273 Matching Results

Search Results

Advanced search parameters have been applied.

Calculation note: hydrogen generation rates at steady-stateflammable gas concentrations for single-shell tanks

Description: This calculation note analyzes headspace concentrations of hydrogen in single shell tanks dependent upon assumed ventilation flow rates provided by the waste tank ventilation system operation or calculated from Standard Hydrogen Monitoring System data. The analyses are based on measured or estimated steady-state hydrogen release rates. Specific analyses include: 1) The hydrogen generation rate at steady- state hydrogen concentrations and 2)The headspace hydrogen concentration as a function of time, as well as the time required to reach 25% and 100% of the Lower Flammability Limit with barometric breathing in the tank.
Date: June 25, 1997
Creator: Stauffer, L.A.
Partner: UNT Libraries Government Documents Department


Description: The ''Drift Shadow'' is defined as the relatively drier region that forms below subsurface cavities or drifts in unsaturated rock. Its existence has been predicted through analytical and numerical models of unsaturated flow. However, these theoretical predictions have not been demonstrated empirically to date. In this project they plan to test the drift shadow concept through field investigations and compare our observations to simulations. Based on modeling studies they have an identified suitable site to perform the study at an inactive mine in a sandstone formation. Pretest modeling studies and preliminary characterization of the site are being used to develop the field scale tests.
Date: January 15, 2006
Creator: G. W. Su, T. J. Kneafsey, T. A. Ghezzehei, B. D. Marshall, and P. J. Cook
Partner: UNT Libraries Government Documents Department

Solids Fraction Measurement with a Reflective Fiber Optic Probe

Description: A method has been developed to extract solids fraction information from a reflective fiber optic probe. The commercially available reflective fiber optic probe was designed to measure axial particle velocity (both up and down directions). However, the reflected light intensity measured is related to particle size and particle concentration. A light reflection model is used to relate the reflected light intensity to solids fraction. In this model we assume that the reflected light intensity is a fixed fraction, K1, of the total light intensity lost in penetration of a solid layer. Also, the solids fraction is related to particle concentration, N, in the light path, by N = K2 (1- ε), where (1-ε) is the solids fraction. The parameters K1 and K2 are determined through a calibration and curve fitting procedure. This paper describes this procedure and the steps taken to derive the values of K1 and K2. It is proposed that the reflective fiber optic can be used for real time measurement of solids fraction in a circulating fluid bed.
Date: November 1, 2006
Creator: Seachman, S.M.; Yue, P.C.; Ludlow, J.C. & Shadle, L.J.
Partner: UNT Libraries Government Documents Department

Ion and Neutral Species in C(2)F(6) and CHF(3) Dielectric Etch Discharges

Description: Relative concentrations of reactive ions, neutral radicals, resist and substrate etch products have been measured in dielectric etch chemistries using an uncollided beam mass spectrometer / ion extractor from Hiden Analytical. Analysis techniques employed include both electron impact ionization and dissociative ionization of neutral gas, and potential bias extraction of positive ions from the reactor discharge volume. Measurements were made in C{sub 2}F{sub 6} and CHF{sub 3} discharges in an inductively coupled plasma (ICP-GEC) research reactor operating with power densities, pressures, gas compositions and wafer materials typical of those found in etch processing tools. Wafer substrates investigated included blanket silicon wafers and silicon wafers with varying amounts of photo-resist coverage of the surface (20%, 80% and 100%). In C{sub 2}F{sub 6} discharges CF{sub 3}{sup +} was consistently the dominant fluorocarbon ion present, in agreement with published cross sections for dissociative ionization [ 1,2.3,4.5,6]. Smaller concentrations of CF+, CF{sub 2}{sup -}, and C{sub 2}F{sub 5}{sup +}, were also observed, though the dissociative ionization production of C{sub 2}F{sub 5}{sup +} was a factor of five smaller than would be expected from published cross section values. The presence of photo-resist, even in small amounts, was found to produce marked changes in the discharge composition. For example in C{sub 2}F{sub 6} discharges, concentrations of SiF{sub x} etch products relative to concentrations of C{sub x}F{sub y} species were notably diminished and larger concentrations of water vapor were observed when resist was present. In CHF{sub 3} discharges, CF{sub 3}{sup +} and CHF{sub 2}{sup +} were found to be the main species present, along with smaller concentrations of CF{sub 2}{sup +}, CF{sup +}, CHF{sup +}, CH{sup +} and F{sup -}.
Date: January 26, 1999
Creator: Hebner, G.; Jayaraman, R.P. & McGrath, R.T.
Partner: UNT Libraries Government Documents Department

