the corresponding mode shapes were calculated. It is shown that the fluid-structure-interaction strongly influences those modes exhibiting a relative displacement between reactor pressure vessel and core barrel. Moreover, by means of the model the shift of eigenfrequencies due to the degradation or to the failure of internal clamping and spring elements was investigated. By comparing the frequency spectra of the normal and of the faulty structure, it could be shown that a recognition of such degradations and failures even inside the reactor pressure vessel is possible by pure excore vibration measurements.

In order to improve the operational surveillance of a VVER-1000 unit of the Ukrainian nuclear power plant Zaporosh'ye a technical monitoring system has been specified. The system will 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. Due to 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 different operational parameters of the unit, 18 radiological parameters of the unit and the plant site and 6 meteorological parameters are monitored.

Recently, the suitability of inelastic X-ray scattering for the investigation of solid and fluid ⁴HE has been demonstraded. For the text experiments an energy resolution of the order of 10-15 meV was used at the backscattering spectrometer INELAX at the storage ring DORIS of DESY, Hamburg. Lattice excitations were observed for momentum transfers along the c axis of h.c.p. helium crystals which were grown in situ at pressures of 54-63 Mpa and at temperatures of 4.2-6.4 K. At 10 k abowve the melting point, engery-loss signals could also be detected from the liquid helium at equivalent momentum transfers.

A focused beam of Co+ ions has been used to produce CoSi2 interconnects by means of ion beam synthesis. Investigations have been performed using polysilicon, amorphous and crystalline silicon substrates. The influence of implantation dose and annealing temperature on the resistivity has been studied. For room temperature implantation and annealing 600°C for 1h, a resistivity of about 60µ(*cm has been obtained independent of the subtrate type. The CoSi2 layers have been found to be stable up to 700°C. CoSi2 interconnects have been fabricated on the slope walls of 200µm deep anisotropically etched grooves using a dynamic focus control of the focused ion beam.

In the framework of the computer code assessment programme for the VVER-440 type Paks Nuclear Power Plant a 1% cold leg break experiment has been conducted on the PMK-2 integral type test facility. It was followed by calculations using RELAP 5Mod3.1 and ATHLET in order to assess code capabilities. This experiment was started from the nominal operational parameters and it was considered that only the high pressure injection system (HPIS) is available and there is no injection from the safety injection tanks (SIT). This experiment was the repetition of the test measured in 1990 with improved data aquisition system. The first part of this report includes a short description of the facility, the measurement description, the test results including the local void measurement and a short interpretation of the main phenomena. In the second part of the report the analysis performed by the RELAP 5Mod3.1 and ATHLET Mod1.1 Cycle A codes are given.

AG₂S embedded into a 100 nm thin film of SiO₂ was fabricated synthetically from ist constituents by ion implantation. The ion sensing characteristics of such film material for Ag⁺ were shown to be analogous to conventional bulk materials, giving sensitivities <=59 mV per concentration decade.

The well-known methods of the acoustic leak localization using the attenuation differences or propagation time differences (e.g. cross correlation analysis) are restricted to the linear geometry of pipe lines. At complicated three-dimensional topologies they fail because there are several modes of the structure-borne sound that have different propagation velocities and because numerous connecting branches generate multiple sound reflexion. Therefore, a new method for detecting and localizing the leaks at complicated geometrical structures was developed and experimentally proved at an original facility. This approach is based on the detection of the leak induced airborne sound or structure-borne sound as well as on the application of pattern recognition procedures. The efficiency both of Fuzzy Logic and neural networks for the acoustic leak localization could be experimentally proved. Though the method has been prototypically developed for Russian pressurized water reactors of VVER-440 type, it can also be used by the self-learning capability of the classifiers at other pressurized facilities.

The report gives an overview on the scientific work of the Institute of Safety Research in 1993.

Hadron production in proton-proton interactions is described in the framework of a collision model, which aims at describing simultaneously all reaction channels in a wide energy region. An empirical matrix element based on the present knowledge of the partonic structure of hadrons is combined with the concept of intermediate subsystems and the calculation of modified statistical weights of the various final states. It is demonstrated that the energy dependence of total cross sections between threshold and about 50 GeV incident energy can be satisfactorily reproduced. This is the basis for concidering theoretical and experimental problems of K^-, η and η´ production in more detail.

