While a number of technologies or methods of subsurface imaging and monitoring exist, most require some adaptation to meet the site-specific objectives of a particular in-situ waste containment/stabilization verification and monitoring program. The selection of methods and their site-specific adaptation must be based on sound, scientific principles. Given this, specific information about the site and the objectives of the containment or remediation are required to design and implement an appropriate and effective verification and monitoring program. Site and technology information that must be considered and how it affects the selection and adaptation of monitoring technologies is presented. In general, this information includes the objectives of the containment or remediation, the verification and monitoring systems, and the physical properties of the site and the waste containment/stabilization system. The objectives of the containment or remediation and the verification and monitoring system must be defined to provide a goal for the technology developer`s design. The physical properties of the site and the waste containment/stabilization system are required to ensure the proper technology is selected. A conceptual framework and examples are given to demonstrate the impacts of these aspects on technology selection.
Mean arc voltage is a process parameter commonly used in vacuum arc remelting (VAR) control schemes. The response of this parameter to changes in melting current (I) and electrode gap (g{sub e}) at constant pressure may be accurately described by an equation of the form V = V{sub 0} + c{sub 1}g{sub e}I + c{sub 2}g{sub e}{sup 2} + c{sub 3}I{sup 2}, where c{sub 1}, c{sub 2} and c{sub 3} are constants, and where the non-linear terms generally constitute a relatively small correction. If the non-linear terms are ignored, the equation has the form of Ohm`s law with a constant offset (V{sub 0}), c{sub 1}g{sub e} playing the role of resistance. This implies that the arc column may be treated approximately as a simple resistor during constant current VAR, the resistance changing linearly with g{sub e}. The VAR furnace arc is known to originate from multiple cathode spot clusters situated randomly on the electrode tip surface. Each cluster marks a point of exist for conduction electrons leaving the cathode surface and entering the electrode gap. Because the spot clusters re highly localized on the cathode surface, each gives rise to an arc column that may be considered to operate independently of other local arc columns. This approximation is used to develop a model that accounts for the observed arc voltage dependence on electrode gap at constant current. Local arc column resistivity is estimated from elementary plasma physics and used to test the model for consistency by using it to predict local column heavy particle density. Furthermore, it is shown that the local arc column resistance increases as particle density increases. This is used to account for the common observation that the arc stiffens with increasing current, i.e. the arc voltage becomes more sensitive to changes in electrode gap as the melting current is increased. This explains why arc voltage is an accurate electrode gap indicator for high current VAR processes but not low current VAR processes.
The collapse of the Soviet Union has left many of its scientific institutes and technical universities without their traditional backbone of financial support. In an effort to stem the export of science to nations advocating nuclear proliferation, and to acquire potentially useful technology, several US government-sponsored programs have arise to mine the best of former USSR scientific advances. In the field of metallurgy, the earliest institutes to be investigated by Sandia National Laboratories are located in Ukraine. In particular, scientists at the State Metallurgical Academy have developed unique porous metals, resembling what could be described as gas-solid ``eutectic``. While porous metals are available in the US and other western countries, none have the remarkable structure and properties of these materials. Sandia began a collaborative program with the Ukrainian scientists to bring this technology to the US, verify the claims regarding these materials, and begin production of the so-called Gasars. This paper will describe the casting process technology and metallurgy associated with the production of Gasars, and will review the progress of the collaborative project.
The authors have performed electron spin resonance and electrical measurements on SiO{sub 2}/Si structures subjected to anneals in 5% H{sub 2}/N{sub 2} or 5% D{sub 2}/N{sub 2} gases and subsequently injected with electrons using corona ions and ultra-violet radiation. Threshold voltage and transconductance measurements have also been made on 0.25 {micro}m metal-oxide-semiconductor transistors subjected to 400 C anneals in the same gases and subsequently aged by hot electron injection. The electrical data on SiO{sub 2}/Si structures indicates that the density of interface states increases as a result of electron injection but that there are only minor differences between H and D passivated interfaces. The data on P{sub b}, trivalent Si dangling bond, centers at the same interfaces observed by electron spin resonance is insufficiently accurate to enable them to observe any significant differences. The hot electron injection experiments on transistors, consistent with other authors, indicate that, for the limited number of measurements they have made, the transistor aging resulting from the generation of interface states is significantly reduced for devices annealed in the D containing gas as compared to those annealed in the H containing gas. The origins of some potential differences in annealing behavior between the SiO{sub 2}/Si structures and the 0.25 {micro}m transistors are suggested.