Status and Directions in Electroseparations

Description: In this presentation, a summary of research conducted in the area of electroseparations at the Chemical Technology Division of Oak Ridge National Laboratory is presented. Fields-driven processes, including (1) phase equilibria modification by electric fields and (2) magnetically seeded separations, as well as transport-enhancement processes by electric fields,including (1) surface area generation and (2) electroconvection, are discussed.It is shown that electric fields can change the concentration of the vapor phase during the distillation of a binary mixture, which may have applications in separations by distillation that consume significant amounts of energy. It is also shown that addition of colloidal seed particles of high magnetic susceptibility to a suspension of non-magnetic particles and subsequent flocculation between seed and non-magnetic particles form paramagnetic flocs that can be removed by high- gradient magnetic filtration. Inverse electrostatic spraying, which is the spraying of a non-conductive fluid (such as air) into a conductive fluid (such as water), is introduced and compared with normal electrostatic spraying, which is the spraying of conductive fluid into a non-conductive fluid. Applications of normal electrostatic spraying, including the development of a bioreactor for oil desulfurization, and inverse electrostatic spraying, including ozonation of an aqueous system, are discussed. It is also shown that electroconvection, caused by electric fields,may result in simultaneous pumping, spraying, and mixing of fluids. In summary,new phenomena caused by electric fields are introduced and their potential applications in electroseparations are discussed.
Date: December 31, 1997
Creator: Tsouris, Costas
Partner: UNT Libraries Government Documents Department

Concentration increases in the isotopic germanium carrier solutions inferred from solution weights

Description: Concentration increases in the isotopic germanium carrier solutions via evaporation would produce weight losses in the carrier solutions. Since the bottle containing each carrier is usually weighed before and after the removal of carrier for a given run, the possibility exists of finding evidence for increasing carrier concentration in this record. With few exceptions the weighings were performed on the same top-loading balance in the external chemistry lab. The primary purpose was to monitor carrier usage, not to look for evidence for increasing carrier concentration. However, in order to look for this evidence, it is necessary only to compare the weights of the closed bottles between the times of carrier removal. This comparison has been performed and is reported here. Bear in mind that there is some evidence that the bottle containing carrier was not always weighted in the same way (e.g. perhaps a plastic bag was not removed from the bottle or the bottle cap was removed before weighing). Another possible source of weighing errors is the occasional buildup of static charges, especially on dry winter days. Such problems of static electricity were easily recognized and overcome. For the most part, the resulting record agrees with the assumption that the weighings were performed consistently. Carrier solution data were analyzed and a correction factor was calculated.
Date: July 1, 1997
Creator: Rowley, J.K.
Partner: UNT Libraries Government Documents Department

The US/UK Actinides Experiment at the Dounreay PFR

Description: The United States and the United Kingdom have been engaged in a joint research program in which samples of higher actinides were irradiated in the 600-MW Dounreay Prototype Fast Reactor in Scotland. Analytical results using mass spectrometry and radiometry for actinides and fission products are now available for the samples in Fuel Pins 1 and 2, which were irradiated for 63 full-power days, and for the samples in Fuel Pin 4, which were irradiated for 492 full-power days. Results from these three fuel pins are providing estimates of integral cross sections and fission yields.
Date: November 1, 1997
Creator: Raman, S., Walker, R.L., Dickens, J.K., Murphy, B.D.
Partner: UNT Libraries Government Documents Department

