MgO is the only engineered barrier certified by EPA for the Waste Isolation Pilot Plant (WIPP) in USA. The German Asse repository will also employ an Mg(OH){sub 2} (brucite)-based engineered barrier. The chemical function of the engineered barrier is to consume CO{sub 2} that may be generated by the microbial degradation of organic materials in waste packages. Experimental results at SNL indicate that MgO is first hydrated as brucite, and then brucite is carbonated as hydromagnesite (5424) (Mg{sub 5}(CO{sub 3}){sub 4}(OH){sub 2} {center_dot} 4H{sub 2}O). As MgO is in excess relative to CO{sub 2} that may be produced, the brucite-hydromagnesite (5424) assemblage would buffer f{sub CO2} in the repository. Consequently, the thermodynamic properties of this assemblage is of great significance to the performance assessment (PA) as actinide solubility is strongly affected by f{sub CO2}. In turn, PA is important to the demonstration of the long-term safety of nuclear waste repositories, as assessed by the use of probabilistic performance calculations. There is a substantial discrepancy for {Delta}{sub f}G{sub brucite}{sup 0} in recent publications, ranging from -830.4 (Harvie et al., 1984; Geochim. Cosmochim. Acta, 723-751), through -831.9 (Brown et al., 1996; J. Chem. Soc., Dalton Trans., 3071-3075), through -833.5 (Robie and Hemingway, 1995; USGS Bull., 2131), and to -835.9 kJ mol{sup -1} (Konigsberger et al., 1999; Geochim. Cosmochim. Acta, 3105-3119). Using the {Delta}{sub f}G{sub hydromagnesite (5424)}{sup 0} from Konigsberger et al., the predicted log f{sub CO2} for this assemblage would range from -5.96 ({Delta}{sub f}G{sub brucite}{sup 0} from Harvie et al.) to -4.84 ({Delta}{sub f}G{sub brucite}{sup 0} from Konigsberger et al.). Therefore, it is desirable to better constrain the {Delta}{sub f}G{sub brucite}{sup 0}. For this reason, a series of solubility experiments involving brucite in NaCl solutions ranging from 0.01 M to 4.0 M have being conducted at SNL. The derived {Delta}{sub f}G{sub brucite}{sup 0} from this study by extrapolation to infinite dilution via Pitzer formalism is -830.8 kJ mol{sup -1}, which is in excellent agreement with recommended values of Harvie et al. and Brown et al.
In the course of a failure investigation, corrosion of the lands was occasionally found in developmental lots of semiconductor bridge (SCB) detonators and igniters. Evidence was found in both detonators and igniters of the gold layer being deposited on top of a corroded aluminum layer, but inspection of additional dies from the same wafer did not reveal any more corroded parts. In some detonators, evidence was found that corrosion of the aluminum layer also happened after the gold was deposited. Moisture and chloride must both be present for aluminum to corrode. A likely source for chloride is the adhesive used to bond the die to the header. Inspection of other SCB devices, both recently manufactured and manufactured about ten years ago, found no evidence for corrosion even in devices that contained SCBs with aluminum lands and no gold. Several manufacturing defects were noted such as stains, gouges in the gold layer due to tooling, and porosity of the gold layer. Results of atmospheric corrosion experiments confirmed that devices with a porous gold layer over the aluminum layer are susceptible to extensive corrosion when both moisture and chlorine are present. The extent of corrosion depends on the level of chlorine contamination, and corrosion did not occur when only moisture was present. Elimination of the gold plating on the lands eliminated corrosion of the lands in these experiments. Some questions remain unanswered, but enough information was gathered to recommend changes to materials and procedures. A second lot of detonators was successfully built using aluminum SCBs, limiting the use of Ablebond{trademark} adhesive, increasing the rigor in controlling exposure to moisture, and adding inspection steps.
Conductive polymers have become an extremely useful class of materials for many optical applications. Additionally, advanced fabrication methods have led to the development of metal based micro-wiregrid polarizers utilizing submicron features. Adapting these fabrication approaches for use with polymer materials leads to optical polarizers with unique properties. The patterning of conductive polymers with the small features required for wiregrid polarizers leads to several challenges. First, the deposition of the polymer must provide a layer thick enough to provide a polarizer with a useful extinction ratio that also has high conductivity and environmental stability. Two deposition approaches have been investigated, spin coating and electrochemical growth, and results of this work will be presented. Also, the polymers considered here are not compatible with basic photoresist processes. Various tactics have been examined to overcome this difficulty including the use of hard bakes of the polymer, protective overcoats and patterned growth. The adaptations required for successfully patterning the polymer will be reviewed. Finally, fabricated devices will be shown and their optical characterization presented.
