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Langevin equation model of dispersion in the convective boundary layer

Description: This dissertation presents the development and evaluation of a Lagrangian stochastic model of vertical dispersion of trace material in the convective boundary layer (CBL). This model is based on a Langevin equation of motion for a fluid particle, and assumes the fluid vertical velocity probability distribution is skewed and spatially homogeneous. This approach can account for the effect of large-scale, long-lived turbulent structures and skewed vertical velocity distributions found in the CBL. The form of the Langevin equation used has a linear (in velocity) deterministic acceleration and a skewed randomacceleration. For the case of homogeneous fluid velocity statistics, this ""linear-skewed" Langevin equation can be integrated explicitly, resulting in a relatively efficient numerical simulation method. It is shown that this approach is more efficient than an alternative using a "nonlinear-Gaussian" Langevin equation (with a nonlinear deterministic acceleration and a Gaussian random acceleration) assuming homogeneous turbulence, and much more efficient than alternative approaches using Langevin equation models assuming inhomogeneous turbulence. "Reflection" boundary conditions for selecting a new velocity for a particle that encounters a boundary at the top or bottom of the CBL were investigated. These include one method using the standard assumption that the magnitudes of the particle incident and reflected velocities are positively correlated, and two alternatives in which the magnitudes of these velocities are negatively correlated and uncorrelated. The constraint that spatial and velocity distributions of a well-mixed tracer must be the same as those of the fluid, was used to develop the Langevin equation models and the reflection boundary conditions. The two Langevin equation models and three reflection methods were successfully tested using cases for which exact, analytic statistical properties of particle velocity and position are known, including well-mixed spatial and velocity distributions. Simulations of laboratory experiments of CBL dispersion show that both homogeneous Langevin equation models can ...
Date: August 1, 1998
Creator: Nasstrom, J S
Partner: UNT Libraries Government Documents Department


Description: >The creep and stress-rupture propenties of annealed and of 15% cold- worked Zircaloy-2 are being determined at of a AgBr fuel-element leak detector for use in watercooled reactors. The development of a thermal-neutronflux monitoring system was directed toward extending the sensing-probe life, increasing the effective instrument range, and improving the instrument reliability. Resistivity of Al/sub 2/O/sub 3/-MoSi/sub 2/-UO/sub 2/ ceramic tubes was determined to investigate the effects of MoSi/sub 2/ propontion and of extrusion pressure. In the development of corrosion-resistant welding alloys for use with Hastelloy F, a number of alloys are being exposed in boiling Sulfex and Niflex solutions to determine corrosion resistance of these liquids. Corrosion tests in 200-C water for 30 days have shown that the Al--35 wt.% U alloys containing Sn or Zr additives are equivalent to the binary Al--35 wt.% U and superior to 2S Al in their resistance to the corrosion attack of 200 deg C water. Work was continued on the development of a radiometric titration method of determining Al and Fe in portland cement. The investigation of the formation and decay of radiation-induced free radicals was continued. The effect of radiation on the nitration of cyclohexane was stadied over the range of 15 to 70 wt.% HNO/ sub 3/ with a 10-to-1 ratio of organic to acid. An investlgation is being conducted on the effects of combined high pressure and temperature on the uranium oxides and on the reactions of uranium oxides with other oxide systems. An irradiation surveillance program on AISI Type 347 stainless steel is continuing. The alloys which are being investigated as alternate cladding materials for the EBR include Nb, Nb-1.84 wt.% Cr, Hb--3.21 wt.% Cr, Nb--4.33 wt.% Zr. Nb--9.95 wt.% Ta--3.31 wt.% Cr, Nb--39.8 wt.% Ti--10.6 wt.% Al, Nb--20.5 wt.% Ti--4.28 wt.% Cr, and V--11.7 wt.% Ti--3.07 wt.% ...
Date: January 1, 1960
Creator: Dayton, R.W. & Tipton, C.R. Jr.
Partner: UNT Libraries Government Documents Department

Study of Dispersant Agents for Thorium Oxide

Description: S>A preliminary study of dispersing agents for thorium oxide was completed and several of the dispersants have possible uses. Also many of the industrial dispersing agents tested are not usable with thorium oxide due to induced behavior causing balling and caking. The effects of nitric acid concentration were observed to also effect each dispersing agent. (auth)
Date: August 1, 1959
Creator: Bate, L. C. & Leddicotte, G. W.
Partner: UNT Libraries Government Documents Department

Nanometer-scale metal dispersions in polymeric matrices

Description: Rutherford backscattering spectrometry was used to measure the depth distribution of gold nanoparticles within thin layers of poly(t-butyl acrylate)(PTBA). The gold nanoparticles were created by evaporation of a discontinuous gold layer onto a thin film of PTBA. A second PTBA film was placed onto these samples to create ``sandwiches`` in which the gold existed between two PTBA films. Gold particle diffusion coefficients were measured from gold particle depth distributions in annealed samples for which the molecular weights of the two PTBA layers were identical. The experiments revealed that particle mobility was decreased by 2 to 3 orders of magnitude compared with predictions of the Stokes-Einstein model of particle diffusion. This is attributed to bridging interactions between particles arising from slow exchange kinetics of polymer segments at the polymer/metal interface. Experiments for which the molecular weights of the two polymer films are different, are sensitive to the ability of polymer molecules to pass through the gold particle layer. Experiments done with thermally evaporated particles are consistent with a picture in which polymer molecules are able to freely pass through the gold particle layer. Results with gold deposited by electron-beam evaporation are different: the gold is not able to diffuse and polymer molecules not able to penetrate the gold layer. These results, combined with optical absorption experiments, indicate that much smaller particles are obtained by electron-beam evaporation than by thermal evaporation.
Date: January 1, 1997
Creator: Shull, K.R.; Cole, D.H.; Rehn, L.E. & Baldo, P.M.
Partner: UNT Libraries Government Documents Department

