bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of the Silicon Nitride on Hydrogenated Amorphous Silicon Interface
Authors: Gelatos A. V. , Kanicki J. 
Published: March 2011

ABSTRACTWe report on our investigation of the silicon nitride on hydrogenated amorphous silicon interface by high frequency capacitance-voltage measurements. We show evidence for the existence of a large number of interface states at energies less than or equal to 0.36 eV below the hydrogenated amorphous silicon conduction band. In addition, we demonstrate that the states responsible for the hysteresis in capacitance-voltage characteristics are located in the silicon nitride layer. Finally, we argue that the ability of hydrogenated amorphous silicon to act as hole diffusion barrier is responsible for the observed flat-band voltage shift.
Growth of Surface Layer During the Leaching of The Simulated Waste Glass and its Barrier Effects on the Leaching
Authors: Ishiguro K. , Kawanishi N. , Sasaki N. , Nagaki H. , Yamamoto M. 
Published: March 2011

ABSTRACTThe growth of surface layers on simulated waste glass during two different types of leaching has been studied in conjunction with their corrosion kinetics. Static and Soxhlet leach tests were performed in distilled water at a temperature of 100°C. Auger and ESCA analyses of solid samples after leaching showed that the layers consisted of two or three sublayers which were distinguished by their different components. The transition elements Fe and Ni, the rare-earths Nd and La, and Zn were concentrated in the layers, while Si, B and alkali were depleted in most of the layers. Growth kinetics of the layers followed approximately linear relations for the two types of leaching. Growth rates and elemental profiles of the layers depended upon the leaching conditions. Comparison between the leaching rate and the thickness of the layer showed that layers did not work as effective diffusion barriers until a threshold thickness was reached, which depended on the layer structures.
Leach Models for a Commercial Nuclear Waste Glass
Authors: Kuhn William L. , Peters Richard D. 
Published: March 2011

ABSTRACTA review of the leaching behavior of 76–68 glass shows that it cannot be explained in terms of diffusion in the glass, which has been the basis for several leach models. Instead, we present two models based on a dissolution rate impeded by surface processes: the accumulation of a protective layer of insoluble reaction products, and adsorption of reaction products on the surface. The resulting predicted time dependences are identical and predict a change from linear to parabolic rate laws for soluble species, which is found to agree with the data over a range of temperatures. Incongruent release is attributed primarily to solubility effects. The relative merits of the models are discussed on the basis of the effect of surface area-to-volume ratio in static leach tests. Their relevance to modeling repository behavior is discussed.
Releasing Behavior of Tritium from Neutron Irradiated Borosilicate Glass
Authors: Yamamoto Yoshimasa , Kitagawa Kazuo , Atsumi Hisao , Yamanaka Shinsuke , Miyake Masanobu 
Published: March 2011

ABSTRACTSpecimens of borosilicate glass were irradiated in a material testing reactor at a neutron fluence of 1019–1020 nvt and a temperature of below 250°c. Tritium released from the specimen was determined by means of a specially designed sampling system and liquid scintillation counter.Temperature and time dependence of the releasing behavior of tritium from borosilicate glass was obtained in the temperature range of 200 – 700°C. Very small amount of tritium as compared with the amount contained in the specimen was released in several hours at temperatures below 700°C. The greater part of tritium released from the specimen was tritium oxide, which is controlled by the diffusion step of tritium in the specimen. The diffusion coefficient of tritium in borosilicate glass was also obtained, which agreed with that of water in glasses.
Laboratory Investigations of Groundwater Interactions with Buried Radioactive Sodium Wastes and Attendant Release and Migration of Tritium in Adjacent Soil
Authors: Subbaraman G. , Steele III O. P. , Witbeck L. C. , Abrams C. S. 
Published: March 2011

