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Understanding the microstructural and phase changes occurring during irradiation and their impact on metallic fuel behavior is integral to research and development of nuclear fuel programs. This paper reports systematic analysis of as-fabricated and irradiated low-enriched U-Mo (uranium-molybdenum metal alloy) fuel using atom probe tomography (APT). This study is carried out on U-7 wt.% Mo fuel particles coated with a ZrN layer contained within an Al matrix during irradiation. The dispersion fuel plates from which the fuel samples were extracted are irradiated at Belgian Nuclear Research Centre (SCK CEN) with burn-up of 52% and 66% in the framework of the SELENIUM (Surface Engineering of Low ENrIched Uranium-Molybdenum) project. The APT studies on U-Mo particles from as-fabricated fuel plates enriched to 19.8% revealed predominantly γ-phase U-Mo, along with a network of the cell boundary decorated with α-U, γ’-U2Mo, and UC precipitates along the grain boundaries. The corresponding APT characterization of irradiated fuel samples showed formation of fission gas bubbles enriched with solid fission products. The intermediate burnup sample showed a uniform distribution of the typical bubble superlattice with a radius of 2 nm arranged in a regular lattice, while the high burnup sample showed a non-uniform distribution of bubbles in grain-refined regions. There was no evidence of remnant α-U, γ’-U2Mo, and UC phases in the irradiated U-7 wt.% Mo samples.

A high-energy Xe ion irradiation experiment was conducted to investigate the temperature dependence of interdiffusion in bilayer Al-UMo samples under irradiation. The amount of interdiffusion achieved at a fixed dose with the increase of temperature showed a clear transition at 175°C (with an estimated error in the range of ±10°C) from temperature-independent to temperature-dependent behavior. The activation energy derived from the curve of interdiffusion quantity vs. irradiation temperature is 0.77±0.16 eV. This information has been utilized to understand the temperature effect on the interdiffusion process that occurred at the interfaces of U-Mo particles and the Al matrix in U-Mo/Al dispersion fuels, whose magnitude significantly impacts the fuel's performance. Although this temperature effect was deemed important, it cannot be examined directly using in-pile irradiation data, as fuel temperatures cannot be measured in reactor irradiation and are highly correlated with fission rate and thermal conductivity evolution. To connect the knowledge accumulated from ion irradiation with in-pile irradiation data, simulation of a full-sized U-Mo/Al dispersion fuel plate irradiated in the FUTURE test in the BR2 reactor was performed with the Dispersion Analysis Research Tool (DART), a dispersion fuel performance code. DART is equipped with an interaction or interdiffusion layer (IL) growth correlation formulated to describe the temperature dependence of ion mixing results. The agreement between calculated and measured fuel meat constituent volume fractions and swelling data demonstrated that the temperature effect on in-pile Al-UMo interdiffusion is well captured with the correlation. In this case, the fitted activation energy is 0.70 eV. Considering the uncertainties associated with the ion irradiation data, the activation energy obtained from in-pile data fitting is in accord with that from ion irradiation results.

The microstructure, growth kinetics, and the high temperature phase equilibria of the U Mn binary system are investigated using differential scanning calorimetry. Alloys with various compositions are prepared in a positive-pressure arc melting furnace in order to examine all possible phase changes within the system. Phase composition and morphology were analyzed using XRD, SEM and EDX. Transformation temperatures and enthalpies have been assessed pertaining to: (i) allotropic phase changes αMn → βMn → γMn →δMn, (ii) two eutectic isotherms UMn2 + βMn → L and U6Mn + UMn2 → L and (iii) melting transitions as a function of composition. The development of the two intermetallic phases U6Mn and UMn2 are observed. A faceted morphology accompanies the formation of UMn2 in a matrix of U6Mn, while grain boundary decomposition is found of UMn2 in αMn. The transformation temperatures are compared to existing phase diagrams and are slightly higher than reported in literature. Experimental observations of the allotropic transformations of αMn to βMn and βMn to γMn are in agreement with a calculated phase diagram. The eutectic composition for UMn2 and αMn is found to be 55 wt%Mn, in agreement with previously reported values, while the enthalpy of fusion associated with this eutectic point is found to be 54 ± 6.5 kJ mol−1. The enthalpies of formation for the two intermetallic phases U6Mn and UMn2 are 71 ± 8.5 kJ mol−1 and 42 ± 5 kJ mol−1 respectively.

Aluminum cladding oxidation of research-reactor fuel elements at high power conditions has a disadvantageous effect on fuel performance due to the lower thermal conductivity of the oxide. The oxide growth prediction models available in the literature were mostly developed for low power conditions. To examine the applicability of the models to high power and high temperature test conditions, the models were studied by coupling with the most frequently employed heat transfer coefficient (HTC) correlations including the Dittus-Boelter correlation, the Colburn correlation, the Sieder-Tate correlation, and KAERI-developed correlation. The Griess model over-predicted the oxide growth while the KAERI-Griess model under-predicted the oxide growth for high power tests. The Kim model, coupled with the Colburn correlation, gave most consistent results with the measured data from two BR2 experiments. However, the Kim model was found to be inapplicable to the EUHFRR conditions at the peak power locations if it was coupled with the Dittus-Boelter correlation. A revision of the prediction models to more closely agree with the measured data was recommended. AG3NE and AlFeNi cladding types were tested in the E-FUTURE experiment, and a noticeable (although small) reduction in oxide thickness on the AlFeNi cladding was observed. However, this difference was believed to be only a secondary effect considering other uncertainties in model predictions, so no attempt was made to model the alloying effect.

