Yucca Mountain, Nevada is a potential site for a high-level radioactive-waste repository. Uncertainty and sensitivity analyses were performed to estimate critical factors in the performance of the site with respect to a criterion in terms of pre-waste-emplacement ground-water travel time. The degree of failure in the analytical model to meet the criterion is sensitive to the estimate of fracture porosity in the upper welded unit of the problem domain. Fracture porosity is derived from a number of more fundamental measurements including fracture frequency, fracture orientation, and the moisture-retention characteristic inferred for the fracture domain.
The potential repository system is intended to isolate high-level radioactive waste at Yucca Mountain according to the performance objective - 10 CFR 60.112. One subsystem that may contribute to achieving this objective is the sealing subsystem. This subsystem is comprised of sealing components in the shafts, ramps, underground network of drifts, and the exploratory boreholes. Sealing components can be rigid, as in the case of a shaft seal, or can be more compressible, as in the case of drift fill comprised of mined rockfill. This paper presents the preliminary seismic response of discrete sealing components in welded and nonwelded tuff. Special consideration is given to evaluating the stress in the seal, and the behavior of the interface between the seal and the rock. The seismic responses are computed using both static and dynamic analyses. Also presented is an evaluation of the maximum seismic response encountered by a drift seal with respect to the angle of incidence of the seismic wave. Mitigation strategies and seismic design considerations are proposed which can potentially enhance the overall response of the sealing component and subsequently, the performance of the overall repository system.
This report contains an outline of the Solar Thermal Design Assistance Center's (STDAC) major activities and accomplishments in Fiscal Year 1992 (FY92). The report describes the resources allocated to fund STDAC and the personnel needed to carry out STDAC activities and accomplishments. It also contains a comprehensive list of persons that called STDAC for consultation in FY92.
A series of constant strain rate, unconfined compression experiments was performed on saturated welded tuff specimens collected from Busted Butte near Yucca Mountain, Nevada. Twenty specimens were loaded to failure at strain rates ranging from 10{sup {minus}9}s{sup {minus}1} to 10{sup {minus}3}s{sup {minus}1}, under ambient pressure and temperature conditions. The strength of the specimens showed a continuous decrease with decreasing strain rate between 10{sup {minus}9} s{sup {minus}1} and 10{sup {minus}5} s{sup {minus}1}. At the highest strain rate, 10{sup {minus}3} s{sup {minus}1}, strengths were less than those observed at 10{sup {minus}5} s{sup {minus}1}, likely due to hydrofracturing within the specimen at rapid loading rates. Reduction in strength, corresponding to the decrease in strain rate, is explained in terms of stress corrosion cracking. A detailed examination of six specimens tested at a strain rate of 10{sup {minus}9} s{sup {minus}1}, using acoustic wave velocities and CT scans, shows a correlation between the nature of the microstructure of the specimens and the observed strengths and elastic moduli.
Pore scale invasion percolation theory is modified for imbibition of.wetting fluids into fractures. The effects of gravity, local aperture field geometry, and local in-plane air/water interfacial curvatureare included in the calculation of aperture filling potential which controls wetted structure growth within the fracture. The inclusion of gravity yields fingers oriented in the direction of the gravitational gradient. These fingers widen and tend to meander and branch more as the gravitational gradient decreases. In-plane interfacial curvature also greatly affects the wetted structure in both horizontal and nonhorizontal fractures causing the formation of macroscopic wetting fronts. The modified percolation model is used to simulate imbibition into an analogue rough-walled fracture where both fingering and horizontal imbibition experiments were previously conducted. Comparison of numerical and experimental results showed reasonably good agreement. This process oriented physical and numerical modeling is-a necessary step toward including gravity-driven fingering in models of flow and transport through unsaturated, fractured rock.
Paramount to the modeling of unsaturated flow and transport through fractured porous media is a clear understanding of the processes controlling fracture-matrix interaction. As a first step toward such an understanding, two preliminary experiments have been performed to investigate the influence of matrix imbibition on water percolation through unsaturated fractures in the plane normal to the fracture. Test systems consisted of thin slabs of either tuff or an analog material cut by a single vertical fracture into which a constant fluid flux was introduced. Transient moisture content and solute concentration fields were imaged by means of x-ray absorption. Flow fields associated with the two different media were significantly different owing to differences in material properties relative to the imposed flux. Richards` equation was found to be a valid means of modeling the imbibition of water into the tuff matrix from a saturated fracture for the current experiment.
