bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Chemical Behavior of Transuranium Elements and Barrier Functions in Natural Aquifer Systems
Authors: Kim Jae-Il 
Published: March 2011

ABSTRACTThe chemical behavior of transuranium elements in natural aquifer systems is governed by a variety of geochemical reactions, such as dissolution reaction (solubility), hydrolysis, complexation with inorganics or organics, redox reaction, colloid formation, geochemical interaction with surfaces of various minerals, coprecipitation, mineralization, etc. This paper reviews the present state of knowledge on some of these particular reactions. The emphasis here is on how the individual reactions can be appraised for long-term prediction of the geochemical behavior of transuranium elements in the natural environment. of the various possible reactions, the primary thermodynamic processes are discussed with notable examples: dissolution of transuranium compounds in aquatic solution; complexation with important anions present in groundwater; and colloid generation. Various laser spectroscopic methods in use for chemical speciation are mentioned briefly for their spectroscopic capability, as well as for their applicability. The present paper attempts to better understand the migration behavior of transuranium elements in natural aquifer systems.
Solidification of Microbiologically Treated Ion-Exchange Resins Using Portland Cement-Based Systems
Authors: Ipatti Ari 
Published: March 2011

ABSTRACTPretreated inactive ion exchange resins from the Loviisa nuclear power plant (NPP) were first reduced to one tenth of the original volume through microbiological treatment. During the process, the granular ion exchange resins were decomposed to result in dregs, which were solidified with two types of Portland cements. The objective of the present experiments was to investigate whether commercial cements are suitable solidification agents for this kind of waste.A total of ten mixtures were pretested for their rheological and setting properties. On the basis of the pretest results, four additional mixtures were chosen and tested for the spread value, density, air content, setting time and bleeding of the fresh waste product and for the dimensional stability and compressive strength of the hardened waste product. The cementing systems incorporated in the tests were ASTM type V Portland cement and ASTM type P Portland Composite cements. The dregs used in the tests were taken from a Pilot-Plant experiment at the Loviisa NPP and contained 2 wt-% solids.The test results were promising in showing that microbiological dregs can very easily be solidified with Portland cements to form a high-quality waste product. Thus, the microbiological treatment of spent ion exchange resins will drastically decrease the amount of solidified waste to be disposed of at the Loviisa NPP.
Laboratory Studies of Gas Generation for the Waste Isolation Pilot Plant
Authors: Brush L. H. , Molecke M. A. , Westerman R. E. , Francis A. J. , Gillow J. B. , Vreeland R. H. , Reed D. T. 
Published: March 2011

ABSTRACTThe design-basis, defense-related, transuranic waste to be emplaced in the Waste Isolation Pilot Plant may, if sufficient H2O, nutrients, and viable microorganisms are present, generate significant quantities of gas in the repository after filling and sealing. We summarize recent results of laboratory studies of anoxic corrosion and microbial activity, the most potentially significant processes. We also discuss possible implications for the repository gas budget.
Recent Advances in the Study of Microbiologically Influenced Corrosion
Authors: Little Brenda , Wagner Patricia 
Published: March 2011

ABSTRACTThe study of microbiologically influenced corrosion (MIC) has progressed from phenomenological case histories to a mature interdisciplinary science including electrochemical, metallurgical, surface analytical, microbiological, biotechnological and biophysical techniques. With gene probes and microelectrodes it is now possible to measure interfacial dissolved oxygen, dissolved sulfide and pH and to further determine the microbial species responsible for the localized chemistry. Biofilms can be tailored to contain consortia of specific microorganisms and naturally occurring biofilms can be dissected into cellular and extracellular constituents. Scanning vibrating electrodes can be used to map the distribution of anodes and cathodes so that localized corrosion can be correlated with the location of microorganisms. The development of environmental scanning electron, atomic force, and laser confocal microscopy makes it possible to image cells on surfaces and to accurately determine the spatial relationship between microorganisms and corrosion. Transport of nutrients through biofilms is being modeled using techniques including optical density measurements to precisely locate the water/ biofilm interface and nuclear magnetic resonance imaging to visualize flow characteristics near surfaces colonized with microorganisms. The ways in which these new techniques can be used to understand fundamental mechanisms and to discriminate critical issues of MIC will be discussed.
Electrochemical Studies of Corrosion of Sinfuel: Simulated Used UO2 Fuel
Authors: Sunder S. , Shoesmith D.W. , Miller N.H. 
Published: March 2011

