12 research outputs found
Separate effects tests on hydrogen combustion during direct containment heating events
Experimente zur Wasserstoffverbrennung bei DCH-Prozessen
Im Rahmen der Forschung zu schweren Unfällen in Leichtwasserreaktoren werden im Institut für Energie- und Kerntechnik des Forschungszentrums Karlsruhe seit 1998 die Versuchanlagen DISCOC und DISCO-H betrieben, konzipiert zur Untersuchung der Druckbelastung des Sicherheitsbehälters durch Schmelzedispersion (Direct Containment Heating, DCH) bei Versagen des Reaktordruckbehälters (RDB). Vorangegangene Experimente haben die Schmelzeverteilung und Druckerhöhung im Sicherheitsbehälter bei verschiedenen europäischen Reaktorgeometrien untersucht, unter Anwendung von Eisen-Aluminium-Schmelzen und Dampf als Modellfluide.
Die Analyse dieser Experimente hat gezeigt, dass der Druckanstieg sowohl durch den Wärmeübergang 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 während des DCH-Prozesses besser beschreiben zu können. Um diese Fragen zu klären, wurden Einzeleffektexperimente in der DISCO-H Versuchsanlage durchgeführt. Mit Ausnahme der Schmelzedispersion laufen in diesen Experimenten die gleichen Prozesse ab, wie sie während des DCH-Vorganges auftreten, das sind das Abblasen einer heißen Wasserstoff-Dampf Mischung in den Sicherheitsbehälter und die Zündung dieses Gasgemisches in einer LuftDampf-Wasserstoff Atmosphäre. Der Effekt der Schmelzepartikel als Zünder wurde mit Thermitkerzen simuliert. Die experimentellen Daten werden benutzt, um Modelle in Verbrennungscodes zu kalibrieren und um auf Reaktormaßstab zu extrapolieren.
Die Experimente wurden in zwei Schritten durchgeführt. Für 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 durchgeführt, bei der das Gas aus der Grube zuerst in einen separaten Reaktorraum und von dort in den Sicherheitsbehälter strömt. Die Versuchsbedingungen waren wie folgt:
• Als Anfangsbedingung im Sicherheitsbehälter wurde eine Luft- bzw. ein Luft-Dampf-Atmosphäre bei 100°C und 2 bar eingestellt, mit Wasserstoffkonzentrationen zwischen 0 und 7 mol%, repräsentativ für die Atmosphäre im Containment bei Versagen des RDB.
• Einblasen eines heißen Dampf-Wasserstoffgemisches in die Reaktorgrube bei 20 bar, repräsentativ für ein Kühlmittelabblasen durch ein Leck im RDB und der Wasserstofferzeugung während dieser Phase.
Die wichtigsten gemessenen Größen waren (1) der Druckanstieg im Sicherheitsbehälter, (2) die Gastemperaturen und (3) die Anzahl der verbrannten Wasserstoffmole. Diese Experimente kennzeichnen die Rate der Wasserstoffverbrennung, die Vollständigkeit 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 Druckerhöhung im Sicherheitsbehälter lag zwischen 46% und 67%.
Spezielle Verbrennungscodes mĂĽssen angewendet werden um zu prĂĽfen, ob diese Ergebnisse auch fĂĽr den ReaktormaĂźstab gelten
Reconstruction of ancient microbial genomes from the human gut
Loss of gut microbial diversity1–6 in industrial populations is associated with chronic diseases7, underscoring the importance of studying our ancestral gut microbiome. However, relatively little is known about the composition of pre-industrial gut microbiomes. Here we performed a large-scale de novo assembly of microbial genomes from palaeofaeces. From eight authenticated human palaeofaeces samples (1,000–2,000 years old) with well-preserved DNA from southwestern USA and Mexico, we reconstructed 498 medium- and high-quality microbial genomes. Among the 181 genomes with the strongest evidence of being ancient and of human gut origin, 39% represent previously undescribed species-level genome bins. Tip dating suggests an approximate diversification timeline for the key human symbiont Methanobrevibacter smithii. In comparison to 789 present-day human gut microbiome samples from eight countries, the palaeofaeces samples are more similar to non-industrialized than industrialized human gut microbiomes. Functional profiling of the palaeofaeces samples reveals a markedly lower abundance of antibiotic-resistance and mucin-degrading genes, as well as enrichment of mobile genetic elements relative to industrial gut microbiomes. This study facilitates the discovery and characterization of previously undescribed gut microorganisms from ancient microbiomes and the investigation of the evolutionary history of the human gut microbiota through genome reconstruction from palaeofaeces.Ethics Overview of samples Reference-based taxonomic composition De novo genome reconstruction Methanobrevibacter smithii tip dating Functional genomic analysis Discussion Online content Method
Reconstruction of ancient microbial genomes from the human gut