A set of detailed geostatistical simulations of porosity has been produced for a layered stratigraphic sequence of welded and nonwelded volcanic tuffs at Yucca Mountain, Nevada. The simulations are produced using a composite. model of spatial continuity and they are highly conditioned to abundant drill hole (core) information. A set of derivative simulations of saturated hydraulic conductivity has been produced, in the absence of conditioning data, using a cross-variable relationship developed from similar data elsewhere. The detailed simulations reproduce both the major stratigraphic units and finer scale layering indicated by the drill hole data. These simulations have been scaled up several order of magnitude to represent block-scale effective hydrologic properties suitable for use in numerical modeling of groundwater flow and transport. The upscaling process involves the reformulation of a previously reported method that iteratively adapts an initial arbitrary grid to ``homogenize`` the detailed hydraulic properties contained within the adjusted cell limits and to minimize the size of cell in highly heterogeneous regions. Although the computation of the block-effective property involves simple numerical averaging, the blocks over which these averages are computed are relatively homogeneous, which reduces the numerical difficulties involved in averaging non-additive properties, such as permeability. The entire process of simulation and upscaling is rapid and computationally efficient compared with alterative techniques. It is thus suitable for the Monte Carlo evaluation of the uncertainty in site characterization as it affects the results of groundwater flow and transport calculations.
Hydrologic properties have been measured on outcrop samples taken from a detailed, two-dimension grid covering a 1.4 km outcrop exposure of the 10-m thick non-welded-to-welded, shardy base microstratigraphic unit of the Tiva Canyon Member of the Miocene Paintbrush Tuff at Yucca Mountain, Nevada. These data allow quantification of spatial trends in rock matrix properties that exist in this important hydrologic unit. Geologic investigation, combined with statistical and geostatistical analyses of the numerical data, indicates that spatial variability of matrix properties is related to deterministic geologic processes that operated throughout the region. Linear vertical trends in hydrologic properties are strongly developed in the shardy base microstratigraphic unit, and they are more accurately modeled using the concept of a thickness-normalized stratigraphic elevation within the unit, rather than absolute elevation. Hydrologic properties appear to be correlated over distances of 0.25 to 0.3 of the unit thickness after removing the deterministic vertical trend. The use of stratigraphic elevation allows scaling of identified trends by unit thickness which may be of particular importance in a basal, topography-blanketing unit such as this one. Horizontal changes in hydrologic properties do not appear to form obvious trends within the limited lateral geographic extent of the ash-flow environment that was examined. Matrix properties appear to be correlated horizontally over distances between 100 and 400 m. The existence and quantitative description of these trends and patterns of vertical spatial continuity should increase confidence in models of hydrologic properties and groundwater flow in this area that may be constructed to support the design of a potential high-level nuclear waste repository at Yucca Mountain.
This paper presents a method of estimating the rock mass properties for the welded and nonwelded tuffs based on currently available information on intact rock and joint characteristics at the Yucca Mountain site. Variability of the expected ground conditions at the potential repository horizon (the TSw2 thermomechanical unit) and in the Calico Hills nonwelded tuffs is accommodated by defining five rock mass quality categories in each unit based upon assumed and observed distributions of the data.
A numerical approach for modeling unsaturated flow is developed for heterogeneous simulations of fractured tuff generated using a geostatistical method. Cross correlations of hydrologic properties and upscaling of moisture retention curves is discussed. The approach is demonstrated for a study of infiltration at Yucca Mountain.
The regulations that currently govern repositories for spent fuel and high-level waste require demonstrations that are sometimes described as impossible to make. To make them will require an understanding of the current and the future phenomena at repository sites; it will also require credible estimates of the probabilities that the phenomena will occur in the distant future. Experts in many fields{emdash}earth sciences, statistics, numerical modeling, and the law{emdash}have questioned whether any amount of data collection can allow modelers to meet these requirements with enough confidence to satisfy the regulators. In recent years some performance assessments have begun to shed light on this question because they use results of actual site investigations. Although these studies do not settle the question definitively, a review of a recent total-system assessment suggests that compliance may be possible to demonstrate. The review also suggests, however, that the demonstration can be only at the ``reasonable`` levels of assurance mentioned, but not defined, in the regulations.
Previous laboratory investigations of tuff have shown that porosity has a dominant, general effect on mechanical properties. As a result, it is very important for the interpretation of mechanical property data that porosity is measured on each sample tested. Porosity alone, however, does not address all of the issues important to mechanical behavior. Variability in size and distribution of pore space produces significantly different mechanical properties. A nondestructive technique for characterizing the internal structure of the sample prior to testing is being developed and the results are being analyzed. The information obtained from this technique can help in both qualitative and quantitative interpretation of test results.
In situ thermomechanical experiments are planned as part of the Yucca Mountain Site Characterization Project that require instruments to measure stress and displacement at temperatures that exceed the typical specifications of existing geotechnical instruments. A high degree of instrument reliability will also be required to satisfy the objectives of the experiments, therefore a study was undertaken to identify areas where improvement in instrument performance was required. A preliminary list of instruments required for the experiments was developed, based on existing test planning and analysis. Projected temperature requirements were compared to specifications of existing instruments to identify instrumentation development needs. Different instrument technologies, not currently employed in geotechnical instrumentation, were reviewed to identify potential improvements of existing designs for the high temperature environment. Technologies with strong potentials to improve instrument performance with relatively high reliability include graphite fiber composite materials, fiber optics, and video imagery.
