bluuebunny/crossref_metadata_2025_split huggingface dataset:
Actinide Sorption onto Silica in the Presence of Humic Substances: Proposal of Retentionmechanisms
Authors: Labonne N. , Moulin V. , Stammose D. 
Published: March 2011

ABSTRACTThe experimental investigation and modelling of radionuclides sorption processes is an essential part of safety analyses of an underground repository of radioactive wastes in geological formations. Physico—chemical phenomena at oxide/solution interfaces have been studied in the case of the system constituted by amorphous silica and americium (III) in the presence of humic substances as organic complexing agents. The retention behaviour of Am(III) onto silica appears dependent on pH, ionic strength and in particular humic concentration. At a ionic strength of 0.1 M, the presence of low concentration of humic acids (1 mg/l) enhances the Am(III) retention in the pH range 3-5.5, whereas at higher pH, its uptake is largely decreased. At lower ionic strength (0.001 M), Am(III) retention on silica is highly lowered, in the pH range 3-7 in the presence of humic acids. Reversibility experiments show the desorption of americium in the absence of humic substances, and also the desorption of the humics on the silica with respect of the pH. The surface complexation model has been applied to our results in the different systems and apparent surface complexation constants have been determined.
Determination of Formation Constants, Solubilities, and Ionic Speciation of Uranium, Plutonium and Thorium in Aqueous and Saturated Salt Solutions for Modelling Safety Aspects of Ilw Repositories
Authors: Bischoff H. , Kramer-Schnabel U. , Esser V. , Xi R.H. , Heppner P.-M. , Marx G. 
Published: March 2011

ABSTRACTThe solubility products of uranyl hydroxide and uranyl carbonate and the formation constants of the complexes present in the solution have been determined at 25ºC and I=0.1 mol dm−3by potentiometry and solubility experiments. The uranyl complexes U02(OH)2'(UO2)2(OH)22+,(UO2)3(OH)5+, UO2CO3', UO2(CO3)22−and UO2(CO3)34−were identified. For the system uranyl-hydroxide the results were verified by analysis of conductance measurements. A similar investigation was carriedout for thorium. Using Pu(IV)-chloride complexes as an example the potential of differential pulse voltarnmetry is demonstrated for the determination of small formation constants.
Recovery and Mutual Separation Process of Noble Metals from Simulated Insoluble Residue of Spent Fuel
Authors: Matsui Tsuneo , Naito Keiji 
Published: March 2011

ABSTRACTRecent results on the various methods for the recovery and the mutual separation of Mo, Ru, Rh and Pd from the simulated insoluble residue in the reprocessing plant, such as liquid lead and zinc extractions, nitric acid dissolution and preferential oxidative vaporization in various atmospheres by the authors are briefly reviewed. By combining these results, four kinds of processes for the recovery and the mutual separation of Mo, Ru, Rh and Pd (and Tc) i.e. two processes composed of Pb (and Zn) extraction(s) and subsequent nitric acid dissolution, and two processes using vaporization in various oxidizing atmospheres at various temperatures are proposed.
Potential Hazard of Ferrocyanide Salts in High-Level Waste Tanks Within the Hanford Tank Farm
Authors: Agnew S. F. , Eisenhawer S. W. , Davidson R. F. , Sullivan L. H. 
Published: March 2011

ABSTRACTOver the past few years, there has been an increased awareness of the potential hazard of energetic chemical reactions in high-level radioactive waste tanks at the Hanford tank farm. In particular, a mixture of Na2NiFe(CN)6 with NaNO3 and NaNO2 in several high-level waste tanks has caused concern. The problem of the FeCN tanks is fundamentally one of a potentially unstable mixture of fuel (the CN- moiety) and oxidizer (NO3- or NO2-).At Los Alamos National Laboratory, we have performed an extensive reanalysis of the safety problems associated with the presence of Na2NiFe(CN)6 mixed with NaNO3/NO2 for a particular tank (104-BY) that contains by far the largest amount of the nickel ferrocyanide salt (∼2E5 mol). Our approach is to use conservative assumptions to bound both the energy density for a potential runaway reaction and the mass that could participate if we assume ignition as the result of bounding radionuclide concentrations. The subsequent progress of the accident is analyzed using an advanced hydrodynamics computer code called MESA to evaluate the loads on the structure and the generation of aerosols. The subsequent doses are shown to be low both on and off the site. The conservatism in the analysis is quite large, and the expected results using more realistic assumptions are discussed.
Effect of Radiation on the Corrosion of Candidate Materials for Nuclear Waste Containers
Authors: Shoesmith D.W. , Ikeda B.M. , King F. 
Published: March 2011

