In the frame of the LACOMECO (large scale experiments on core degradation, melt retention and containment behavior) project of the 7th European Framework Program, a test in the DISCO (dispersion of corium) facility was performed in order to analyze the phenomena which occur during an ex-vessel fuel-coolant interaction (FCI). The test is focused on the premixing phase of the FCI with no trigger used for explosion phase. The objectives of the test were to provide data concerning the dispersion of water and melt out of the pit, characterization of the debris and pressurization of the reactor compartments for scenarios, where the melt is ejected from the reactor pressure vessel (RPV) under pressure. The experiment was performed for a reactor pit geometry close to a French 900 MWe reactor configuration at a scale of 1:10. The corium melt was simulated by a melt of iron-alumina with a temperature of 2400K. A containment pressure increase of 0.04MPa was measured, the total pressure reached about 0.24MPa. No spontaneous steam explosion was observed. About 16% of the initial melt (11.62 kg) remained in the RPV vessel, 60% remained in the cavity mainly as a compact crust. The fraction of the melt transported out of the pit was about 24%.

In order to optimise the use of the available means and to constitute sustainable research groups in the European Union, the Severe Accident Research NETwork of Excellence (SARNET) has gathered, between 2004 and 2008,51 organizations representing most of the actors involved in severe accident (SA) research in Europe plus Canada. This project was co-funded by the European Commission (EC) under the 6th Euratom Framework Programme. Its objective was to resolve the most important pending issues for enhancing, in regard of SA, the safety of existing and future nuclear power plants (NPPs).SARNET tackled the fragmentation that existed between the national R&D programmes, in defining common research programmes and developing common computer codes and methodologies for safety assessment. The Joint Programme of Activities consisted in:- Implementing an advanced communication tool for accessing all project information, fostering exchange of information, and managing documents;- Harmonizing and re-orienting the research programmes, and defining new ones;- Analyzing the experimental results provided by research programmes in order to elaborate a common understanding of relevant phenomena;- Developing the ASTEC code (integral computer code used to predict the NPP behaviour during a postulated SA) by capitalizing in terms of physical models the knowledge produced within SARNET;- Developing scientific databases, in which the results of research experimental programmes are stored in a common format;- Developing a common methodology for probabilistic safety assessment of NPPs;- Developing short courses and writing a text book on severe accidents for students and researchers;- Promoting personnel mobility amongst various European organizations.This paper presents the major achievements after four and a half years of operation of the network, in terms of knowledge gained, of improvements of the ASTEC reference code, of dissemination of results and of integration of the research programmes conducted by the various partners.Most initial objectives were reached but the continuation of the SARNET network, co-funded by EC in the 7th Framework Programme (SARNET2 project that started in April 2009 for 4 years), will consolidate the first assets and focus mainly on the highest priority pending issues as determined during the first period. The objective will be also to make the network evolve towards a complete self-sustainability. (C) 2011 Elsevier B.V. All rights reserved.

The objectives of the SARNET network are to define common research programmes in the field of severe accidents and to develop common computer tools and methodologies for safety assessment in this field. To reach these objectives, one of the work packages, named "Severe Accident Research Priorities" (SARP), aimed at reviewing and reassessing the priorities of research issues as a basis to harmonize and to re-orient research programmes, to define new ones, and to close - if possible - resolved issues on a common basis. The work was performed in close collaboration with 8 participating institutions, led by GRS, representing technical safety organisations, industry and utilities (IRSN, CEA, EDF, FZK, GRS, KTH, TUS, VTT). This action made use notably of (1) the outcomes of the EURSAFE project in the 5th Framework Programme, i.e. the Phenomena Identification and Ranking Tables (PIRT) on severe accidents, (2) the results of the validation and benchmarking activities on ASTEC, (3) the results of reactor calculations carried out in the other SARNET tasks, and (4) the outcome of the research performed in the three thematic sub-domains of SARNET (corium, containment and source term).The main outcome of EURSAFE was a list of 21 topics which included recommendations for experimental programmes and code developments. This list formed the basis of the work in SARP. Also the methodology applied in EURSAFE to consider both the risk potential and the severe accident issues where large uncertainties still subsist was adopted. The analyses of the progress of research and development activities considered whether (1) any research issue was resolved due to reduction of uncertainties or gain of scientific insights, (2) any new issue had to be added to the list of needed research, (3) any new process or phenomenon had to be included in the general PIRT list taking into account the safety relevance and the lack of knowledge, and (4) any new accident management program has to be developed to cope with unresolved problems. Furthermore a strategy plan was elaborated to ensure a wide consensus with the end-user requirements and the objectives of SARNET research activities. (C) 2009 Published by Elsevier Ltd.