ABSTRACTThe corrosion of SIMFUEL, simulated high-burnup CANDU (CANadian Deuterium Uranium) fuel, was investigated in 0.1 mol·dm−3 NaClO4 solution (pH ∼ 9.5) as a function of dissolved oxygen concentration using electrochemical techniques and X-ray photoelectron spectroscopy (XPS). Electrodes were constructed of SIMFUEL pellets with compositions close to those of a natural UO2 fuel that has undergone burnup of 3 at% and 6 at%. The XPS analysis of freshly polished SIMFUEL pellets showed that the extent of uranium oxidation in SIMFUEL was equivalent to that in stoichiometric UO2. The SIMFUEL electrodes showed higher conductivity and electrochemical reactivity than the pure UO2 electrodes. A comparison of the open circuit corrosion potentials of the SIMFUEL electrodes with that of a pure UO2 electrode in oxygenated solutions showed a much faster increase in the potential for the SIMFUEL electrodes at short times. This suggests that the initial stages of UO2 oxidation, i.e., UO2 → UO2+x → UO2.33, are facilitated by fission product impurities in the UO2 matrix. However, the “steady-state” oxidation of uranium in SIMFUEL by the dissolved O2 was similar to that observed in pure UO2 under similar conditions.
Susceptibility of Stainless Steel Weldments to Microbiologically Influenced Corrosion
Authors: Borenstein Susan Watkins 
Published: March 2011

ABSTRACTMicrobiologically influenced corrosion (MIC) is the term used for the phenomenon where corrosion is initiated or accelerated by microorganisms. Biofilms of bacteria form on metal surfaces when exposed to natural waters. The activity of these biofilms and how they attach themselves to metal surfaces directly influence corrosion mechanisms.This paper describes the mechanisms for MIC and the factors which influence the susceptibility of austenitic stainless steel weidments to MIC. The metallurgical, microbiological and electrochemical factors that influence MIC are discussed. Case histories of MIC-related failures and field test results of austenitic stainless steel weldments in various welded conditions are presented.
Moisture Adsorption and Volume Change of Partially Saturated Bentonite Buffer Materials
Authors: Kanno Takeshi , Wakamatsu Hisao 
Published: March 2011

ABSTRACTWater vapor adsorption characteristics of buffer materials to be used for the geologic disposal of high-level radioactive waste have been investigated. Highly compacted blocks of Japanese Na bentonite were used as the buffer material. Initial dry density of the blocks was 1.8 g/cm3. Volume changes and water contents of the blocks in equilibrium with surrounding moist air were measured. The humidity of the surrounding air was kept constant, and the suction of the block at equilibrium has been determined by the humidity. The temperature of the surrounding air was varied between 20°C and 60°C.The volumetric strain was observed to vary approximately between −3% and 13% depending on the humidity of 0.6% to 95%. Some analytical expressions derived from these experiments on moisture adsorption are presented in this paper. Water vapor adsorption isotherm of the bentonite blocks was also obtained. The swelling pressures calculated from the analytical expressions are compared with literature data for this bentonite.
Radiolytically-Induced Gas Production in Plutonium-Spiked Wipp Brine
Authors: Reed D. T. , Okajima S. , Brush L. H. , Molecke M. A. 
Published: March 2011

ABSTRACTGas generation due to alpha particle deposition was investigated in four WIPP relevant brines; WIPP brine A, ERDA-6, DH-36 and G8-B. This was done by spiking each brine with plutonium-239 and periodically sampling the gas phase to determine the nature of the gaseous products and the rates of gas generation. The predominant gas generated radiolytically was hydrogen, with yields ranging from 0.6 to 1.5 molec/100 eV for the four brines tested. Plutonium (VI) was stable in two synthetic brines, WIPP brine A and ERDA-6 but was rapidly reduced in the underground collected brines DH-36 and G8-B, although most of the plutonium remained in solution.
Evaluation of the Retention Capability of Backfill Materials in the Presence of Cement Waste Form
Authors: Ghattas N.K. , Adham K.A.El , Eskander S.B. , Mahmoud N.S. 
Published: March 2011