Irradiation responses of U–Mo/Al dispersion fuel have been investigated by irradiation with 84 MeV Xe26+ ions. Dispersion fuels fabricated with uncoated and ZrN-coated fuel particles were irradiated to various doses at ∼350 °C. The highest dose achieved was 2.9 × 1017 ions/cm2 (∼1200 displacement per atom (dpa)). Following the irradiation, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) experiments were carried out to characterize the microstructures of the irradiated samples. The post irradiation examinations (PIE) revealed that: (1) crystalline interdiffusion product (UMo)Alx developed at locations where no coating or compromised coating layer is present; (2) intact ZrN coating layers effectively blocked the interdiffusion between U–Mo and Al; (3) SEM-observable Xe bubbles distributed along grain/cell boundaries in U–Mo; and (4) gas bubble interlinkage was observed at a dose of 2.9 × 1017 ions/cm2.

The superlattice and domain structures exhibited by ordered titanium monoxide Ti5O5 are disrupted by low energy electron beam irradiation. The effect is attributed to the disordering of the oxygen and titanium sublattices. This disordering is caused by the displacement of both oxygen and titanium atoms by the incident electrons and results in a phase transformation of the monoclinic phase Ti5O5 into cubic B1 titanium monoxide. In order to determine the energies required for the displacement of titanium or oxygen atoms, i.e. threshold displacement energies, a systematic study of the disappearance of superstructure reflections with increasing electron energy and electron bombardment dose has been performed in situ in a transmission electron microscope (TEM). An incident electron energy threshold between 120 and 140 keV has been observed. This threshold can be ascribed to the displacements of titanium atoms with 4 as well as with 5 oxygen atoms as nearest neighbors. The displacement threshold energy of titanium atoms in Ti5O5 corresponding with the observed incident electron threshold energy lies between 6.0 and 7.5 eV. This surprisingly low value can be explained by the presence of either one or two vacant oxygen lattice sites in the nearest neighbors of all titanium atoms.

The fusion plasma, with a typical temperature of 10 keV, has to be brought into contact with a physical wall in order to remove the helium produced and drain the excess energy in the fusion plasma. The fusion plasma is far too hot to be brought into direct contact with a physical wall. It would degrade the wall and the debris from the wall would extinguish the plasma. Therefore, schemes are developed to cool down the plasma locally before it impacts on a physical surface. The resulting plasma wall-interaction in ITER is facing several challenges including surface erosion, material redeposition and tritium retention. In JET facility both beryllium and carbon are used together as plasma facing materials, and the resultant surfaces show considerable mixing between the two elements. In this work a first XPS characterisation has been performed on the surface of several PFC (plasma facing components) samples obtained from various JET tiles from the Mk II GB divertor in JET. The substrates of the tiles are CFC, and the deposited films have various D/C ratios depending on the position in the tokamak. Ion beam analysis shows that the D/C ratio is ∼1 in the shadowed areas and Be/C ∼1–2 in the plasma-exposed regions of the inner divertor. These values could give rise to the formation of beryllium carbides, and indications of a carbide component are found in the XPS spectra. The processes for material migration and the morphology of the deposits are discussed.

Valence states of uranium in three ternary uranates KUO 3 , NaUO 3 and Ba 2 U 2 O 7 were studied using X-ray photoelectron spectroscopy (XPS). The analysis of the U4f photoelectron peak positions, peak widths at half maximum and satellite positions of U4f peaks, shows that the uranium in these compounds is present in a single valence state, namely U 5 + . Since the surface of these compounds is extremely susceptible to oxidation, the XPS spectra were measured after a carefully controlled etching of the surface using an Ar + ion beam so that the surface oxidation does not affect the XPS studies.

Simultaneous refinements of X-ray and neutron powder diffraction patterns taken on the M UO 3 perovskite compounds with M =Na, K and Rb, were performed to reveal anisotropy in the temperature factors, mainly of oxygen. No anisotropic thermal motion was found. The magnetic ordering of the compounds has been investigated with low temperature neutron diffraction. It is found that all these compounds show G-type antiferromagnetic ordering with a similar, orthorhombic magnetic unit cell. The propagation vector could only be determined for the orthorombic NaUO 3 compound and was found to point in the z -direction. The refined magnetic moment for U 5+ in these structures was found to be around 0.20(3) μ B .

