Volker Heinzel

Fluid oscillations in flat plate boiling water collectors

Abstract Boiling water collectors with an internal two-phase thermosiphon and buoyancy driven circulation are apt for process steam generation in the temperature range 70–150°C. Exploiting the advantages of boiling heat transfer requires mastering the instabilities of two-phase flow natural convection. With electrically heated mock-up test devices the boundaries for stable flow conditions were investigated. Between these boundaries, periodic mass flow fluctuations occur and may stimulate resonances of collector components. The fluctuation frequencies measured with the collector mock-up were below 1 Hz. The origin of the oscillations is still under investigation.

DOSE RATE ANALYSES FOR THE HIGH ENERGY BEAM TRANSPORT SECTION OF IFMIF

Abstract This work presents neutronic analyses to support the layout of the high energy beam transport (HEBT) section of the IFMIF neutron source in the framework of the Broader Approach (BA) EVEDA activities. In the HEBT section, neutron back streaming from the lithium target can cause significant damage to accelerator components and result in their activation. In order to estimate the resulting radiation doses, detailed neutron and photon flux distributions inside the Target Interface Room (TIR) and the Radiation Isolation Room (RIR) during operation are evaluated by using the Monte Carlo code McDeLicious, which is an enhancement to MCNP5. The obtained results show that the major contribution to the TIR dose during operation will come from neutrons streaming from the target through the beam ducts and from secondary photons produced in these parts. It seems to be impossible to use any semiconductor devices inside TIR, while for mechanical devices there should be no problem. The dose after shutdown due to decay gammas was preliminarily estimated for the beam duct at the most activated place in TIR. In order to reduce the shutdown dose rate, the use of a low-Mn-content aluminium alloy is proposed.

Numerical Analysis of Unsteady Flow Behavior in Flow Conditioner of IFMIF Liquid-Lithium Target

Abstract IFMIF (International Fusion Materials Irradiation Facility) is an accelerator based deuteron-lithium (D-Li) neutron source to simulate the neutron irradiation field in a fusion reactor. The target assembly of the IFMIF consists of the flow conditioners and the nozzle, which has to form a stable lithium jet. This work focuses on a numerical study of the flow conditioner efficiency, in which two different types of flow conditioners are compared by means of a detailed numerical analysis with respect to specific hydraulic effects in the pipe elbow and the inflow conditioners. The adequateness of two modelling approaches - Large Eddy Simulation (LES) and Detached Eddy Simulation (DES) - to simulate an unstable flow through a 90° bend of circular cross section has been examined. Both methods investigated exhibit a reasonable agreement with the experimental data, but the DES approach does not require a very fine grid resolution and is less time consuming. The further conducted numerical analysis of the flow conditioner uses a DES approach. The calculations show that a honeycomb-screen combination is not capable to suppress effectively large scale swirl motions emerging from the bend. A frequency analysis of the static pressure fluctuation reveals instabilities in the shear layer between the separation zone and the accelerated outer region, which additionally increase the inhomogeneity of the axial velocity distribution.

Overview of Material Challenges in IFMIF Test Cell Design

Abstract As the core region of IFMIF, the test cell (TC) suffers intense neutron and gamma irradiations. Major material challenges of the TC faced during engineering design phase are outlined and the current key material allocations are described. Actively cooled magnetite concrete is selected as the major biological shielding material for the TC, and actively cooled closed liner made of 316L stainless steel is selected to cover the complete TC internal surfaces. Material selections for sealing gaskets and electric insulations inside the TC are preliminarily defined based on dose rate maps at different locations. Metal based sealing gaskets and glass/ceramic electric insulations are applied in the areas with high dose rate, while organic based gaskets and conventional insulation materials can only be arranged behind sufficient biological shielding. Leak tight welding seams between removable interface shielding plugs and the TC liner are located in the region with very low helium generation rate (<0.01 appm/fpy) in steel so that cutting and re-welding during the complete IFMIF life span is guaranteed.

Einfluss der Konzentration auf solarthermische Systeme

Die solare Einstrahlung gleicht der eines schwarzen Strahlers mit 5576 K und besitzt eine hohe Exergie. Die Leistungsdichte dagegen entspricht einem Strahler mit 121 °C. Fur viele Anwendungen ist dies zu wenig, um eine ausreichende Betriebstemperatur (oder Exergie) sowie eine wirtschaftliche Flachennutzung zu erreichen. Mittels konzentrierender Spiegel wird die Leistungsdichte am Empfanger erhoht. Das Konzentrationsverhaltnis aus Spiegel- und Empfangerflache ist jedoch begrenzt. Die theoretische Begrenzung wird im Folgenden mittels des 2. Hauptsatzes der Thermodynamik abgeleitet. Wichtiger sind jedoch Einschrankungen durch die technischen oder physikalischen Eigenschaften der Spiegel oder Konzentratoren und den Empfanger oder Absorber. Den Zusammenhang von deren Qualitat und Anwendungsfallen werden aufgezeigt.