ABSTRACTShallow land burial of sodium-bearing low-level wastes requires an assessment of safetyconsequences relating to (1) groundwater interactions with the residual sodium in the event of a breach of containment and (2) release of tritium dissolved in sodium along with hydrogen (both of which will permeate through adjacent soil). This paper describes the tests and evaluations being performed to establish a data base on safety consequences of burying low-level radioactive sodium wastes (RSW). This data base can be used in establishing the amounts of sodium that may be tolerated in burying RSW and in establishing related criteria.
Correlation Between Dynamic Leach Test Results and Geochemical Observations
Authors: Barkatt Aaron , Macedo Pedro B. , Sousanpour William , Barkatt Alisa , Boroomand Morad A. , Szoke Peter , Rogers Victor L. 
Published: March 2011

ABSTRACTA test method based on partial leachant exchange at constant intervals until leachate concentrations become stabilized has been used to obtain a data-base in evaluating long-term leaching patterns. Applied to basalt and granite specimens and compared with ground-water analyses, correlations which can be used in long-term leachability extrapolations have been established. They are based on the following principles: (i) Control of solubilities of major components by combined aluminosilicate species; (ii) Continued increase in levels of soluble species, e.g. Na+ and Cl−, with time; (iii) Initial rapid leaching of SO42−, along with Ca2+ and K+, followed by slowing down, probably due to the presence of selectively leachable phases; (iv) Initial retardation of Mg and Fe leaching followed by regrowth as sorption sites become saturated.
Comparison of 200 Liter and 40 Milliliter Leach Tests
Authors: Westsik J. H. , Harvey C. O. , Roberts F. P. , Ross W. A. , Thornhill R. E. 
Published: March 2011

ABSTRACTDuring the past year we have conducted a modified MCC-1 leach test on a 145 kg block of a cast cement waste form. The leach vessel was a 200 liter Teflon®-lined drum and contained 97.5 liters of deionized water. The results of this large-scale leach test were compared with the results of standard MCC-1 tests (40 ml) on smaller samples of the same waste form. The ratio of leachate volumes between the large and small scale tests was 2500 and the ratio of sample masses was 150,000. The cast cement samples for both tests contained plutonium-doped incinerator ash.The leachates from these tests were analyzed for both plutonium and the matrix elements. Evaluation of plutonium plateout in the large-scale test indicated that the majority of the plutonium leached from the samples deposits onto vessel walls and little (<3 × 10−12M) remains in solution. Comparison of elemental concentrations in the leachates indicates some differences up to 5X in the concentration in the large- and small-scale tests. The differences are attributed to differences in the solubilities of Ca, Si, and Fe at pH ˜11.5 and at pH ˜12.5. The higher pH observed for the large-scale test is a result of the larger quantities of sodium in the large block of cement.
Correlation of 137Cs Release From Small-Scale to Large-Scale Cement Waste Forms
Authors: Morcos Nabil , Dayal Ramesh , Milian Laurence , Hayde Philip , Weiss Allen J. 
Published: March 2011

ABSTRACTA study correlating the leachability of 137 Cs from small-scale to large-scale cement forms was performed. The waste forms consisted of (a) organic ion exchange resins incorporated in Portland I cement, with a waste-to-cement ratio of 0.6 and a water-to-cement ratio of 0.4 (as free water) and (b) boric acid waste (12% solution) incorporated in Portland III cement, with a waste-to-cement ratio of 0.7. 137Cs was added to both waste types prior to solidification. The sample dimensions varied from 1 in. ×1 in. to 22 in. × 22 in. (diameter × height). Leach data extending over a period of 260 days were obtained using a modified IAEA leach test. A method based on semi-infinite plane source diffusion model was applied to interpret the leach data, which allows prediction of the amount of 137Cs leached from the forms as a function of leaching time and waste form dimensions. A reasonably good agreement between the experimental and calculated data was obtained for both types of cement waste forms.
Microcracks and Radioactive Waste Disposal
Authors: Simmons Gene , Caruso Louis 
Published: March 2011

ABSTRACTExamination of microcracks in crystalline rocks has shown that the open microcracks form a spatially continuous network that communicates with larger openings. The open cracks become filled with new minerals that often contain U and LREEs. The crystalline rocks most desirable as a host for a repository have low crack porosity, moderate alteration, and occur in an environment that promotes rapid sealing.
Effect of Channelling in a Porous Medium on Radionuclide Migration
Authors: Ray Asit K. , Nair Shyam 
Published: March 2011

