Nitriding model for zirconium based fuel cladding in severe accident codes

A model has been developed to describe the nitriding of partially oxidized zirconium based cladding during an air ingress sequence when the reaction has become starved of oxidant (oxygen and/or steam), and the subsequent re-oxidation of nitride following of restoration of coolant. Key aspects of the model are the estimation of oxygen-stabilised alpha zirconium, α-Zr(O), formed during pre-oxidation and its reaction with the nitrogen. Nitriding of metallic Zr is much slower than α-Zr(O), and plays a comparatively minor role. The model is based on data from separate-effects tests comprised pre-oxidation, nitriding in the absence of oxidant, and re-oxidation in the absence of nitrogen, which were used to derive the kinetic parameters for the main reaction processes. Developmental assessment was performed using the test results, demonstrating favourable agreement for the main reaction signatures. Independent assessment against Integral Test data is underway

Analytical pre-test support of boil-down test QUENCH-11

Analytische Unterstützung zur Vorbereitung des Ausdampf-Versuchs QUENCH-11 Im QUENCH-Vorhaben des Forschungszentrums Karlsruhe soll das Fluten eines teilweise zerstörten Kerns untersucht werden. Der zweite LACOMERA Versuch Q-L2 (QUENCH-11) beginnt mit einer Ausdampfphase des Bündels, bis der Wasserspiegel das untere Bündel¬ende erreicht hat. Ein derartiger Versuch wurde bislang noch nicht in der QUENCH-Anlage durchgeführt, so dass mit SCDAP/RELAP5 mod3.2.irs eine Machbarkeitsstudie erforderlich war. Die Ergebnisse zeigen, dass eine Zusatzheizung im unteren Plenum notwendig ist, um den Wasserstand und die Verdampfungsrate (Dampfmassenstrom in der Ausdampfphase) unabhängig von der angestrebten Maximaltemperatur im Bündel zu regeln. Für eine verläss¬liche Versuchsplanung sowie zur Erstellung der Energiebilanz muss die Zusatzheizung in¬nerhalb des unteren Plenums unterhalb der Wasseroberfläche installiert werden, damit die Heizleistung vollständig in das Wasser eingekoppelt wird. Um die Verdampfungsrate über längere Zeit aufrecht zu erhalten, muss zusätzlich Wasser in das untere Plenum eingespeist werden. Anhand dieser Rechnungen wird der Testablauf im Detail diskutiert. Eine entsprechende Studie zeigte die Durchführbarkeit eines solchen Ausdampftests und war die Grundlage für die oben erwähnten Änderungen in der Anlage und der Versuchs-Durchführung gegenüber früheren Tests. Eine Reihe von Vorversuche wurde durchgeführt, um die Brauchbarkeit der Änderungen an der Anlage und der geplanten Versuchsführung zu prüfen und um Daten für das thermohydraulische Verhalten der Anlage zu bekommen, an denen die Code-Modelle für die Voraus- und Nachrechnungen von QUENCH-11 getestet werden können. Im Anschluss an die Vorversuche wurden wie bei früheren QUENCH-Tests detaillierte Vorausrechnungen mit verschiedenen Codes zu Versuchsablauf und -steuerung durchgeführt. Drei Forschungs¬einrichtungen in der EU waren beteiligt. Die berechneten Ergebnisse reagieren empfindlich auf Änderungen der Versuchsparameter wie das anfängliche axiale Temperaturprofil und die eingespeiste elektrische Leistung, wie es auch für die untersuchten physikalischen Bedin¬gungen im Versuch erwartet werden kann

Harmonic Generation from Relativistic Plasma Surfaces in Ultra-Steep Plasma Density Gradients

Harmonic generation in the limit of ultra-steep density gradients is studied experimentally. Observations demonstrate that while the efficient generation of high order harmonics from relativistic surfaces requires steep plasma density scale-lengths ($L_p/\lambda < 1$) the absolute efficiency of the harmonics declines for the steepest plasma density scale-length $L_p \to 0$, thus demonstrating that near-steplike density gradients can be achieved for interactions using high-contrast high-intensity laser pulses. Absolute photon yields are obtained using a calibrated detection system. The efficiency of harmonics reflected from the laser driven plasma surface via the Relativistic Oscillating Mirror (ROM) was estimated to be in the range of 10^{-4} - 10^{-6} of the laser pulse energy for photon energies ranging from 20-40 eV, with the best results being obtained for an intermediate density scale-length

Ground-based off-line aerosol measurements at Praia, Cape Verde, during the Saharan Mineral Dust Experiment: Microphysical properties and mineralogy

A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. This work reports on the aerosol mass concentrations, size distributions and mineralogical composition of the aerosol arriving at Praia. Three dust periods were recorded during the measurements, divided by transitional periods and embedded in maritime-influenced situations. The total suspended particle mass/PM10/PM2.5 were 250/180/74μg/m3 on average for the first dust period (17–21 January) and 250/230/83μg/m3 for the second (24–26 January). The third period (28 January to 2 February) was the most intensive with 410/340/130 μg/m3. Four modes were identified in the size distribution. The first mode (50–70 nm) and partly the second (700–1100 nm) can be regarded as of marine origin, but some dust contributes to the latter. The third mode (2–4 μm) is dominated by advected dust, while the intermittently occurring fourth mode (15–70 μm) may have a local contribution. The dust consisted of kaolinite (dust/maritime period: 35%wt./25%wt.),K-feldspar (20%wt./25%wt.), illite (14%wt./10%wt.), quartz (11%wt./8%wt.), smectites (6%wt./4%wt.), plagioclase (6%wt./1%wt.), gypsum (4%wt./7%wt.), halite (2%wt./17%wt.) and calcite (2%wt./3%wt.)