In-line ultrasonic monitoring of waste slurry suspended solids

Description: During the transport of tank waste, it is very important to quantitatively measure the percent solids concentration (PSC) of the waste, which indicates the flow conditions and the extent of solids settling. At Argonne National Laboratory, an in-line, real-time, a nonintrusive ultrasonic monitoring system has been developed to measure the PSC and flow density of tank waste by measuring sound velocity and attenuation in the flow. This system consists of a pair of longitudinal transducers bonded to waveguides on the opposite sides of the pipe and operating at IMHz simultaneously in pulse-and-echo and pitch-and-catch modes. The PSC measurement is provided by attenuation, while the density measurement is calculated by impedance and sound velocity. A thermocouple is attached to one of the waveguides for automatic temperature correction of the measurements. This system was one of four evaluated for in-line measurement of slurry at Oak Ridge National Laboratory in 1998. The results indicate that the measurements are in good agreement with a Coriolis meter and that the system can be used to monitor PSC up to 40 wt.%. However, the system is greatly affected by entrained air bubbles within the solid flow during Puisair mixing. A different mixing mechanism will solve this problem.
Date: May 25, 2000
Creator: Chien, H.-T.; Sheen, S.-H. & Raptis, A. C.
Partner: UNT Libraries Government Documents Department

Rheology Control of Highly Concentrated Mullite Suspensions with Polyelectrolyte for Robocasting

Description: Highly concentrated, aqueous mullite slurries were characterized and stabilized at solids concentrations as high as 60 vol% using less than 2 vol% of an organic polyelectrolyte dispersant. The maximum slurry concentration (60 vol%) is within 3 vol% of the maximum consolidated density of the slurry. The slurries were subsequently cast into parts by a solid freeform fabrication technique termed robocasting and characterized. Sedimentation analysis and viscometry provided the means of slurry characterization, while knowledge of polyelectrolyte and interparticle forces was used to interpret the sedimentation and viscometry data. Through proper control of slurry conditions, pseudoplastic mullite slurries were fabricated for use in the robocasting process. The slurries were robocast at 52 vol% solids and subsequently yielded a green density of 55 vol%. Fired densities of the robocasted slurries were high, with mullite >96% dense at 1,650 C.
Date: June 12, 2000
Partner: UNT Libraries Government Documents Department

The effects of pressure, temperature and concentration on the reactivity of alkanes; experiments and modeling in a rapid compression machine

Description: Experiments in a rapid compression machine have examined the influences of variations in pressure, temperature, and equivalence ratio on the autoignition of n-pentane. Equivalence ratios included values from 0.5 to � 2.0, compressed gas initial temperatures were varied between 675K and 980K, and compresed gas initial pressures varied from 8 to 20 bar. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism. The results are interpreted in terms of a low temperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Idealized calculations are reported which identify the major reaction paths at each temperature. Results indicate that in most cases, the reactive gases experience a two-stage autoigni tion. The first stage follows a low temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. Results also show that in some cases, the first stage ignition takes place during the compression stroke in the rapid compression machine, making the interpretation of the experiments somewhat more complex than generally assumed. At the highest compression temperatures achieved, little or no first stage ignition is observed.
Date: January 8, 1998
Creator: Curran, H J; Griffiths, J F; Mohamed, C; Pitz, W J; Westbrook, C & Wo, S K
Partner: UNT Libraries Government Documents Department

Gradient-driven diffusion using dual control volume grand canonical molecular dynamics

Description: The dual control volume grand canonical molecular dynamics (DCV-GCMD) method, designed to enable the dynamic simulation of a system with a steady state chemical potential gradient is first briefly reviewed. A new, novel implementation of the method which enables the establishment of a steady state chemical potential gradient in a multicomponent system without having to insert or delete one of the components is then presented and discussed.
Date: June 14, 1998
Creator: Thompson, A.M.; Ford, D.M. & Heffelfinger, G.S.
Partner: UNT Libraries Government Documents Department