ABSTRACTA mathematical model has been developed to study the effect of channelling in a porous medium surrounding a repository on the migration of radionuclides. The porous medium is treated as an infinite medium containing parallel, unconnected channels; each channel is surrounded by a rock matrix. The migration in the channel is controlled by convection and diffusion processes in the direction of the flow, whereas in the rock matrix it is dominated by anisotropic diffusion in the longitudinal and transverse directions. Unsteady state convective-diffusion equations for this system have been solved. At the channel-rock matrix interface the concentration and flux were watched to obtain concentration profiles and discharge rates at downstream locations. By means of a parametric study the effects of channel thickness, diffusion coefficients, and flow velocity on the migration rate are elucidated.
Differential Scanning Calorimetry of Metamict Pu-Substituted Zirconolite
Authors: Peterson Dean E. , Clinard Frank W. 
Published: March 2011

ABSTRACTSamples of CaPuTi2O7 were prepared by cold pressing and sintering. Plutonium was substituted for zirconium in order to characterize radiation damage effects. The energy stored in a sample which had reached saturation in swelling after storage at ambient temperature was measured with a differential scanning calorimeter. The total energy of 6.6±0.1 cal/g is released over the range 485–715° C. The activation energy of annealing of the damage is 1.22±0.05 eV. The temperature dependence of the rate constant is described by kT= 5.96E4 exp(−1.22/kBT) s−1 where kB and T are the Boltzmann's constant and temperature(K) respectively. A sample stored at 600°C was similarly evaluated and showed no release of stored energy to the precision of the apparatus (±0.1 cal/g). These results are applied to analysis of waste incorporation in Synroc and are correlated with analogous parameters for other materials.
Glass Surface area to Solution Volume Ratio and its Implications to Accelerated Leach Testing
Authors: Pederson Larry R. , Buckwalter Charles Q. , Mcvay Gary L. , Lynn Riddle B. 
Published: March 2011

ABSTRACTLeaching tests of PNL 76–68 glass in deionized water have been performed using the standard MCC-l static leaching procedure but with varied glass surface area to solution volume ratios (SA/V). It was found that leaching could be strongly influenced by the SA/V ratio, due largely to an effect of silicon solubility limitations. The conclusion that solubility and not solid state diffusion is most important in regulating leaching rates is supported by (1) the similarities in depth profiles of all soluble glass components with none depleted to depths greater than that of silicon despite vastly different solid state diffusivities, and (2) the lack of dependence of leaching rates on reaction layer thicknesses. To more directly examine the influence of dissolved silicon on glass leaching rates, leaching tests were performed in silicic acid solutions and in two actual groundwaters. As expected, leaching rates of all soluble glass components were reduced by amounts roughly proportional to the silicon saturation fraction.
Since solubility modifies leaching rates in all but very dilute solutions, short-term tests at high SA/V values can be used to predict solution concentrations for long-term tests at low SA/V values, although reaction layers formed are not of the same thickness. Glass leaching data for a range of leaching times and SA/V values can be represented by a single curve when plotted versus the product of SA/V and time. However, the use of SA/V variations may have limited usefulness in accelerated leach testing for multicomponent systems. Events such as silica colloid and certain alteration phase formations modify the above relationship.
Approximations for Adapting Porous Media Radionuclide Transport Models to Analysis of Transport in Jointed, Porous Rock
Authors: Erickson K. L. 
Published: March 2011

ABSTRACTInitial criteria are defined which determine when radionuclide transport in jointed, porous rock can be approximated as occurring in an equivalent porous medium. For systems satisfying those criteria, the retardation factor to be used in the equivalent porous media model also is defined.
The Scepter Waste Package Subsystem Computer Model for Performance Assessment
Authors: Brecher Aviva , Pearson F. J. 
Published: March 2011

