bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of Sphagnum Peat, Calcium Carbonate, and Hydrated Lime for Immobilizing Uranium Tailings Leachate
Authors: Longmire P. A. , Brookins D. G. , Thomson B. M. , Eller P. G. 
Published: March 2011

ABSTRACTBatch experiments, mineralogical studies, and geochemical modeling were conducted to evaluate the effectiveness of sphagnum peat, calcium carbonate, and hydrated lime in removing dissolved concentrations of As, Mo, NO3, and U present in uranium-tailings pore water at Gunnison, Colorado. Amounts of As, Mo, and U removal by sphagnum peat, calcium carbonate, and hydrated lime at 5.0, 2.5, and 2.5 wt.%, respectively, were typically above 97 %. Nitrate removal ranged between 55 and 80 %. Significant contaminant removal was achieved by sphagnum peat alone at pH 3.18. Addition of 2.5 wt.% calcium carbonate to the sphagnum peat-tailings system resulted in formation of soluble uranyl carbonato complexes, which decreased the amount of U(VI) fixed onto sphagnum peat by a factor of 2. Addition of 2.5 wt.% hydrated lime to the acidic tailings increased Mo concentrations by a factor of 2 under moderately alkaline conditions (pH 12). During neutralization of tailings-pore water, precipitation of ferric oxyhydroxides may provide additional removal of As, Mo, and U(VI) from solution through adsorption and coprecipitation processes.
Leach Rate Excursions in Borosilicate Glasses: Effects of Glass and Leachant Composition
Authors: Barkatt Aa. , Olszowka S. A. , Sousanpour W. , Adel-Hadadi M. A. , Adiga R. , Barkatt Al. , Marbury G. S. , Li S. 
Published: March 2011

ABSTRACTLeach tests on borosilicate glasses using a partial-replenishment technique show that in certain cases large excursions in leach rate may appear at the end of periods ranging between 1 and 20 months. The extent and time of these leach rate transients are very sensitive to glass and leachant composition and to S/V ratio, and they may be eliminated by slight increases in Si and Al levels in the glass or by using a neutrally buffered leachant. This phenomenon, which may reflect cracking of the initial surface layer, can have a considerable effect on the results and complicate the modeling of leach tests which strongly reflect the extent of leaching during the early stages of glass/leachant interaction. However, these effects appear to have relatively little significance in the long term.
Prediction of Uranium Adsorption by Crystalline Rocks: The Key Role of Reactive Surface Area
Authors: Wanty Richard B. , Rice Cynthia A. , Langmuir Donald , Briggs Paul , Lawrence Errol P. 
Published: March 2011

ABSTRACTAdsorption processes are important in controlling U concentrations in ground water. Quantifying such processes is extremely difficult in that in situ conditions cannot be directly measured. One rock characteristic that must be known to quantify adsorption is the specific surface area of reactive minerals exposed to the ground water. We evaluate here three methods for estimating specific surface area in situ. The first is based on the dissolution kinetics of sodium feldspars, the second on emanation of radon-222 and the third on adsorption of naturally-occurring U. The radon-222 method yields estimates 5 to 8 orders of magnitude greater than those obtained via the other two methods; too large probably because of effects related to fracture geometry. Estimates of specific surface area based on modelling adsorption of natural U by aquifer materials are of comparable magnitude to those from the feldspar-dissolution kinetics approach. These conclusions are based on analyses of water from 145 wells in crystalline-rock aquifers from Pennsylvania, New Jersey, Maryland, and Colorado. Computer modelling of the chemical data using PHREEQE [1] showed that uraninite or coffinite approach saturation in reducing water, limiting total U to <2 × 10−9 m. Generally, U minerals are below saturation in oxidizing ground water, where uranyl-carbonate complexes are the dominant dissolved U species. Autoradioluxographs of thin sections show areas of concentration of radioactivity in the rocks and establish that U is concentrated along fracture boundaries and on ferric oxyhydroxide grain coatings. Because U minerals generally are undersaturated, U mobility is limited by adsorption onto ferric oxyhydroxides and other mineral surfaces. Calculations of uranyl adsorption from the ground water onto goethite using the program M1NTEQ [2] show that adsorption decreases with increased carbonate concentrations due to the formation of uranyl-carbonate complexes. Results of this paper improve our understanding of the mobility of U that might be released into oxidized ground water in crystalline rock from a breached radioactive-waste repository.
Temporal Changes in Decay-Series Isotope Concentrations in Response to Flow Conditions in the Sssdp Well, Salton Sea, California
Authors: Leslie Bret W. , Hammond Douglas E. , Ku Teh-Lung 
Published: March 2011

