Nucleation and growth of lead oxide particles in liquid lead-bismuth eutectic

Liquid lead-bismuth eutectic (LBE) is an important candidate to become the primary coolant of future, generation IV, nuclear fast reactors and Accelerator Driven System (ADS) concepts. One of the main challenges with the use of LBE as a coolant is to avoid its oxidation which results in solid lead oxide (PbO) precipitation. The chemical equilibria governing PbO formation are well understood. However, insufficient kinetic information is currently available for the development of LBE-based nuclear technology. Here, we report the results of experiments in which the nucleation, growth and dissolution of PbO in LBE during temperature cycling are measured by monitoring dissolved oxygen using potentiometric oxygen sensors. The metastable region, above which PbO nucleation can occur, has been determined under conditions relevant for the operation of LBE cooled nuclear systems and was found to be independent of setup geometry and thus thought to be widely applicable. A kinetic model to describe formation and dissolution of PbO particles in LBE is proposed, based on Classical Nucleation Theory (CNT) combined with mass transfer limited growth and dissolution. This model can accurately predict the experimentally observed changes in oxygen concentration due to nucleation, growth and dissolution of PbO, using the effective interfacial energy of a PbO nucleus in LBE as a fitting parameter. The results are invaluable to evaluate the consequences of oxygen ingress in LBE cooled nuclear systems under normal operating and accidental conditions and form the basis for the development of cold trap technology to avoid PbO formation in the primary reactor circuit

Complete genome sequences of three African foot-and-mouth disease viruses from clinical samples isolated in 2009 and 2010

&lt;p&gt;The complete genome sequences of three foot-and-mouth disease viruses (one virus of each serotype SAT1, SAT2 and O) were directly sequenced from RNA extracted from clinical bovine samples, demonstrating the feasibility of full-genome sequencing from strong positive samples taken from symptomatic animals. &lt;/p&gt;</p

Comparison of the Transport Mechanism in Underdoped High Temperature Superconductors and in Spin Ladders

Recently, the normal state resistivity of high temperature superconductors (in particular in La2-xSrxCuO4 single crystals) has been studied extensively in the region below Tc by suppressing the superconducting state in high magnetic fields. In the present work we report on the normal state resistance of underdoped La2-xSrxCuO4 thin films under epitaxial strain, measured far below Tc by applying pulsed fields up to 60 T. We will compare the transport measurements on these high temperature superconductors with transport data reported for the Sr2.5Ca11.5Cu24O41 spin ladder compound. This comparison leads to an interpretation of the data in terms of the recently proposed 1D quantum transport model and the charge-stripe models.Comment: 5 pages, PDF fil

Multi-composite wire for high performance pulsed magnets

The Multi-Composite (MC) wire is a new concept in the pursuit of obtaining the ideal conductor for high performance pulsed magnets. The MC wire consists of a braided, insulating sleeve enclosing a bundle of thin wires: conductor (Cu, CuNb) and reinforcement (e.g., high strength steel), with all free spaces filled by a tight packing of high strength fibers that do not need to be insulating (e.g., carbon fibers). The MC concept is based on the fact that thin wires are inherently stronger. This concept allows winding around a small bore and much flexibility: the composition and geometry of the MC core can be varied even along the length of a continuous wire-to obtain the desired properties of strength and electrical conductivity. Prototype MC wires were made with soft Cu and carbon as core materials, with ultimate tensile strength of 1.2 GPa and 1.7 GPa and conductivity of 38% IACS at 300 K. Several coils were designed and manufactured with similar bore (18 mm) and pulse duration as our standard user coils with internal reinforcement. Although the coil structure was not yet optimized, fields in excess of 50 T were obtained, leaving much room for improvement.status: publishe

False-positive results in metagenomic virus discovery: a strong case for follow-up diagnosis

A viral metagenomic approach using virion enrichment, random amplification and next-generation sequencing was used to investigate an undiagnosed cluster of dairy cattle presenting with high persistent fever, unresponsive to anti-microbial and anti-inflammatory treatment, diarrhoea and redness of nose and teat. Serum and whole blood samples were taken in the predicted hyperviraemic state of an animal that a few days later presented with these clinical signs. Bioinformatics analysis of the resulting data from the DNA virus identification workflow (a total of 32 757 sequences with average read length 335 bases) initially demonstrated the presence of parvovirus-like sequences in the tested blood sample. Thorough follow-up using specific real-time RT-PCR assays targeting the detected sequence fragments confirmed the presence of these sequences in the original sample as well as in a sample of an additional animal, but a contamination with an identical genetic signature in negative extraction controls was demonstrated. Further investigation using an alternative extraction method identified a contamination of the originally used Qiagen extraction columns with parvovirus-like nucleic acids or virus particles. Although we did not find any relevant virus that could be associated with the disease, these observations clearly illustrate the importance of using a proper control strategy and follow-up diagnostic tests in any viral metagenomic study

Formation and transport of lead oxide in a non-isothermal lead-bismuth eutectic loop

Lead oxide (PbO) formation can occur in Lead-Bismuth Eutectic (LBE)-cooled nuclear systems in case of oxygen ingress or temperature decrease of the coolant beyond the normal operation ranges. In the present work the formation of lead oxide in an actively cooled LBE flow is studied. Computational fluid dynamics (CFD) is used to predict the nucleation, growth and dissolution of PbO particles. Solid oxide particles are modeled as a pseudocontinuous phase, using the Kinetic Theory of Granular Flow (KTGF) to account for particle-flow interaction. The particle size distribution (PSD) is accounted for using Population Balance Equations/Models (PBE/PBM). The results obtained from the model are qualitatively in good agreement with experimental results obtained in the MEXICO loop at SCK.CEN. The calculated PSD reveals that the majority of the oxide particles are expected to be in the sub-micron range. Experimental results indicate that in the studied conditions PbO nucleates in the LBE bulk leading to suspended particles in the LBE flow

Electrochemical measurement of solubility product of metal oxides in liquid metals by coulometric titration of oxygen

We propose a new electrochemical method for the measurement of the solubility product of the oxide of a metal impurity, in a liquid metal solvent that is less easily oxidized than the metal impurity. When a known amount of oxygen is continuously added into the liquid metal by coulometric titration, the dissolved metal impurity reacts with the added dissolved oxygen, forming a metal oxide. By measuring the concentration of dissolved oxygen in the liquid metal solvent during the titration, the solubility product of the impurity metal oxide in the liquid metal solvent can be derived. From this solubility product, using thermochemical data of the known chemical species involved in the oxidation reaction, i.e. Sieverts’ constant of dissolved oxygen in the liquid metal solvent and the Gibbs free energy of formation of the impurity metal oxide, the elemental solubility of the metallic impurity element in the liquid metal solvent can be derived as well. In this work, we validate the method by measuring the solubility product of magnetite (Fe3O4) in molten lead-bismuth eutectic alloy (LBE), in the temperature range of 723–826 K.info:eu-repo/semantics/publishe