ABSTRACTThe present study focused on the retention capability of the different local backfill materials and on horizontal and vertical radionuclide migration in simulated repository conditions of a saturated static humid environment, using single or combined components of the near-field. The results obtained from semi-field experiment show that no migration of cesium radionuclide was detected outside the backfill zone within the time interval of the experiment. This reflects the possible efficiency, of the backfill materials used, for the confinement of radioactivity to the disposal site. On the other hand laboratory experiments show the effect of simulated repository condition on the sorption and desorption properties of backfill materials. It is clear from the results obtained that the presence of cement waste forms in equilibrium with underground water affect the retention capability of the backfill materials. The motivation of the work was a desire to provide a basis for minimizing radioactive waste processing by improving nonradioactive engineering barriers.
Study of the Performance of Sealing Systems for Access Shafts in a High-Level Waste Repository
Authors: Saotome A. , Hara K. , Okamoto J. 
Published: March 2011

ABSTRACTShaft sealing in a high-level waste(HLW) disposal system functions to minimize the water flow passage, and retard the radionuclide transport from the repository to the accessible environment. It is important to estimate the radionuclide migration along the sealed shaft from the viewpoint of the design and the performance assessment of the sealing system.This study presents the results of sensitivity analyses on the radionuclide migration in the vicinity of the access shaft of a repository in order to evaluate the effects of the length of a plug, as well as the number of plugs, and curtain grouts.In this study, the upward hydraulic gradient of the groundwater flow along shafts was used, based on transient coupled thermo-hydraulic analyses around a repository. Hydraulic conductivities of the backfill material and the disturbed zones around the shaft tunnels were also assumed to be one order and two orders of magnitude higher than that of the host rock, respectively.The results show that the velocity of the groundwater within the shaft and the disturbed zone is reduced by a factor of one third by installing a few plugs into the shaft filled with backfill material. The curtain grouts have the effect of retarding the radionuclide migration from the repository to the ground surface at a factor of approximately five. A few plug installations have the same effect. The sealing system properly constituted with backfill, plugs, and grouts can provide the same performance as the original host rock.
Uranium Mineral – Groundwater Equilibration at the Palmottu Natural Analogue Study Site, Finland
Authors: Ahonen Lasse , Ervanne H. , Ruskeeniemi T. , Jaakkola T. , Blomqvist R. 
Published: March 2011

ABSTRACTThe redox-potential, pH, chemical composition of fracture waters, and uraninite alteration associated with the Palmottu uranium mineralization, have been studied. The data have been interpreted by means of thermodynamic calculations. The results indicate equilibrium between uraninite, ferric hydroxide and groundwater in the bedrock of the study site. Partially oxidized uraninite (UO2.33) and ferric hydroxide are in equilibrium with the fresh, slightly acidic and oxidized water type, while primary uraninite is stable with deeper waters that have a higher pH and lower Eh. Measured Eh-pH values of groundwater cluster within a relatively narrow range indicating buffering by heterogenous redox-processes. A good consistency between measured Eh and analyzed uranium oxidation states was observed.
Oxidative Alteration of Uraninite at the Nopal I Deposit, Mexico: Possible Contaminant Transport and Source Term Constraints for the Proposed Repository at Yucca Mountain
Authors: Leslie Bret W. , Pearcy English C. , Prikryl James D. 
Published: March 2011

ABSTRACTThe Nopal I uranium deposit at Pefla Blanca, Mexico is being studied as a natural analog of the proposed high-level nuclear waste repository at Yucca Mountain. Identification of secondary uranium phases at Nopal I, and the sequence of their formation after uraninite oxidation, provides insight into the source term for uranium, and suggests that uranophane may control uranium release and transport in a silicic, tuffaceous, chemically oxidizing, and hydrologically unsaturated environment. Possible constraints on contaminant transport at Nopal I are derived from the spatial distribution of uranium and from measurements of 238U decay-series isotopes. The analyses indicate that flow of U-bearing fluids was influenced strongly by fracture density, but that the flow of these fluids was not restricted to fractures. Gamma spectroscopic measurements of 238U decay-series isotopes indicate secular equilibrium, which suggests undetectable U transport under present conditions.
A Modelling Study on the Fractionation of Uranium Among Minerals During Rock Weathering
Authors: Ohnuki Toshihiko , Murakami Takashi , Yanase Nobuyuki 
Published: March 2011