ABSTRACTSeveral radionuclides of the naturally occurring 238U, 235U and 232Th decay series have been measured in high-temperature (300–350 °C) brines from several flow tests of the Sal ton Sea Scientific Drilling Project (SSSDP) well. Activities (dpm/kg) at the initial flow test of the well were 222Rn (2130), 226Ra (2200), 228Ra (1120), 224Ra (1010), 223Ra (6), 210Pb (3260), and 212Pb (2250). In contrast, activities of U and Th isotopes were much lower (< 1 dpm/kg). Following the first flow test (12/85), the well was deepened and sampled again during a short flow test (3/86). Radium and uranium concentrations were about two times lower during the second flow test, while other elements had similar concentrations. During a subsequent 20 day flow test of the well (6/88), flow rates were regulated at the wellhead to investigate reservoir characteristics, and 226Ra and 210Pb activities were found to be negatively correlated with the flow rate and positively correlated with the wellhead pressure. The 226Ra activity varied by a factor of five, roughly the variation in total flow rate, while well-head pressure varied only by 25% and 210Pb activity varied by a factor of two. Ratios of short-lived daughters to longer-lived parents increased in these flow tests. Results from mass balance calculations incorporating reaction kinetics suggest that differences in the degree of radium adsorption, rates of precipitation and dissolution of reservoir minerals exist in different flow zones.
Study on Role of 234Th in Uranium Series Nuclides Migration
Authors: Ohnuki Toshihiko , Watanabe Shoji , Murakami Takashi 
Published: March 2011

ABSTRACTThe role of 234Th, a daughter nuclide of 238U having a half life of 24 days, in the migration of uranium series nuclides has been studied to understand the mechanism which gives a higher migration velocity of 238U than that of 234U. We assume that 234Th is adsorbed at two different sites; one, where 234Th is reversibly adsorbed, and the other, where 234Th is irreversibly fixed. Calculations have shown that the fixation of ^Th to a rock can cause the apparent migration velocity of 234U to be reduced compared to that of 238U and this agrees with observed field data. Changes in the fixation rate constants affect the relative mobility of 238U and 234U, and this can account for the different migration behavior at different depths in the Koongarra ore deposit.
Migration of Radionuclides in Geologic Media: Fundamental Research Needs
Authors: Reed D. T. , Zachara J. M. , Wildung R. E. , Wobber F. J. 
Published: March 2011

ABSTRACTAn assessment of the fundamental research needs in understanding and predicting the migration of radionuclides in the subsurface is provided. Emphasis is on the following three technical areas: (1) aqueous speciation of radionuclides, (2) the interaction of radionuclides with substrates, and (3) intermediate-scale interaction studies. This research relates to important issues associated with environmental restoration and remediation of DOE sites contaminated with mixed radionuclide-organic wastes.
The Role of Surface Layers in Glass Leaching Performance
Authors: Bates J. K. , Ebert W. L. , Mazer J. J. , Bradley J. P. , Bradley C. R. , Dietz N. L. 
Published: March 2011

ABSTRACTThe examination of reacted layers that form as glass reacts can provide insight into reaction mechanisms that control long-term glass reaction, and into processes by which radionuclides are released to solution. Examples are given for the natural glasses obsidian and tektite, and the nuclear waste glasses 131 and 165, where the layers form bothin-situand precipitated from solution, where they are both amorphous and crystal 1ine, where selective incorporation of actinide elements Into stable phases may offer a barrier to release, and where sloughing of the layers from the glass acts as an alternative radionuclide release process to solubility-limited control.Several reaction processes occur simultaneously as glass reacts, and the projection of glass performance to long time periods requires the identification of those processes that dominate the long-term reaction.
Demonstration of a System Performance Assessment Process
Authors: Dormuth Kenneth W. 
Published: March 2011

