A methodology for determining the probability spent-fuel cladding breach due to normal and accident class B cask transport conditions is introduced. This technique uses deterministic stress analysis results as well as probabilistic cladding material properties, initial flaws, and breach criteria. Best estimates are presented for the probability distributions of irradiated Zircaloy properties such as ductility and fracture toughness, and for fuel rod initial conditions such as manufacturing flaws and PCI part-wall cracks. Example analyses are used to illustrate the implementation of this methodology for a BWR (GE 7 {times} 7) and a PWR (B&W 15 {times} 15) assembly. The cladding breach probabilities for each assembly are tabulated for regulatory normal and accident transport conditions including fire.
Residual stress states that are a direct result of fabrication and processing are known to exist inside wound capacitors. Considerable insights into the nature of these mechanical and thermomechanical stress states have been gained through the application of analytical prediction capabilities that have been developed for that purpose. For example, analysis shows where roll slip may occur in the capacitor due to steep wound tension gradients or low radial pressures, and how the tension loss of individual plies is distributed throughout the capacitor. Significant tension loss differences between dielectric and conducting plies has also been predicted, with conducting plies not only losing their initial winding tension, but actually experiencing a net compressive value of wound tension. While the results of these predictions are both quantitative and qualitative, only qualitative verification has been obtained thus far, such as visual observation of wrinkled conducting plies discovered in unwrapped capacitors. The purpose of this paper is to describe two experimental activities that were undertaken to support the analytical modeling effort and provide quantitative, experimental verification of some of the analysis predictions.
The technical issues brought about by recent federal mandates are reviewed and discussed. Progress made in the elimination of CFCs is briefly reviewed. The problems, implications, and status of pending anti-lead legislation and taxation are discussed at length. Recommendations are made for the enactment of rational, fair, and orderly legislation and taxation.
This paper describes current research and development on a miniaturized sensing system for use during in situ characterization of nuclear waste storage tanks. Sandia is designing this sensing system as a tool for a large robotic arm that is deployed through an access port in the top of a storage tank. While the robot arm scans the sensing package over the waste, a distributed computing system acquires sensor data, correlates the data with the position of the robot, and produces maps of the chemical and radiological contents of the tanks in real time. We have built and demonstrated a first prototype system containing eight sensors. 53 refs.
Two revisions of the CONTAIN code, CONTAIN 1.11 and 1.12 , have recently been released. The purpose of this paper is to highlight the new features of these revisions and to discuss other new code features currently under development. The features of CONTAIN 1.11 discussed here include a quasi-mechanistic concrete outgassing model, the connected structure option for heat conduction between compartments, and a new approach for modeling forced convective heat transfer. The direct containment heating (DCH) models released as part of CONTAIN 1.12 are also discussed. New code features currently under development include a revised gas combustion model and a new multifield DCH model. New features of the revised combustion model include the treatment of spontaneous recombination and diffusion flames. CONTAIN plant calculations comparing the old and the revised combustion models are presented. The new features of the multifield DCH model are discussed, and demonstration calculations using this model to analyze a small scale experiment are presented.
A previous investigation of laser-induced damage mechanisms and corresponding thresholds in step-index, multimode fibers was motivated by an interest in optical systems for firing explosives. In the initial study, the output from a compact, multimode Nd/YAG laser was coupled into fiber cores of pure fused silica. End-face polishing steps were varied between successive fiber lots to produce improved finishes, and each fiber was subjected to a sequence of progressively increasing energy densities up to a value more than 80 J/cm{sup 2}. Essentially all of the tested fibers experienced a ``laser conditioning`` process at the front fiber face, in which a visible plasma was generated for one or more laser shots. Rather than produce progressive damage at the front surface, however, this process would eventually cease and leave the surface with improved damage resistance. Once past this conditioning process, the majority of fibers damaged at the rear end face. Other modes of damage were observed either at locations of fixturing stresses or at a location of high static tensile stress resulting from bends introduced to the fiber. The current experiments were conducted with a new laser having a shorter pulsewidth and a significantly different mode structure. The beam was injected into the fiber using a geometry that had been successful in the previous study in minimizing a damage mechanism which can occur at the core/cladding interface within the first few hundred fiber diameters. However, the different mode structure of the new laser apparently resulted in this mechanism dominating the current results.