For a lithium liquid metal ion source (LMIS) an especially high angular intensity and a low energy broadening is expected because of the low mass of lithium. For a Li LMIS the axial angular intensity and the FWHM of the energy distributation have been measured. The results have been compared with the theoretial predictions and with experimental results for gallium, the metal most widly used in LMIS. A correlation between angular intensity and the energy broadening is found. The Li LMIS has a high angular intensity, especially at low currents, compared to the Ga LMIS. With increasing emission current the rise of the angular intensity as well as the ernergy broadening is smaller than than for the gallium source.

Es ist bekannt, daß die Magnus-Kraft in einer aufwärtsgerichteten Zweiphasenströmung bei erzwungener Flüssigkeitsströmung aufgrund des Geschwindigkeitsprofils der Flüssigkeit in Richtung der Kanalwand wirkt. In einem senkrechten Rohr müßten demnach Gasgehaltsprofile zu beobachten sein, die in der Nähe der Rohrwand ihr Maximum aufweisen. In der Realität sind solche Profile nur bei sehr kleinen Gasvolumenstromdichten existent. Meist liegen Profile vor, die ein Maximum des Gasanteils im Zentrum der Rohrleitung aufweisen. Es wird vermutet, daß in diesem Fall die Turbulenz den Einfluß der Magnus-Kraft überwiegt und für die Herausbildung des Maximums im Zentrum verantwortlich ist. Zur genaueren Untersuchung des Übergangs zwischen den beiden Strömungsformen wurden Messungen der radialen Verteilung des volumetrischen Gasanteils an einer drucklosen, mit Luft-Wasser-Gemisch betriebenen Testschleife durchgeführt. Die Anlage verfügt über einen senkrechten Testkanal (NW 50). Zur Messung des Gasgehaltes dienten nadelförmige Leitfähigkeitssonden. Insgesamt wurden 8 Sonden über den Radius des Rohrs verteilt und deren Signale synchron aufgezeichnet. Die Lufteinspeisung erfolgte gleichmäßig über dem Querschnitt der Rohrleitung. Die maximalen Volumenstromdichte des Wassers betrug 2.8 m/s, der eingeperlte Gasstrom wurde von 0 bis ca. 0.4 m/s variiert. Durch eine Einlauflänge von 40 Rohrdurchmessern traten am Sondenkamm trotz der gleichmäßigen Einperlung ausgeprägte Gasgehaltsprofile auf. Dabei wurden für entsprechend kleine Luftdurchsätze Verteilungen erhalten, die ein stark ausgeprägtes Maximum am Rand der Rohrleitung aufweisen. Bei Vergrößerung des Luftstromes findet in einem bestimmten Durchsatzbereich ein kontinuierlicher Rückgang des Randmaximums statt. Gleichzeitig tritt das für die turbulente Verteilung typische Maximum im Zentrum auf und es stellt sich ein parabelförmiges Profil ein. Z.B. für eine Volumenstromdichte des Wassers von 0.7 m/s findet dieser Übergang bei einer Volumenstromdichte von ca. 0.2 m/s statt. Der Bereich der stabilen, durch die Magnus-Kraft gesteuerten Gasgehaltsverteilung wurde aufgezeichnet. Der Übergang zur parabelförmigen Verteilung des Gasgehalts verschiebt sich bei wachsender Wassergeschwindigkeit hin zu höheren Werten des Luftvolumenstroms.

interne Projektstudie

This paper presents a solution of the AER benchmark problem specified for the 7th cycle of the Paks-2 VVER-440 reactor. The problem concerns control rod worth for both the beginning and the end of burnup cycle states. The burnup distribution of cycle 7 was calculated starting from the burnup values of the third cycle. The calculations were carried out by using the burnup option of the DNYN3D code and a MAGRU group data library. The results are compared with calculations published by other authors on AER meetings. Furthermore the influence on reactivity of some control rod properties typical for VVER-440 was studied.