The electronics radiation hardness-testing community uses the ASTM E722-93 Standard Practice to define the energy dependence of the nonionizing neutron damage to silicon semiconductors. This neutron displacement damage response function is defined to be equal to the silicon displacement kerma as calculated from the ORNL Si cross-section evaluation. Experimental work has shown that observed damage ratios at various test facilities agree with the defined response function to within 5%. Here, a covariance matrix for the silicon 1-MeV neutron displacement damage function is developed. This uncertainty data will support the electronic radiation hardness-testing community and will permit silicon displacement damage sensors to be used in least squares spectrum adjustment codes.
Typical industrial ESR melting practice includes operation at a constant current. This constant current operation is achieved through the use of a power supply whose output provides this constant current characteristic. Analysis of this melting mode indicates that the ESR process under conditions of constant current is inherently unstable. Analysis also indicates that ESR melting under the condition of a constant applied voltage yields a process which is inherently stable. This paper reviews the process stability arguments for both constant current and constant voltage operation. Explanations are given as to why there is a difference between the two modes of operation. Finally, constant voltage process considerations such as melt rate control, response to electrode anomalies and impact on solidification will be discussed.
Approximate probabilities of inclusion survival through an electron beam melting hearth are computed from nitride dissolution rates, flotation velocities, and residence times. Dissolution rates were determined by measuring shrinkage rates of pure TiN and nitrided sponge in small pools of molten titanium in an electron beam melting hearth. Flotation velocities were calculated using correlations for fluid flow around spheres, and show that particles sink or float unless their densities are extremely close to that of molten titanium. Flow field characteristics which lead to effective inclusion removal are discussed in terms of heat flux pattern required to produce them, based on the electron beam`s unique ability to impart a nearly arbitrary heat flux pattern to the melt surface.
New dosimetry cross-section evaluations have been made available to the reactor community. Most dosimetry-quality evaluations include a section (File 33) that defines the uncertainty and covariance matrix for the dosimetry reaction cross section. This paper compares the latest computed cross-section activities for benchmark neutron fields with experimental data. Uncertainty data is usually reported with experimental measurements. This work also presents uncertainty data for the calculated activities. The calculated uncertainty values include a full uncertainty propagation using the cross-section evaluation, energy-dependent covariance data as well as the uncertainty attributed to the knowledge of the neutron spectrum.
Deterioration of monuments, buildings, and works of art constructed of carbonate-based stone potentially can be arrested by applying a combination of chemical passivants and consolidants that prevent hydrolytic attack and mechanical weakening. The authors used molecular modeling and laboratory synthesis to develop an improved passivating agent for the calcite mineral surface based on binding strength and molecular packing density. The effectiveness of the passivating agent with and without a linked outer layer of consolidant against chemical weathering was determined through leaching tests conducted with a pH-stat apparatus at pH 5 and 25 C. For the range of molecules considered, modeling results indicate that the strongest-binding passivant is the trimethoxy dianionic form of silylalkylaminocarboxylate (SAAC). The same form of silylalkylphosphonate (SAP) is the second strongest binder and the trisilanol neutral form of aminoethylaminopropylsilane (AEAPS) is ranked third. Short-term leaching tests on calcite powders coated with the trisilanol derivative of SAAC, the triethoxy neutral form of SAP, and the trimethoxy neutral form of AEAPS show that the passivant alone does not significantly slow the dissolution rate. However, all passivants when linked to the sol consolidant result in decreased rates. Combined AEAPS plus consolidant results in a coating that performs better than the commercial product Conservare{reg_sign} OH and at least as well as Conservare{reg_sign} H. The modeling results indicate that there may be a threshold binding energy for the passivant above which the dissolution rate of calcite is actually enhanced. More strongly-binding passivants may aid in the dissolution mechanism or dissociate in aqueous solution exposing the calcite surface to water.
An optoelectronic integrated circuit for generating mm-wave frequencies is demonstrated and design issues detailed. A monolithically integrated ring laser, optical amplifier, and photodiode generate electrical signals up to 85.2 GHz.