The Department of Energy`s (DOE`s) Office of Civilian Radioactive Waste Management (OCRWM) is in the process of developing a new generation of casks to transport spent fuel from commercial nuclear reactor facilities to federal waste facilities. In evaluating the needs of the cask development program a number of unresolved technical issues with potential impacts on the transportation system were identified. This paper provides three samples of issues being addressed by the Cask Systems Development Program for technical resolution: (1) burn-up credit, (2) containment source term evaluation, and (3) weeping.
SMILE is a coaxial Self Magnetically Insulated Transmission Line voltage adder. It replaces the original beam line of the RADLAC II accelerator by a 12.5 m long cathode electrode. The anode electrode remains practically the same, consisting of the original eight insulating stacks or feeds which are connected with equal diameter stainless steel cylinders. The beam is produced at the end of the accelerator and is free of all the possible instabilities associated with accelerating gaps and magnetic vacuum transport. Annular beams with {beta}{perpendicular} {le} 0.1 and radius r{sub b} {le} 1 cm were routinely obtained and extracted from a small magnetically-immersed foilless electron diode. Results of the experimental evaluation are presented and compared with design parameters and numerical simulation predictions. 4 refs.
In this paper, measurements on the quasi-isentropic compression of tungsten to stress levels of 250 GPa are reported. Results of these experiments have been compared to those obtained under shock loading conditions to comparable stresses. These experiments have allowed the determination of temperature, pressure, and loading rate effects on the dynamic yield strength of tungsten up to 250 GPa. These results show that the dynamic yield strength of tungsten is dependent on the loading rate with the strength being higher for the relatively slower rates of loading along the quasi-isentropic. The pressure dependence of the yield strength of tungsten is determined nearly independent of temperature effects from quasi-isentropic loading experiments to 250 GPa, because the temperature rise in an quasi-loading experiment is much lower than those associated with shock loading experiments.
Continuum dynamics codes are categorized as Lagrangian or Eulerian according to the motion of the mesh. A Lagrangian code`s mesh moves with the material, so no mass flows between cells. An Eulerian code`s mesh is stationary, so mass flows between the cells. Eulerian codes have improved to the point where they are routinely used to solve a broad variety of large deformation solid and fluid dynamics problems ranging from air flow over an airplane wing to meteor impact on space structures. This presentation will concentrate on multi-fluid Eulerian codes capable of modeling transient were propagation in solids. These codes use a two-step process to integrate the physics across a time step. The first step, referred to as the Lagrangian step, integrates the physics on a Lagrangian mesh across the time step. The field values are then at the new time, but they are on the distorted Lagrangian mesh. The second step, referred to as the remap step, remaps the data on the distorted Lagrangian mesh back to the original Eulerian mesh thus completing one time step. The algorithms used in the first step are similar to those used in modern Lagrangian codes but they must be extended to handle multi-material cells. The algorithms used in the second step are complex and must be very carefully chosen to minimize errors. These algorithms include second-order, monotone advection equations to calculate the quantities flowing between cells. They also require algorithms that construct material interfaces inside multi-material cells. The strength and limitations of currently used numerical techniques will be discussed. New code development activities that combine the best features on both Lagrangian and Elueian codes will also be discussed. These new codes will employ the strengths of both technologies to address problems that cannot be adequately solved at this time.
The Hybrid Thin-Slot Algorithm (HTSA) integrates a transient integral-equation solution for an aperture in an infinite plane into a finite-difference time-domain (FDTD) code. The technique was introduced for linear apertures and was extended to include wall loss and lossy internal gaskets. A general implementation for arbitrary thin slots is briefly described here. The 3-D FDTD-code TSAR was selected for the implementation. The HTSA does not provide universal solutions to the narrow slot problem, but has merits appropriate for particular applications. The HTSA is restricted to planar slots, but can solve the important case that both the width and depth of the slot are narrow compared to the FDTD spatial cell. IN addition, the HTSA is not bound to the FDTD discrete spatial and time increments, and therefore, high-resolution solutions for the slot physics are possible. The implementation of the HTSA into TSAR is based upon a ``slot data file`` that includes the cell indices where the desired slots are exist within the FDTD mesh. For an HTSA-defined slot, the wall region local to the slot is shorted, and therefore, to change the slot`s topology simply requires altering the file to include the desired cells. 7 refs.