The mixing of cooling fluid in rod bundles from one subchannel to another through the gaps between the rods reduces the temperature differences in the coolant as well as along the perimeter of the rods. The phenomenon of natural mixing was first intensively investigated in the 1960s and remains a topic of research up to the present time. The paper describes the main stations on the way to understand the nature of the flow in rod bundles and generally in compound channels with the focus on work performed at Research Center Karlsruhe (FZK).(1)Earlier, it was noticed that the mixing rates where higher than could be accounted for by turbulent diffusion alone. For more than 20 years attempts were made to prove experimentally and by code application that secondary flows could account for the measured mixing rates, although the measured secondary flow velocities were much too low. Measurements of the turbulence structure by hot wire anemometry confirmed the existence of cyclic flow pulsations, which had been postulated earlier on the basis of thermocouple measurements. More sophisticated hot wire measurements revealed the nature of these pulsations as periodic, coupled to gap width and Reynolds number. Finally, the extension of the investigation to other compound channel types and flow visualization revealed the true nature of the mixing process as a vortex train moving along the gap between rods or in the narrow part of a compound channel. These findings have been confirmed by LES calculations. Based on these results CFD codes with improved turbulence models calculated successfully the flow in rod bundles including the macroscopic oscillations. (C) 2010 Elsevier B.V. All rights reserved.

The platform LACOMECO at Karlsruhe Institute of Technology (KIT) provides European research institutions access to several experimental facilities which are designed to study the remaining severe accident safety issues, including the coolability of a degraded core, corium coolability in RPV, possible melt dispersion to the reactor cavity, and hydrogen mixing and combustion in the containment. These facilities are unique in its own specified field and the experiments are designed to be complementary to other European facilities and experimental platforms to form a coherent European nuclear experimental network. The LACOMECAL platform at KIT includes: a) QUENCH facility designed for the investigation of early and late phases core degradation in prototypical geometry for different reactor designs and cladding alloys; b) LIVE facility, a large scale 3D facility for the investigation of in-vessel late phase behaviour of in-core melt pool and melt pool in the lower head of RPV; c) DISCO facility, the only operating facility worldwide to investigate the melt dispersion to the reactor cavity and direct containment heating (DCH); d) HYKA including a series of large and medium scale experimental facilities which investigate the whole hydrogen behaviour in containment under well controlled conditions. The LACOMECO program is founded by European Commission and KIT. It is free of all charge to the interested users and provided all the needed supports to perform the experiments.

The DISCO test facility at Forschungszentrum Karlsruhe (FZK) has been used to perform experiments to investigate direct containment heating (DCH) effects during a severe accident in European nuclear power plants, comprising the EPR, the French 1300 MWe plant P'4, the VVER-1000 and the German Konvoi plant. A high-temperature iron-alumina melt is ejected by steam into scaled models of the respective reactor cavities and the containment vessel. Both heat transfer from dispersed melt and combustion of hydrogen lead to containment pressurization. The main experimental findings are presented and critical parameters are identified.The consequences of DCH are limited in reactors with no direct pathway between the cavity and the containment dome (closed pit). The situation is more severe for reactors which do have a direct pathway between the cavity and the containment (open pit). The experiments showed that substantial fractions of corium may be dispersed into the containment in such cases, if the pressure in the reactor coolant system is elevated at the time of RPV failure. Primary system pressures of 1 or 2 MPa are sufficient to lead to full scale DCH effects. Combustion of the hydrogen produced by oxidation as well as the hydrogen initially present appears to be the crucial phenomenon for containment pressurization. (C) 2009 Elsevier B.V. All rights reserved.