The use of commercial off-the-shelf (COTS) microelectronics for nuclear weapon applications will soon be reality rather than hearsay. The use of COTS for new technologies for uniquely military applications is being driven by the so-called Perry Initiative that requires the U.S. Department of Defense (DoD) to accept and utilize commercial standards for procurement of military systems. Based on this philosophy, coupled with several practical considerations, new weapons systems as well as future upgrades will contain plastic encapsulated microelectronics. However, a conservative Department of Energy (DOE) approach requires lifetime predictive models. Thus, the focus of the current project is on accelerated testing to advance current aging models as well as on the development of the methodology to be used during WR qualification of plastic encapsulated microelectronics. An additional focal point involves achieving awareness of commercial capabilities, materials, and processes. One of the major outcomes of the project has been the definition of proper techniques for handling and evaluation of modern surface mount parts which might be used in future systems. This program is also raising the familiarity level of plastic within the weapons complex, allowing subsystem design rules accommodating COTS to evolve. A two year program plan is presented along with test results and commercial interactions during this first year.
Studies by academia, industry, and government indicate that applying a sound systems engineering process to development programs is an important tool for preventing cost and schedule overruns and performance deficiencies. There is an enormous body of systems engineering knowledge. Where does one start? How can the principles of systems engineering be applied in the Sandia environment? This road map is intended to be an aid to answering these questions.
The traditional geometry for surface mount devices is the peripheral array where the leads are on the edges of the device. As the technology drives towards high input/output (I/O) count (increasing number of leads) and smaller packages with finer pitch (less distance between peripheral leads), limitations on peripheral surface mount devices arise. The leads on these fine pitch devices are fragile and can be easily bent. It becomes increasingly difficult to deliver solder past to leads spaced as little as 0.012 inch apart. Too much solder mass can result in bridging between leads while too little solder can contribute to the loss of mechanical and electrical continuity. A solution is to shift the leads from the periphery of the device to the area under the device. This scheme is called areal array packaging and is exemplified by the ball grid array (BGA) package. A system has been designed and constructed to deposit an entire array of several hundred uniform solder droplets onto a printed circuit board in a fraction of a second. The solder droplets wet to the interconnect lands on a pc board and forms a basis for later application of a BGA device. The system consists of a piezoelectric solder pulse unit, heater controls, an inert gas chamber and an analog power supply/pulse unit.
On-Machine Acceptance (OMA) is an agile manufacturing concept being developed for machine tools at SNL. The concept behind OMA is the integration of product design, fabrication, and qualification processes by using the machining center as a fabrication and inspection tool. This report documents the final results of a Laboratory Directed Research and Development effort to qualify OMA.
Molecular Beam Epitaxy (MBE) of semiconductor heterostructures for advanced electronic and opto-electronic devices requires precise control of the surface composition and strain. The development of advanced in situ diagnostics for real-time monitoring and process control of strain and composition would enhance the yield, reliability and process flexibility of material grown by MBE and benefit leading-edge programs in microelectronics and photonics. The authors have developed a real-time laser-based technique to measure the evolution of stress in epitaxial films during growth by monitoring the change in the wafer curvature. Research has focused on the evolution of stress during the epitaxial growth of Si{sub x}Ge{sub 1{minus}x} alloys on Si(001) substrates. Initial studies have observed the onset and kinetics of strain relaxation during the growth of heteroepitaxial layers. The technique has also been used to measure the segregation of Ge to the surface during alloy growth with monolayer sensitivity, an order of magnitude better resolution than post-growth characterization. In addition, creation of a 2-dimensional array of parallel beams allows rapid surface profiling of the film stress that can be used to monitor process uniformity.
This work is comprised of two major sections. In the first section the authors develop multivariate image classification techniques to distinguish and identify surface electronic species directly from multiple-bias scanning tunneling microscope (STM) images. Multiple measurements at each site are used to distinguish and categorize inequivalent electronic or atomic species on the surface via a computerized classification algorithm. Then, comparison with theory or other suitably chosen experimental data enables the identification of each class. They demonstrate the technique by analyzing dual-polarity constant-current topographs of the Ge(111) surface. Just two measurements, negative- and positive-bias topography height, permit pixels to be separated into seven different classes. Labeling four of the classes as adatoms, first-layer atoms, and two inequivalent rest-atom sites, they find excellent agreement with the c(2 x 8) structure. The remaining classes are associated with structural defects and contaminants. This work represents a first step toward developing a general electronic/chemical classification and identification tool for multivariate scanning probe microscopy imagery. In the second section they report measurements of the diffusion of Si dimers on the Si(001) surface at temperatures between room temperature and 128 C using a novel atom-tracking technique that can resolve every diffusion event. The atom tracker employs lateral-positioning feedback to lock the STM probe tip into position above selected atoms with sub-Angstrom precision. Once locked the STM tracks the position of the atoms as they migrate over the crystal surface. By tracking individual atoms directly, the ability of the instrument to measure dynamic events is increased by a factor of {approximately} 1,000 over conventional STM imaging techniques.