The one-electron energy levels of icosahedral boron clusters have been calculated as a function of intericosahedral spacing maintaining the intraicosahedral spacing of {alpha}-boron. For crystalline lattice constants greater than 1.25 times the equilibrium one, band overlap occurs with concomitant metallic behavior. At smaller lattice constants, orbitals(bands) associated with bonds to adjacent icosahedra are lowered and orbitals(bands) associated with ``antibonds`` are raised. Four bands which were three quarters full become empty, while three bands which were empty become filled. This leads to an energy gap between the filled states and the empty states which accounts for the experimentally observed insulating behavior of this elemental material with three valence electrons per atom.
Verifying the velocity accuracy of a GPS receiver or an integrated GPS/INS system in a dynamic environment is a difficult proposition when many of the commonly used reference systems have velocity uncertainities of the same order of magnitude or greater than the GPS system. The results of flight tests aboard an aircraft in which multiple reference systems simultaneously collected data to evaluate the accuracy of an integrated GPS/INS system are reported. Emphasis is placed on obtaining high accuracy estimates of the velocity error of the integrated system in order to verify that velocity accuracy is maintained during both linear and circular trajectories. Three different reference systems operating in parallel during flight tests are used to independently determine the position and velocity of an aircraft in flight. They are a transponder/interrogator ranging system, a laser tracker, and GPS carrier phase processing. Results obtained from these reference systems are compared against each other and against an integrated real time differential based GPS/INS system to arrive at a set of conclusions about the accuracy of the integrated system.
Computer-aided molecular design methods were used to tailor binding sites for small substrate molecules, including CO{sub 2} and methane. The goal is to design a cavity, adjacent to a catalytic metal center, into which the substrate will selectively bind through only non-bonding interactions with the groups lining the binding pocket. Porphyrins are used as a basic molecular structure, with various substituents added to construct the binding pocket. The conformations of these highly-substituted porphyrins are predicted using molecular mechanics calculations with a force field that gives accurate predictions for metalloporhyrins. Dynamics and energy-minimization calculations of substrate molecules bound to the cavity indicate high substrate binding affinity. The size, shape and charge-distribution of groups surrounding the cavity provide molecular selectivity. Specifically, calculated binding energies of methane, benzene, dichloromethane, CO{sub 2} and chloroform vary by about 10 kcal/mol for metal octaethyl-tetraphenylporphyrins (OETPPs) with chloroform, dichloromethane, and CO{sub 2} having the lowest. Significantly, a solvent molecule is found in the cavity in the X-ray structures of Co- and CuOETPP crystals obtained from dichloromethane. 5 refs., 3 figs., 3 tabs.
Single Event Upset Imaging utilizes the scanning of a micro-focused MeV ion beams across an integrated circuit to test the upset response of the circuit to energetic heavy ions. Using this technique, the position dependence of logic state upsets, as well as the charge collection efficiency of an integrated circuit, can be directly measured with micron resolution. We present in this paper a review of a series of measurements carried out on the TA670 16K static random access memory chip which display this technique`s capabilities.
Hot cracking, or solidification cracking, is one of the most extensively studied phenomenon in welding metallurgy. The efforts made to identify the causes of this type of cracking have been driven by the negative commercial and engineering consequences resulting from the formation of these defects. Through judicious weld joint design, the mechanical restraint can be minimized, but it can never be entirely eliminated simply because metals expand and contract when heated and cooled, respectively. The localized nature of heat input in fusion welding insures a non-homogeneous thermal field being applied to the parts being welded, resulting in the development of strains in the as-solidifying weld metal. With the inherent limitations on the mechanical restraint factor, much research has gone into identifying those alloy compositions which minimize the microstructural factor required for hot cracking to occur. Examples from the author`s own research are presented as a tutorial to show how differential thermal analysis techniques have been used to study the chemical/microstructural factors associated with solidification and fusion zone hot cracking in nickel based engineering alloys. References to other uses of these techniques in related welding metallurgy studies are also given.