As a follow-on to Sandia`s 1991 preliminary total-system performance assessment of the Yucca Mountain site, this paper presents results of some sensitivity analyses that were done using results from the 1991 study. Two conceptual models of unsaturated-zone flow and transport at Yucca Mountain were included in the study, including both aqueous and gaseous releases. The sensitivities are quite different for the two models. For the composite-porosity model, the results are most sensitive to groundwater percolation flux, gaseous transport time, container lifetime, and fuel-matrix-alteration rate. For the weeps model, the results are most sensitive to parameters used to characterize fracture flow (fracture aperture and fracture connectivity) and infiltration (percolation flux and weep-episode factor).
The event-tree method of scenario construction has been chosen for the Yucca Mountain performance assessment. Its applicability and suitability to the problem are discussed and compared with those of the Nuclear Regulatory Commission (NRC) method. The event-tree method is appropriate for an incompletely characterized site, where there must be an evolving understanding, over time, of the processes at work, for a site that may require analysis of details in specific context, and when the scenario functions to guide site characterization. Anticipating the eventual requirement for using the NRC method, we show that the event-tree method can be translated to the NRC format after final scenario screening.
Chemical vapor deposition (CVD) is a widely used method for depositing thin films of a variety of materials. Applications of CVD range from the fabrication of microelectronic devices to the deposition of protective coatings. New CVD processes are increasingly complex, with stringent requirements that make it more difficult to commercialize them in a timely fashion. However, a clear understanding of the fundamental science underlying a CVD process, as expressed through computer models, can substantially shorten the time required for reactor and process development. Research scientists at Sandia use a wide range of experimental and theoretical techniques for investigating the science of CVD. Experimental tools include optical probes for gas-phase and surface processes, a range of surface analytic techniques, molecular beam methods for gas/surface kinetics, flow visualization techniques and state-of-the-art crystal growth reactors. The theoretical strategy uses a structured approach to describe the coupled gas-phase and gas-surface chemistry, fluid dynamics, heat and mass transfer of a CVD process. The software used to describe chemical reaction mechanisms is easily adapted to codes that model a variety of reactor geometries. Carefully chosen experiments provide critical information on the chemical species, gas temperatures and flows that are necessary for model development and validation. This brochure provides basic information on Sandia`s capabilities in the physical and chemical sciences of CVD and related materials processing technologies. It contains a brief description of the major scientific and technical capabilities of the CVD staff and facilities, and a brief discussion of the approach that the staff uses to advance the scientific understanding of CVD processes.
Photovoltaic (PV) systems offer a cost-effective solution to provide electrical power for a wide variety of applications, with battery performance playing a major role in their success. This paper presents some of the results of an industry meeting regarding battery specifications and ratings that photovoltaic system designers require, but do not typically have available to them. Communications between the PV industry and the battery industry regarding appropriate specifications have been uncoordinated and poor in the past. This paper also discusses the effort under way involving the PV industry and battery manufacturers, and provides a working draft of specifications to develop and outline the information sorely needed on batteries. The development of this information is referred to as ``Application Notes for Batteries in Photovoltaic Systems.`` The content of these ``notes`` has been compiled from various sources, including the input from the results of a survey on battery use in the photovoltaic industry. Only lead-acid batteries are discussed
In one design of molten-salt central receivers, the molten salt flows in a serpentine path, down one panel of tubes then up the next and down again continuing in this fashion through the receiver. There have been concerns about this design because in the down flow sections, the heat flux incident on the tubes can cause flow instability since the flow is in direct opposition to the buoyant forces. In extreme cases the buoyant forces can cause flow stagnation or reversal. An analysis of flow stability within individual tubes and down flow sections of receiver panels is presented. When the partial derivative of the pressure drop with respect to mass flow rate is negative ({partial_derivative}{Delta}P/{partial_derivative}{sup {lg_bullet}} < 0), the flow is unstable and could cause serious damage to the receiver. Stability maps are developed that show safe operating regimes where inertial forces dominate over buoyant forces. The data is then normalized using the Grashof and Reynolds numbers.
United States Department of Energy has established its first Advanced Research Objective in the Solids Transport Program. The scientific, engineering, and management goals are discussed in some detail. Scientific progress to date is summarized. Comments are made on the technical direction of further Advanced Research Objectives.
