bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid-Liquid Phase Separation and Phase Diagrams of Simulated Fernald Waste Glasses
Authors: Wang E. , Perez-Cardenas F. , Kuang H. , Buechele A.C. 
Published: March 2011

ABSTRACTPrevious study of crystallization behavior in heat-treated Fernald waste glasses has produced an extensive data base of crystal phases likely to appear in various composition ranges and their corresponding liquidus temperatures. In addition, we have frequently observed amorphous phase separation in these glasses and, occasionally, evidence of crystallization originating from such phase separation. These glasses contain more than 10 components. The composition ranges for the major components are: MgF2 10–26 wt%; CaO 4–27 wt%; Al2O3 3–15 wt%; SiO2 25–40 wt%. The morphology of the phase separation as observed in the Scanning Electron Microscope (SEM) is dark, spherical globules dispersed in a continuous matrix. Globules are depleted in Mg, Ca and F, and enriched in Al and Si compared to the matrix. Phase separation occurs more frequently in melts relatively higher in Si and F. A more systematic study on a simplified and simulated seven component system (Al2O3, B2O3, CaO, Fe2O3, SiO2, Na2O and MgF2) has been undertaken to determine the subliquidus miscibility gap and liquidus curve data. Glasses were formulated by varying the concentrations of MgF2, CaO, Al2O3 and SiO2 within the ranges specified above at fixed levels of Fe2O3, B2O3 and Na2O. The miscibility gap and liquidus curve were obtained by heat-treating the glass samples at different temperatures and observing any phase separation and crystallization in the SEM and the Transmission Electron Microscope (TEM). We report here the results of this study to enhance the understanding of the thermodynamic properties of multi-component silicate systems which are usually the basis of nuclear waste glasses.
Continuous-Melter Vitrification of Fernald Mixed Wastes: Distribution of Contaminants Between Glass, Scrubber Solutions and Off-Gases
Authors: Matlack Keith S. , Hojaji Hamid , Fu Sabrina S. , Pegg Ian L. , Macedo Pedro B. 
Published: March 2011

ABSTRACTResults are presented from treatability studies on the vitrification of hazardous and low-level radioactive soils and sludges from the Fernald site. The majority of the contaminants of concern are contained in large volumes of sludges accumulated from uranium and thorium production operations that are presently stored in pits at Fernald. These sludges present particular challenges to the vitrification process in that they contain significant amounts of fluorides (mostly magnesium and calcium). In this study, glass formulations used sludges, soils and a minimum amount of additives resulting in waste loadings as high as 94%. Several of these formulations were evaluated by continuous feeding of slurries into a joule-heated vitrification system. Melter off-gases were treated in a two-stage NaOH scrubbing system. HF acid fumes were neutralized, resulting in the formation of a NaF solid precipitate which is removed from the scrubber and recycled to subsequent melter feeds. Elemental and isotope compositions of the glasses, scrubber solutions, NaF precipitate and off-gases show that greater than 99.7% of uranium and thorium, 95% of Pb, Cd, Ni, Sb, Cr, and Hg were retained in the glass. Fluoride and other gaseous emissions from the scrubber system were below regulatory limits, even before HEPA filtration.
Constraints on the Affinity Term for Modeling Long-Term Glass Dissolution Rates
Authors: Bourcier William L. , Carroll Susan A. , Phillips Brian L. 
Published: March 2011

ABSTRACTPredictions of long-term glass dissolution rates are highly dependent on the form of the affinity term in the rate expression. Analysis of the quantitative effect of saturation state on glass dissolution rate for CSG glass (a simple analog of SRL-165 glass), shows that a simple (1-Q/K) affinity term does not match experimental results. Our data at 100°C show that the data is better fit by an affinity term having the form where σ =10.
Hydrotalcite Formed by Alteration of R7T7 Nuclear Waste Glass and Basaltic Glass in Salt Brine at 190°C
Authors: Abdelouas A. , Crovisier J. L. , Lutze W. , Müller R. , Bernotat W. 
Published: March 2011

