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Minimum Critical Values Study

Description: This report provides minimum critical values for various 30-cm water-reflected uranium and plutonium oxide and nitrate aqueous mixtures as calculated by the SCALE CSAS1X sequence using the 238-group ENDF/B-V neutron cross-section library. The minimum values were determined through parametric searches in one-dimensional geometry. The calculations have been performed to obtain the minimum values: critical volume and mass for spheres, critical radius for cylinders, critical thickness for slabs, and minimum critical concentration (infinite geometry) for the following homogeneous mixtures: (1) UO{sub 2}-H{sub 2}O for 3, 4, 5, 20, and 100 wt % {sup 235}U; (2) UNH for 3, 4, 5, 20, and 100 wt % {sup 235}U; (3) PuO{sub 2}-H{sub 2}O for 100/0/0, 95/5/0, 90/5/5, 80/10/10, and 71/17/11/1 wt % of {sup 239}Pu/{sup 240}Pu/{sup 241}Pu(/{sup 242}Pu); and (4) PuNH for 100/0/0, 95/5/0, 90/5/5, 80/10/10, and 71/17/11/1 wt % of {sup 239}Pu/{sup 240}Pu/{sup 241}Pu(/{sup 242}Pu). All bounding surfaces were fully reflected by 30 cm of H{sub 2}O.
Date: July 11, 2005
Creator: Fox, P.B.
Partner: UNT Libraries Government Documents Department

Experimental investigation of the Richtmyer-Meshkov instability.

Description: The Richtmyer-Meshkov instability (RMI) is experimentally investigated using several different initial conditions and with a range of diagnostics. First, a broadband initial condition is created using a shear layer between helium+acetone and argon. The post-shocked turbulent mixing is investigated using planar laser induced fluorescence (PLIF). The signature of turbulent mixing is present in the appearance of an inertial range in the mole fraction energy spectrum and the isotropy of the late-time dissipation structures. The distribution of the mole fraction values does not appear to transition to a homogeneous mixture, and it is possible that this effect may be slow to develop for the RMI. Second, the influence of the RMI on the kinetic energy spectrum is investigated using particle image velocimetry (PIV). The influence of the perturbation is visible relatively far from the interface when compared to the energy spectrum of an initially flat interface. Closer to the perturbation, an increase in the energy spectrum with time is observed and is possibly due to a cascade of energy from the large length scales of the perturbation. Finally, the single mode perturbation growth rate is measured after reshock using a new high speed imaging technique. This technique produced highly time-resolved interface position measurements. Simultaneous measurements at the spike and bubble location are used to compute a perturbation growth rate history. The growth rates from several experiments are compared to a new reshock growth rate model.
Date: September 1, 2011
Creator: Weber, Christopher R. (University of Wisconsin-Madison, Madison, WI)
Partner: UNT Libraries Government Documents Department

Consequence analysis of IWTS metal water reactions (Fauske and Associates report 99-35)

Description: The report describes the consequences of postulated thermally unstable conditions in the IWTS knock out pot. The consequence analysis shows that both the knock out pot and particulate bed will stay intact, and that releases will be minor. Reaction rate limitations prevent knock out pot pressure and/or temperature from even approaching values that would threaten structural integrity. Source term calculations based on a particle bed with a homogeneous mixture of metal and oxide particles yield a release above the K Basin pool of about 12 grams.
Date: July 28, 1999
Creator: DUNCAN, D.R.
Partner: UNT Libraries Government Documents Department

