Publications

A molten salt cavity receiver was solar tested at Sandia National Laboratories during a year-long test program. Upon completion of testing, an analysis was performed to determine the effect of thermal cycling on the receiver. The results indicate substantial fatigue damage accumulation for the receiver when the relatively short test time is considered. This paper describes the methodology used to analyze the cycling, the results, and how they affect future receiver design. The test receiver was configured as a C-shaped cavity with eight multipass heat absorption panels. The tubes were Alloy 800. The heat exchange medium was a molten nitrate salt mixture (60% sodium nitrate, 40% potassium nitrate by weight). The operating temperature range was from 288°C to 566°C.

Under compressive stresses, brittle polycrystalline materials fail as the result of the growth, interaction and coalesence of microcracks. To predict the deformation of damaging material, constitutive laws developed for such materials must incorporate the effects of crack size, density, orientation, and interaction.A method of incorporating the accumulation and growth of microcracks into a continuum model is to use a measure of microcrack growth and interaction defined as damage. Although a number of damage theories have been proposed, there is no generally accepted experimental technique for detecting and measuring damage. Acoustic emissions (AE) have been correlated with microcrack nucleation and growth. We propose that AE locations and density are useful measures of damage that can be correlated with calculated damage. Our approach is to use acoustic emissions (AE) and computer modeling to study the development of damage in geomaterials.

Consideration is given to the problem of stabilizing a plant using a suboptimal stable compensator of fixed order. The resulting equations are a modified form of the optimal projection equations, with the separation principle not holding in either the full- or reduced-order case. An overbounding technique on the state covariance guarantees that the compensator is stable if nonnegative definite solutions exist to the design equations.

The Function Point (FP) concept was introduced to define'' a measure for applications development and maintenance functions avoiding the problems inherent in productivity measures in the late 1970s. At that time, Albrecht outlines three essentials elements for software size measurement: the measure must be technology independent; the technique must measure all the application functions delivered to the end customer; and the technique must measure only the application functions as delivered. Using these three attributes of a measurement, further concentrated analysis could be performed for languages, technologies, methodologies, and tools. The characterization of systems and the quality of the product are motives for subscribing to FPs. Since the inception of FPs, attempts have been made to improve the process of quantifying FPs. Some of these attempts have strayed from the intended use of FPs and have diverted valuable energy away from consistent application. The purpose of this article is to describe the process and the quantification of complexity factors for each of the five Unadjusted FPs. 4 refs.

Light ion fusion research has developed ion diodes that have unique properties when compared to other ion diodes. These diodes involve relativistic electrons, ion beam stagnation pressures that compress the magnetic field to the order of 10 Tesla, and large space-charge and particle current effects throughout the accelerating region. These diodes have required new theories and models to account for effects that previously were unimportant. One of the most important effects of the magnetic field compression and large space-charge has been impedance collapse. The impedance collapse can lead to poor energy transfer efficiency, beam debunching, and rapid change of the beam focus. This paper discusses our current understanding of these effects, some of the methods we are using to ameliorate them, and the future directions our theory and modeling will take. 40 refs., 6 figs.

A new scanning electron microscopy imaging technique has been developed to examine the logic state of conductors on passivated CMOS integrated circuits. This technique employs a modified Resistive Contrast Imaging system to acquire image data on powered devices. The image is generated by monitoring subtle shifts in the power supply current of an integrated circuit as an electron beam is scanned over the device surface. The images produced with this new technique resemble voltage contrast data from devices with the passivation removed and the surface topography subtracted. Non-destructive applications of this imaging method to functional and failed integrated circuits are described. Possible irradiation effects and methods to minimize them are also discussed. 2 refs., 1 fig.

Transit time, the time from bridgewire burst until breakout of detonation from the output pellet of an exploding bridgewire detonator, was measured as a function of burst current. From this data, in conjunction with known equations for run distance versus pressure, unreacted explosive Hugoniots, and detonation properties of the initial pressing pellet, the run distance in the initial pressing explosive pellet and shock pressure from the exploding bridgewire were determined, both as a function of burst current.

