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.
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.
Nash, T.J.; Spielman, R.B.; Ruggles, L.; Vargas, M.
Using Saturn as a driver, we are pursuing both photoresonantly pumped and photoionization/recombination lasers. Our lasing targets are gas cells with thin windows that are pumped by a z pinch 2 cm away radiating 10 TW. In both schemes the lasant and gas fill is neon. To increase our chances of measuring the resonantly photopumped lasing transition we have introduced potassium into a sodium z pinch and have eliminated oxygen from the gas cell windows. We have measured the spatial dependence of ionization balance across the gas cell, and this measurement is consistent with propagation of a shock front across the gas cell target. We have measured blue-shifted satellites to several Li-like neon transitions that may indicate return-current driven jetting a high 1.5e8 cm/sec velocity. Using a gold z-pinch we have shown that key radiation is necessary to excite the He-like lines of neon. An attempt at a single shot gain measurement also indicates that radiation is not the only source of gas cell heating.
This paper presents a full-field dye concentration measurement technique that extends our experimental capabilities to the measurement of transient dye concentration fields within steady state flow fields under unsaturated or saturated conditions. Simple light absorption theory provides a basis for translating images into high resolution dye concentration fields. A series of dye pulse experiments that demonstrate the combined use of the full-field saturation and dye concentration techniques was conducted at four different degrees of saturation. Each of these experimental sequences was evaluated with respect to mass balance, the results being within 5% of the known dye mass input. An image windowing technique allowed us to see increased dispersion due to decreasing moisture content, tailing of concentration at the rear of the dye pulse and slight velocity changes of the dispersive front due to changes in moisture content. The exceptional resolution of dye concentration in space and time provided by this laboratory technique allows systematic experimentation for examining basic processes affecting solute transport within saturated/unsaturated porous media. Future challenges for this work will be to use these techniques to analyze more complex systems involving heterogeneities, scaling laws, and detailed investigations of the relationship between transverse and longitudinal dispersion in unsaturated media.
The Beam Characterization System is being employed at the Sandia`s National Solar Thermal Test Facility to characterize the optical performance of heliostats, point-focus solar collectors, and their optical sub-elements as part of the on-going task to develop solar thermal technologies. With this measurement system, images of concentrated solar flux are acquired using digital imaging and processed to obtain such measures of the collector`s optical performance as beam power, flux distribution, and beam diameter. Key system elements are a diffusely reflective target for imaging collector beams, meteorological instrumentation including a flux gauge to measure flux at one point in the beam, and a calibration technique to establish a pixel-intensity-to-flux-density conversion factor for the image. The system is employed in a variety of collector tests such as beam quality, tracking error, and wind effects. The paper describes the Beam Characterization System and its components and presents, for illustration, sample test results. An analysis of the Beam Characterization System`s sources of measurement error is presented. Lastly, measurement techniques that employ the BCS to align heliostats and to measure or estimate collector surface slope errors are described.
We have measured the laser emission spectra of several vertical cavity surface emitting lasers following pulsed laser excitation, with a time resolution of < 1 ps. Correlations between the observed pulse widths and cavity lifetimes were observed.
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.