Semi-Discrete Systems and Intracellular Calcium Dynamics

Description: Intracellular calcium is sequestered in closed membranes such as the sarcoplasmic or endoplasmic reticula and released at discretely distributed protein/receptor channels. The release kinetics can result in the propagation of waves of elevated calcium concentration. The main physical processes are reactions at the release sites and diffusion between the sites. The theory of chemical wave propagation in reaction-diffusion systems is in large part devoted to the study of systems in which there are no extrinsic inhomogeneities. The discrete distribution of the release sites plays a key role in determining the nature of the propagating wave. The authors analyze some simple reaction-diffusion models in order to elucidate the role of discreteness for chemical wave propagation.
Date: October 24, 1998
Creator: Pearson, J.; Dawson, S.P. & Mitkov, I.
Partner: UNT Libraries Government Documents Department

Overview of D-T results from TFTR

Description: Experiments with plasmas having nearly equal concentrations of deuterium and tritium have been carried out on TFTR. To date, the maximum fusion power has been 10.7 MW, using 39.5 MW of neutral-beam heating, in a supershot discharge and 6.7 MW in a high-{beta}{sub p} discharge following a current ramp-down. The fusion power density in the core of the plasma has reached 2.8 MWm{sup {minus}3}, exceeding that expected in the International Thermonuclear Experimental Reactor (ITTER). The energy confinement time, {tau}{sub E}, is observed to increase in D-T, relative to D plasmas, by 20% and the n{sub i}(O){center_dot}{tau}{sub E} product by 55%. The improvement in thermal confinement is caused primarily by a decrease in ion heat conductivity in both supershot and limiter-H-mode discharges. Extensive lithium pellet injection increased the confinement time to 0.27 s and enabled higher current operation in both supershot and high-{beta}{sub p} discharges. First measurements of the confined alpha particles have been performed and found to be in good agreement with TRANSP simulations assuming classical confinement. Measurements of the alpha ash profile have been compared with simulations using particle transport coefficients from helium gas puffing experiments. The loss of energetic alpha particles to a detector at the bottom of the vessel is well described by the first-orbit loss mechanism. No loss due to alpha-particle-driven instabilities has yet been observed. ICRF heating of a D-T plasma, using the second harmonic of tritium, has been demonstrated. D-T experiments on TFTR will continue both to explore the physics underlying the ITER design and to examine some of the physics issues associated with an advanced tokamak reactor.
Date: October 1, 1995
Creator: Bell, M.G.; McGuire, K.M. & Arunasalam, V.
Partner: UNT Libraries Government Documents Department


Description: Synchrotron X-ray microtomography shows vesicular structures for toluene/cement mixtures, prepared with 1.22 to 3.58 wt% toluene. Three-dimensional imaging of the cured samples shows spherical vesicles, with diameters ranging from 20 to 250 {micro}m; a search with EPMA for vesicles in the range of 1-20 {micro}m proved negative. However, the total vesicle volume, as computed from the microtomography images, accounts for less than 10% of initial toluene. Since the cements were cured in sealed bottles, the larger portion of toluene must be dispersed within the cement matrix. Evidence for toluene in the cement matrix comes from {sup 29}Si MAS NMR spectroscopy, which shows a reduction in chain silicates with added toluene. Also, {sup 2}H NMR of d{sub 8}-toluene/cement samples shows high mobility for all, toluene and thus no toluene/cement binding. A model that accounts for all observations follows: For loadings below about 3 wt%, most toluene is dispersed in the cement matrix, with a small fraction of the initial toluene phase separating from the cement paste and forming vesicular structures that are preserved in the cured cement. Furthermore, at loadings above 3 wt%, the abundance of vesicles formed during toluene/cement paste mixing leads to macroscopic phase separation (most toluene floats to the surface of the cement paste).
Date: July 22, 1999
Creator: BUTLER,L.G.
Partner: UNT Libraries Government Documents Department