ABSTRACTThe published information on the effect of radiation on the corrosion of potential waste container materials is reviewed. The materials discussed are irons and carbon steels, copper and copper alloys, stainless steels, nickel-based alloys, and titanium alloys. In general, a dose rate of >5 Gy·h-1 is required to accelerate the general corrosion of corrosionallowance materials. The effects of radiation on the localized corrosion of corrosion-resistant materials appear to be contradictory. In some cases, localized corrosion is induced, whereas in others it is inhibited.
Diffusion of Lead from a Perforated Titanium-Shell Lead-Matrix Container
Authors: Mathew P. Mani , Krueger Paul A. , Krause M. 
Published: March 2011

ABSTRACTThis paper describes experiments and analyses conducted to determine the range of apparent diffusion coefficients of lead diffusing from an intentionally perforated lead-matrix titanium-shell container into a compacted 1:1 (by dry mass) silica-sand/sodium-bentonite buffer mixture saturated with Standard Canadian Shield Saline Solution at 363 K. Analysis of the experimental data using a single apparent diffusion coefficient could not explain the findings. A possible explanation of the behaviour is presented here. It uses a 2–D finite-element model with six lead species having six different apparent diffusion coefficients. The model can explain the data satisfactorily. Sixty-three percent of the source concentration consisted of slow-moving species, with an apparent diffusion coefficient of 10-15 m2 /s, whereas the fastest species, with an apparent diffusion coefficient of 10-10 m2 /s, constituted only three percent of the source concentration.
Lifetimes of Titanium and Copper Containers for the Disposal of Used Nuclear Fuel
Authors: Johnson Lawrence H. , Shoesmith D.W. , Ikeda B.M. , King F. 
Published: March 2011

ABSTRACTTitanium and copper have been proposed as suitable container materials for disposal of nuclear fuel waste in plutonic rock of the Canadian Shield. Studies of the corrosion of these materials have led to the development of container failure models to predict long-term performance. Crevice corrosion and hydrogen-induced cracking of titanium have been identified as potential failure mechanisms, and these two processes have been studied in detail. Using data from these studies as well as a number of conservative assumptions, titanium container lifetimes of 1200 to 7000 a have been estimated. For copper, general corrosion has been studied in detail in bulk solution and in compacted clay-based buffer material. Results indicate that the copper corrosion rate is likely to be controlled by the rate of transport of copper species away from the container surface. An assessment of copper pitting data suggests that pitting is an extremely improbable failure mechanism. The copper container failure model predicts minimum container lifetimes of 30 000 a. The results demonstrate that long lifetime containment can be provided, should performance assessment studies indicate the need for such an option.
Radionuclide Transport by Groundwater Colloids at the Koongarra Uranium Deposit
Authors: Payne T.E. , Edis R. , Seo T. 
Published: March 2011

ABSTRACTGroundwater and entrained particles were sampled from several boreholes at the Koongarra uranium deposit in the Northern Territory of Australia. Conventional filtration techniques, hollow fibre ultrafiltration, and stirred-cell ultrafiltration were used to separate dissolved species, large particles (> 1 μm) and colloids (< 1 μm). The colloids and particles included clay minerals, particularly kaolinite, and chlorite, together with fine quartz grains. Iron was present as particle coatings, and in a separate colloidal form. The amount of238U associated with colloids (expressed as a percentage of the total238U which passed through the 1.0 μm filter) ranged up to 6.5%. The corresponding figures for Th were 10-85%. However, the amount of230Th which passed through the 1.0 μm filter was extremely small, and230Th was associated to a much greater extent with larger particles, which are unlikely to be mobile in natural groundwaters. In some fine particle and colloidal fractions, the227Th/230Th activity ratio in the thorium alpha spectrum was unusually high, indicating the presence of substantial quantities of227Ac. This suggested that actinium could be present as a mobile colloid phase. Overall, there was very little colloidal material in these groundwaters, with only iron, uranium, actinium, and thorium showing a significant association with colloids.
Natural Analogue study on the Long-Term Durability of Bentonite –Time-temperature condition and water chemistry on illitization at the Murakami deposit, Japan.–
Authors: G. Kamei , Y. Yusa , N. Sasaki 
Published: March 2011