Mathematical benchmark are widely used and accepted means of verifying the reliability of numerical simulations. The present benchmark is aimed at assessing the discrepancies between three-dimensional core models used for transient calculations in VVER-reactor cores.
The second AER benchmark problem was defined at the 3nd AER Symposium in Pieštany (1993). The problem and the complete set of input data for a control rod ejection accident in a VVER-440 was described. An asymmetric control rod with a worth approximately 2 ßeff was ejected at hot zero power (HZP). The Doppler effect being the main feedback effect for this type of transients is the only feedback taken into account by an adiabatic model of fuel temperature. Therefore it was possible to calculate this type of transient with codes which do not contain a complete thermo-hydraulic model.
Results of the four codes BIPR-8 (RRI Moskau), DYN3D/M2 (RCR Rossendorf), HEXTRAN (VVT Espoo) and KOKO3D (KFKI-AERI Budapest) were obtained and analyzed by comparisons. The agreement of the results is quite satisfactory, however there exist some discrepancies.

Das Pilotprojekt Freital zur Einspeisung von Solarwärme in ein Fernwärmenetz wird vorgestellt und diskutiert. An sonnenscheinreichen Tagen wird die Rücklauftemperatur des Fernwärmenetzes von 58 °C auf 75°C erhöht. Der Kollektorkreiswirkungsgrad liegt an solchen Tagen bei Werten von über 40 %.

Ein Gerät zur Messung der Kennlinien von Photovoltaik-Generatoren wurde entwickelt. Es handelt sich ein transportables, PC-gesteuertes Gerät zur Messung von Generatoren im Leistungsbereich zwischen 1 und 5 kWp. Als leistungsmodulierbares Bauelement wird erstmalig ein MOS-Transistor genutzt. Erste Meßergebnisse werden vorgestellt.

The Rossendorf focused ion beam IMSA-100 was contructed and used for writing implantation of cobalt to form CoSi2-submicron strutures on silicon by ion beam synthesis. Two types of cobalt containing liquid alloy ion source were developed with Co-Nd and Co-Ge alloys. The fabrication of CoSi2 structures by stoichiometric implantation of Co+ (E = 30-35 keV, Iion = 1.3 nA) and Co2+ ions (E = 60 keV, Iion = 0.6 nA) at doses between 0.3 and 5x1017 cm-2 and a subsequent two step annealing (600°C, 60 min; 1000°C, 30 min in N2) is demonstrated. The dose dependence as well as the influence of the substrate temperature between room temperature and 400°C during ion implantation on the ion beam synthesis process were studied. The quality of the silicide submicron structures was investigated by scanning electron microscopy, energy dispersive x-ray analysis, and electrical measurments. While the room temperature implantation and subsequent annealing generate an inhomogeneous CoSi2 film, 400°C substrate heating during implantation leads to a countinuous film with a resistivity below 20µ( cm, comparable with broad beam implantation.

Die zwei größten solarthermischen Anlagen Sachsens werden im Anlagenaufbau und hinsichtlich der bisher vorliegenden Betriebserfahrungen vorgestellt und verglichen. Dies ist zum einen eine Anlage in Freital mit 90 m² Absorberfläche zur Warmwassererzeugung und Fernwärmeeinspeisung. Zum zweiten handelt es sich um sieben Anlagen mit je 100 m² Absorberfläche zur Warmwasserbereitung in Wohnblöcken in Oederan. Beide Anlagen arbeiten störungsfrei. Die geplanten solaren Erträge konnten in der ersten Betriebsperiode nicht erreicht werden. In der Freitaler Anlage lag die Rücklauftemperatur des Fernwärmenetzes etwa 20 K über der Auslegungstemperatur, was zu schlechten Kollektorwirkungsgraden führte. In Oederan betrug der Warmwasserbedarf nur ca. 60 % des Auslegungswertes mit dem gleichen negativen energetischen Effekt.

The semi-magic nucleus ₃₉ ⁸⁹Y₅₀ has been
studied in the framework of the spherical shell model. Relative to a hypothetical
⁶⁶Ni core the expanded configuration space (0f_5/2,
1p_3/2, 1p_1/2, 0g_9/2) and (1p_1/2,
0g_9/2, 1d_5/2, 0g_7/2) for protons and neutrons,
respectively, has bveen considered. The results, both for the excitation
energies and electromagnetic transition probabilities, suggest for the
positive-parity states above 4.5 MeV with 17/2 <= I <=23/2 significant
admixtures of the neutron [(0g_9/2)^-1(1d_5/2)]
excitation coupled to the odd proton occupying the 0g_9/2 orbital.
The calculations predict that the experimentally observed states above
7.2 MeV with 23/2 <= I <=31/2 are generated by the additional excitation
of one proton to the 0g_9/2 orbital resulting in a parity alteration.
The strength of the electric dipole transitions connecting the levels of
the two proposed high-spin structures might be explained by small contributions
of the neutron 0h_11/2 excitation to the involved wave functions.