We have developed a Li/SOCl{sub 2} ``D`` cell for applications requiring 10 to 15 years life at very low drain rates, typically less than 150 {mu}A. Maximizing cell safety and reliability, while delivering very good energy density, have been the goals of our study. We have achieved these goals by designing the cell to be application specific. The low-rate cell has been optimized to deliver up to 16 Ah at drain rates of less than 70 mA. By virtue of its low surface area, 145 cm{sub 2}, the cell has demonstrated excellent safety behavior. Safety testing has been performed on individual cells as well as on two-cell and four-cell batteries. Single cells did not vent when short-circuited. We were able to produce benign venting in a two cell string, but only when the string was partially discharged before shorting. The vent mechanism is a 300 psi rupture pressure burst disc manufactured by BS&B Safety Systems. We define benign venting as full opening of the 3/8 in. dia vent hole without deformation of the case. Material is expelled from the cell without flame, and the cell stack remains largely intact. We have not produced venting of the Sandia-designed low rate cell under any other abuse test conditions. The vent functions as an ultimate safety mechanism in the case of severe abuse, but resistance to venting under normal use and mild abuse conditions is key to the achievement of high reliability.
A new class of ion-exchange materials that can selectively separate low parts per million level concentrations of Cs{sup +} from 3--6 molar concentrations of Na{sup +} over a wide pH range has recently been developed as a result of a collaborative effort between Sandia National Laboratories and Texas A&M University. The materials, called crystalline silicotitanates, show potential for application in the treatment of aqueous nuclear waste solutions.
In order to develop a procedure for measuring cation diffusion coefficients below 1000{degrees}C, we have examined the suitability of several diffusion couple configurations involving single crystals of garnet. Initial experiments using an enriched {sup 25}MgCl{sup 2} proved ineffective in providing a uniform and coherent surface for analysis by ion microprobe. A technique was developed using thin film deposition. Thin films ({approximately} 1000 {Angstrom}) of MgO{sub x} (x < 1) can be applied to polished mineral surfaces by evaporating MgO powder under high vacuum with a thermal-resistance strip heater. Thermal resistance evaporation is efficient. Samples of single crystal grossular and pyrope garnets with thin films of MgO, as created by these techniques, were annealed for various times at 800, 900, and 1000{degrees}C, at several log fO{sub 2} values, and 1 atm. Optical, SEM, and ion microprobe analyses reveal no disruption of the interface. Profiles of elemental counts vs depth exhibit expected patterns going through the thin film into the garnet substrate. Our experimental matrix of garnet diffusion runs includes over 60 cut and polished crystals of pyrope composition that are being run at various oxygen fugacity conditions from 600 to 1000{degrees}C.
The Los Alamos National Laboratory (LANL) Mechanical Engineering and Electronics Division, in partnership with Sandia National Laboratories and Programmed Composites, is advancing the development of thin-walled, high modulus short-fiber compression-molded composite materials fabrication. In this paper, we investigate component uniformity, structural integrity, thermal conductivity, and radiation resistance; discuss the scanning-electron microscopic inspection of the graphite fiber distribution and orientation, and describe the process used in selecting the reinforcement fiber length and modulus and for choosing the hydrophobic, cyanate-ester resin.
During the last two decades there has been considerable interest in developing alternatives to conventional chemical propulsion for space missions. Laser propulsion has been identified as a serious contender for the task of inexpensively delivering small payloads to low-earth orbit. Recent advances in the development of lasers powered directly by nuclear reaction products offer the potential for new propulsion methods, namely, reactor-laser propulsion. Such systems would allow ``nuclear propulsion`` without placing nuclear systems in space.
Alternate organometallic Sb sources are being investigated to improve the characteristics of InSb grown by MOCVD. InSb grown using trimethylindium (TMIn) and trimethylantimony (TMSb) or triethylantimony (TESb) yielded similar quality materials under similar growth conditions. InSb grown using triethylindium (TEIn) and TESB under similar growth conditions yielded very poor quality n-type material. Three new organometallic Sb sources, triisopropyl-antimony (TIPSb), tris(dimethylamino)antimony (TDMASb), and tertiarybutyldimethylantimony (TBDMSb) are being investigated. Growth of InSb using TIPSb, TDMASb, or TBDMSb and TMIn was investigated over 350 to 475{degrees}C. InSb grown from TDMASb had similar properties to InSb grown from TMIn and TMSb when using a similar temperature and V/III ratio range. Growth rates of InSb using TMIn and either TIPSb or TBDMSb at temperatures {le} 425{degrees}C were proportional to both TMIn flow rate and temperature. Surface morphology of InSb grown using either TIPSb or TBDMSb was rough for growth temperatures {le} 425{degrees}C; this may be due to complex decomposition and methyl groups on surface. The InSb with the highest mobility was grown at 400{degrees}C and a V/III ratio of 3 using TIPSb. It was n-type with a carrier concentration of 2.5 {times} 10{sup 15} cm{sup {minus}3} and a mobility of 78,160 cm{sup 2}/Vs at 77 K. Both n- and p-type InSb were grown using TBDMSb with mobilities up to 67,530 and 7773 cm{sup 2}/Vs, respectively at 77 K. Mobility for InSb using either TIPSb or TBDMSb was optimized by going to lower temperatures, pressures, V/III ratios; however, surface morphology improved with higher temperature, pressure, V/III ratio. High mobility InSb with smooth surfaces at T {le} 425{degrees}C was not obtained with TIPSb or TBDMSb and TMIn.