A Study of Detonation Diffraction in the Ignition-and-Growth Model

Description: Heterogeneous high-energy explosives are morphologically, mechanically and chemically complex. As such, their ab-initio modeling, in which well-characterized phenomena at the scale of the microstructure lead to a rationally homogenized description at the scale of observation, is a subject of active research but not yet a reality. An alternative approach is to construct phenomenological models, in which forms of constitutive behavior are postulated with an eye on the perceived picture of the micro-scale phenomena, and which are strongly linked to experimental calibration. Most prominent among these is the ignition-and-growth model conceived by Lee and Tarver. The model treats the explosive as a homogeneous mixture of two distinct constituents, the unreacted explosive and the products of reaction. To each constituent is assigned an equation of state, and a single reaction-rate law is prescribed for the conversion of the explosive to products. It is assumed that the two constituents are always in pressure and temperature equilibrium. The purpose of this paper is to investigate in detail the behavior of the model in situations where a detonation turns a corner and undergoes diffraction. A set of parameters appropriate for the explosive LX-17 is selected. The model is first examined analytically for steady, planar, 1-D solutions and the reaction-zone structure of Chapman-Jouguet detonations is determined. A computational study of two classes of problems is then undertaken. The first class corresponds to planar, 1-D initiation by an impact, and the second to corner turning and diffraction in planar and axisymmetric geometries. The 1-D initiation, although interesting in its own right, is utilized here as a means for interpretation of the 2-D results. It is found that there are two generic ways in which 1-D detonations are initiated in the model, and that these scenarios play a part in the post-diffraction evolution as well. For the parameter ...
Date: April 14, 2006
Creator: Kapila, A K; Schwendeman, D W; Bdzil, J B & Henshaw, W D
Partner: UNT Libraries Government Documents Department

Strategy Plan A Methodology to Predict the Uniformity of Double-Shell Tank Waste Slurries Based on Mixing Pump Operation

Description: This document presents an analysis of the mechanisms influencing mixing within double-shell slurry tanks. A research program to characterize mixing of slurries within tanks has been proposed. The research program presents a combined experimental and computational approach to produce correlations describing the tank slurry concentration profile (and therefore uniformity) as a function of mixer pump operating conditions. The TEMPEST computer code was used to simulate both a full-scale (prototype) and scaled (model) double-shell waste tank to predict flow patterns resulting from a stationary jet centered in the tank. The simulation results were used to evaluate flow patterns in the tank and to determine whether flow patterns are similar between the full-scale prototype and an existing 1/12-scale model tank. The flow patterns were sufficiently similar to recommend conducting scoping experiments at 1/12-scale. Also, TEMPEST modeled velocity profiles of the near-floor jet were compared to experimental measurements of the near-floor jet with good agreement. Reported values of physical properties of double-shell tank slurries were analyzed to evaluate the range of properties appropriate for conducting scaled experiments. One-twelfth scale scoping experiments are recommended to confirm the prioritization of the dimensionless groups (gravitational settling, Froude, and Reynolds numbers) that affect slurry suspension in the tank. Two of the proposed 1/12-scale test conditions were modeled using the TEMPEST computer code to observe the anticipated flow fields. This information will be used to guide selection of sampling probe locations. Additional computer modeling is being conducted to model a particulate laden, rotating jet centered in the tank. The results of this modeling effort will be compared to the scaled experimental data to quantify the agreement between the code and the 1/12-scale experiment. The scoping experiment results will guide selection of parameters to be varied in the follow-on experiments. Data from the follow-on experiments will be used to ...
Date: December 1, 1990
Creator: Bamberger, J. A.; Liljegren, L. M. & Lowery, P. S.
Partner: UNT Libraries Government Documents Department

Improvements in Neutronics/Thermal-Hydraulics Coupling in Two-Phase Flow Systems Using Stochastic-Mixture Transport Models

Description: In this NEER project, researchers from Oregon State University have investigated the limitations of the treatment of two-phase coolants as a homogeneous mixture in neutron transport calculations. Improved methods of calculating the neutron distribution in binary stochastic mixtures have been developed over the past 10-15 years and are readily available in the transport literature. These methods are computationally more expensive than the homogeneous (or atomic mix) models, but can give much more accurate estimates of ensemble average fluxes and reaction rates provided statistical descriptions of the distributions of the two materials are know. A thorough review of the two-phase flow literature has been completed and the relevant mixture distributions have been identified. Using these distributions, we have performed Monte Carlo criticality calculations of fuel assemblies to assess the accuracy of the atomic mix approximation when compared to a resolved treatment of the two-phase coolant. To understand the benefit of more advanced binary stochastic mixture models, we have also compared Levermore-Pomraning BSM transport calculations to atomic mix and benchmark calculations in mixtures of a material in a near void. These comparisons yield valuable information about both the ensemble average scalar flux and the variance in the scalar flux.
Date: September 8, 2003
Creator: Palmer, Todd S. & Wu, Qiao
Partner: UNT Libraries Government Documents Department