This article discusses an architecture using monitoring feedback as an assisting factor for delivering QoS on packet-based networks. The handling of this feedback is done in an automated way, through the use of a policy-based management architecture. For this, a formal model for describing data plane and measurement objects was translated into an XML-based configuration language. On top of this, a proof-of-concept management architecture was developed and evaluated, using both a modified network simulator and enhanced Linux prototype routers.

A new method to determine the reflection of substrate modes in finite substrate planar circuits is proposed. The perfectly matched layer (PML) concept is used to transform the open problem into a closed one. The discrete set of substrate, evanescent, and Berenger modes of the resulting anisotropic waveguides are then used in a mode-matching scheme to deduce the scattering coefficients of the substrate modes for oblique incidence on the edge of the substrate. We show results for single- and double-layered substrates and compare with finite-difference time-domain (FDTD) results. The combined perfectly matched layer (PML) mode-matching technique turns out to be very efficient.

We describe Delta-I noise caused by power plane resonances in multilayer boards. First, we study the effect of power plane resonances on the ground bounce of the system by performing finite-difference time-domain (FDTD) simulations. We simulate the voltage fluctuations at one point of the printed circuit board (PCB) due to a current surge between the power planes in a different point. Next, two methods to prevent this ground bounce effect are investigated. The first method consists of adding lumped capacitances to the design. The effect of one large capacitor is compared to the effect of adding a "wall" of smaller capacitors. A second approach is to isolate the chips by etching a slot around the sensitive integrated circuits (ICs) and connecting both sides by a small inductor. Both methods provide excellent protection against power plane resonances.

We investigated the local atomic and electronic structures of two related systematic sets of ternary uranium oxides, NaUO3–KUO3–RbUO3 and BaUO3–Ba2U2O7–BaUO4, by measuring the X-ray absorption near edge structure (XANES). The results are compared with calculations based on a self-consistent real space full multiple scattering analysis. We found a very good agreement between measured and calculated spectra, which indicates that the uranium ions are in a pure U5+ oxidation state in these compounds. The low energy shoulder observed in the U L3 edge XANES is an intrinsic feature of the uranium unoccupied 6d electronic states of the U5+ ions within the studied materials. Specific double shoulder features in the higher energy range of the U L3 edge XANES can be interpreted as indicative of the pure cubic perovskite structure.

This paper describes the design of a novel tunnel set-up mechanism for Ethernet access networks. The establishment of VLAN-based tunnels is realised with a "scoped refresh" extension of the GVRP standard. For the distribution of QoS-related reservation parameters, a new GARP-based protocol (G2RP) is developed with a closed loop design for updating the reservation parameters and hop-by-hop admission control. Both protocols are implemented on a Linux test bed using the click modular router. Extensive performance evaluations were performed. The results are compared with Linux implementations of the other tunnel set-up mechanisms.

The redox properties of D-amino acid oxidase (D-amino-acid: O2 oxidoreductase (deaminating) EC1.4.3.3) have been measured at 18 degrees C in 20 mM sodium pyrophosphate, pH 8.5, and in 50 mM sodium phosphate, pH 7.0. Over the entire pH range, 2 eq are required per mol of FAD in D-amino acid oxidase for reduction to the anion dihydroquinone. The red anion semiquinone is thermodynamically stable as indicated by the separation of the electron potentials and the quantitative formation of the semiquinone species. The first electron potential is pH-independent at -0.098 +/- 0.004 V versus SHE while the second electron potential is pH-dependent exhibiting a 0.060 mV/pH unit slope. The redox behavior of D-amino acid oxidase is consistent with that observed for other oxidase enzymes. On the other hand, the behavior of the benzoate-bound enzyme under the same conditions is in marked contrast to the thermodynamics of free D-amino acid oxidase. Spectroelectrochemical experiments performed on inhibitor-bound (benzoate) D-amino acid oxidase show that benzoate binding regulates the redox properties of the enzyme, causing the energy levels of the benzoate-bound enzyme to be consistent with the two-electron transfer catalytic function of the enzyme. Our data are consistent with benzoate binding at the enzyme active site destroying the inductive effect of the positively charged arginine residue. Others have postulated that this positively charged group near the N(1)C(2) = O position of the flavin controls the enzyme properties. The data presented here are the clearest examples yet of enzyme regulation by substrate which may be a general characteristic of all flavoprotein oxidases.

Many existing Grid technologies and resource management systems lack a standardized job submission interface in Grid environments or e-Infrastructures. Even if the same language for job description is used, often the interface for job submission is also different in each of these technologies. The evolvement of the standardized Job Submission and Description Language (JSDL) as well as the OGSA - Basic Execution Services (OGSA-BES) pave the way to improve the interoperability of all these technologies enabling cross-Grid job submission and better resource management capabilities. In addition, the BytelO standards provide useful mechanisms for data access that can be used in conjunction with these improved resource management capabilities. This paper describes the integration of these standards into the recently released UNICORE 6 Grid middleware that is based on open standards such as the Web Services Resource Framework (WS-RF) and WS-Addressing (WS-A).