We present the use of an STM to make quantitative observations of time-dependent mass flow associated with the decay of two-dimensional clusters on the Au(lll) surface. When formed and observed in air, layered islands with well-defined edges located on larger terraces are generally found to decay in such a way that their areas decrease linearly in time over periods ranging from minutes to several hours depending on the island size. This is in contrast to the behavior of similar features formed and observed under ultra high vacuum conditions, which do not appear to decay over experimental periods of several days. The linear decay is consistent with models that have been used previously to describe growth of 2-dimensional clusters on surfaces. We discuss possible decay mechanisms`, and the role that adsorbates may play in influencing the decay.
In support of the UST, WeDID, VOC/Non-Arid, and VOC/Arid, and VOC/Arid Integrated Demonstrations, organic contaminants and nitrates in Hanford Underground Storage Tank (UST) wastes, polymeric organics in weapon components, and chlorocarbon soil contaminants have been destroyed by exposure to high-temperature steam during bench tests with a quartz reactor and full-scale tests that used the Synthetica Detoxifier, a commercial one-ton-per-day steam reforming waste destruction system. Reactivation of Granular Activated Carbon (GAC) in the Detoxifier and Thermal Gravimetric Analyses (TGA) of the decomposition of sodium nitrate have also been performed.
We have successfully grown ZnMnTe alloys by molecular beam epitaxy using GaAs as a substrate. Bulk MnTe has the wurtzite crystal structure but the structural phase of the material was confirmed to be zinc-blende by standard {theta}-2{theta} x-ray diffraction techniques. The composition was also determined using x-ray diffraction techniques. Manganese concentration was also estimated from magnetization measurements taken as a function of temperature. Magnetoluminescence studies were performed at 1.4K on the acceptor-bound exciton in the semimagnetic semiconductor ZnMnTe alloys. As expected, the photoluminescence peak energy decreased with increasing magnetic field.
At some landfills, hazardous wastes were placed into disposal pits with other waste oils. Volatile organic wastes, such as cleaning solvents, when combined with oil are much more difficult to remove from the soils because the oil makes the volatile organic chemical evaporate much slower. The typical vacuum extraction remediation method could become a lengthy campaign. Since all chemicals evaporate faster when they are heated, if the contaminated soil could be heated, the chemicals would be easier to remove from the soil. By using heating techniques developed by the Oil and Gas Industry to enhance the removal of oil and gas resources from the soil, the problem of removing contamination from the soils could be solved. The Thermal Enhanced Vapor Extraction System (TEVES) demonstration will combine vacuum vapor extraction technology with powerline frequency soil heating and radiofrequency soil heating to accelerate the soil decontamination process. The premise that soil heating technology can actually reduce the costs of soil decontamination is complicated by the high capital costs of the soil heating equipment and the cost of electrode installation. By performing this field demonstration, Sandia will be able to collect the information needed to see if this new technology will improve the decontamination of soils.
Sandia National Laboratories is a large multiprogram Research and Development laboratory which is operated by a contractor for the US Department of Energy. In the Laboratories, lasers are both the subject of research and the tools that are used in other research, development, and testing activities. Since 1979, laser safety training has been the primary focus of the Laboratories` laser safety program. Approximately 1 100 personnel have been trained in formal courses during that time period. The formal course, presented on site by a contractor, consists of two full days of instruction. The course contents include the following topics: Laser technology and safety overview; Federal and ANSI laser standards summaries; Biological effects of laser radiation; Classification of lasers; Laser hazard analysis; Review of ANSI Z136.1 control measures; Laser eye protection. Recent emphasis on regulatory requirements, conduct of operations, and quality management has revealed a need to change the laser safety training curriculum. A new course for users of low power lasers (Class 2 and 3a) is being developed. A refresher course, a management awareness (self-study) course, and major changes in the current course are planned.
A solar photocatalytic process has been under development at both Sandia National Laboratories and the National Renewable Energy Laboratory (formerly the Solar Energy Research Institute). This process uses solar ultraviolet light to activate a titanium dioxide catalyst which oxidizes organic contaminants in water. In the summer of 1991, a solar photocatalytic detoxification of water system was installed and tested at a California Superfund Site located at Lawrence Livermore National Laboratory. The site was designated a Superfund Site because of widespread groundwater contamination which resulted from the release of chlorinated solvents, principally trichloroethylene, when the site was a Naval Air Station in the early 1940s. The objectives of these experiments were to measure the effects of process variables and the process efficiency in an actual remediation setting, to collect experimental data and operating experience in photocatalytic oxidation of organic contaminants, to develop accurate models of the system operation and to develop control strategies.