A Dynamic Hohlraum (DH) is formed when arrays of tungsten wires driven by a high-current pulse implode and compress a cylindrical foam target. The resulting radiation is confined by the wire plasma and forms an intense, ~200–250 eV Planckian x-ray source. The internal radiation can be used for indirect drive inertial confinement fusion. The radiation emitted from the ends can be employed for radiation flow and material interaction studies. This external radiation is accompanied by an expanding blowoff plasma. In this paper, we have diagnosed this blowoff plasma using K-shell spectra of Mg tracer layers placed at the ends of some of the Dynamic Hohlraum targets. A similar diagnosis of the interior hohlraum has been carried out using Al and Mg tracers placed at 2mm depth from the ends. It is found that the blowoff plasma is about 20–25% as dense as that of the interior hohlraum, and that its presence does not significantly affect the outward flow of the nearly Planckian radiation field generated in the hohlraum interior. Finally, however, the electron temperature of the blowoff region, at ~120 eV, is only about half that of the interior hohlraum plasma.
Jacobs, Benjamin W.; Ayres, Virginia M.; Petkov, Mihail P.; Halpern, Joshua B.; He, Maoqi; Baczewski, Andrew D.; Mcelroy, Kaylee; Crimp, Martin A.; Zhang, Jiaming; Shaw, Harry C.
Here, we report a new biphasic crystalline wurtzite/zinc-blende homostructure in gallium nitride nanowires. Cathodoluminescence was used to quantitatively measure the wurtzite and zinc-blende band gaps. High-resolution transmission electron microscopy was used to identify distinct wurtzite and zinc-blende crystalline phases within single nanowires through the use of selected area electron diffraction, electron dispersive spectroscopy, electron energy loss spectroscopy, and fast Fourier transform techniques. A mechanism for growth is identified.
This report documents measurements and analytical modeling of electromagnetic transfer functions to quantify the ability of cloud-to-ground lightning strokes (including horizontal arc-channel components) to couple electromagnetic energy into the Sago mine located near Buckhannon, WV. Two coupling mechanisms were measured: direct and indirect drive. These transfer functions are then used to predict electric fields within the mine and induced voltages on conductors that were left abandoned in the sealed area of the Sago mine.
The purpose of this report is to define a standard interface for storing and retrieving novel, non-traditional partial differential equation (PDE) discretizations. Although it focuses specifically on finite elements where state is associated with edges and faces of volumetric elements rather than nodes and the elements themselves (as implemented in ALEGRA), the proposed interface should be general enough to accommodate most discretizations, including hp-adaptive finite elements and even mimetic techniques that define fields over arbitrary polyhedra. This report reviews the representation of edge and face elements as implemented by ALEGRA. It then specifies a convention for storing these elements in EXODUS files by extending the EXODUS API to include edge and face blocks in addition to element blocks. Finally, it presents several techniques for rendering edge and face elements using VTK and ParaView, including the use of VTK's generic dataset interface for interpolating values interior to edges and faces.
Ceramic materials such as lead zirconium titanates (PZT), low temperature co-fired ceramics and silica glasses are used in several of Sandia's mission critical components. Brittle fracture, either during machining and processing or after many years in service, remains a serious reliability and cost issue. Despite its technological importance, brittle fracture remains poorly understand, especially the onset and propagation of sub-critical cracks. However, some insights into the onset of fracture can be gleaned from the atomic scale structure of the amorphous material. In silica for example, it is well known [1] that the Si-O-Si bonds are relatively weak and, in angle distribution functions determined from scattering experiments, the bonds exhibit a wide spread around a peak at 150. By contrast the O-Si-O bonds are strong with a narrow peak in the distribution around the 109 dictated by the SiO{sub 4} tetrahedron. In addition, slow energy release in silica, as deduced from dissolution experiments, depends on the distribution of 3-fold and higher rings in the amorphous structure. The purpose of this four month LDRD project was to investigate the atomic structure of silica in the bulk and in the vicinity of a crack tip using molecular dynamics simulations. Changes in the amorphous structure in the neighborhood of an atomically sharp tip may provide important clues as to the initiation sites and the stress intensity required to propagate a sub-critical crack.
A deep geologic repository for high level radioactive waste is under development by the U.S. Department of Energy at Yucca Mountain (YM), Nevada. As mandated in the Energy Policy Act of 1992, the U.S. Environmental Protection Agency (EPA) has promulgated public health and safety standards (i.e., 40 CFR Part 197) for the YM repository, and the U.S. Nuclear Regulatory Commission has promulgated licensing standards (i.e., 10 CFR Parts 2, 19, 20, etc.) consistent with 40 CFR Part 197 that the DOE must establish are met in order for the YM repository to be licensed for operation. Important requirements in 40 CFR Part 197 and 10 CFR Parts 2, 19, 20, etc. relate to the determination of expected (i.e., mean) dose to a reasonably maximally exposed individual (RMEI) and the incorporation of uncertainty into this determination. This presentation describes and illustrates how general and typically nonquantitive statements in 40 CFR Part 197 and 10 CFR Parts 2, 19, 20, etc. can be given a formal mathematical structure that facilitates both the calculation of expected dose to the RMEI and the appropriate separation in this calculation of aleatory uncertainty (i.e., randomness in the properties of future occurrences such as igneous and seismic events) and epistemic uncertainty (i.e., lack of knowledge about quantities that are poorly known but assumed to have constant values in the calculation of expected dose to the RMEI).