ABSTRACTA modelling study has been carried out to understand the effect of rock alteration on the fractionation of uranium among coexisting minerals (chlorite, vermiculite, kaolinite, amorphous and crystalline iron minerals) at the Koongarra ore deposit, Australia. The model considers the chlorite weathering process, its mechanism and rate, and assumes the presence of reversible and irreversible sorption sites in the secondary minerals. The calculated uranium concentrations at the two different sites in the minerals were compared with the results of sequential extraction experiments. Good agreement between the calculated and observed uranium concentrations was obtained only when an appropriate fraction of uranium is fixed to the irreversible sorption sites of the altered clay minerals. However, a conventional Kd model gave inconsistent uranium concentrations. The calculated results show that the crystalline iron minerals sorb uranium during all stages of weathering, and that the uranium fractionation among the minerals varies with time until the end of the weathering.
Photothermal Deflection Spectroscopy Investigations of Uranium Electrochemistry
Authors: Rudnicki James D. , Russo Richard E. 
Published: March 2011

ABSTRACTPhotothermal Deflection Spectroscopy (PDS) has been successfully applied to the study of uranium oxide electrochemistry. A brief description of PDS and preliminary results that demonstrate the technique are presented. Concentration gradients formed at the electrode surface are measured by this technique. The gradients give insight into the reaction mechanisms. There is some evidence of the initiation of non-electrochemical dissolution of the uranium oxide. Optical absorption by the uranium oxide is measured by PDS and the first results indicate that the absorption of the surface does not change during electrochemical experiments. This result is contrary to literature measurements of bulk samples that indicate that the optical absorption should be strongly changing.
Kinetically Controlled Dissolution of UO2(s) Under Oxidizing Conditions. A Combined Dissolution-Okidation Model.
Authors: Casas Ignasi , Gimenez J. , Marti V. , Torrero M.E. , De Pabloc J. 
Published: March 2011

ABSTRACTThe release of uranium from three samples of UO2(S) with different particle sizes (100–300 μm, 900–1100 μm, pellet) has been studied as a function of time. In all cases, the same pH, ionic medium, temperature, and oxygen partial pressure were used.Two distinctive trends were observed in the three cases, with a relatively fast initial uranium release followed, after 10–15 days, by a slower dissolution rate. The experiments were continued during 200 days; no change in the second dissolution rate was noticed.The uranium released as a function of time has been successfully fitted with a mathematical expression which combines an oxidation-dissolution mechanism.
Repassivation Potentials for Long-Term Life Prediction of Localized Corrosion
Authors: Sridhar Narasi , Cragnolino Gustavo 
Published: March 2011

ABSTRACTThe effect of pit growth on repassivation potentials (Erp) of type 316L stainless steel (SS) and alloy 825 is investigated using a decreasing potential staircase technique. The Erp decreases initially with increasing pit depth and then attains a value which is relatively independent of pit depth. The Erp also decreases with increasing potential scan rate because of the decreasing time for repassivation with decreasing potential. The Erp, is explained in terms of the effect of applied potential on changes in solution composition inside growing pits and its use is recommended as a bounding parameter for long-term prediction of localized corrosion.
Dissolution of UO2(s) in MgCl2-Brines Under Different Redox Conditions.
Authors: Casas Ignasi , Gimenez J. , De Pablo J. , Torrero M.E. 
Published: March 2011