ABSTRACTTime-temperature conditions and water chemistry on illitization at the Murakami deposit in central Japan were determined. The extent of the illitization and timetemperature condition estimated were as follows: the duration for conversion from 0 to 80%illite (volumetric ratio) was approximately 3.5Ma in the temperature range from 340 to 100°C. Conversion from 0 to 40% requires approximately 3.0Ma in the temperature range from 240 to 100°C. During 2.0Ma in the temperature range from 160 to 100°C, however, illite was scarcely observed. Water chemistry is estimated from two approaches, namely laboratory experiment and numerical analysis. The former is an interactive experiment between seawater and the tuff of the deposit. The latter is a calculation based on the difference of bulk composition between illitized and non-illitized tuff. The extent of each ionic concentration is inferred to be as follows: K+; 560 to 6400, Mg2+; 800 to 1700, Ca2+; 360 to 2900, Na+; 9400 to 15000 (mg/l).
Settlement of An Embedded Nuclear Waste Container Due to Creep of a Surrounding Geological Barrier
Authors: Selvadurai A.P.S. 
Published: March 2011

ABSTRACTThe paper discusses the influence of creep deformations of either engineered or natural geological barriers on the long term settlement of waste containers located within them. The paper describes, briefly, the potential application of numerical procedures for the estimation of the creep settlement rigid cylindrical containers embedded in engineered and natural geological media.
Fast Model for Calculating Steady State Release of Radionuclides from the Near Field
Authors: Nilson Lennart , Romero Leonardo , Moreno Luis , Neretnieks Ivars 
Published: March 2011

ABSTRACTA model has been developed which describes the steady state transport of dissolving species of radionuclides from a single canister in a repository for spent nuclear fuel into the passing water in fractures in the surrounding rock. The steady state transport of nuclides is described by a network of transport resistances, coupled together in the same way as an electrical circuit network. With the model a number of calculations are done for various sets of fracture geometry data. The calculations indicate that the resistance network model gives results comparable to those of a complex 3-dimensional numerical model. The present model is very simple and fast.
The Impact of Episodic Nonequilibrium Fracture-Matrix Flow on Repository Performance at the Potential Yucca Mountain Site
Authors: Buscheck Thomas A. , Nitao John J. , Chesnut Dwayne A. 
Published: March 2011

ABSTRACTAdequate representation of fracture-matrix interaction during episodic infiltration events is crucial in making valid hydrological predictions of repository performance at Yucca Mountain. Approximations have been applied to represent fracture-matrix flow interaction, including the Equivalent Continuum Model, which assumes capillary equilibrium between fractures and matrix, and the Fracture-Matrix Model, which accounts for nonequilibrium fracture-matrix flow. We analyze the impact of matrix imbibition on episodic nonequilibrium fracture-matrix flow and transport for the eight major hydrostratigraphic units in the unsaturated zone at Yucca Mountain.
The Assessment of the Performance of the Engineered Barriers in a Repository for the Disposal of Low- and Intermediate-Level Radioactive Waste
Authors: Atkinson A. , Harris A.W. , Naish C.C. , Sharland S.M. , Smith A.C. 
Published: March 2011

ABSTRACTCurrent plans for the disposal of low- and intermediate-level radioactive waste in the U.K. comprise emplacement of steel or concrete containers of waste in a deep underground repository where they will be surrounded by a cementitious backfill. Research is in progress to assess the effectiveness of steel and concrete as barriers to radionuclide release from the repository. A joint experimental and modelling approach is used. Studies of the transport properties of dissolved radionuclides and gases through concrete, and the ability of the concrete to control the pH in the repository are described. Localised and uniform corrosion of carbon and stainless steels are investigated in the high pH conditions of the repository. The research shows that engineered barriers of concrete and steel can provide useful physical containment in the short term and contribute to chemical containment for hundreds of thousands of years.
A Model for Nearfield Performance Assessment in the Presence of a Permeable Engineered Barrier
Authors: Broc D. , Lamoureux M. , Durin M. , Voinis S. , Raimbault P. 
Published: March 2011