Mercury-Free Dissolution of Aluminum-Based Nuclear Material: From Basic Science to the Plant

Description: Conditions were optimized for the first plant-scale dissolution of an aluminum-containing nuclear material without using mercury as a catalyst. This nuclear material was a homogeneous mixture of plutonium oxide and aluminum metal that had been compounded for use as the core matrix in Mark 42 nuclear fuel. Because this material had later failed plutonium distribution specifications, it was rejected for use in the fabrication of Mark 42 fuel tubes, and was stored at the Savannah River Site (SRS) awaiting disposition. This powder-like material was composed of a mixture of approximately 80 percent aluminum and 11 percent plutonium. Historically, aluminum-clad spent nuclear fuels [13] have been dissolved using a mercuric nitrate catalyst in a nitric acid (HNO3) solution to facilitate the dissolution of the bulk aluminum cladding. Developmental work at SRS indicated that the plutonium oxide/aluminum compounded matrix could be dissolved without mercury. Various mercury-free conditions were studied to evaluate the rate of dissolution of the Mark 42 compact material and to assess the corrosion rate to the stainless steel dissolver. The elimination of mercury from the dissolution process fit with waste minimization and industrial hygiene goals to reduce the use of mercury in the United States. The mercury-free dissolution technology was optimized for Mark 42 compact material in laboratory-scale tests, and successfully implemented at the plant.
Date: May 14, 2003
Creator: Crooks, W.J. III
Partner: UNT Libraries Government Documents Department

Neutronics Benchmarks for the Utilization of Mixed-Oxide Fuel: Joint U.S./Russian Progress Report for Fiscal Year 1997, Volume 4, Part 7 - Homogeneous Mixtures of Polystyrene-Moderated Plutonium and Uranium Oxides

Description: In the 1970s at the Battelle Pacific Northwest Laboratory (PNL), a series of critical experiments using a remotely operated Split-Table Machine was performed with homogeneous mixtures of (Pu-U)O{sub 2}-polystyrene fuels in the form of square compacts having different heights. With respect to Pu enrichments and moderation [H/(Pu+U) atomic] ratios (MR), four-different homogeneous (Pu-U)O{sub 2}-polystyrene mixtures were considered: (Mixture 1) 7.6 wt% Pu with 19.5 MR, (Mixture 2) 7.89 wt% Pu with 51.8 MR, (Mixture 3) 14.62 wt% Pu with 30.6 MR, and (Mixture 4) 30.0 wt% Pu with 47.4 MR. The Pu{sup 240} isotopic contents in Pu were 23 wt% for Mixture 1 and 8 wt% for Mixtures 2-4. In all mixtures, the uranium was depleted to about 0.151 wt% U{sup 235}. The critical geometric dimensions for both fully Plexiglas{trademark} reflected and unreflected configurations were reported for Mixture 3 and 4 experiments. The dimensions for Mixture 1 and 2 experiments were given for fully-reflected assemblies. This evaluation contains a total of 39 critical (fully reflected and bare) experimental configurations as well as 3 slab geometry critical dimensions.
Date: May 1, 1999
Creator: Yavuz, M.
Partner: UNT Libraries Government Documents Department

A method to remove Ammonia using a Proton-Conducting Ceramic Membrane

Description: An apparatus and method for decomposing NH{sub 3}. A fluid containing NH{sub 3} is passed in contact with a tubular membrane that is a homogeneous mixture of a ceramic and a first metal, with the ceramic being selected from one or more of a cerate having the formula of M' Ce{sub 1-x} M''O{sub 3-{delta}}, zirconates having the formula M'Zr{sub 1-x} M''3-{delta}, stannates having the formula M'Sn{sub 1-x}M''O{sub 3}-{delta}, where M' is a group IIA metal, M'' is a dopant metal of one or more of Ca, Y, Yb, In, Nd, Gd or mixtures thereof and {delta} is a variable depending on the concentration of dopant and is in the range of from 0.001 to 0.5, the first metal is a group VIII or group IB element selected from the group consisting of Pt, Ag, Pd, Fe, Co, Cr, Mn, V, Ni, Au, Cu, Rh, Ru and mixtures thereof. The tubular membrane has a catalytic metal on the side thereof in contact with the fluid containing NH{sub 3} which is effective to cause NH{sub 3} to decompose to N{sub 2} and H{sub 2}. When the H{sub 2} contacts the membrane, H{sup +} ions are formed which pass through the membrane driving the NH{sub 3} decomposition toward completion.
Date: September 22, 1999
Creator: Balachandran, Uthamalingam & Bose, Arun C.
Partner: UNT Libraries Government Documents Department