We have developed a video detection algorithm for measuring the residue left on a printed circuit board after a soldering process. Oblique lighting improves the contrast between the residue and the board substrate, but also introduces an illumination gradient. The algorithm uses the Boundary Contour System/Feature Contour System to produce an idealized clean board image by discounting the illuminant, detecting trace boundaries, and filling the trace and substrate regions. The algorithm then combines the original input image and ideal image using mathematical models of the normal and inverse Weber Law to enhance the residue on the traces and substrate. The paper includes results for a clean board and one with residue.
The Materials Interface Interaction Tests (MIIT) program involves the comparative performance-evaluation testing of multiple US and foreign nuclear waste glasses (nonradioactive), potential canister and overpack metals, brine, and geologic materials in the rock salt repository environment at the Waste Isolation Pilot Plant (WIPP) facility. We emplaced about 2000 materials specimens onto fiftn, separate test assemblies and exposed them to a heated, salt-brine environment at the WIPP for multi-year periods. We successfully terminated the in situ conduct of the MIIT in July 1991, after five years of testing, and retrieved all samples for posttest laboratory analyses. These 5-year glass and metal samples, along with samples previously retrieved after 0.5, 1, and 2 years, are being analyzed in multiple international laboratories, in a cooperative testing effort. Individual test participants will present available laboratory results, and interpretations, on MIIT specimens in this workshop. Our focus in this paper is to summarize technical details and repository-relevant observations on the in situ conduct, sampling, and termination operations of the MIIT experimental program. Such information should be useful for the interpretation of the laboratory-based analyses. This information also will be relevant and instructive for other organizations contemplating, planning, or conducting additional materials-related, in situ tests.
A comparison between numerical calculations with use of commercial thermal analysis software packages and experimental data simulating a horizontally oriented spent fuel rod array was performed. Twelve cases were analyzed using air and helium for the fill gas, with three different heat dissipation levels. The numerically predicted temperatures are higher than the experimental data for all levels of heat dissipation with air as the fill gas. The temperature differences are 4{degree}C and 23{degree}C for the low heat dissipation and high heat dissipation, respectively. The temperature predictions using helium as a fill gas are lower than the experimental data for the low and medium heat dissipation levels. The temperature predictions are 1{degree}C and 6{degree}C lower than the experimental data for the low and medium heat dissipation, respectively. For the high heat dissipation level, the temperature predictions are 16{degree}C higher than the experimental data. Differences between the predicted and experimental temperatures can be attributed to several factors. These factors include experimental uncertainty in the temperature and heat dissipation measurements, actual convection effects not included in the model, and axial heat flow in the experimental data. This work demonstrates that horizontally oriented spent fuel rod surface temperature predictions can be made using existing commercial software packages. This work also shows that end effects, such as axial heat transfer through the spent fuel rods, will be increasingly important as the amount of dissipated heat increases.
Magnetic force microscopy (MFM) has been applied to image currents in internal IC conductors. We present a model for the MFM imaging of IC currents, describe MFM signal generation, and demonstrate the ability to analyze current direction and magnitude with a sensitivity of {approximately} 1 mA dc and {approximately} 1 {mu}A ac. Our experimental results are a significant improvement on the 100 mA ac resolution previously reported using an electron beam to detect IC currents [1].
The Waste Isolation Pilot Plant: (WIPP) in southeastern New Mexico is being developed by the US Department of Energy as a disposal facility for transuranic waste. In support of this project, Sandia National Laboratories is conducting an ongoing performance assessment (PA) for the WIPP. The ordered triple- representation for risk proposed by Kaplan and Garrick is used to provide a clear conceptual structure for this PA. This presentation describes how the preceding representation provides a basis in the WIPP PA for (1) the definition of scenarios and the calculation of scenario probabilities and consequences, (2) the separation of subjective and stochastic uncertainties, (3) the construction of the complementary cumulative distribution functions required in comparisons with the US Environmental Protection Agency`s standard for the geologic disposal of radioactive waste (i.e., 40 CFR Part 191, Subpart B), and (4) the performance of uncertainty and sensitivity studies. Results obtained in a preliminary PA for the WIPP completed in December of 1991 are used for illustration.