ABSTRACTTo help evaluate the concept of nuclear fuel waste disposal in plutonic rock of the Canadian Shield, the long-term performance of a hypothetical disposal facility is being studied. This case study uses information from a Shield research area, laboratories, and conceptual engineering. It illustrates the use of performance assessment to derive constraints on the siting, construction, and operation of a disposal facility, and to demonstrate the feasibility of safe disposal of nuclear fuel waste.
On the Problem of Consistency of Chemical Thermodynamic Data Bases
Authors: Wanner Hans 
Published: March 2011

ABSTRACTThe geochemical modelling in support of the performance assessment of radioactive waste disposal systems calls for a large number of chemical thermodynamic data. For realistic modelling it is essential that the data used are fully consistent. The verification of consistency of existing data bases is complicated by the fact that it requires the knowledge of a considerable amount of primary information to ensure:1.Consistency with the fundamental laws of thermodynamics2.Consistency within a chemical model3.Consistency with auxiliary data4.Consistency in the data correction proceduresThis paper includes selected examples for each of the four items to visualize the problems. It should be noted that there are numerous other systems that could serve as examples as well, and the range of cases reported here is far from being exhaustive.Realistic geochemical modelling depends not only on the quality of the data base, but also on the quality of the chemical model used. For the establishment of a chemical model, additional information is needed that is not contained in thermodynamic data bases.
Estimation of the Migration Parameters for the Boom Clay Formation by Percolation Experiments on Undisturbed Clay Cores
Authors: Put Martin J. , Monsecour Marcel , Fonteyne Alfons , Yoshida Hidekazu 
Published: March 2011

ABSTRACTThe safety assessment of the repository for high level radioactive waste in the Boom clay formation requires reliable data for the migration parameters. The experimental set-up and the interpretation method is briefly described for percolation experiments on undisturbed clay cores drilled from the formation and results are reported. The undisturbed clay cores are drilled perpendicular and parallel to the stratification of the formation to study the isotropy of the formation. To represent the real situation as close as possible, in-situ interstitial clay pore water is used as percolating liquid.Parameter values determined in the percolation experiments are presented for bromine, iodine and tritiated water. Darcy velocity and effective stress are used as variables. Anisotropy of the formation is demonstrated for the hydraulic conductivity, but is found to be trivial for the dispersion parameters. A general relation between the apparent dispersion constant, the diffusion accessible porosity and the Darcy velocity is also given.
Comparison of Granite, Tuff, and Basalt as Geologic Media for Long-Term Storage of High-Level Nuclear Waste
Authors: Grandstaff D. E. , Grassi V. J. , Lee A. C. , Ulmer G. C. 
Published: March 2011

ABSTRACTSystematic differences in pH, cation/proton ion activity ratios, and redox have been observed between solutions produced in rock-water hydrothermal experiments with tuff, granite, and basalt. Stable pH values in tuff-water experiments may be as much as 1.5 pH units more acidic than basalt-water experiments at the same temperature and ionic strength. Redox (log fO2) values in 300°C tuff experiments are 4–7 orders of magnitude more oxidizing than basalt experiments and ca. 4 log units more oxidizing than the magnetite-hematite buffer. Such fluid differences could significantly affect the performance of a high-level nuclear waste repository and should be considered in repository design and siting.
Heat-Pipe Effect on the Transport of Gaseous Radionuclides Released from a Nuclear Waste Container
Authors: Zhou W. , Chambré P. L. , Pigford T. H. , Lee W. W.-L. 
Published: March 2011