Fifty-one organisations network in SARNET (Severe Accident Research NETwork of Excellence) their research capacities in order to resolve the most important pending issues for enhancing, with regard to Severe Accidents (SA). the safety of existing and future Nuclear Power Plants (NPPs). This project. co-funded by the European Commission (EC) under the 6th Framework Programme, has been defined in order to optimise the use of the available means and to constitute sustainable research groups in the European Union. SARNET tackles the fragmentation that may exist between the different national R&D programmes, in defining common research programmes and developing common computer tools and methodologies for safety assessment. SARNET comprises most of the organisations involved in SA research in Europe, plus Canada.To reach these objectives, all the organisations networked in SARNET contributed to a joint Programme of Activities, which consisted of:Implementation of an advanced communication tool for accessing all project information, fostering exchange of information, and managing documents:Harmonization and re-orientation of the research programmes, and definition of new ones;Analysis of the experimental results provided by research programmes in order to elaborate a common understanding of relevant phenomena;Development of the ASTEC code (integral computer code used to predict the NPP behaviour during a postulated SA), which capitalizes in terms of physical models the knowledge produced within SARNET;Development of Scientific Databases in which all the results of research programmes are stored in a common format (DATANET);Development of a common methodology for Probabilistic Safety Assessment of NPPs;Development of short courses and writing a textbook on Severe Accidents for students and researchers;Promotion of personnel mobility amongst various European organisations.This paper presents the major achievements after four and a half years of operation of the network, in terms of knowledge gained, of improvement of the ASTEC reference code, of dissemination of results and of integration of the research programmes conducted by the various partners.After this first period (2004-2008), co-funded by the EC, a further contract SARNET2 with the EC for the next four years started in April 2009 as part of the 7th Framework Programme. During this period, the networking activities will focus mainly on the remaining pending issues as determined during the first period, experimental activities will be directly included in the common work and the network will evolve toward complete self-sustainability. The bases for such an evolution are presented in the last part of the paper. (C) 2009 Elsevier Ltd. All rights reserved.

Counter-current flow regimes of air and water are investigated in the WENKA test facility at the Forschungszentrum Karlsruhe. With the fluorescent-particle image velocimetry (PIV) measurement technique, velocity and velocity fluctuations are measured up to the free surface. A statistical model is presented to correlate the measured void fraction with the turbulent kinetic energy calculated from the measured velocity fluctuations. The experimental data are used to develop a phase interaction model to simulate stratified flows. Two different approaches are compared for turbulence modelling. The Prandtl mixing length model and an extended k–ω model for the two-phase region are applied to supercritical flow conditions.

As a near-infrared (NIR) wide field interferometric imager offering an angular resolution of about 10 milliarcseconds LINC-NIRVANA at the Large Binocular Telescope will be an ideal instrument for imaging the center of the Milky Way especially in conjunction with mm/sub-mm interferometers like CARMA, ATCA or, in the near future, ALMA. Sagittarius A* (Sgr A*) is the electromagnetc manifestation of the ~4×106M super-massive black hole (SMBH) at the Galactic Center. First results from a mult-wavelength campaign focused on Sgr A*, based on the VLT and on CARMA, ATCA, and the IRAM 30m-telescope, in May 2007 show that the NIR data are consistent with partially depolarized non-thermal emission from confined hot spots in relativistic orbits around SgrA*. A 3mm flare following a May 2007 NIR flare is consistent with SSC emission from adiabatically expanding plasma in a wind or jet. With the LBT and ALMA we will be able to study the spectral evolution of NIR/sub-mm/mm flare emission in order to constrain the emission mechanism, the jet/wind physics, and possibly determine the angular momentum of the SMBH. LINC/NIRVANA will also serve to investigate the stellar population and dynamics in the cluster surrounding Sgr A*. A particular emphasis will lie on examining dust embedded and young stars and to unravel the star formation history in the cluster. For the 0.3 parsec core radius central star cluster the investigation of will be investigated.