Fifteen years of solar thermal technology development have produced a considerable amount of knowledge relating to the production of electricity from central receiver power plants. This body of knowledge is under examination by researchers from the United States and the Federal Republic of Germany for the purpose of defining the next generation central receiver electricity producers. This second generation power plant is expected to represent a significant step towards commercialization of these systems. During the course of the study, specific activities needed to realize this next-step technology are being defined. The study is an international team effort. Under the International Energy Agency Small Solar Power Systems project, researchers from DLR, Interatom, Sandia National Laboratories, and Bechtel have designed a study in which technologies relating to existing systems are quantified, logical next-step systems are characterized, and future potential advances are identified. The receiver concepts under investigation are: salt-in- tube, volumetric, and direct absorption. Two plant performance levels are examined, 30 and 100 MW{sub e}. Each concept is applied with common capacity factors, solar multiples, and types and sizes of heliostats at each performance level. Availability and uncertainty analyses are also performed. Annual energy production figures are calculated using the SOLERGY computer code. Capital and Operation and Maintenance cost methodologies are mutually agreed upon in order that levelized energy cost calculations will be consistent for each power plant. During the course of this effort, further potential advances in central receiver technology have continued to become apparent. These possible areas for improvement will be described. An additional comparison is being made between central receivers and trough-based systems. 8 refs., 2 figs.

A hierarchical control architecture for telerobotic vehicles intended to yield a modular, flexible, and easily expanded control system is presented. This architecture is proposed for applications where simple teleoperation is required but where additional capabilities might be quickly added without major changes to the control system. Similarities to the NASREM architecture are noted. Results are given from hardware implementation of the control system on a telerobotic vehicle, Raybot, at Sandia National Laboratories.

A systematic study is described which addresses the technical issues associated with launching flier-plates intact to hypervelocitites. First, very high pressures are needed to launch the flier plates to hypervelocitites, and second this high pressure loading must be uniform and nearly shockless. To achieve both these criteria, a graded-density material referred to as a pillow'' is used to impact a flier plate. When this graded-density material is used to impact a flier plate at high velocities on a two-stage light-gas gun, nearly shockless megabar pressure pulses are introduced into the flier plate. Since the loading on the flier plate is shockless, melting of the flier plate is prevented. This technique has been used to launch a 2-mm thick titanium alloy (Ti-6Al-4V) plate to a velocity of 8.1 km/s, and a 1-mm thick aluminum alloy (6061-T6) plate to a velocity of 10.4 km/s. A method is described by which the flier plate velocities could be further augmented to velocities approaching 14 km/s. 18 refs., 16 figs.

A new technique is reported for the rapid determination of interstitial oxygen (O{sub i}) in heavily doped n{sup +} and p{sup +} silicon. This technique includes application of a selective electrochemical thinning (SET) process and FTIR transmittance measurement on a limited area of a silicon wafer. The O{sub i} is calculated using ASTM F1188--88 with the IOC 88 calibration factor. An advantage of SET over mechanical thinning is that the original wafer thickness and diameter are maintained for additional processing. 1 tab.

The Shippable Storage Cask Demonstration Project is intended to demonstrate casks which can be used for both shipping and storing spent nuclear fuel assemblies. The demonstration included the requirement that the casks be certified for shipping by the US Nuclear Regulatory Commission (NRC). After a lengthy review process which resulted in the resolution of several important technical issues, designs for two similar casks have been certified. This paper describes the certification phase of the demonstration. Based on experience gained during certification phase of the demonstration. Based on experience gained during certification, observations and recommendations have been developed which can benefit others seeking NRC approval of transportation cask designs.

Reviews of normal breakdown and current induced avalanche breakdown mechanisms in silicon power transistors are presented. We show the applicability of the current induced avalanche model to heavy ion induced burnouts. Finally, we present solutions to current induced avalanche in silicon power semiconductors. 7 refs., 5 figs.

The electronic properties of heavily and orderly Si-doped nipi structures in GaAs are studied theoretically using the ab-initio self-consistent pseudopotential method within the local density approximation. Two nipi configurations are considered. Besides investigating the nature of the impurity-related band edge states, the xy-planar-averaged local ionic and self-consistent potentials are also analyzed. The screening effect of the host crystal on the doping induced potential is found to be small. The effects of the doping induced electric field and the strain due to dopings are also examined. 13 refs., 9 figs., 2 tabs.