Cryogenic Homogenization and Sampling of Heterogeneous Multi-Phase Feedstock

Description: An apparatus and process for producing a homogeneous analytical sample from a heterogeneous feedstock by: providing the mixed feedstock, reducing the temperature of the feedstock to a temperature below a critical temperature, reducing the size of the feedstock components, blending the reduced size feedstock to form a homogeneous mixture; and obtaining a representative sample of the homogeneous mixture. The size reduction and blending steps are performed at temperatures below the critical temperature in order to retain organic compounds in the form of solvents, oils, or liquids that may be adsorbed onto or absorbed into the solid components of the mixture, while also improving the efficiency of the size reduction. Preferably, the critical temperature is less than 77K (-196 C). Further, with the process of this invention the representative sample maybe maintained below the critical temperature until being analyzed.
Date: September 21, 1999
Creator: Doyle, Glenn M.; Ideker, Virgene D. & Siegwarth, James D.
Partner: UNT Libraries Government Documents Department

Iron-Phosphate Ceramics for Solidification of Mixed Low-Level Waste

Description: A method of immobilizing mixed low-level waste is provided which uses low cost materials and has a relatively long hardening period. The method includes: forming a mixture of iron oxide powders having ratios, in mass %, of FeO: Fe{sub 2}O{sub 3}: Fe{sub 3}O{sub 4} equal to 25-40: 40-10: 35-50, or weighing a definite amount of magnitite powder. Metallurgical cinder can also be used as the source of iron oxides. A solution of the orthophosphoric acid, or a solution of the orthophosphoric acid and ferric oxide, is formed and a powder phase of low-level waste and the mixture of iron oxide powders or cinder (or magnetite powder) is also formed. The acid solution is mixed with the powder phase to form a slurry with the ratio of components (mass %) of waste: iron oxide powders or magnitite: acid solution = 30-60: 15-10: 55-30. The slurry is blended to form a homogeneous mixture which is cured at room temperature to form the final product.
Date: August 7, 1998
Creator: Aloy, Albert S.; Kovarskaya, Elena N.; Koltsova, Tatiana I.; Macheret, Yevgeny; Medvedev, Pavel G. & Todd, Terry
Partner: UNT Libraries Government Documents Department

Neutronics Benchmarks for the Utilization of Mixed-Oxide Fuel: Joint U.S./ Russian Progress Report for Fiscal Year 1997, Volume 4, Part 8 - Neutron Poison Plates in Assemblies Containing Homogeneous Mixtures of Polystyrene-Moderated Plutonium and Uranium Oxides

Description: In the 1970s at the Battelle Pacific Northwest Laboratory (PNL), a series of critical experiments using a remotely operated Split-Table Machine was performed with homogeneous mixtures of (Pu-U)O{sub 2}-polystyrene fuels in the form of square compacts having different heights. The experiments determined the critical geometric configurations of MOX fuel assemblies with and without neutron poison plates. With respect to PuO{sub 2} content and moderation [H/(Pu+U)atomic] ratio (MR), two different homogeneous (Pu-U) O{sub 2}-polystyrene mixtures were considered: Mixture (1) 14.62 wt% PuO{sub 2} with 30.6 MR, and Mixture (2) 30.3 wt% PuO{sub 2} with 2.8 MR. In all mixtures, the uranium was depleted to about O.151 wt% U{sup 235}. Assemblies contained copper, copper-cadmium or aluminum neutron poison plates having thicknesses up to {approximately}2.5 cm. This evaluation contains 22 experiments for Mixture 1, and 10 for Mixture 2 compacts. For Mixture 1, there are 10 configurations with copper plates, 6 with aluminum, and 5 with copper-cadmium. One experiment contained no poison plate. For Mixture 2 compacts, there are 3 configurations with copper, 3 with aluminum, and 3 with copper-cadmium poison plates. One experiment contained no poison plate.
Date: May 1, 1999
Creator: Yavuz, M.
Partner: UNT Libraries Government Documents Department