Loss of gut microbial diversity in industrial populations is associated with chronic diseases, underscoring the importance of studying our ancestral gut microbiome. However, relatively little is known about the composition of pre-industrial gut microbiomes. Here we performed a large-scale de novo assembly of microbial genomes from palaeofaeces. From eight authenticated human palaeofaeces samples (1,000–2,000 years old) with well-preserved DNA from southwestern USA and Mexico, we reconstructed 498 medium- and high-quality microbial genomes. Among the 181 genomes with the strongest evidence of being ancient and of human gut origin, 39% represent previously undescribed species-level genome bins. Tip dating suggests an approximate diversification timeline for the key human symbiont Methanobrevibacter smithii. In comparison to 789 present-day human gut microbiome samples from eight countries, the palaeofaeces samples are more similar to non-industrialized than industrialized human gut microbiomes. Functional profiling of the palaeofaeces samples reveals a markedly lower abundance of antibiotic-resistance and mucin-degrading genes, as well as enrichment of mobile genetic elements relative to industrial gut microbiomes. This study facilitates the discovery and characterization of previously undescribed gut microorganisms from ancient microbiomes and the investigation of the evolutionary history of the human gut microbiota through genome reconstruction from palaeofaeces
Melt dispersion and direct containment heating (DCH) experiments in the DISCO-H test facility
Low pressure corium dispersion experiments in the DISCO test facility with cold simulant fluids
Melt dispersion and direct containment heating (DCH) experiments in the DISCO-H test facility
The DISCO-H Test Facility at Forschungszentrum Karlsruhe was set up to perform scaled experiments that simulate melt ejection scenarios under low system pressure in Severe Accidents in Pressurized Water Reactors (PWR). These experiments are designed to investigate the fluid-dynamic, thermal and chemical processes during melt ejection out of a breach in the lower head of a PWR pressure vessel at pressures below 2 MPa with an iron-alumina melt and steam. In the past, a detailed study of pressure and geometry effects on the fluid dynamics of the melt dispersion process had been performed with cold model fluids in the facility DISCO-C. The main components of the facility are scaled about 1:18 linearly to a large European pressurized water reactor. Standard test results are: pressure and temperature history in the RPV, the cavity, the reactor compartment and the containment, post test melt fractions in all locations with size distribution of the debris, video film in reactor compartment and containment (timing of melt flow and hydrogen burning), and pre-and post test gas analysis in the cavity and the containment. The results of six experiments are presented here. All experiments were done with 10.6 kg of iron-alumina melt (scaling to 16 m"3 corium), and a hole of 56 mm diameter (1 m scaled) or 28 mm at the center of the lower head. For comparison with a similar experiment conducted in a larger scale (1:10), the basis experiment was performed with an open path from the reactor pit to the containment (open pit), with prototypical conditions concerning the steam driven ejection out of the RPV, and a containment atmosphere, that was part air and part steam at an elevated pressure, with 3 mole-% hydrogen. In this and other tests, hydrogen production and combustion occurred. In one experiment the hydrogen effect was excluded by using only nitrogen as driving gas and a pure air atmosphere in the containment. In some tests the direct path to the containment was closed (closed pit). The pressure rise in the containment is highest with an open pit and hydrogen combustion. With a closed pit the gas and the debris have to flow first into the subcompartment and then through relatively small cross sections into the containment. Considerable less hydrogen was produced and burned in this case. In the test without steam, no hydrogen effect was present, but, with the direct path to the containment open, a large amount of debris was dispersed into the containment, and efficiently transferred heat to its atmosphere. (orig.)Available from TIB Hannover: ZA 5141(6988) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman
Versuchsanlage zur schnellen Gasinjektion in einen wassergefuellten Behaelter
SIGLECopy held by FIZ Karlsruhe; available from UB/TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman
Draft genome sequences of three Actinobacteria strains presenting new candidate organisms with high potentials for specific P450 cytochromes
The three Actinobacteria strains Streptomyces platensis DSM 40041, Pseudonocardia autotrophica DSM 535, and Streptomyces fradiae DSM 40063 were described to selectively oxyfunctionalize several drugs. Here, we present their draft genomes to unravel their gene sets encoding promising cytochrome P450 monooxygenases associated with the generation of drug metabolites