Graph partitioning is an important abstraction used in solving many scientific computing problems. Unfortunately, the standard partitioning model does not incorporate considerations that are important in many settings. We address this by describing a generalized partitioning model which incorporates the notion of partition skew and is applicable to a variety of problems. We then develop enhancements to several important partitioning algorithms necessary to solve the generalized partitioning problem. Finally we demonstrate the benefit of employing several of these generalized methods to static decomposition of parallel computing problems.
Fast z-pinch implosions can convert more than 10% of the stored electrical energy in a pulsed-power accelerator into x rays. These x rays are produced when an imploding cylindrical plasma, driven by the magnetic field pressure associated with very large axial currents, stagnates upon the cylindrical axis of symmetry. On the Saturn pulsed-power accelerator at Sandia National Laboratories, for example, currents of 6 to 8 MA with a risetime of less than 50 ns are driven through cylindrically-symmetric loads, producing implosions velocities as high as 100 cm/{mu}s and x-ray energies as high as 500 kJ. The keV component of the resulting x-ray spectrum has been used for many years 8 a radiation source for material response studies. Alternatively, the x-ray output can be thermalized into a near-Planckian x-ray source by containing it within a large cylindrical radiation case. These large volume, long-lived radiation sources have recently been used for ICF-relevant ablator physics experiments as well as astrophysical opacity and radiation-material interaction experiments. Hydromagnetic Rayleigh-Taylor instabilities and cylindrical load symmetry are critical, limiting factors in determining the assembled plasma densities and temperatures, and thus in the x-ray pulse widths that can be produced on these accelerators. In recent experiments on the Saturn accelerator, these implosion nonuniformities have been minimized by using uniform-fill gas puff loads or by using wire arrays with as many a 192 wires. These techniques produced significant improvements in the pinched plasma quality, Zn reproducibility, and x-ray output power. X-ray pulse widths of less than 5 ns and peak powers of 75{+-}10 TW have been achieved with arrays of 120 tungsten wires. These powers represent greater than a factor of three in power amplification over the electrical power of the Saturn n accelerator, and are a record for x-ray powers in the laboratory.
A popular method for updating finite element models with modal test data utilizes optimization of the model based on design sensitivities. The attractive feature of this technique is that it allows some estimate and update of the physical parameters affecting the hardware dynamics. Two difficulties are knowing which physical parameters are important and which of those important parameters are in error. If this is known, the updating process is simply running through the mechanics of the optimization. Most models of real systems have a myriad of parameters. This paper discusses an implementation of a tool which uses the model and test data together to discover which parameters are most important and most in error. Some insight about the validity of the model form may also be obtained. Experience gained from applications to complex models will be shared.
The disposition of the large back-log of plutonium residues at the Rocky Flats Environmental Technology Site (Rocky Flats) will require interim storage and subsequent shipment to a waste repository. Current plans call for disposal at the Waste Isolation Pilot Plant (WIPP) and the transportation to WIPP in the TRUPACT-II. The transportation phase will require the residues to be packaged in a container that is more robust than a standard 55-gallon waste drum. Rocky Flats has designed the Pipe Overpack Container to meet this need. It is desirable to use this same waste packaging for interim on-site storage in non-hardened buildings. To meet the safety concerns for this storage the Pipe Overpack Container has been subjected to a series of tests at Sandia National Laboratories in Albuquerque, New Mexico. In addition to the tests required to qualify the Pipe Overpack Container as a waste container for shipment in the TRUPACT-II several tests were performed solely for the purpose of qualifying the container for interim storage. This report will describe these tests and the packages response to the tests. 12 figs., 3 tabs.
There is a void of public specifications for pulse discharge capacitor applications. Sandia National Laboratories has developed, over the past 25 years, specifications and test procedures for evaluating capacitor designs for this specialized use. There are three primary destructive tests that are used to assess the reliability potential of a given design at a required rated voltage. These are ultimate short time breakdown strength, life at voltage, and pulse discharge life. The strategy of the method is to accelerate the test conditions so that failures are observable and then extrapolate to the desired use conditions where the failure rates are low. This paper will present the statistical methodologies employed to analyze experimental data and to provide a point estimate of reliability with a lower confidence bound as a function of rated voltage. In addition, methods for establishing lot-acceptance-criteria specifications will be discussed. The techniques will be illustrated with actual data on a commercially available, low-inductance, pulse-discharge capacitor. The capacitor is an impregnated dual dielectric (mica-paper/polymer film), extended-foil type.
