Qucosa – Hemholtz-Zentrum Dresden-Rossendorf
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Untersuchung der Bildung der Eisensilizide während der Ionenstrahlsynthese und der ionenstrahlinduzierten Phasenbildung
Get PDFCoolant mixing in pressurized water reactors
Get PDFFor the analysis of boron dilution transients and main steam line break scenarios the modelling of the coolant mixing inside the reactor vessel is important. The reactivity insertion due to overcooling or deboration depends strongly on the coolant temperature and boron concentration. The three-dimensional flow distribution in the downcomer and the lower plenum of PWR's was calculated with a computational fluid dynamics (CFD) code (CFX-4). Calculations were performed for the PWR's of SIEMENS KWU, Westinghouse and VVER-440 / V-230 type. The following important factors were identified: exact representation of the cold leg inlet region (bend radii etc.), extension of the downcomer below the inlet region at the PWR Konvoi, obstruction of the flow by the outlet nozzles penetrating the downcomer, etc. The k- turbulence model was used. Construction elements like perforated plates in the lower plenum have large influence on the velocity field. It is impossible to model all the orifi! ces in the perforated plates. A porous region model was used to simulate perforated plates and the core. The porous medium is added with additional body forces to simulate the pressure drop through perforated plates in the VVER-440. For the PWR Konvoi the whole core was modelled with porous media parameters. The velocity fields of the PWR Konvoi calculated for the case of operation of all four main circulation pumps show a good agreement with experimental results. The CFD-calculation especially confirms the back flow areas below the inlet nozzles. The downcomer flow of the Russian VVER-440 has no recirculation areas under normal operation conditions. By CFD calculations for the downcomer and the lower plenum an analytical mixing model used in the reactor dynamic code DYN3D was verified. The measurements, the analytical model and the CFD-calculations provided very well agreeing results particularly for the inlet region. The difficulties of analytical solutions and the uncertainties of turbulence models for the numerical solutions require additional experiments. Therefore a 1:5 scaled plexiglas model is under construction at RC Rossendorf. The model can be used variably for PWR's of KONVOI- and EPR- types including the primary loops. The measurements of the mixing effects will be performed with modern wire mesh sensors based on conductivity differences and LDA is used to measure the flow conditions
Erhöhung der Zuverlässigkeit der Bestimmung der Neutronenbelastung von WWER-Reaktorkomponenten zwecks Ableitung von Vorschlägen für eine sicherere Betriebsführung von WWER-Reaktoren
Get PDFThe results of a project sponsored by the German Bundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie are presented. The Project aimed to improve the safety against embrittlement of VVER-1000 type reactors by a more reliable and accurate determination of the neutron load of reactor pressure vessels. Therefore, six scientist from three Russian research institutions were sponsored to support with their work another BMBF project of the FZR aimed at the same goal. By providing reliable data for the evaluation of ex-vessel neutron activation experiments at two VVER-1000 and formulating the corresponding reactor models a basis has been established for further investigations as well in the FZR as well as in several Russian and Western research institutions. The leading Russian nuclear data library ABBN/MULTIC has been improved and tested. The uncertainties affecting the calculations of the fluence spectrum at the outer boundary of the pressure vessel have been analysed and a spectrum covariance matrix has been derived. The methodologies for the experimental determination of activation rates and for calculations of fluence spectra and activation rates have been further developed and tested by interlaboratoy comparisons. Measurements of different laboratories were compared with each other, as well as the corresponding calculations. Moreover, measurements and calculations were compared against each other, partly with participation of further Russian, Czech and Western institutes. The results of the Intercomparisons have been evaluated by the "International Workshop on the Balakovo-3 Interlaboratory Dosimetry Experiment" in September 1997 in Rossendorf. As a result of these works a better evaluation of the reached accuracies was possible and proposals for an improvement of the used methods could be derived
Theoretical Support to the NOKO Experiments