The near field surrounding buried waste in the proposed high level nuclear waste repository in Yucca Mountain, Nye County, Nevada, is a region where strongly heat driven processes can exist. These strongly heat driven processes further complicate an already very difficult problem, i.e,. predicting groundwater flow and chemical transport through unsaturated fractured, heterogeneous porous media. The coupling between fluid flow and heat emanation is central to understanding these strongly heat driven processes. Although it is important that all of couplings be investigated, the intent of this paper is to discuss the mathematical models and associated computer codes that can be used in investigating the coupled heat emanation and fluid flow in unsaturated porous media. The information in this paper should be useful to those studying these phenomena, validating these models, or investigating the coupling of fluid flow and heat emanation with the other phenomena. The codes implementing these models are commonly referred to as nonisothermal two-phase flow codes. 5 refs., 4 tabs.

The United States Department of Energy (DOE) is developing the Waste Isolation Pilot Plant (WIPP), located in southeastern New Mexico, for disposal of transuranic wastes generated by defense programs. The DOE must first demonstrate compliance with the Environmental Protection Agency's (EPA) Environmental Standards for the Management and Disposal of Spent Nuclear Fuel, High-Level and Transuranic Radioactive Wastes hereafter called the Standard. The Containment Requirements in Subpart B of the Standard set limits on the probability that cumulative radionuclide releases to the accessible environment during the 10,000 years following decommissioning of the repository will exceed certain limits. To comply with these requirements, performance assessments must construct a modeling system that can adequately simulate all realistic future states of the repository that might result in radionuclide releases. Because the regulatory limits are probabilistic, performance assessments must accurately reflect variability and uncertainty within all factors that contribute to the simulation, including variability and uncertainty within all factors that contribute to the simulation, including variability in material properties, probabilities of future human actions, and uncertainties inherent in the conceptual and numerical models that simulate reality. This paper describes conceptual and numerical improvements in the performance assessment methodology made during 1990, and summarizes the present status of WIPP performance assessment. All results to date are preliminary, and cannot be used to determine compliance or non-compliance. The DOE anticipates determining compliance after evaluating a final performance assessment in 1994. 11 refs., 3 figs.

Low pressure (200 Torr) metalorganic chemical vapor deposition (MOCVD) of InSb has been examined through variation of the Column III (TMIn) and Column V (TMSb or TESb) precursor partial pressures. The use of lower growth pressure significantly enhanced the range of allowable Column III Column V partial pressures in which specular morphology InSb could be obtained without the formation of In droplets or Sb crystals. In addition, a 70% improvement in the average hole mobility was obtained, compared to InSb grown in the same reactor at atmospheric pressure. SIMS analysis revealed that Si at the substrate/epitaxial layer interface is an important impurity that may contribute to degradation of the mobility. Substitution of TESb for TMSb did not result in any improvement in the purity of the InSb. 6 refs.

The long length and relatively small cross sectional area of the robotic arms envisioned for use inside of the underground nuclear waste storage tanks will require the control of flexible structures. This will become an important problem in the characterization and remediation of these tanks. We are developing control strategies to actively damp residual vibrations in flexible robotic arms caused by high speed motion and abrupt external forces. A planar, two-link flexible arm is currently being used to test these control strategies. In this paper, two methods of control are discussed. The first is a minimum-time control approach which utilizes a finite element model and and optimization program. These tools plan the motor torque profiles necessary for the tip of the arm to move along a straight line, in minimum time, within the motors' torque constraints, and end in a quiescent state. To account for modeling errors in the finite element model, errors in joint angles, velocities, and link curvatures are added to the optimal torque trajectory. Linear quadratic Gaussian (LQG) regulatory design theory is used to determine the feedback gains. The second method of control is a teleoperated joystick controller which uses an input shaping technique to alter the commands of the joystick so as to reduce the residual vibration of the fundamental modes. Approximating the system as linear, the natural frequency and damping ratio are estimated on-line for the complete system, which includes the structure plus a lower level proportional derivative controller. An input shaping filter is determined from the estimated natural frequency, estimated damping ratio, and the desired transfer function of the system. 11 reps., 9 figs.