Existing thermal hydraulic best-estimate codes have to undergo a procedure of extended verification in respect to the special qualities of VVERs. Concerning then VVER-1000 the Russian test facility ISB-VVER only is available, which is located in Elekrtogorsk near Moscow. It was put into operation in October 1992 and was used as the source of experimental data for the first Russian Standard Problem, a 2.4 % small break KOCA test. The present paper deals with a series of tests dedicated ro an 11 % break at the upper plenum of the reactor vessel. ISB-VVER is a two-loop model of the VVER-1000. The elevations are kept 1:1, while the volume and power scales are 1:3000. The four loops of the original plant are modelled as one single loop with one and a triple loop with three parallel steam generators. During the experiments needle shaped conductivity probes of the Recearch Center Rossendorf were applied for void measurements. The tests have shown that in case of a leak in the upper plenum, the cooling capability of the high-pressure injection system strongly depends on the location of the injection. The most favourable condictions for the core cooling are achieved by the injection in both the cold and the hot leg simultaneousely. In this case, an 11 % break in the upper plenum can be safely ruled over without fuel rod overheating by operating the HPIS only. In some cases, oscillations of void fractions and water levels were found.

Im Beitrag werden erste Ergebnisse der Messungen (Zeitraum Juli-Dezember 1994) an der Solaranlage vorgestellt. Kollektorkreis, Pufferspeicherladekreis, Brauchwasserladekreis und Fernwärmeeinspeisung werden im Einzelnen analysiert. Die Betriebsergebnisse bestätigen die Auslegung, aufgrund erhöhter Rücklauftemperaturen des Fernwärmenetzes liegen die energetischen Ergebnisse der Solaranlage unter den projektierten Werten.

The tenser analyzing power T-20 and the polarization transfer kappa in the deuteron break-up reaction Dp --> pX are calculated within a relativistic approach based on the Bethe-Salpeter equation with a realistic meson-exchange potential. Our results on T-20, kappa and the cross section are compared with experimental data and non-relativistic calculations and with the outcome of a relativization procedure of the deuteron wave function.

In the framework of the computer code assessment programme for the VVER-440 type Paks Nuclear Power Plant a 1% cold leg break experiment has been executed on the PMK-2 integral type test facility. For the test it was considered that only high pressure injection system (HPIS) is available and there is no injection from the safety injection tanks (SIT). The experiment was the repetition of the test measured in 1990, with improved data aquisition system. In the report the results of the experiment were discussed and a description of the phenomena was given.

We formulate the asymptotic theory of thermocapillary instability in a planar fluid layer heated from below in the presence of a strong magnetic field corresponding to high Hartmann number. Explicit asymptotic expressions are derived for the velocity perturbation, temperature perturbation and electric current density. Their spatial structure is characterized in terms of Hartmann boundary layers - a concept which permits a physical understanding of more complicated situations involving surface deformation, buoyancy and thermoelectric effects. The physical nature of large scale instabilities in the case of a deformable surface is clarified.

Im Rahmen eines vom Sächsischen Staatsministeriums für Wissenschaft und Kunst geförderten Vorhabens wurden 1994 die Untersuchungen zu den Aufgaben, zu den zu erwartenden Kosten und zu den Realisierungschancen für ein internationales Zentrum für Information und Frühwarnung bei nuklearen Ereignissen in mittel- und osteuropäischen Kernkraftwerken planmäßig fortgesetzt und das laufende Projekt mit dem Abschlußbericht zum 31.12.1994 abgeschlossen.
Für die anstehenden Aufgaben, nämlich Abschätzung der Emissionen, Prognose der Radioaktivitätsausbreitung, Verfolgung der Lageentwicklung und Mitwirkung bei der Vorbereitung von Notfallschutzmaßnahmen sind im wesentlichen radiologische Meßwerte über die freigesetzten radioaktiven Stoffe und meteorologischen Kennwerte zur Beschreibung der Ausbreitungsbedingungen an das Zentrum zu übertragen. Betriebliche Informationen über den Anlagenzustand sind nur im Sinne von Hintergrundinformationen erforderlich, wozu 8 bis 10 ausgewählte sicherheitsrelevante Betriebsparameter ausreichend sind.