Mixing Effects on the Precipitation and Cross Flows Filtration of a Hanford Simulated Precipitated Radioactive Waste

Description: As part of the River Protection Project at Hanford, Washington, Bechtel National, Inc. has been contracted by the United States Department of Energy to design a Waste Treatment and Immobilization Plant to stabilize liquid radioactive waste. Because of its experience with radioactive waste stabilization, the Savannah River Technology Center of the Westinghouse Savannah River Company is working with Bechtel National and Washington Group International, to help design and test certain parts of the Waste Treatment Plant. One part of the process is the separation of radioactive isotopes from the liquid waste by a precipitation reaction and cross-flow ultrafiltration. To better understand those combined processes an experiment was performed using a simulated radioactive waste, made to prototypically represent the chemical and physical characteristics of a Hanford waste in tank 241-AN-102 and precipitated under prototypic conditions. The resultant slurry was then filtered using a cross-flow filter prototypic in porosity, length, and diameter to the plant design. An important aspect of filtration for waste treatment is the rate at which permeate is produced. There are many factors that affect filtration rate and one of the most difficult to obtain is the effect of particles in the waste streams. The Waste Treatment Plant will filter many waste streams, with varying concentrations and types of dissolved and undissolved solids. An added complication is the need to precipitate organic complexants so they can be efficiently separated from the supernatant. Depending on how precipitation is performed, the newly created solids will add to the complicating factors that determine permeate flux rate. To investigate the effect of precipitated solids on filter flux a pilot-scale test was performed and two different mixing mechanisms were used for the precipitation reaction. A standard impeller type mixer, which created a homogeneous mixture, and a pulse jet mixer, which created a ''less than'' ...
Date: March 31, 2004
Partner: UNT Libraries Government Documents Department

Mixing and solid suspension of up-down agitators in a slab tank

Description: Seven different up-down agitators were studied for their ability to produce mixing and solid suspension in a slab tank. Mixing times were measured as the time needed to disperse injected dye. The solid suspension studies determined the minimum stroke frequency of the agitators needed for complete off-bottom suspension. The effects of stroke frequency, n; amplitude, a; blade width, w; blade clearance, c; and liquid depth, h, and weight percent solids, X, were studied. The most effective geometry, in terms of mixing, solid suspension and design simplicity, was a single flat blade with minimum off-bottom clearance and a blade width/tank thickness ratio, w/T, of 0.74 at the maximum stroke amplitude studied. 15 refs., 7 figs.
Date: January 1, 1989
Creator: Ramsey, C.J. (Texas A and M Univ., College Station, TX (USA). Dept. of Mechanical Engineering); Kyser, E.A. III & Tatterson, G.B. (Savannah River Lab., Aiken, SC (USA))
Partner: UNT Libraries Government Documents Department

A combined volumetric verification procedure based on bubble-tube manometry and lutetium spike

Description: Bubble-tube manometry is the most accurate currently available method for precision volumetric measurements of solutions in process tanks containing special nuclear materials. Bubble tubes installed in the accountability tank by the facility operator are instrumented with a precision pressure transducer and a programmable pneumatic multiplexing system. In a process-solution measurement technique currently under development, a spike solution containing a known amount of lutetium is added to the Accountability appropriate measures are taken to homogenize the tank contents, and a sample of the homogenized solution is analyzed by isotopic dilution mass spectrometry. Each method offers unique advantages when applied to independent verification of the special nuclear material content of process solutions for the purposes of international safeguards. The methods are compared with regard to attributes such as intrusiveness, authentication independent of the facility operator, value for process operations, suitability for continuous unattended process monitoring, technical implementation challenges, accuracy, inspection effort and cost. A solution-volume verification proce-dure emphasizing the complementary aspects of both methods is proposed.
Date: August 1, 1994
Creator: Lemley, J. R.; Suda, S.; Keisch, B.; Belew, W. & Smith, D. H.
Partner: UNT Libraries Government Documents Department

A Preliminary Analysis of Dose Rates Associated with ITER CVCS Equipment/Area Location