ABSTRACTOne of the options envisaged by ANDRA for some of the engineered barriers in a geological repository in hard rock is the use of a permeable granular material (clay/sand or clay/crushed rock mixtures).This choice will lead to modification of the flow distribution around the repository borehole and the consequences on the migration behaviour in the near field need to be evaluated.The aim of this study is to develop a borehole model which describes the release in the borehole from the waste matrix through the engineered barrier. This model can be readily integrated in a near field model of the waste storage area.
Fluid and Solute Transport in a Network of Channels
Authors: Moreno Luis , Neretnieks Ivars 
Published: March 2011

ABSTRACTA model is proposed to describe flow and transport in fractured rocks. It is based on the concept of a network of channels. This approach is backed by observations in drifts and tunnels that flow in fractured rocks takes place in sparse narrow channels with widths typically less than 10 cm and a channel frequency of one channel per a few square meters to one channel per more than a hundred square meters. Observations in boreholes also indicate that there are large distances, tens to hundreds of meters, between the most conductive sections in boreholes.For visualization purposes our model is displayed on a rectangular grid. The individual channels are given stochastically selected conductances and volumes. Flowrate calculations have been performed in grids of sizes 20*20*20 channels in most cases but larger grids have also been used. For large standard.deviations in conductances, greater than 1.6 in the log normal distribution (base 10), channeling becomes pronounced with most of the water flowing in a few paths. The effluent patterns and flowrate distributions obtained in the simulations have been compared to three different field measurements in drifts and tunnels. Standard deviations of channels conductances were found to be between 1.6 and 2.4 or more in some cases. Channel lengths were found to vary between 1.2 m and 10.2 m in the different sites. In one site where detailed borehole measurements were available the channel length could be assessed independently and was found to be 1.2 m as compared to the 1.7 m obtained from the drift inflow measurements.A particle tracking technique was used to simulate solute transport in the network. Nonsorbing as well as sorbing tracer transport can be simulated and by a special technique also tracers which diffuse into the rock matrix can be simulated.Tracer measurements in one site, Stripa, were used to compare dispersivities. These were found to be large, having Peclet numbers less than 5 both in simulations and the field results. From the Stripa tracer data it was also found that the tracers were taken up into the rock matrix by molecular diffusion. The surface area needed for this uptake was estimated to be between 0.2-20 m2/m3 for different tracers. The wetted surface for the model estimated from flowrate distribution data indicate a wetted surface of 0.2- 0.4 m2/m3.
Tracer Tests in a Small Fracture Zone at Stripa
Authors: Birgersson Lars , Neretnieks Ivars , WidÙn Hans , Ågren Thomas 
Published: March 2011

ABSTRACTA large scale tracer test has been performed as a part of the Site Characterization and Validation (SCV) Project in the Stripa experimental mine. Tracers were injected in a fracture zone intersecting a newly excavated drift and collected in plastic sheets and sump holes. The experiment gave information on the variability of flow and transport properties in a fracture zone.
The Effect of Microbial Activity on the Near and Far Fields of a Swiss Type b Repository
Authors: West J.M. , Cave M. , Higgo J.J.W. , Milodowski A.E. , Rochelle C.A. , Ross C.A.M. 
Published: March 2011

ABSTRACTA series of batch laboratory experiments (‘black boxes’) were set up to study the gross effects of microbial activity on repository geochemistry, radionuclide sorption and the integrity of repository and host rock materials in a Swiss type B repository. The observed principal chemical exchanges and precipitations were confirmed by modelling and could be interpreted by excluding microbiological effects. However, mineralogical studies showed steel corrosion to be localised in deep pits with microbiology playing a possible role. Talc was precipitated in all of the cells which lowered ambient pH through removal of OH- causing dissolution of CSH compounds. This has implications for the long term stability of cements. Microbiology influenced far-field radiochemistry experiments in which added microbes increased Cs sorption particularly under anaerobic conditions.
Amorphous Silicon Thin Film Transistors With High Electron Field Effect Mobility
Authors: Andújar J.L. , Bertrán E. , Canillas A. , Campmany J. , Cifre J. 
Published: March 2011