As applications for hybrid circuits and multichip modules create demand for higher density circuits and higher power components, new substrate materials are required to deal with the heat generated on the circuit. Sandia National Laboratories is developing diamond substrate technology to meet the requirements of high thermal conductivity. Thin film processes were developed and characterized to delineate conductor-resistor networks on free standing diamond substrates having fine line gold conductors and low and high sheet resistivity resistors. Thin film hybrid circuit technology was developed on CVD-processed, polycrystalline diamond substrates having as-deposited surface finishes as well as those with polished surfaces. Conductors were defined by pattern plating gold and resistors were processed from sputtered tantalum nitride films which were deposited to sheet resistivities of 5 and/or 100 ohms per square. Resistor films on diamond substrates were evaluated for Temperature Coefficient of Resistance (TCR), stability with time and temperature, and trimmability using YAG laser processing. Plated gold conductors were patterned on diamond to feature sizes of 25 microns and successfully tested for adhesion and bondability. Advanced YAG laser trimming techniques were developed to allow resistor trims on both low and high value resistors to within 1% of desip value while maintaining required resistor stability, new trim techniques were needed to offset the carbonization of diamond in the laser trim area. Reliability studies were carried out on the diamond thin film networks which showed them to compare favorably with the same thin film technology on alumina substrates.
Photocreation mechanisms and properties of nitrogen dangling bonds in amorphous hydrogenated silicon nitride (a-SiN{sub x}:H) thin films are investigated. We find that the creation kinetics are strongly dependent on the post-deposition anneal; this thermal process can be described by a simple exponential function which yields an activation energy of 0.8 eV. The compositional dependence of the nitrogen dangling bond center suggests that its energy level lies close to the valence band edge, in agreement with theoretical calculations. This energy level position can explain why a-SiN{sub x}:H films often become conducting following a high post-deposition anneal.
Path planning needs to be fast to facilitate real-time robot programming. Unfortunately, current planning techniques are still too slow to be effective, as they often require several minutes, if not hours of computation. To overcome this difficulty, we present an adaptive algorithm that uses previous experience to speed up future performance. It is a learning algorithm suitable for incrementally-changing environments such as those encountered in manufacturing of evolving products and waste-site remediation. The algorithm extends our previous work for stationary environments in two directions: For minor environmental change, an object-attached experience abstraction scheme is introduced to increase the flexibility of the learned experience; for major environmental change, an on-demand experience repair scheme is also introduced to retain those experiences that remain valid and useful. In addition to presenting this algorithm, we identify three other variants with different repair strategies. To analyze the respective performance of these algorithms, we develop an analytic model that quantifies and relates training effort, experience value and utility, and environmental change through intuitive terms of energy and work. It is a general and simple model that should be very useful in characterizing other types of learning processes as well. Using this model, we formalize the concept of incremental change, and prove the optimality of our proposedalgorithm under such change. Empirically, we also characterize the performance curve of each variant, confirm our theoretical optimality results, and demonstrate the practicality of our algorithm.
A method of solving the two-phase fluid flow equations using a genetic algorithm on a NCUBE multiprocessor computer is presented. The topics discussed are the two-phase flow equations, the genetic representation of the unknowns, the fitness function, the genetic operators, and the implementation of the algorithm on the NCUBE computer. The efficiency of the implementation is investigated using a pipe blowdown problem. Effects of varying the genetic parameters and the number of processors are presented.
The restoration of environmentally contaminated sites at DOE facilities has become a major effort in the past several years. The variety of wastes involved and the differing characteristics have driven the development of new restoration and monitoring technologies. One of the new remediation technologies is being demonstrated at the Savannah River Site near Aiken, South Carolina. In conjunction with this demonstration, a new technology for site characterization and monitoring of the remediation process has been applied by Sandia National Laboratories.
We used surface-profile data taken with a noncontact laser profilometer to determine the aperture distribution within a natural fracture and found the surfaces and apertures to be isotropic. The aperture distribution could be described equally well by either a normal or a lognormal distribution, although we had to adjust the standard deviation to `fit` the data. The aperture spatial correlation varied over different areas of the fracture, with some areas being much more correlated U= others. The fracture surfaces did not have a single fractal dimension over all length scales, which implied that they were not self-similar. We approximated the saturated flow field in the fracture by solving a finite-difference discretization of the fluid-flow continuity equation in two dimensions. We then calculated tracer breakthrough curves using a particle-tracking method. comparing the breakthrough curves obtained using both coarse- and fine-resolution aperture data (0.5- and 0.05-mm spacing between points, respectively) over the same subset of the fracture domain suggests that the spacing between the aperture data points must be less than the correlation length to obtain accurate predictions of fluid flow and tracer transport. In the future, we will perform tracer experiments and numerical modeling studies to determine exactly how fine the aperture data resolution must be (relative to the correlation length) to obtain accurate predictions.
A method is described for parallelizing molecular dynamics (MD) simulations by block-decomposing the matrix of bonded and non-bonded force computations. It is particularly useful for organic simulations (polymers, proteins) because unlike spatial-decomposition methods, it requires no geometric information about the simulation domain. Because its communication cost scales as N/{radical}P. rather than N as in the all-to-all broadcast or ring-exchange techniques commonly used in this type of MD simulation, larger numbers of processors can be used effectively, yielding greater parallel speed-ups.