ABSTRACTThe dissolution of unirradiated UO2(s), with a particle size of 1 mm, has been studied in MgCl2 brines at 298 K under both reducing and oxidizing conditions. Results obtained under reducing conditions (H atmosphere in the presence of a palladium catalyst) show an initial increase of the total uranium concentration in solution and a subsequent decrease until equilibrium (or steady state) values are reached. Results obtained under oxidizing conditions (nominal oxygen partial pressures of 0.05, 0.21 and 1 atm) show two different trends. A relatively fast initial dissolution rate and, after approximately two or three weeks, a slower dissolution rate. X-Ray Photoelectron Spectroscopy (XPS) has shown that the UO2 surface composition changes during the experiment.
Some Important Mechanisms and Processes in the Near Field of the Swedish Repository for Spent Nuclear Fuel
Authors: Neretnieks Ivars 
Published: March 2011

ABSTRACTIn repositories for nuclear waste there are many processes that will be instrumental in damaging the canisters and releasing the nuclides. Based on experiences from studies of the performance of repositories and of an actual design, the major mechanisms influencing the integrity and performance of a repository are described and discussed. The paper addresses only conditions in crystalline rock repositories. The low water flow rate in fractures and channels plays a dominant role in limiting the interaction between water and waste. Molecular diffusion in the backfill and rock matrix, as well as in the mobile water, is an important transport process, but actually limits the exchange rate because diffusive transport is slow. Solubility limits of both waste matrix and of individual nuclides are also important. Complicating processes include alpha-radiolysis, which may change the water chemistry in the near-field. The sizes and locations of water flowpaths and damages in the canisters considerably influence the release rates. Uncertainties in data are large. Nevertheless the system is very robust in the sense that practically no reasonably conceivable assumptions or data will lead to large nuclide releases. Several natural analogues have been found to exhibit similarities with a waste repository and help to validate concepts and to increase our confidence that all major issues have been considered.
Performance Assessment of Engineered Barriers Using the Vault Model.
Authors: Johnson L.H. , Leneveu D.M. 
Published: March 2011

ABSTRACTThe Vault Model for assessing engineered barrier performance has been developed as part of the preparation of an Environmental Impact Statement to be presented to a Federal Environmental Assessment Review Panel reviewing the Canadian nuclear fuel waste disposal concept. The model describes the behaviour of titanium containers, radionuclide release from used fuel, and migration of radionuclides through buffer and backfill materials and into the surrounding geosphere. Vault Model simulations have shown that the release of radionuclides from the engineered barrier system is dominated by the release from the fuel-sheath gap and grain boundaries in used fuel. Sensitivity and uncertainty analyses have illustrated how releases from the vault are affected by both the uncertainty in model parameters and the assumptions made in the development of the models. It is likely that the combined effects of a number of conservatisms in the model result in the releases from the engineered barrier system being overpredicted by several orders of magnitude.
The IAEA Coordinated Research Programme on the Performance of High-Level Waste Forms and Packages Under Repository Conditions
Authors: Tsyplenkov Vladimir S. 
Published: March 2011

ABSTRACTThe IAEA initiated, in 1991, a Coordinated Research Programme (CRP), with the aim of promoting the exchange of information on the results obtained by different countries in the performance of high-level waste forms and waste packages under conditions relevant to final repository. These studies are being undertaken to obtain reliable data as input to safety assessments and environmental impact analyses, for final disposal purposes. The CRP includes studies on waste forms that are presently of interest worldwide: borosilicate glass, Synroc and spent fuel.Ten laboratories leading in investigation of high-level waste form performance have already joined the programme. The results of their studies and plans for future research were presented at the first Research Coordination Meeting, held in Karlsruhe, Germany, in November 1991. The technical contributions concentrated on effecting an understanding of dissolution mechanisms of waste forms under simulated repository conditions. A quantitative interpretation of the chemical processes in the near field is considered a prerequisite for long-term predictions and for the formulation of a "source term" for performance assessment studies.
Near-Field Performance Assessment for the Saltstone Disposal Facility
Authors: Seitz Roger R. , Walton John C. , Dicke Craig A. , Cook James R. 
Published: March 2011

ABSTRACTA near-field performance assessment (PA) was conducted for the Saltstone Disposal Facility (SDF) at the Savannah River Site in South Carolina. The analysis was conducted in four parts: general screening calculations, degradation calculations, and flow and transport through the fractured and nonfractured facility. Modeling approaches and example sensitivity analysis results from the simulations of the fractured facility are discussed. Design considerations that may not be apparent without addressing flow and transport through fractures and lessons learned during the process are also presented.