ABSTRACTThe Waste Package Performance Assessment (WAPPA) code has recently been completed, verified, and documented within the SCEPTER program for ONWI. This is a systems model of the gradual degradation of physical and retardation barriers comprising a nuclear waste package, under repository isolation conditions, in various geologic media. The model describes and predicts the temporal and spatial extent of the loss of containment capability for each barrier and for the entire waste package, on timescales of hundreds of thousands of years. The output quantifies the residual state of integrity of waste package components as a function of time and calculates heat, and radionuclide fluxes to the repository.The model includes five distinct degradation process models (Radiation, Thermal, Mechanical, Corrosion, and Leaching), which are driven both internally by waste decay and externally by repository stress and fluids. The process models are coupled at system level via state and coupling variables. The approach to degradation modeling adopted is barrier-integrated and process-sequential, allowing modification of the entire waste package sequentially by the five process models within each time step.The code is intended to serve as a tool for evaluating both the relative and the absolute performance of waste package design concepts, for guiding or selecting a preliminary design among conceptual designs, and for support of licensing activities.
The Formulation of an Integrated Physicochemical-Hydrologic Model for Predicting Waste Nuclide Retardation in Geologic Media
Authors: Muller A. B. , Langmuir D. , Duda L. E. 
Published: March 2011

ABSTRACTThe inability of empirical single value elemental Rd values to model radionuclide retardation in natural groundwater systems has demonstrated the need for developing a comprehensive integrated phenomenological model of the physicochemical and hydrologic mechanisms involved in retardation. The model must account for: (1) radioactive decay, (2) chemical precipitation/dissolution of bulk phases, (3) chemical substitution reactions, (4) isotopic exchange reactions, (5) cation and anion exchange, (6) specific adsorption, (7) diffusion into adjacent flow paths, (8) diffusion into fluid not involved in flow, (9) diffusion into the solid matrix and (10) ultrafiltration. The formulation of such a model is proposed, based on a reaction-path-simulation code with modifications for adsorption processes (by a surface-complexation site-binding model) and diffusional processes. The coupling of the physicochemical portion of this model to a ground-water transport code can be achieved by alternately iterating through the chemical and physical portions of the code during each time step. Sensitivity analysis used to determine dominant species, dominant retardation mechanisms and temporal and spatial homogeneities in the flow system will allow the integrated model to be reduced to a manageable form.
The Oak Ridge National Laboratory Hydrofracture Process for the Disposal of Radioactive Waste
Authors: Weeren Herman , Mcdaniel Earl 
Published: March 2011

ABSTRACTThe hydrofracture process is currently being used at Oak Ridge National Laboratory (ORNL) for the permanent disposal of locally generated radioactive waste solutions. In this process, the waste solution is mixed with a blend of cement and other solid additives; the resulting grout is then injected into an impermeable shale formation at a depth of 200 to 300 m (700 to 1000 ft). The grout sets a few hours after completion of the injection, fixing the radioactive waste in the shale formation.Between 1966 and 1979, ORNL has used hydrofracture to dispose of more than 8 million L (2 million gal) of waste grout containing more than 600,000 Ci of radionuclide activity. Calculations show that operational costs are on the order of $0.16/L ($0.60/gal). Construction of a new hydrofracture disposal facility has been completed, and operational injections were initiated in June 1982.
RA-226 Radioassay of Soil and Tailings
Authors: Sabau Cabmen S. , Rayno Donald R. , Kretz Norbert D. , Zelle Phillip W. 
Published: March 2011

ABSTRACTStudies of inactive uranium tailings piles have shown that tailings sands containing Ra-226 and other radionuclides may be dispersed by wind and water erosion, causing contamination of adjacent areas. To conduct an effective cleanup operation, it is necessary that boundaries of contamination be well defined. To accomplish this, data from surface gamma-ray surveys made under the Measurement Monitoring Program of the U.S. DOE's Uranium Mill Tailings Remedial Action Project (UMTRAP) are first used to delineate a general outline of the contaminated area. Then, data fram portable scintillometer surveys and fran sealed-can gammaray analyses of soil samples are used to more precisely define the perimeter of Ra-226 contamination. These field measurements are supported by radiochemical analyses of randomly selected samples. Because of its adaptability to the widely varying chemical composition of the material in these samples, the camplexing agent EDTA is used in a complexometric leaching procedure to analyze Ra-226. By this procedure, natural concentrations of Ra-226 in soil (∼1 pCi/g) can be measured routinely. The potential limit of detection is in the 0.1–0.5 pCi/g range. Details of the method, which includes leaching of radium followed by radon de-eranation, are described. Comparative data for various soil and tailings samples are presented.
Analyses of Soils from the Commercial Radioactive Waste Disposal Sites at Barnwell, Sc, and Hanford, Wa
Authors: Piciulo Paul L. , Shea Colleen E. , Barletta Robert E. 
Published: March 2011