Two major initiatives are underway in the US that are creating a significant financial impact on both the US taxpayer and on users of electric power. First, the US Department of Energy (DOE) has been tasked with cleaning-up the defense complex. This task is managed under the direction of the Office of Environmental Restoration and Waste Management (EM) of the DOE. The waste that EM must address includes radioactive, hazardous, and mixed that consists of both radioactive and hazardous constituents. Second, the DOE is required by the Nuclear Waste Policy Act (NWPA) to take title to commercial nuclear spent fuel assemblies starting in 1998. The DOE Office of Civilian Radioactive Waste Management (OCRWM) was established to carry out this charter. Since a final repository is not scheduled for opening until 2010 at the earliest, the DOE is planning on providing a Monitored Retrievable Storage (MRS) facility for centralized storage to bridge the time gap between 1998 and 2010. The NWPA requires that nuclear utilities pay a fee into a specific fund that Congress uses to pay the DOE for the development of the MRS, the transportation system, and the repository. This fund, along with the EM budget, constitutes a multi-billion dollar effort to manage DOE nuclear waste and to store and dispose of commercial spent nuclear fuel. These two seemingly unrelated problems have aspects of commonality that can be considered for the benefit of both programs, the US taxpayer, and the utility rate payer. Both programs are the responsibility of the DOE, and both will require engineered packages for storage, transportation, and disposal of the EM waste and commercial spent fuel. Rather than using specialized systems for each step (storage, transport, and disposal), a concept for a Universal Container System has been developed that could potentially simplify the overall waste management system, reduce expensive handling operations, and reduce total system cost.
Inadvertent alloying of Cu braze metal can compromise metal/ceramic seals. Electron microprobe analyses have quantified alloying of Cu brazes in metal/ceramic feedthroughs. Pin material and processing parameters above 1084C both affect alloying levels. Using either Kovar or Ni-plated 316L stainless steel pins limits alloying compared to Palco pins. Minimizing the time during which the braze is molten also avoids excessive alloying. The original thickness of the Ni plating on the Mo-Mn metallization of the ceramic also influences the alloying content of these brazes. Metal/ceramic brazes made with long brazing cycles, Mo-Mn metallization, and Kovar components grow a layer of Mo{sub 6}(Fe{sub 3.5}CO{sub 3.5}){sub 7} on the metallization. Layer thicknesses observed do not appear to compromise joint integrity. Ni additions of approximately 10 and 20 wt.% to Cu apparently increases the stress required for stress relaxation during cooldown. to maintain creep rates required for stress relaxation during cooldown. Relative to unalloyed Cu, this strengthening effect tends to increase as temperature is decreased.
In this paper we investigate the applicability of the feature extraction mechanisms found in the neurophysiology of mammals to the problem of object recognition in synthetic aperture radar imagery. Our approach is to present multiple views of objects to be recognized to a two-stage self-organizing neural network architecture. The first stage, a two-layer Neocognitron, performs feature extraction in each layer The resulting feature vectors are presented to the second stage, an ART-2A classifier self-organizing neural network which clusters the features into multiple object categories. The feature extraction operators resulting from the self-organization process are compared to the feature extraction mechanisms found in the neurophysiology of vision. In a previous paper, the Neocognitron was trained on raw SAR imagery. The architecture was able to recognize a simulated vehicle at arbitrary azimuthal orientations at a single depression angle while rejecting clutter as well as other vehicles. Feature extraction on raw imagery yielded features that were robust but very difficult to interpret. In this paper we report the results of some new experiments in which the self-organization process is applied separately to shadow and bright returns from objects to be recognized. Feature extraction on shadow returns yield oriented contrast edge operators suggestive of bipartite simple cells observed in the striate cortex of mammals. Feature extraction on the specularity patterns in bright returns yield a collection of operators resembling a twodimensional Haar basis set. We compare the performance of the earlier two-stage neural network trained on raw imagery with a modified network using the new feature set.
The Mixed Waste Landfill Integrated Demonstration (MWLID) is testing noninvasive site characterization methods at several locations, including the Chemical Waste Landfill (CWL) at Sandia National Laboratories. The CWL comprises shallow, unlined pits that were used for the disposal of acids, oils, solvents, and inorganic compounds from 1962 until the CWL was closed in 1985. The soils of the landfills are alluvial, predominantly sand, gravels and cobbles with small quantities of silts and clays. The focus of this study is an unlined chromic acid pit (UCAP). The UCAP pit is rectangular (approximately 4 {times} 10 m), which reportedly received unknown volumes of chromium in the form of chromic acid (liquid) and other hazardous materials. At this location, we have demonstrated a continuous waveform (CW) system for site characterization. During this year, we will also utilize a crossborehole pulsed radar system. Both methods are sensitive to variations in either electrical conductivity or dielectric constant in the soils or host rock at a waste site. These earth properties are some of the most responsive geophysical indicators of metallic, acidic and water-based subsurface contaminants.