Description: A preliminary analysis of the ITER Chemical and Volume Control System (CVCS) Area was performed to assess dose rates outside the walls and ceiling of the facility after 1.5 years of operation at shutdown, 2 days, and 10 days after shutdown. For this purpose a simplified Monte Carlo computer model was developed using the MCNP (MCNP5 Ver. 1.51) code. Two components are included: the smaller filter tank and the larger ion exchanger. These pieces of equipment are associated with the Integrated Blanket ELM Divertor Primary Heat Transfer System, which will have the largest dose rates associated with activated corrosion products during operation in comparison with other systems. The ion exchanger contained two source regions, a 1.2-m-thick resin bed above a 0.55 m-thick skirt, and a 0.8-m-thick water region. The filter constituted an additional source. Thus the model consisted of three sources (filter, resin, water), homogeneously distributed within the appropriate source regions. However, much of the results (that address individual isotopes) are presented with the two sources in the ion exchanger combined. In these cases the sources are referred to as the 'ion exchanger source' and the 'filter source.' Dimensions for the facility and components, as well as source isotopes and strengths, and material densities, were supplied by US ITER. Because of its simplification, the model does not contain pipes. Consequently, radiation streaming through pipe penetrations, radiation emanating from the pipes, and shielding from the pipes were not considered in this analysis. Dose rates on the outside of two walls and the ceiling were calculated. The two walls are labeled as the 'long' wall (aligned with the X-axis) and the 'short' wall (aligned with the Y-axis). These walls and ceiling were nominally set to 30-cm-thick concrete. In the original analysis, standard concrete (2.3 g/cc density) was used. In addition to the ...
Date: March 1, 2012
Creator: Blakeman, Edward D; Ilas, Dan & Petrov, Andrei Y
Partner: UNT Libraries Government Documents Department


Description: The Enhanced Chemical Cleaning (ECC) process uses ozone to effect the oxidation of metal oxalates produced during the dissolution of sludge in the Savannah River Site (SRS) waste tanks. The ozone reacts with the metal oxalates to form metal oxide and hydroxide precipitants, and the CO{sub 2}, O{sub 2}, H{sub 2}O and any unreacted O{sub 3} gases are discharged into the vapor space. In addition to the non-radioactive metals in the waste, however, the SRS radioactive waste also contains a variety of radionuclides, hence, hydrogen gas is also present in the vapor space of the ECC system. Because hydrogen is flammable, the impact of this resultant gas stream on the Lower Flammability Limit (LFL) of hydrogen must be understood for all possible operating scenarios of both normal and off-normal situations, with particular emphasis at the elevated temperatures and pressures of the typical ECC operating conditions. Oxygen is a known accelerant in combustion reactions, but while there are data associated with the behavior of hydrogen/oxygen environments, recent, relevant studies addressing the effect of ozone on the flammability limit of hydrogen proved scarce. Further, discussions with industry experts verified the absence of data in this area and indicated that laboratory testing, specific to defined operating parameters, was needed to comprehensively address the issue. Testing was thus designed and commissioned to provide the data necessary to support safety related considerations for the ECC process. A test matrix was developed to envelope the bounding conditions considered credible during ECC processing. Each test consists of combining a gas stream of high purity hydrogen with a gas stream comprised of a specified mixture of ozone and oxygen in a temperature and pressure regulated chamber such that the relative compositions of the two streams are controlled. The gases are then stirred to obtain a homogeneous mixture and ...
Date: January 12, 2012
Creator: Sherburne, C.
Partner: UNT Libraries Government Documents Department

Inflation in spherically symmetric inhomogeneous models

Description: Exact analytical solutions of Einstein's equations are found for a spherically symmetric inhomogeneous metric in the presence of a massless scalar field with a flat potential. The process of isotropization and homogenization is studied in detail. It is found that the time dependence of the metric becomes de Sitter for large times. Two cases are studied. The first deals with a homogeneous scalar field, while the second with a spherically symmetric inhomogeneous scalar field. In the former case the metric is of the Robertson-Walker form, while the latter is intrinsically inhomogeneous. 16 refs.
Date: November 1, 1986
Creator: Stein-Schabes, J.A.
Partner: UNT Libraries Government Documents Department