Analytical requirements of the 234-5 Project

Description: At this time it is desirable that preliminary estimates be made of the manpower, equipment, space, layout and facility requirements of the analytical section for the 234-5 Project. To arrive at these requirements a rough estimate of the required analyses, their scope and their frequency has been compiled. This is expected to serve as a basis for the Laboratories Division to outline their space and equipment requirements as soon as possible and to assemble the required personnel for operation later. Crucial elements encountered in the process are classed as light impurities or as metallurgical impurities. The light elements are undesirable due to the {alpha}, n reaction with plutonium. The metallurgical impurities are undesirable since they change the physical properties of plutonium. The light elements undesirable in the finished product and the approximate tolerances (in ppM of plutonium) acceptable for each are listed assuming all other elements listed are absent. A list of the undesirable metallurgical impurities with the tolerances (again expressed in ppM of plutonium) for each element, assuming the other elements are absent are given.
Date: October 23, 1947
Creator: Work, J.B.
Partner: UNT Libraries Government Documents Department

Neutralization of Plutonium and Enriched Uranium Solutions Containing Gadolinium as a Neutron Poison

Description: Materials currently being dissolved in the HB-Line Facility will result in an accumulated solution containing an estimated uranium:plutonium (U:Pu) ratio of 4.3:1 and an 235U enrichment estimated at 30 per cent The U:Pu ratio and the enrichment are outside the evaluated concentration range for disposition to high level waste (HLW) using gadolinium (Gd) as a neutron poison. To confirm that the solution generated during the current HB-Line dissolving campaign can be poisoned with Gd, neutralized and discarded to the Savannah River Site (SRS) high level waste (HLW) system without undue nuclear safety concerns the caustic precipitation of surrogate solutions was examined. Experiments were performed with a U/Pu/Gd solution representative of the HB-Line estimated concentration ratio and also a U/Gd solution. Depleted U was used in the experiments as the enrichment of the U will not affect the chemical behavior during neutralization, but will affect the amount of Gd added to the solution. Settling behavior of the neutralized solutions was found to be comparable to previous studies. The neutralized solutions mixed easily and had expected densities of typical neutralized waste. The neutralized solids were found to be homogeneous and less than 20 microns in size. Partially neutralized solids were more amorphous than the fully neutralized solids. Based on the results of these experiments, Gd was found to be a viable poison for neutralizing a U/Pu/Gd solution with a U:Pu mass ratio of 4.3:1 thus extending the U:Pu mass ratio from the previously investigated 0-3:1 to 4.3:1. However, further work is needed to allow higher U concentrations or U:Pu ratios greater than investigated in this work.
Date: April 1, 2004
Partner: UNT Libraries Government Documents Department

Diagnostic evaluation of power fade phenomena and calendar lifereduction in high-power lithium-ion batteries

Description: High-power Li-ion cells with graphite anodes and LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathodes that were cycled and stored at elevated temperatures showed a significant impedance rise and capacity fade, which were associated primarily with the LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2} cathode. A combination of electrochemical, physical, and chemical diagnostic techniques, including Raman, SEM, and current-sensing AFM, was used to characterize the cathodes from these cells in order to produce a clear picture of the mechanism for cell degradation. Systematic Raman mapping of 50 x 80 {mu}m areas at 0.9 {mu}m spatial resolution produced semi-quantitative composition maps of cathode surfaces. Raman microscopy surface composition maps and SEM images of cathodes from tested cells revealed that cell cycling or storage at elevated temperatures led to significant changes in the LiNi{sub 0.8}Co{sub 0.15}Al{sub 0.05}O{sub 2}/elemental-carbon surface concentration ratio. The loss of conductive carbon correlated with the power and capacity fade of the tested cathodes and the loss of surface electronic conductivity.
Date: May 1, 2004
Creator: Kostecki, Robert & McLarnon, Frank
Partner: UNT Libraries Government Documents Department