Experimente zur Wasserstoffverbrennung bei DCH-Prozessen Im Rahmen der Forschung zu schweren Unfallen in Leichtwasserreaktoren werden im Institut fur Energie- und Kerntechnik des Forschungszentrums Karlsruhe seit 1998 die Versuchanlagen DISCOC und DISCO-H betrieben, konzipiert zur Untersuchung der Druckbelastung des Sicherheitsbehalters durch Schmelzedispersion (Direct Containment Heating, DCH) bei Versagen des Reaktordruckbehalters (RDB). Vorangegangene Experimente haben die Schmelzeverteilung und Druckerhohung im Sicherheitsbehalter bei verschiedenen europaischen Reaktorgeometrien untersucht, unter Anwendung von Eisen-Aluminium-Schmelzen und Dampf als Modellfluide. Die Analyse dieser Experimente hat gezeigt, dass der Druckanstieg sowohl durch den Warmeubergang von der Schmelze an das Gas, aber auch zum nicht unerheblichen Teil durch Wasserstoffverbrennung verursacht wurde. So hat sich die Notwendigkeit ergeben, die charakteristischen Eigenschaften der Wasserstoffverbrennung wahrend des DCH-Prozesses besser beschreiben zu konnen. Um diese Fragen zu klaren, wurden Einzeleffektexperimente in der DISCO-H Versuchsanlage durchgefuhrt. Mit Ausnahme der Schmelzedispersion laufen in diesen Experimenten die gleichen Prozesse ab, wie sie wahrend des DCH-Vorganges auftreten, das sind das Abblasen einer heisen Wasserstoff-Dampf Mischung in den Sicherheitsbehalter und die Zundung dieses Gasgemisches in einer LuftDampf-Wasserstoff Atmosphare. Der Effekt der Schmelzepartikel als Zunder wurde mit Thermitkerzen simuliert. Die experimentellen Daten werden benutzt, um Modelle in Verbrennungscodes zu kalibrieren und um auf Reaktormasstab zu extrapolieren. Die Experimente wurden in zwei Schritten durchgefuhrt. Fur eine Serie von 6 Tests wurde eine vereinfachte Geometrie benutzt, um die Hauptparameter der Verbrennung zu studieren. Dann wurden zwei Tests in einer prototypischeren Geometrie durchgefuhrt, bei der das Gas aus der Grube zuerst in einen separaten Reaktorraum und von dort in den Sicherheitsbehalter stromt. Die Versuchsbedingungen waren wie folgt: • Als Anfangsbedingung im Sicherheitsbehalter wurde eine Luft- bzw. ein Luft-Dampf-Atmosphare bei 100°C und 2 bar eingestellt, mit Wasserstoffkonzentrationen zwischen 0 und 7 mol%, reprasentativ fur die Atmosphare im Containment bei Versagen des RDB. • Einblasen eines heisen Dampf-Wasserstoffgemisches in die Reaktorgrube bei 20 bar, reprasentativ fur ein Kuhlmittelabblasen durch ein Leck im RDB und der Wasserstofferzeugung wahrend dieser Phase. Die wichtigsten gemessenen Grosen waren (1) der Druckanstieg im Sicherheitsbehalter, (2) die Gastemperaturen und (3) die Anzahl der verbrannten Wasserstoffmole. Diese Experimente kennzeichnen die Rate der Wasserstoffverbrennung, die Vollstandigkeit und die Art der Verbrennung bei verschiedenen Anfangsbedingungen. Der Anteil des verbrannten Wasserstoffs betrug zwischen 55% und 100% der Gesamtmenge in der einfachen Geometrie und 46% bzw. 67% in der mehr prototypischen Geometrie. Der Wirkungsgrad hinsichtlich Druckerhohung im Sicherheitsbehalter lag zwischen 46% und 67%. Spezielle Verbrennungscodes mussen angewendet werden um zu prufen, ob diese Ergebnisse auch fur den Reaktormasstab gelten.

The LACOMERA project at the Forschungszentrum Karlsruhe, Germany, is a 4 year action within the 5th Framework Programme of the EU which started in September 2002. Overall objective of the project is to offer research institutions from the EU member countries and associated states access to four large-scale experimental facilities QUENCH, LIVE, DISCO, and COMET. These facilities are being used to investigate core melt scenarios from the beginning of core degradation to melt formation and relocation in the vessel, possible melt dispersion to the reactor cavity, and finally corium concrete interaction and corium coolability in the reactor cavity. The paper summarizes the main results obtained in the following three experiments: QUENCH-L2: Boil-off of a flooded bundle. The test is of a generic interest for all reactor types, provided a link between the severe accident and design basis areas, and would deliver oxidation and thermal hydraulic data at high temperatures. DISCO-L2: Fluid-dynamic, thermal, and chemical processes during melt ejection out of a breach in the lower head of a pressure vessel of the VVER-1000/320 type of reactor. COMET-L2: Investigation of long-term melt-concrete interaction of metallic corium in a cylindrical siliceous concrete cavity under dry conditions with decay heat simulation of intermediate power during the first test phase, and subsequently at reduced power during the second test phase.