Impuls- und Energietransport in solarthermischen Systemen

Die Abschn. 3.3–3.5 behandelten bereits die Berechnung des Kollektorwirkungsgrades und der darin auftretenden Verluste. Dort wurde auf die detaillierte Diskussion der einzelnen passiven wie insbesondere auch aktiven Verlustmechanismen verzichtet. Die Erarbeitung der passiven Mechanismen zur Aufnahme solarer Einstrahlung im vierten Kapitel erlaubt nun einen neuen und fundierteren Einblick in die Beurteilung der konstruktiven Gestaltung sowie der anlagenbaulichen Realisation solarthermischer Systeme. Die darin gewonnen Erkenntnisse zeigen, dass durch die physikalischen Prozesse ein hoher Anteil der solaren Einstrahlung in Warme umgesetzt werden kann. Begrenzungen ergeben sich hauptsachlich durch konstruktive Rahmenbedingungen sowie materialspezifische Begrenzungen. Bei adaquater Material- und Temperaturwahl sowie konstruktiver Gestaltung lassen sich im passiven Bereich ca. 80 % an Energieumsetzung erreichen. Der Gesamtwirkungsgrad solarthermischer Systeme liegt jedoch deutlich unterhalb dieser Werte. Woran liegt dies? Eine Ursache ist der konvektive Transport des ein- oder mehrphasigen Warmetragers in den Rohrleitungen sowie in den im Solarsystem auftretenden Komponenten wie Pumpen, Ventile, Rohrleitungen und/oder Speicher, die alle verlustbehaftet sind und damit zu einer Verringerung des Wirkungsgrads fuhren.

Passive Mechanismen in der Solarenergie

Der Begriff passive Nutzung oder passive Masnahmen spielt in der modernen Solarthermie eine zentrale Schlusselrolle, ohne die ein effizienter Einsatz dieser Technologie undenkbar ware.

Assessment of the Operational Dose Rate in Polymer Insulators in the Test Cell of the IFMIF Neutron Source

Insulators for electrical connections of the test modules in the test cell of the International Fusion Materials Irradiation Facility (IFMIF) neutron source will be exposed to intense ionizing radiation even if they are located away from the neutron source. The aim of this work was to check whether radiation-hard polymers, for example polyimide, would be sufficiently long-lasting in such an environment. The calculations presented here were survey calculations to aid with the decisions on possible insulator candidates. The calculations have been done with the McDeLicious code and a detailed 3-D neutronics model of the IFMIF test cell. Mesh tallies were utilized to calculate dose rate maps 10 cm below the ceiling of the test cell where the connectors would be located. The calculated dose deposited within one full power year would be higher than 200 MGy nearly everywhere in the test cell. This value excludes most polymers as candidates for insulators, but even polyimide would reach its limits. It was found that the calculated dose contribution from gamma rays was considerably dependent on the nuclear data library used for describing the lithium in the lithium loop. We have also checked the effect of an additional lead shield of 10 cm thickness which reduced the deposited dose by a factor of 2-5. A new neutronics model has become available recently which was derived from the latest IFMIF test cell design. We have performed preliminary calculations for dose rates in anticipated locations of connector insulators. The results confirm the high dose rate values calculated with the previous neutronics model.

Assessment of the operational dose rate in polymer insulators in the test cell of the IFMIF neutron source

Insulators for electrical connections of the test modules in the test cell of the International Fusion Materials Irradiation Facility (IFMIF) neutron source will be exposed to intense ionizing radiation even if they are located away from the neutron source. The aim of this work was to check whether radiation-hard polymers, for example polyimide, would be sufficiently long-lasting in such an environment. The calculations presented here were survey calculations to aid with the decisions on possible insulator candidates. The calculations have been done with the McDeLicious code and a detailed 3-D neutronics model of the IFMIF test cell. Mesh tallies were utilized to calculate dose rate maps 10 cm below the ceiling of the test cell where the connectors would be located. The calculated dose deposited within one full power year would be higher than 200 MGy nearly everywhere in the test cell. This value excludes most polymers as candidates for insulators, but even polyimide would reach its limits. It was found that the calculated dose contribution from gamma rays was considerably dependent on the nuclear data library used for describing the lithium in the lithium loop. We have also checked the effect of an additional lead shield of 10 cm thickness which reduced the deposited dose by a factor of 2-5. A new neutronics model has become available recently which was derived from the latest IFMIF test cell design. We have performed preliminary calculations for dose rates in anticipated locations of connector insulators. The results confirm the high dose rate values calculated with the previous neutronics model.

Large Eddy Simulations of Taylor-Görtler Instabilities in Transitional and Turbulent Boundary Layers

Free surface liquid metal targets are considered in several high power targets as a tool to produce secondary particles, since their power density exceeds material sustainable limits. Many target designs consider due to the high power deposited in the liquid a concave formed back plate in order to yield a higher boiling point. Upstream the free surface target domain the liquid metal flow is conditioned by a nozzle. However, a back-wall curvature as well as a concave shaped exit nozzle contour can lead to the occurrence of secondary motions in the flow caused by Taylor-Gortler (TG) instabilities. These motions may impact the hydrodynamic stability the flow and also lead to an undesired heat transfer from the hottest region produced within the liquid target towards the uncooled back plate. In this study, the suitability of the Large Eddy Simulation (LES) technique to simulate the formation, development and destruction TG instabilities in transitional and turbulent boundary layers was tested by comparing the simulation results with experimental data reported in literature. All comparisons exhibit a qualitative and quantitative good agreement between experimental data and numerical predictions regarding the mean flow parameters and unsteady large-scale structures caused by TG instabilities.Copyright