ABSTRACTWe present analytic studies of the transport of gaseous species released from a spent-fuel waste package, as affected by a heat-pipe of counterflowing liquid and vaporized water in the surrounding rock. A heat-pipe is caused by heating which vaporizes pore water near the waste, releasing vapor into the fractures. Driven by its pressure gradient, the vapor flows away from the waste and condenses where the rock is cooler. Because of capillary pressure gradient due to non-uniform liquid saturation, condensate flows towards the waste through the porous rock. We first develop analytic solutions for the time-dependent transport of energy and fluid from the waste container to the surrounding fractured porous rock. From the mass fluxes of liquid and vapor, we solve the advective-diffusive transport of a gaseous species released from the waste. The major assumptions are quasi-steady-state, local thermodynamic equilibrium, no noncondensable gases, and no sorption. Our results include the extent of the heat-pipe zone as function of time, the vapor velocity distribution in the heat-pipe zone, radionuclide concentration in water vapor, and the flux of radionuclide at the waste surface normalized to the surface concentration. We find that the vapor velocity in the heat-pipe zone is 1000-fold greater than the local air velocity if there were no heat pipe. If the gaseous species release mechanism maintains a near-constant concentration of gaseous species in the gas outside and near the waste container surface, the mass rate of transport of that species would be increased 1.3 to 7 times greater than if there were no heat pipe. However, if the release rate of the gaseous species is affected little by the concentration of that species outside the container, the heat-pipe can have little affect on the transport rate of that species.
Loading Rate Effects on Ductile-Phase Toughening in In-Situ Niobium Silicide-Niobium Composites
Authors: Rigney J.D. , Lewandowski JJ , Matson L. , Mendiratta M.G. , Dimiduk D.M. 
Published: March 2011

ABSTRACTBrittle silicide intermetallics such as Nb5Si3 have been significantly toughened by Nb particles incorporated during in-situ processing techniques. Ten-fold increases in toughness as well as resistance-curve behavior have been realized at conventional testing rates with these ductile Nb particles. Under more rapid loading rates the efficiency of the body-centered cubic (bcc) Nb particles in enhancing the toughness may be affected due to the strain-rate sensitivity of the Nb and/or the possible strain-rate sensitivity of interfacial debonding. Toughness tests conducted at loading rates of 0.0042 to 8.5 mm/sec have indicated a significant sensitivity to testing rate, with a drop in fracture toughness from 28 to 9 MPa√m over this range accompanied by a change in fracture mode from primarily ductile to cleavage failure in the Nb.
Phase and Microstructure Morphologies in Combustion Synthesized Nb-Al-B Composites
Authors: Ho C.T. , Sekhar J.A. 
Published: March 2011

ABSTRACTResults of an experimental study on unidirectional wave combustion synthesized Nb-Al-B composite alloys are described. The effect of combustion initiation temperature and composition on the microstructural morphology and phases is studied. Correlations with the initial parameters and reaction velocities have been sought to understand the kinetics of the rate controlling step for sustained combustion and for the explanation of the synthesized microstructures. Strategies for controlling the distribution of the reinforcement phases (both ductile and hard) in the composite are discussed.
Empirical Interatomic Potentials for L1O Tial and B2 Nial
Authors: Rao Satish I. , Woodward C. , Parthasarathy T.A. 
Published: March 2011

ABSTRACTRecent studies have suggested a particular relationship between the degree of covalent bonding in TiAl and the mobility of dislocation[1,2]. Ultimately such electronic effects In ordered compounds must dictate the dislocation core structures and at the same time the dislocation mobility within a given compound. However, direct modelling of line defects Is beyond the capability of todays electronic structure techniques. Alternatively, significant steps toward extending our understanding of the flow behaviour of structural intermetallics may come through general application of empirical interatomic potential methods for calculating the structure and mobility of defects. Toward this end, we have constructed semi-empirical interatomic potentials within the embedded atom formalism for L1O and B2 type structures. These potentials have been determined by fitting to known bulk structural and elastic properties of TIAl and NiAl, using least squares procedures. Simple expressions that relate the parameters of the potentials to the bulk properties are used in the fitting procedure. Calculations of dislocation core structures and planar fault energies using these potentials are considered. The differences between the optimized bulk properties predicted from the potentials and the values for these properties are discussed in terms of non-spherical nature of the electron density distribution. Empirical methods which incorporate these effects into interatomic potentials are briefly discussed.
Alloying Behavior of Ni3Si and the 900°C Isotherms of Several Ni-Si-X Systems At Ni-Rich Corner
Authors: Tianxiang Zhang , Yundong Li , Zhi Zheng , Yaoxiao Zhu 
Published: March 2011