The scanning force microscopies (notably the Atomic Force Microscope--AFM), because of their applicability to nearly all materials, are presently the most widely used of the scanning-probe techniques. However, the AFM uses a deflection sensor to measure sample/probe forces which suffers from an inherent mechanical instability that occurs when the rate of change of the force with respect to the interfacial separation becomes equal to the spring constant of the deflecting member. This instability dramatically limits the breadth of applicability of AFM-type techniques to materials problems. In the course of implementing a DOE sponsored basic research program in interfacial adhesion, a self-balancing force sensor concept has been developed and incorporated into an Interfacial Force Microscopy (IFM) system by Sandia scientists. This sensor eliminates the instability problem and greatly enhances the applicability of the scanning force-probe technique to a broader range of materials and materials parameters. The impact of this Sandia development was recognized in 1993 by a Department of Energy award for potential impact on DOE programs and by an R and D 100 award for one of the most important new products of 1994. However, in its present stage of development, the IFM is strictly a research-level tool and a CRADA was initiated in order to bring this sensor technology into wide-spread availability by making it accessible in the form of a commercial instrument. The present report described the goals, approach and results of this CRADA effort.
In this presentation, the authors will investigate the use of hybrid meshes for modeling RCS and antenna problems in three dimensions. They will consider two classes of hybrid basis functions. These include combinations of quadrilateral and triangular meshes for arbitrary 3D geometries, and combinations of axisymmetric body-of-revolution (BOR) basis functions and triangular facets. In particular, they will focus on the problem of enforcing current continuity between two surfaces which are represented by different types of surface discretizations and unknown basis function representations. They will illustrate the use of an operator-based code architecture for the implementation of these formulations, and how it facilitates the incorporation of the various types of boundary conditions in the code. Both serial and parallel code implementation issues for the formulations will be discussed. Results will be presented for both scattering and antenna problems. The emphasis will be on accuracy, and robustness of the techniques. Comparisons of accuracy between triangular meshed and quadrilateral meshed geometries will be shown. The use of hybrid meshes for modeling BORs with attached appendages will also be presented.
The Surtsey Test Facility is used to perform scaled experiments simulating High Pressure Melt Ejection accidents in a nuclear power plant (NPP). The experiments investigate the effects of direct containment heating (DCH) on the containment load. The results from Zion and Surry experiments can be extrapolated to other Westinghouse plants, but predicted containment loads cannot be generalized to all Combustion Engineering (CE) plants. Five CE plants have melt dispersal flow paths which circumvent the main mitigation of containment compartmentalization in most Westinghouse PWRs. Calvert Cliff-like plant geometries and the impact of codispersed water were addressed as part of the DCH issue resolution. Integral effects tests were performed with a scale model of the Calvert Cliffs NPP inside the Surtsey test vessel. The experiments investigated the effects of codispersal of water, steam, and molten core stimulant materials on DCH loads under prototypic accident conditions and plant configurations. The results indicated that large amounts of coejected water reduced the DCH load by a small amount. Large amounts of debris were dispersed from the cavity to the upper dome (via the annular gap). 22 refs., 84 figs., 30 tabs.
This report presents automatic motion planning algorithms for robotic manipulators performing a variety of tasks. Given a task and a robot manipulator equipped with a tool in its hand, the motion planners compute robot motions to complete the task while respecting manipulator kinematic constraints and avoiding collisions with objects in the robot`s work space. To handle the high complexity of the motion planning problem, a sophisticated search strategy called SANDROS is developed and used to solve many variations of the motion planning problem. To facilitate systematic development of motion planning algorithms, robotic tasks are classified into three categories according to the dimension of the manifold the robot tool has to travel: visit-point (0 dimensional), trace-curve (1 dimensional) and cover-surface (2 dimensional) tasks. The motion planner for a particular dimension is used as a sub-module by the motion planner for the next-higher dimension. This hierarchy of motion planners has led to a set of compact and systematic algorithms that can plan robot motions for many types of robotic operations. In addition, an algorithm is developed that determines the optimal robot-base configuration for minimum cycle time. The SANDROS search paradigm is complete in that it finds a solution path if one exists, up to a user specified resolution. Although its worst-case time complexity is exponential in the degrees of freedom of the manipulator, its average performance is commensurate with the complexity of the solution path. Since solution paths for most of motion planning problems consist of a few monotone segments, the motion planners based on SANDROS search strategy show approximately two-orders of magnitude improvements over existing complete algorithms.