Obwohl der Sinn eines solchen Vorhabens außer Frage steht, sind die Realisierungschancen ohne eine umfassende Förderung durch die EG und andere internationale Organisationen - World Association of Nuclear Operators WANO, International Atomic Energy Agency IAEA - gering.

Bestrahlungsinduzierte Ausscheidungen gelten als die strukturelle Ursache der Neutronenversprödung von Reaktordruckbehälterstahl (RDB-Stahl). Am Beispiel des WWER-440 RDB-Stahls 15Cr2MFA wird die Korrelation zwischen dem Volumenanteil an bestrahlungsinduzierten Ausscheidungen und der Erhöhung der Sprödbruchübergangstemperatur diskutiert. Es wird eine bimodale Abhängigkeit dieser beiden Größen gefunden. Ursache des bimodalen Verhaltens sind möglicherweise unterschiedliche Arten von bestrahlungsinduzierten Ausscheidungen, die vom Gehalt an Verunreinigungselementen bestimmt sind.
Erste resonante Röntgenkleinwinkelstreuexperimente an Material mit niedrigem Cu-Gehalt zeigen, daß Vanadium ein wesentlicher Bestandteil der bestrahlungsinduzierten Ausscheidungen ist. Die Ergebnisse von Neutronenkleinwinkelstreuung und Positronenannihilationsspektroskopie unterstützen die Hypothese, daß es sich bei den Ausscheidungen im RDB-Stahl 15Cr2MFA um Vanadiumkarbide handelt.

The New Rossendorf Nuclear Microprobe¹⁾
F. Herrmann and D. Grambole

Recently a 3 MV tandetron accelerator was put into operation at the Research Center Rossendorf. At this accelerator we have installed a new nuclear microprobe. The object forming aperture can be changed continuously from 0 to 150 µm and in each direction independently. The magnetic quadrupole triplet delivered by Danfysik has an energy mass product of 45 MeV.amu. Magnetic coils placed behind it scan the beam over an area up to 1 x 1 mm². A manipulator with X-Y-Z-translation, 360° rotation, and tilt enables us together with the adequate detectors to apply ERDA, PIXE, RBS, and NRA. A PC based CAMAC system acquires data from four ADCs. Up to four elemental maps with up to 128 x 128 pixels can be displayed on-line. All events are stored together with their coordinates in list mode for further analysis.
A general problem for a quantitative analysis is the accuracy of charge measurement. Using the whole target chamber as a Faraday cup which would be the best method is impossible in our installation. A negatively biased electrode in front of the target for suppressing the secondary electrons cannot be used either. Therefore a precise current integrator was developed which can operate with a positive offset voltage of several hundred volts at the input. The principle of this integrator will be described as well as first experiences and comparisons to other charge measuring methods. Furthermore, a beam monitoring system based on this integrator was set up for an easy control of the beam.

¹⁾ The project was supported by Bundesminister für Forschung und Technologie under contract 03-GR3ROS

The report contains results of the analysis of the transients "Loop connection" and "SG tube rupture" for NPP with VVER-440 type reactors. To obtain detailled informations about NPP's dynamic characteristics, various variants of initial and boundary conditions are considered.
Calculation of these transients was performed with use of the code SiTAP developed at the Nuclear Safety Institute of Russian Research Centre "Kurchatov Institute". SiTAP is a multi-functional computer tool for fast analysis of transient and accidental processes of VVER type reactors for engineers working in the field of NPP dynamics.
SiTAP can be used for comparative analysis of several variants of accident scenarios to find out the conditions leading to the most severe consequences from safety point of view. For this cases, additional analyses using best-estimate codes should be carried out.
The results from SiTAP for faulty loop connection leading to a boron dilution accident are intended to be used as boundary conditions for a more detailled analysis by the help of the three-dimensional reactor core model DYN3D, developed in the Research Centre Rossendorf for the simulation of reactivity initiated accidents.