ABSTRACTBrookhaven National Laboratory, in order to provide technical assistance to the NRC, has measured a number of physical and chemical characteristics of soils from two commercial radioactive waste disposal sites: one at Barnwell, SC, and the other near Richland, WA. Materials commonly used for the containment and the solidification of radioactive waste are subject to underground corrosion. The data reported can be used to assess the corrosivity of each burial environment on a waste form or high integrity container. Samples of trench backfill soil, believed to be representative of the soil that will contact the buried waste forms were collected and analyzed. Earth resistivities were measured at each site. Laboratory measurement of the resistivities of water saturated backfill soils from both sites show values greater than 104ohm-cm. This is indicative of soils having relatively small amounts of soluble ions and of soils likely to be very mildly corrosive to steel. The backfill soil from the Barnwell site is acidic having a pH ∼5. Measurements on Hanford backfill soil indicate a neutral environment; pH ∼7. The exchange acidity of the backfill soils from both sites was <2 meq per 100 g of soil and in most cases an alkaline reaction was observed. The pHs and exchange acidities of these soils are consistent with those of mildly corrosive soils. Aqueous extracts of saturated pastes were used to determine the concentrations of the following ions: Ca2+, Mg2+, K+, Na+, HCO3−, SO4=, and Cl−. The sulfide content of each of the soils was measured in a mixture of soil and an antioxidant buffer solution.
Some Effects of Microstructure and Chemistry on Corrosion and Hydrogen Embrittlement of Ticode–12
Authors: Ruppen J. A. , Diegle R. B. , Glass R. S. , Headley T. J. 
Published: March 2011

ABSTRACTEffects of microstructure and chemistry on corrosion and hydrogen embrittlement of TiCode-12 have been investigated. Heat treating mill-annealed TiCode-12 in the temperature range 500–750°C results in a sensitization effect, i.e., an increase in the uniform corrosion rate when tested in either boiling 1N HCl or a MgCl2brine. This effect is caused by microstructural changes involving the precipitation of Ti2Ni. Electrochemical studies indicate that sensitization results from galvanic coupling between Ti2Ni, acting as cathode, and the α-Ti matrix with resultant shifts in corrosion potential. Increasing the Fe content of the alloy promotes the sensitization effect.Hydrogen embrittlement of TiCode-12 was studied using the slow strain rate technique. Hydrogen concentrations to 130 wppm did not cause embrittlement. However, above 220 wppm hydrogen, degradation was observed as a decrease in mechanical behavior and the appearance of cleavage-like secondary cracks. The embrittlement was dependent on temperature and alloy chemistry but not environment (air or brine).
Fixation of high Level Solid Waste (HLSW) in a TiO2 Base Ceramic Matrix Provided with an Integrated Overpack
Authors: Bauer Christof , Ondracek Gerhard 
Published: March 2011

In the past years a lot of research work has been done in several countries to find a waste form capable of accommodating the wide variety of elements present in commercial high level waste (HLW) and which at the same time, has a higher leaching resistance than the currently favoured high level waste glass. The main problems arising from a product made up of different phases, each of them taking up a certain fraction of the HLW-elements into solid solution, are1) the necessity of very intimate mixing of the HLW-elements and the inert additives because otherwise undesired highly leachable phases might be formed;2) the detrimental effect transmutation of the radioactive elements will most probably have on the crystal structure in which they are present. Fracturing and loss of the low solubility of the products are likely to occur.