Get PDFSeveral approaches have been undertaken in a number of European countries to study and demonstrate the feasibility of innovative passive safety systems. The European BWR R&D Cluster combines experimental and analytical efforts that are mainly directed to the introduction of passive safety systems into boiling water reactor technology. The main objectives are to use the large scale European test facilities NOKO (Jülich, Germany), PANDA, LINX (Villingen, Switzerland), PANTHERS (Piacenza, Italy) as well as the demonstration power plant Dodewaard (Netherlands) for a synergistic experimental R&D program. The project should additionally contribute to validating and improving thermalhydraulic computer codes. In 1997 a BWR Physics and Thermohydraulic Complementary Action (BWRCA) was established to further assist and broaden the objectives of the EU BWR R&D Cluster. The work presented in this report is performed in the Workpackage Theoretical support to the NOKO experiments and divided into three tasks: Implementation of two phase flow instrumentation, ATHLET calculations of NOKO experiments and approach for the optimization of passive components. FZR is developing two phase flow measurement instrumentation (e.g. conductivity probes), which is installed in parallel to the emergency condenser test bundle. The experimental data are used for the validation of the improved ATHLET condensation model. The evaluation of these experiments shows an undesired accumulation of noncondensable gases in front of the water level and give valuable insights to the phenomena caused by noncondensables. An improved twophase flow instrumentation is suggested based on the collected experience and taking into account the detected problems. Within the BWRCA FZR had performed 10 post test calculations and an additional blind test calculation of NOKO experiments. The results of these calculations are presented and discussed in detail. These calculations show that ATHLET is able to perform proper calculations. At least goals for an optimization of the emergency condenser are discussed. This is desirable because it allows the decrease of the pressurized BWR surface and the possibility of leakages
Institute of Safety Research; Annual Report 1997
Get PDFThe report gives an overview on the scientific work of the Institute of Safety Research in 1997
Thermal Dilepton Signal Versus Dileptons from Open Charm and Bottom Decays in Heavy-Ion Collisions
Get PDFBericht der Herbsttagung der Studiengruppe für Elektronische Instrumentierung vom 28.-30. September 1998 im Forschungszentrum Jülich
Get PDFDetektion von duktiler Rißinitiierung durch Schallemission
Get PDFEs wird eine Kerbschlagbiegeanordnung vorgestellt, mit der simultan Schlagkraft, Rißöffnung, Schallemission und magnetische Emission gemessen werden können. Grundbaustein der Anordnung ist ein invertiertes Pendelschlagwerk. Mit dieser Anordnung wurden seitgekerbte, vorermüdete ISO-V-Proben aus Stählen mit unterschiedlichen Festigkeits-Zähigkeitseigenschaften geprüft. Die Untersuchung soll aufzeigen, ob Schallemission zur Detektion der stabilen Rißinitiierung an hochzähen Stählen geeignet ist und folglich auf diesem Wege die dynamische Rißinitiierungszähigkeit zuverlässig bestimmt werden kann. Dazu wurden andere Bestimmungsverfahren herangezogen. Als zuverlässigste Verifizierungsbasis wird die physikalische Rißinitiierungszähigkeit betrachtet, die auf der Grundlage der Messung der Stretchzone und der Rißwiderstandskurve in einem Mehrprobenverfahren ermittelt wird. Außer im unteren Übergangsbereich, in dem nur sehr geringer duktiler Rißfortschritt auftritt, konnte mit Schallemission in allen Fällen stabile Rißinitiierung nachgewiesen werden. Die damit bestimmte Rißinitiierungszähigkeit liefert über das gesamte Spektrum der untersuchten Stähle eine nahezu 1:1-Korrelation zur physikalischen Rißinitiierungszähigkeit. Im Einzelfall treten aber auch beträchtliche Streuungen auf und Rangfolgen werden innerhalb einer Versuchsserie nicht rangordnungsgerecht wiedergegeben. Alle anderen untersuchten Einprobenverfahren schneiden in diesem Vergleich deutlich schlechter ab und sind somit als Verifizierungsbasis nicht geeignet. Die Untersuchung läßt nicht zwingend erkennen, daß Schallemission tatsächlich direkt mit dem Übergang der maximalen Rißabstumpfung zum stabilen Rißwachstum in Verbindung steht. Offensichtlich werden aber Prozesse detektiert, die im zeitlichen und örtlichen Umfeld der Rißinitiierungsprozesses stattfinden. Somit kann im instrumentierten Kerbschlagbiegeversuch mit Hilfe einer zusätzlich in die Hammerfinne integrierten Schallemissionssonde eine brauchbare Schätzung des bruchmechanischen Parameters dynamische Rißinitiierungszähigkeit effektiv und ohne großen Aufwand erhalten werden
Can One Discriminate the Thermal Dilepton Signal Against the Open Charm and Bottom Decay Background in Ultrarelativistic Heavy-Ion Collisions?
Get PDFIn ultrarelativistic heavy-ion collisions at √s > 20 (120) A GeV a copious production of charm (bottom) production sets in which, via correlated semileptonic DD (BB) decays, gives rise to a dilepton yield at invariant mass M ≈ 2 - 3 GeV in excess of the Drell-Yan yield and the thermal dilepton signal from deconfined matter as well. We show that appropriate single-electron transverse momentum cuts (suitable for ALICE at LHC) cause a threshold like behavior of the dilepton spectra from heavy-quark meson decays and the Drell-Yan process and can allow to observe a thermal dilepton signal from hot deconfined matter