ABSTRACTNormal staggered hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFT) were prepared by rf plasma deposition through a three-step process. The TFTs were constituted by an a-SiN/a-Si:H structure grown on NiCr source-drain electrodes evaporated on glass substrates. The intrinsic a-Si:H active layer (Fermi level at EC-EF = 0.7 eV) was deposited from pure SiH4 rf plasma, and the insulator layer of a-SiN was grown using a high rf power plasma (200 mW/cm2) of SiH4-N2 mixture with a SiH4 fraction of 0.5 %. Ellipsometric measurements showed that a very transparent a-SiN film was grown with an abrupt interface insulator/a-Si:H. TFTs with 0.2 μm thick a-Si:H layer and 10 μm channel length have on-off current ratios of 5 104, electron field effect mobility of 1.5 cm2/V-s (dielectric constant εri ≈ 7.9), and threshold voltage around 5 V. The results are discussed in terms of low hydrogen content and low porosity of these a-SiN films prepared from silane-nitrogen.
Studies of the Stability of Amorphous Silicon Thin Film Transistors
Authors: Globus T. , Shur M. , Hack M. 
Published: March 2011

ABSTRACTOur experimental studies confirm that changes in a-Si Thin Film Transistors (TFTs) under voltage stress occur in the device channel and not in the contacts. We demonstrate that stressing an a-Si TFT not only shifts the device threshold voltage but can also changes the slope of the semilog subthreshold current dependence on the gate voltage. In addition, stressing can decrease the minimum leakage current. The creation of new localized states in the amorphous silicon under voltage stress qualitatively explains all these effects, while carrier tunneling and trapping in the gate insulator layer cannot by itself explain our data. At large negative gate voltages, the leakage current increases due to the holes injected into the channel. This hole current is also affected by voltage stress as can be predicted by the state creation mechanism.
Electron Transport Mechanisms in Nickel Schottky Barrier Contacts to Hydrogenated Amorphous Silicon
Authors: Heller D.E. , Gunes M. , Rubinelli F. , Dawson R.M. , Nag S. , Fonash S.J. , Wronski C.R. 
Published: March 2011

ABSTRACTDark J-V characteristics of Ni Schottky diodes on a-Si:H films of various thicknesses were measured as a function of device temperature. Room-temperature photoconductivity and sub-bandgap absorption v. wavelength measurements of the intrinsic layers were also performed. Detailed numerical modelling was employed to determine the nature, density and energy distribution of sub- bandgap states. Best-fit modelling of photoconductivity, sub-bandgap absorption and dark JR-VR indicates that Nc=Nv=2.5×1020 cm-3, vR=2×106 cm/s, μn=33 cm2/V-s and μp=0.15 cm2/V-s for these films. It is found that a joint thermionic emission-drift/diffusion mechanism, as envisaged by Crowell and Sze, appears to be the most accurate picture of electron transport in Schottky diodes on intrinsic a-Si:H films.
High Performance Input Scanning Arrays Using Amorphous Silicon Photodiodesand Thin-Film Transistors
Authors: Weisfield Richard L. 
Published: March 2011

ABSTRACTThe use of large area hydrogenated amorphous silicon (a-Si:H) technology has enabled compact, full page width scanners to be built inexpensively, and is now the dominant method for fabricating low-end facsimile machines. This technology has now been extended to scanners with considerably higher levels of performance. High speed, high resolution, full-width input scanning arrays have been developed using a-Si:H photodiodes and thin-film transistors (TFTs). A 12” long array has been designed to scan 3 colors at 400 spots per inch, and operates at speeds of up to 40 pages per minute, achieving a signal/noise ratio of 400:1 at intensities of 30 μWcm-2.The color scan array is made using 3 rows of a-Si:H photodiodes, one per color, addressed by TFTs which share sets of common data lines. The data lines are arranged in a low capacitance non-crossing configuration which allows the scanner to achieve high responsivity with low crosstalk. The data lines are connected to a number of readout chips, each of which amplifies and multiplexes the photosignals onto a single video output line. Optoelectronic test results and images obtained from this device will be presented. These results indicate that high quality color images can be obtained from a-Si:H scanners, and that the present scanner is more limited by the speed of the readout chips than by the a-Si: H devices themselves.