High temperature vacuum-annealing system

Description: A system is described for use in homogenizing poly- and single-crystal metal samples at temperatures up to about 1300/sup 0/C. The furnace tube may be evacuated to a dynamic vacuum of 10/sup -3/ to 10/sup -4/ torr. A provision exists for pushing the sample from the hot zone into a zone the walls of which are at room temperature.
Date: February 1, 1972
Creator: Kayser, F. X. & Diesburg, D. E.
Partner: UNT Libraries Government Documents Department


Description: Issues affecting the implementation, public perception and acceptance of nuclear power include: proliferation, radioactive waste, safety, and economics. The thorium cycle directly addresses the proliferation and waste issues, but optimization studies of core design and fuel management are needed to ensure that it fits within acceptable safety and economic margins. Typical pressurized water reactors, although loaded with uranium fuel, produce 225 to 275 kg of plutonium per gigawatt-year of operation. Although the spent fuel is highly radioactive, it nevertheless offers a potential proliferation pathway because the plutonium is relatively easy to separate, amounts to many critical masses, and does not present any significant intrinsic barrier to weapon assembly. Uranium 233, on the other hand, produced by the irradiation of thorium, although it too can be used in weapons, may be ''denatured'' by the addition of natural, depleted or low enriched uranium. Furthermore, it appears that the chemical behavior of thoria or thoria-urania fuel makes it a more stable medium for the geological disposal of the spent fuel. It is therefore particularly well suited for a once-through fuel cycle. The use of thorium as a fertile material in nuclear fuel has been of interest since the dawn of nuclear power technology due to its abundance and to potential neutronic advantages. Early projects include homogeneous mixtures of thorium and uranium oxides in the BORAX-IV, Indian Point I, and Elk River reactors, as well as heterogeneous mixtures in the Shippingport seed-blanket reactor. However these projects were developed under considerably different circumstances than those which prevail at present. The earlier applications preceded the current proscription, for non-proliferation purposes, of the use of uranium enriched to more than 20 w/o in {sup 235}U, and has in practice generally prohibited the use of uranium highly enriched in {sup 235}U. They were designed when the expected burnup ...
Date: August 1, 2004
Partner: UNT Libraries Government Documents Department

Modeling and analysis of ORNL horizontal storage tank mobilization and mixing

Description: The retrieval and treatment of radioactive sludges that are stored in tanks constitute a prevalent problem at several US Department of Energy sites. The tanks typically contain a settled sludge layer with non-Newtonian rheological characteristics covered by a layer of supernatant. The first step in retrieval is the mobilization and mixing of the supernatant and sludge in the storage tanks. Submerged jets have been proposed to achieve sludge mobilization in tanks, including the 189 m{sup 3} (50,000 gallon) Melton Valley Storage tanks (MVST) at Oak Ridge National Laboratory (ORNL) and the planned 378 m{sup 3} (100,000 gallon) tanks being designed as part of the MVST Capacity Increase Project (MVST-CIP). This report focuses on the modeling of mixing and mobilization in horizontal cylindrical tanks like those of the MVST design using submerged, recirculating liquid jets. The computer modeling of the mobilization and mixing processes uses the TEMPEST computational fluid dynamics program (Trend and Eyler 1992). The goals of the simulations are to determine under what conditions sludge mobilization using submerged liquid jets is feasible in tanks of this configuration, and to estimate mixing times required to approach homogeneity of the contents.
Date: June 1, 1994
Creator: Mahoney, L. A.; Terrones, G. & Eyler, L. L.
Partner: UNT Libraries Government Documents Department

The evaporative vector: Homogeneous systems

Description: Molecular beams of van der Waals molecules are the subject of much current research. Among the methods used to form these beams, three-sputtering, laser ablation, and the sonic nozzle expansion of neat gases - yield what are now recognized to be ''warm clusters.'' They contain enough internal energy to undergo a number of first-order processes, in particular that of evaporation. Because of this evaporation and its attendant cooling, the properties of such clusters are time-dependent. The states of matter which can be arrived at via an evaporative vector on a typical laboratory time-scale are discussed. Topics include the (1) temperatures, (2) metastability, (3) phase transitions, (4) kinetic energies of fragmentation, and (5) the expression of magical properties, all for evaporating homogeneous clusters.
Date: May 1, 1987
Creator: Klots, C.E.
Partner: UNT Libraries Government Documents Department