ABSTRACTThe solid solubilities of 15 common alloying elements in the L12-type intermetallic compound Ni3Si have been determined at 900°C, and their substitution mode has been deduced from the direction of solubility lobe of the compound. It is shown that the alloying behavior in Ni3Si is determined by both size and electronic factors, i.e, the substitution mode is governed by electronic configuration and solubility by the both. The solubilities of alloying elements can be explained on the two dimensional map proposed by Alonso and Simozar.Four isotherms of Ni-Si-X (X = Fe,Cr, Co,Cu) have been obtained. They are very similar in structure.
Microstructure of Titanium-Aluminides after Thermomechanical Treatment
Authors: Seeger J. , Hartig C. , Bartels A. , Mecking H. 
Published: March 2011

ABSTRACTForging in the α2+γ-phase field results in grain refined zones by dynamic recrystallization, but still coarse γ-grains and a residual amount of α2/γ-lamellae are observed. During subsequent heat treatment in the α+γ-phase field the recrystallization leads to inhomogeneous distributions of α2-Ti3Al and grain sizes of γ-TiAl. Due to these inhomogeneities a significant increase of the room temperature ductility is not found.
Short-Range to Long-Range Ordering Reactions in a Ni-25Mo-8Cr Alloy
Authors: Kumar Mukul , Vasudevan Vijay K. 
Published: March 2011

ABSTRACTThe transformation from short-range↔long-range order in Haynes® Alloy 242, a nominal Ni-25Mo-8Cr (in wt.%) alloy, during both continuous heating and cooling and isothermal holding at temperatures between 550 and 750°C is reported using dilatometry and microhardness measurements, and optical and transmission electron microscopy The long-range to short-range order transformation temperature was observed to increase with an increase in the degree of prior order. Aging below the transformation temperature led to considerable hardening; this hardening was associated with the formation of a very high volume fraction of Ni2Mo domains/precipitates. On aging at 700°C and below, the hardness initially increases and then levels off, with no evidence of overaging for times to 2000 hours. The role of both short- and long-range order on the transformation temperature, thermal expansion and hardening behavior and the mechanisms of transformation from short-range to long-range order were established and will be discussed.
Dislocation Nucleation Versus Cleavage in Ni3AI and Ni
Authors: Sun Yuemin , Rice James R. , Truskinovsky Lev 
Published: March 2011

ABSTRACTRecent advances in the modelling of dislocation nucleation from a crack tip are used here to compare the critical energy release rate associated with emission in Ni3Al and Ni. The method for analyzing nucleation makes use of a Peierls-type stress versus displacement relation ahead of the crack tip. It has been shown recently by Rice [1] that the energy release rate for emission scales with γus, the “unstable stacking” energy associated with the sliding of atomic planes past one another. The advantage of this approach is that it allows for an extended dislocation core during nucleation, thus eliminating the need for a core cutoff radius. Preliminary calculations which take into account only the shear stress on a slip plane show that it is more difficult to emit a dislocation in Ni3Al than in Ni. Working within the framework of the competition between atomic decohesion and blunting by dislocation emission, the implications for explaining the brittleness of Ni3Al are also discussed.
Deformation Microstructures in B2-Type CoTi Single Crystals
Authors: Yoshida M. , Takasugi T. 
Published: March 2011

ABSTRACTB2-type CoTi single crystals which exhibit the yield strength anomaly were deformed at various temperatures and on various compression axis in order to investigate the deformation microstructures. The morphological feature and Burgers vectors of the activated dislocations were investigated by means of transmission electron microscopy. At a low temperature of 300 K, relatively straight dislocations with the <001>-type Burgers vector were observed. They consisted of the mixed components of edge and screw, and strongly tended to form the dipoles. At a temperature of 773 K where the yield stress increases with increasing temperature, the screw components of dislocations with a <001>-type Burgers vector were dominant and showed peculiar morphology revealing the pinning or cross slip. However, the examination using the weak-beam method could not show the evidence of any dissociation. At a high temperature of 973 K above the peak temperature, the Burgers vectors of activated dislocations were determined to be a <001>- type for compressive orientation axes close to [111] and [011] whereas a <110>-type for orientation axis close to [001]. These dislocation microstructures were discussed in correlation with the yield strength anomaly observed in these intermetallics.