Dependance of TWRS FSAR X/Qs on distance and example doses at Highway 240 with stationary and moving receptors

Description: A discussion of the reasons for the dependance of X/Q on receptor distance and compass sector is presented. In addition, X/Qs are calculated for three receptor scenarios on Highway 240 including a moving receptor. Example radiological doses and toxicological exposures at Highway 240 are calculated for two accidents already analyzed in the TWRS FSAR.
Date: September 23, 1996
Creator: Himes, D.A.
Partner: UNT Libraries Government Documents Department

A model for simulating airflow and pollutant dispersion around buildings

Description: A three-dimensional, numerical mode1 for simulating airflow and pollutant dispersion around buildings is described. The model is based on an innovative finite element approach and fully implicit time integration techniques. Linear and nonlinear eddy viscosity/diffusivity submodels are provided for turbulence parameterization. Mode1 predictions for the flow-field and dispersion patterns around a surface-mounted cube are compared with measured data from laboratory experiments.
Date: February 24, 1999
Creator: Chan, S T & Lee, R L
Partner: UNT Libraries Government Documents Department

ARAC dispersion modeling of the August 1998 Tracy, California tire fire

Description: At about 4:30 pm PDT on Friday, August 7, 1998 a fire ignited the large tire disposal pit of Royster Tire Co. on Macarthur Drive about 5 km (3 miles) south of downtown Tracy, California. While providing on-scene mutual aid late Friday night, the LLNL Fire Department called and requested that the Atmospheric Release Advisory Capability (ARAC) make a plume forecast for Saturday. The response team in the field was interested in the forecasted location as well as an estimate of potential health effects on the following day. Not having any previous experience with tire fire source terms, ARAC assessors used a constant unit source rate (1 g/s) of particulate and produced plots showing only the location of the ground-level normalized time-integrated air concentrations from the smoke plume. Very early Saturday morning the assessors faxed plots of ground-level smoke air concentrations forecasted for Saturday from 6 am through 6 pm PDT to the Tracy Fire Emergency Operations Center. (As a part of standard procedure, before delivering the plots, the assessors notified ARAC's DOE sponsor.) Fortunately due to the intense heat from the fire, the dense black smoke immediately lofted into the air preventing high ground-level concentrations close to the tire dump. Later on Saturday morning ARAC forecasted a second set of plume integrated air concentrations for Sunday. By Monday the intensity of the fire lessened, and ARAC's support was no longer requested. Following ARAC's response, we made a third calculation on a large scale of the continuous smoke dispersion for 3 days after the fire. A newspaper photograph showed the plume initially rising toward the northeast and the upper part of the smoke cloud turning counterclockwise toward the north. Winds from ARAC's mesoscale prognostic model reproduced this plume structure, while data from the Friday afternoon sounding from Oakland did not. ...
Date: August 28, 1998
Creator: Aluzzi, F J; Baskett, R L; Bowen, B M; Foster, C S; Pace, J C; Pobanz, B et al.
Partner: UNT Libraries Government Documents Department


Description: An evaluation of the efficiency of a sprinkler system as an airborne fission product containment mechanism Is presented. The primary inadequacies and objections to such a system are outlined and data on droplet efficiencies are included. (J.R.D.)
Date: January 12, 1960
Creator: Wegmann, G.L.
Partner: UNT Libraries Government Documents Department


Description: The integrity and suitability of 35 vol.% U/sub 3/ O/sub 8/ dispersion in Al as a fuel for foreign reactors were determined. The fuel was exposed in the beryllium reflector of the MTR. Sample fabrication and conditions of exposurne are described, and the results are tabulated. (J.R.D.)
Date: October 18, 1958
Creator: Leitten, C.F. & Kucera, W.J.
Partner: UNT Libraries Government Documents Department


Description: The interpretation of the dimensional instability of U- Zr alloy containing small amounts of boron has raised the question of whether the observed low-temperature swelling can be related to the temperatureswelling characteristics of either the U-Zr alloy or Zr- B alloys by themselves. To obtain such information on the Zr--B system to compare with the more detailed study of thc alloy early results of which were reported in KAPL-1562, pieces of previously irradiated Zr- B alloys and dispersions were annealed in vacuum at temperatures between 350 and 750 C. (auth)
Date: May 12, 1958
Creator: Johnston, W.V. & Noonan, J.E.
Partner: UNT Libraries Government Documents Department

Recoil Range of Fission Fragments in Zirconium

Description: The recoil ranges of fission fragruents in zirconium were measured by irradiating small pieces of a Zircaloy-2 ribbon containing 492 ppm of homogeneously dispersed U/sup 235/. The samples were wrapped in aluminum foil during the irradiation to catch the fission fragments escaping from the surface of the Zircaloy-2. Average values of 10.1 and 8.15 microns were obtained for the recoil ranges of the median light and heavy fission fragments, respectively; these values compare quite well with values calculated from empirical equations. (auth)
Date: November 1, 1959
Creator: Smith, E. R. & Frank, P. W.
Partner: UNT Libraries Government Documents Department