Heat transfer in fuel assemblies for a High Performance Light Water Reactor can be achieved either with artificial surface roughness of the fuel claddings or by a spiral cross flow between the fuel pins, for which purpose a staircase type grid spacer has been designed. An application of earlier test results with rough claddings for gas cooled reactors to supercritical water conditions, together with new heat transfer estimates for a spiral flow, indicates that the heat transfer coefficient of the coolant at the cladding surface can be increased by more than a factor of two, which will reduce the peak cladding temperature by at least 50°C. This improvement shall allow either to increase the core outlet temperature at a given cladding temperature or to reduce the peak temperature at the envisaged core outlet temperature. The paper includes analyses and design details for realization of such enhancement of heat transfer.

51 organizations network in SARNET (S__-evere A__-ccident R__-esearch ___-work of Excellence) their capacities of research in order to resolve the most important remaining uncertainties for enhancing, in regard of Severe Accidents (SA), the safety of existing and future Nuclear Power Plants (NPPs). This project, co-funded by the European Commission (EC), has been defined in order to optimise the use of the available means and to constitute sustainable research groups in the European Union. SARNET tackles the fragmentation that exists between the different R&D national programmes, in defining common research programmes and developing common computer tools and methodologies for safety assessment. SARNET comprises most of the actors involved in SA research in Europe (plus Canada). To reach these objectives, all the organizations networked in SARNET contribute to a so-called Joint Programme of Activities (JPA), which consists in: ・Implementing an advanced communication tool for accessing all project information, fostering exchange of information, and managing documents; ・Harmonizing and re-orienting the research programmes; ・Jointly analysing the experimental results provided by research programmes in order to elaborate a common understanding of relevant phenomena; ・Developing the ASTEC code (integral computer code used to predict the NPP behaviour during a postulated SA), which capitalizes in terms of physical models the knowledge produced within SARNET; ・Developing Scientific Databases, in which all the results of research programmes are stored in a common format (DATANET); ・Developing a common methodology for Probabilistic Safety Assessment (PSA) of NPPs; ・Developing courses and writing a text book on SA for students and researchers; ・Promoting personnel mobility between various European organizations. After the first period (2004-2008), co-funded by the EC, the network will progressively evolve toward self-sustainability. The bases for such an evolution, still under discussion, are presented in the last part of the paper.

Quarante-neuf organismes européens rassemblent dans le réseau SARNET (Severe Accident Research and management NETwork) leurs moyens de recherche sur les accidents graves de réacteur, afin de réduire les problèmes importants en suspens dans ce domaine, et ainsi contribuer à l'amélioration de la sûreté des centrales nucléaires actuelles et futures. Le projet a été défini en prenant en compte la nécessité d'optimiser l'utilisation des moyens disponibles en Europe, et d'associer de manière pérenne les complémentarités des laboratoires de recherche. SARNET s'attaque à la fragmentation existant entre les différents programmes nationaux de R&D, notamment en élaborant en commun des programmes de recherche ainsi que des outils de calcul et des méthodologies pour les évaluations de sûreté. Coordonné par l'IRSN le réseau SARNET rassemble la plupart des acteurs impliqués dans la recherche sur les accidents graves en Europe.Pour atteindre ces objectifs, toutes les membres du réseau SARNET contribuent à un programme d'activités commun (JPA), constitué de plusieurs éléments :• Mise en oeuvre d'un outil de communication avancée pour favoriser l'échange d'informations ;• Harmonisation et réorientation de programmes de recherche et définition commune de nouveaux programmes ;• Analyse des résultats expérimentaux fournis par les programmes de recherche afin d'aboutir à une compréhension commune des phénomènes concernés ;• Développement du logiciel ASTEC (outil de calcul permettant de simuler le comportement d'un réacteur nucléaire lors d'un accident grave) qui capitalise en termes de modèles physiques les connaissances élaborées par SARNET ;• Développement de bases de données scientifiques dans lesquelles tous les résultats des programmes de recherche sont stockés ;• Développement d'une méthodologie commune pour les évaluations probabilistes de sûreté des réacteurs ;• Enseignement, formation et rédaction d'ouvrages ;• Mise en oeuvre d'un programme de mobilité de personnels entre les divers organismes membres du réseau.Le réseau a atteint en terme de compétence, dans le domaine des accidents graves et pour l'ensemble des réacteurs nucléaires en Europe, la masse critique nécessaire à la réalisation et l'interprétation de programmes expérimentaux ainsi qu'au développement de modèles et à leur intégration dans le logiciel ASTEC. Quelques organismes couvrent un large éventail de compétences, qui sont compétées par l'apport de contributions spécialisées dans des domaines très spécifiques.Afin de préserver les intérêts des différents membres du réseau, une politique claire en termes de protection de la propriété intellectuelle a été définie. Les documents contenant des données "protégées" ne sont remis qu'aux membres qui, de par l'activité qu'ils proposent, augmentent de manière importante la valeur des données (production d'analyses, développement de modèles et évaluation). Néanmoins, les méthodologies d'évaluation de sûreté et le logiciel ASTEC, produits intégrateurs des connaissances et modèles élaborés au sein de SARNET, seront disponibles pour tous les membres du réseau et les autres organismes européens désireux de les utiliser pour des évaluations de sûreté ou pour l'amélioration de leurs centrales nucléaires.