Dislocation formation in InAs{sub 1-x}Sb{sub x} buffer layers grown by metal-organic chemical vapor deposition is shown to be reproducibly enhanced by p-type doping at levels greater than or equal to the intrinsic carrier concentration at the growth temperature. To achieve a carrier concentration greater than 2 {times} 10{sup 18} cm{sup {minus}3}, the intrinsic carrier concentration of InSb at 475 C, p-type doping with diethylzinc was used. Carrier concentrations up to 6 {times} 10{sup 18} cm{sup {minus}3} were obtained. The zinc doped buffer layers have proven to be reproducibly crack free for InAs{sub 1-x}Sb{sub x} step graded buffer layers with a final composition of x = 0.12 and a strained layer superlattice with an average composition of x = 0.09. These buffer layers have been used to prepare SLS infrared photodiodes. The details of the buffer layer growth, an explanation for the observed Fermi level effect and the growth and characterization of an infrared photodiode are discussed.
The use of coatings on carbon-carbon materials to reduce the oxidation of carbon is of interest for the production of non-ablative aerospace structures. The arc-jet ground test facility can produce the high energy oxidizing environment necessary to simulate hypersonic flight in which to test candidate coatings. The test conditions usually required are characterized by material temperature and length of time the material remains at that temperature. Material specimens were exposed to high energy supersonic air exhausting from the NASA-Ames Research Center`s 20-MW arc-jet facility. The carbon-carbon materials were heated to required temperatures with arc-heated air for specified lengths of time. This report describes the test methodology and observations of those tests.
We described a new family of versatile, cascadable, optical switches with different functional characteristics -- latching, non-latching, and bistable -- using a single epitaxial structure base don the monolithic integration of photothyristors and surface-emitting layers. High performance optical switching characteristics have been achieved for all three switch archetypes. We also demonstrate the AND, OR, NAND, NOR, and INVERT optical logic functions using monolithic switch structures. 7 refs.
A boundary integral equation method for steady unsaturated flow in nonhomogeneous porous media is presented. Steady unsaturated flow in porous media is described by the steady form of the so-called Richards equation, a highly nonlinear Fokker-Planck equation. By applying a Kirchhoff transformation and employing an exponential model for the relation between capillary pressure and hydraulic conductivity, the flow equation is rendered linear in each subdomain of a piece-wise homogeneous material. Unfortunately, the transformation results in nonlinear conditions along material interfaces, giving rise to a jump in the potential along these boundaries. An algorithm developed to solve the nonhomogeneous flow problem is described and verified by comparison to analytical and numerical solutions. The code is applied to examine the moisture distribution in a layered porous medium due to infiltration from a strip source, a model for infiltration from shallow ponds and washes in arid regions.
Structural system identification is undergoing a period of renewed interest. Probabilistic approaches to physical parameter identification in analysis finite element models make uncertainty in test results an important issue. In this paper, we investigate this issue with a simple, though in many ways representative, structural system. The results of two modal parameter identification techniques are compared and uncertainty estimates, both through bias and random errors, are quantified. The importance of the interaction between test and analysis is also highlighted. 25 refs.
Pre-exposure induced stress corrosion cracking (SCC) of an Al-Li-Cu, AA 2090, was studied using a variety of test techniques. Results from SCC testing in a simulated isolated pit solution are correlated with electrochemical corrosion rate data obtained for individual phases in the subgrain boundary region. These experimental data, combined with existing data on the crevice chemistry of isolated pits in Al-Li alloys and X-ray diffraction studies of solid corrosion products formed in crevice environments are used to propose a model for pre-exposure induced cracking based on anodic dissolution along subgrain boundaries. Key features of the model are selective dissolution of the subgrain boundary T{sub 1} phase (Al{sub 2}CuLi) at the crack tip and passivation of crack walls by the formation of an Li{sub 2}[Al{sub 2}(OH){sub 6}]{sub 2}{center_dot}CO{sub 3}{center_dot}nH{sub 2}O barrier film.
The transportation risk evaluation code RADTRAN 4 is designed to evaluate doses and risks associated with the transportation of radioactive materials (Ne92). RADTRAN 4 may be used to calculate dose consequences for incident-free transportation and dose risks for accidents. Consequences of normal (or incident-free) transportation include doses to crew members, persons at stops, and members of the public sharing a route segment (on-link) and residing near the segment (off-link) during normal transportation. These dose estimates are not multiplied by a probability factor and, hence, are referred to as dose consequences. Calculated doses that might be incurred during accidents are multiplied by the probabilities of those accidents, and hence are referred to as dose risks. RADTRAN 4 includes a LINK option that allows the user to characterize each link or segment of a transportation route in greater detail than that provided by average or default values for route-related parameters.