The concept of solar driven chemical reactions in a commercial-scale volumetric receiver/reactor on a parabolic concentrator was successfully demonstrated in the CAtalytically Enhanced Solar Absorption Receiver (CAESAR) test. Solar reforming of methane (CH{sub 4}) with carbon dioxide (CO{sub 2}) was achieved in a 64-cm diameter direct absorption reactor on a parabolic dish capable of 150 kW solar power. The reactor was a catalytic volumetric absorber consisting of a multi-layered, porous alumina foam disk coated with rhodium (Rh) catalyst. The system was operated during both steady-state and solar transient (cloud passage) conditions. The total solar power absorbed reached values up to 97 kW and the maximum methane conversion was 70%. Receiver thermal efficiencies ranged up to 85% and chemical efficiencies peaked at 54%. The absorber performed satisfactorily in promoting the reforming reaction during the tests without carbon formation. However, problems of cracking and degradation of the porous matrix, nonuniform dispersion of the Rh through the absorber, and catalyst deactivation due to sintering and possible encapsulation, must be resolved to achieve long-term operation and eventual commercialization. 17 refs., 11 figs., 1 tab.

We have performed MD simulations of adhesive phenomena, on an atomic scale, between metals possessing both smooth and stepped-surfaces. Studies of adhesion between identical metals, consisting of either Au, Cu, or Ni, with (001) or (111) orientations, reveal the existence of adhesive avalanches as the bodies are brought to within a critical separation ({approximately}2 {angstrom}). That is, as the surfaces approach one another, one or both surface layers becomes unstable, and abruptly moves toward the other. This signals a transition from an initial system with two distinct surfaces to one possessing no identifiable surfaces. The presence of adhesive avalanches will pose difficulties in determining adhesive forces and energies by means of atomic force microscopy at sub-nanometer separations of probe tip and sample surface. 7 refs., 3 figs.

An improved standard total-dose test method is described to qualify electronics for a low-dose radiation environment typical of space systems. The method consists of {sup 60}Co irradiation at a dose rate of 1--3 Gy(Si)/s (100--300 rad(Si)/s) and a subsequent 373 K (100{degree}C) bake. New initiatives in radiation hardness assurance are also briefly discussed, including the Qualified Manufacturers List (QML) test methodology and the possible use of 1/f noise measurements as a nondestructive screen for oxide-trap charge related failure. 8 refs.

A two-stage data compression technique that provides for exact, bit-for-bit recovery is described. The first stage is a modified form of conventional linear prediction which generates an error or residue sequence in such a way that exact reconstruction of the original data sequence can be accomplished with a simple recovery algorithm. The second stage is bi-level sequence coding. Even though the residue sequence from the first stage is essential white and Gaussian with seismic or other similar waveform data, bi-level sequence coding will generally provide further compression. The complete technique is described briefly in this summary, and examples of its performance are presented. A full paper on the algorithm is available from the author. 12 refs., 2 figs., 2 tabs.

We have synthesized a new tool, a lasing phase diagram, for designing high efficiency surface-emitting laser resonators and have demonstrated its usefulness by fabricating and operating many different laser resonators. 4 refs., 4 figs.

This paper is concerned with controlling the morphology of microporous polymers prepared via thermal demixing of solutions. 2 wt % solutions of poly(acrylonitrile) in maleic anhydride, a poor solvent, are first cooled to produce separated polymer-rich and solvent-rich phases. Removing the solvent by freeze drying then produces a microporous material having a density of 33 mg/cm{sup 3}, a void fraction of 97%, and a pore size of about 10 {mu}m. We find that the morphology cannot be explained by existing models, which focus on phase diagrams and kinetics of phase transformations during cooling of the solution. In conflict with those models, we find that two radically different morphologies can be produced even when the polymer concentration and cooling path are held strictly constant. A hypothesis that polymer degradation causes the different morphologies is not supported by GPC, {sup 13}C NMR, and FTIR experiments. Instead, we offer evidence that the different microporous morphologies are caused by different polymer conformations in solutions having the same concentration and temperature. 11 refs., 3 figs.

The nuclear industry uses sensitive or classified parts and material that must be protected and accounted for. We believe there is a need for an automated system that can help protect and inventory these parts and material. In response to this need Sandia National Laboratories Division 5245 is developing a personnel and material tracking system named PAMTRAK to safeguard sensitive parts and material at selected Department of Energy facilities. This paper describes the project's background, design goals and features.