The supermassive black hole at the Galactic Center, Sgr A*, shows frequent radiation outbursts, so-called flares. In the near-infrared some of these flares were reported to show intrinsic quasi-periodicities of 18 ± 3min. In 2005, we have carried out polarimetric observations of these QPOs in the K-band. These observations allow for a detailed investigation of Sgr A* within the hot spot model. In this model, inhomogeneities in the accretion flow are represented as confined orbiting material. By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we address the question whether these changes are consistent with the hot spot model, in which the interplay of relativistic effects plays the major role. We consider all general relativistic effects that imprint on the polarization lightcurves. As the synchrotron mechanism is most likely responsible for the intrinsic polarization, we consider two different magnetic field configurations as approximations to the complex structure of the magnetic field in the accretion flow. Considering the quality of the fit, we think that the spot model is favoured. Finally, our confidence contours give constraints to the spin parameter and the inclination of the supermassive black hole associated with Sgr A*.

AbstractWe report on recent polarimetric observations of the 18± 3 min quasi-periodicity present in near-infrared flares from Sagittarius A*. Observations in the K-band allow us a detailed investigation of the flares and their interpretation within the hot spot model. The interplay of relativistic effects plays a major role. By simultaneous fitting of the lightcurve fluctuations and the time-variable polarization angle, we give constraints to the parameters of the hot spot model, in particular, the dimensionless spin parameter of the black hole and its inclination. We consider all general relativistic effects that influence the polarization lightcurves. The synchrotron mechanism is most likely responsible for the intrinsic polarization. We consider two different magnetic field configurations as approximations to the complex structure of the magnetic field in the accretion flow. Considering the quality of the fit, we suggest that the spot model is a good description of the origin for the QPOs in NIR flares.

Current and future opportunities for interferometric observations of the Galactic Center in the near- and mid-infrared (NIR/MIR) wavelength domain are highlighted. Main emphasis is being put on the Large Binocular Telescope (LBT) and the Very Large Telescope Interferometer (VLTI). The Galactic Center measurements of stellar orbits and strongly variable NIR and X-ray emission from Sagittarius A* (SgrA*) at the center of the Milky Way have provided the strongest evidence so far that the dark mass concentration at this position is associated with a super massive black hole. Similar dark mass concentrations seen in many galactic nuclei are most likely super massive black holes as well. High angular resolution interferometric observations in the NIR/MIR will provide key information on the central massive black hole and the stellar cluster it is embedded in. These observations have already started: Recent results on the luminous dust enshrowded star IRS3 using MIDI at the VLTI are presented and future scientific possibilities in the GC using MIDI at the VLTI in the MIR and GRAVITY in the NIR are highlighted. As a NIR wide field interferometric imager offering an angular resolution of about 10 milliarcseconds LINC/NIRVANA at the Large Binocular Telescope will be an ideal instrument for imaging galactic nuclei including the center of the Milky Way.

When a leakage, a "loss-of-coolant accident," occurs in a light water reactor, the emergency cooling system is able to supply large amounts of coolant to ensure residual heat removal. This supply can be routed through a special emergency cooling pipe, the "scoop," into the horizontal section of the main coolant pipe, the "hot leg." At the same time, hot steam from the superheated, partly voided core flows against the coolant. This gives rise to a two-phase flow in the opposite direction. A factor of primary interest in this situation is whether the coolant supplied by the emergency cooling system will reach the reactor core. The research project is being conducted in order to compute the rate of water supply by numerical methods. The WENKA test facility has been designed and built at the Karlsruhe Research Center to verify numerical calculations. It can be used to study the fluid dynamics phenomena expected to arise in emergency coolant feeding into the hot leg; the necessary local data can be determined experimentally. An extensive database for validating the numerical calculations is then available to complete the experimental work.