Size distribution, mass concentration, chemical and mineralogical composition and derived optical parameters of the boundary layer aerosol at Tinfou, Morocco, during SAMUM 2006

During the SAMUM 2006 field campaign in southern Morocco, physical and chemical properties of desert aerosols were measured. Mass concentrations ranging from 30μgm−3 for PM2.5 under desert background conditions up to 300 000μgm−3 for total suspended particles (TSP) during moderate dust storms were measured. TSP dust concentrations are correlated with the local wind speed, whereasPM10 andPM2.5 concentrations are determined by advection from distant sources. Size distributions were measured for particles with diameter between 20 nm and 500μm (parametrizations are given). Two major regimes of the size spectrum can be distinguished. For particles smaller than 500 nm diameter, the distributions show maxima around 80 nm, widely unaffected of varying meteorological and dust emission conditions. For particles larger than 500 nm, the range of variation may be up to one order of magnitude and up to three orders of magnitude for particles larger than 10μm. The mineralogical composition of aerosol bulk samples was measured by X-ray powder diffraction. Major constituents of the aerosol are quartz, potassium feldspar, plagioclase, calcite, hematite and the clay minerals illite, kaolinite and chlorite. A small temporal variability of the bulk mineralogical composition was encountered. The chemical composition of approximately 74 000 particles was determined by electron microscopic single particle analysis. Three size regimes are identified: for smaller than 500 nm in diameter, the aerosol consists of sulphates and mineral dust. For larger than 500 nm up to 50μm, mineral dust dominates, consisting mainly of silicates, and—to a lesser extent—carbonates and quartz. For diameters larger than 50μm, approximately half of the particles consist of quartz. Time series of the elemental composition show a moderate temporal variability of the major compounds. Calcium-dominated particles are enhanced during advection from a prominent dust source in Northern Africa (Chott El Djerid and surroundings). The particle aspect ratio was measured for all analysed particles. Its size dependence reflects that of the chemical composition. For larger than 500 nm particle diameter, a median aspect ratio of 1.6 is measured. Towards smaller particles, it decreases to about 1.3 (parametrizations are given). From the chemical/mineralogical composition, the aerosol complex refractive index was determined for several wavelengths from ultraviolet to near-infrared. Both real and imaginary parts show lower values for particles smaller than 500 nm in diameter (1.55–2.8 × 10−3i at 530 nm) and slightly higher values for larger particles (1.57–3.7 × 10−3i at 530 nm)

Observation of energetic terahertz pulses from relativistic solid density plasmas

We report the first experimental observation of terahertz (THz) radiation from the rear surface of a solid target while interacting with an intense laser pulse. Experimental and two-dimensional particle-in-cell simulations show that the observed THz radiation is mostly emitted at large angles to the target normal. Numerical results point out that a large part of the emission originates from a micron-scale plasma sheath at the rear surface of the target, which is also responsible for the ion acceleration. This opens a perspective for the application of THz radiation detection for on-site diagnostics of particle acceleration in laser-produced plasmas

Towards a renormalizable standard model without fundamental Higgs scalar

We investigate the possibility of constructing a renormalizable standard model with purely fermionic matter content. The Higgs scalar is replaced by point-like fermionic self-interactions with couplings growing large at the Fermi scale. An analysis of the UV behavior in the point-like approximation reveals a variety of non-Gaussian fixed points for the fermion couplings. If real, such fixed points would imply nonperturbative renormalizability and evade triviality of the Higgs sector. For point-like fermionic self-interactions and weak gauge couplings, one encounters a hierarchy problem similar to the one for a fundamental Higgs scalar.Comment: 18 pages, 4 figure

All-in-one visible-light-driven water splitting by combining nanoparticulate and molecular co-catalysts on CdS nanorods

Full water splitting into hydrogen and oxygen on semiconductor nanocrystals is a challenging task; overpotentials must be overcome for both half-reactions and different catalytic sites are needed to facilitate them. Additionally, efficient charge separation and prevention of back reactions are necessary. Here, we report simultaneous H-2 and O-2 evolution by CdS nanorods decorated with nanoparticulate reduction and molecular oxidation co-catalysts. The process proceeds entirely without sacrificial agents and relies on the nanorod morphology of CdS to spatially separate the reduction and oxidation sites. Hydrogen is generated on Pt nanoparticles grown at the nanorod tips, while Ru(tpy)(bpy)Cl-2-based oxidation catalysts are anchored through dithiocarbamate bonds onto the sides of the nanorod. O-2 generation from water was verified by O-18 isotope labelling experiments, and time-resolved spectroscopic results confirmed efficient charge separation and ultrafast electron and hole transfer to the reaction sites. The system demonstrates that combining nanoparticulate and molecular catalysts on anisotropic nanocrystals provides an effective pathway for visible-light-driven photocatalytic water splitting