ABSTRACTThe R7T7 and synthetic basaltic glasses were submitted to corrosion in a saline MgCl2dominated solution at 190°C. For both glasses, the early alteration product is a hydrotalcite-like compound in which HPO42-, SO4-2and Cl-substitutes to CO32. The measured d003spacing is 7.68 Å for the hydrotalcite formed from R7T7 glass and 7.62 Å for the hydrotalcite formed from basaltic glass which reflect the high aluminium content. Chemical microanalyses show that the hydrotalcite is subsequently covered by a silica-rich gel which evolves into saponite after few months.
Experimental Investigation of Aqueous Corrosion of R7T7 Nuclear Glass at 90°C in the Presence of Humic Acids: a Kinetic Approach
Authors: Gin S. , Godon N. , Mestre J.P. , Vernaz E.Y. , Beaufort D. 
Published: March 2011

ABSTRACTThe dissolution kinetics of the French “R7T7” nonradioactive LWR reference glass in solutions containing dissolved humic acids were investigated at 90°C during static tests with imposed or free pH. Experiments conducted in highly dilute media, with a glass-surface-area-to-solution-volume (SA/V) ratio of 5 m-1, showed that the glass dissolution surface reaction is catalyzed by humic acids. With higher degrees of reaction progress (SA/V = 100 m-1 and free pH) the humic acids impose pH modifications on the system compared with inorganic media; moreover, they directly or indirectly enhance the dissolution of certain alkali metals and transition elements, forming aqueous complexes with the latter. During experiments with an imposed pH of 8.5 (SA/V = 1300 and 5300 m-1), the humic acids appear to cause increased silica solubility that cannot be accounted for by the formation of silica complexes. A residual corrosion rate in the humic acid media exceeding the rate measured in inorganic media suggests that, in addition to silica, one or more element complexes formed by humic acids may be a kinetically limiting factor. This hypothesis must be confirmed, however, as the quantity of humic acids per unit glass surface area was too small in this experiment to allow unambiguous characterization of the phenomenon.
Analytical Electron Microscopy Examination of Solid Reaction Products in Long-Term Tests of Srl 200 Waste Glasses
Authors: Buck E. C. , Fortner J. A. , Bates J. K. , Feng X. , L Dietz N. , Bradley C. R. , Tani B. S. 
Published: March 2011

ABSTRACTAlteration phases, found on the leached surfaces and present as colloids in the leachates of 200-based frit (fully active and simulated) nuclear waste glass, reacted under static test conditions, at a surface area to leachate volume ratio of 20,000 m-1 for 15 days to 728 days, have been examined by analytical electron microscopy. The compositions of the secondary phases were determined using X-ray energy dispersive spectroscopy and electron energy loss spectroscopy, and structural analysis was accomplished by electron diffraction. Long-term samples of simulated glass, which had undergone an acceleration of reaction after 182 days, possessed a number of silicate secondary phases, including; smectite (iron silicate and potassium iron alumino-silicate), weeksite (uranium silicate), zeolite (calcium potassium alumino-silicate), tobermorite (calcium silicate), and a pure silica phase. However, uranium silicates and smectite have also been observed in tests which have not undergone the acceleration of reaction, in both the leachate and leached layer, suggesting that these phases are not responsible for the acceleration of reaction.
Field-Based Tests of Geochemical Modeling Codes: New Zealand Hydrothermal Systems
Authors: Bruton Carol J. , Glassley William E. , Bourcier William L. 
Published: March 2011

ABSTRACTHydrothermal systems in the Taupo Volcanic Zone, North Island, New Zealand are being used as field-based modeling exercises for the EQ3/6 geochemical modeling code package. Comparisons of the observed state and evolution of the hydrothermal systems with predictions of fluid-solid equilibria made using geochemical modeling codes will determine how the codes can be used to predict the chemical and mineralogical response of the environment to nuclear waste emplacement. Field-based exercises allow us to test the models on time scales unattainable in the laboratory.Preliminary predictions of mineral assemblages in equilibrium with fluids sampled from wells in the Wairakei and Kawerau geothermal field suggest that affinity-temperature diagrams must be used in conjunction with EQ6 to minimize the effect of uncertainties in thermodynamic and kinetic data on code predictions.
Formation, Oxidation and Alteration of Ianthinite
Authors: Finch Robert J. , Ewing Rodney C. 
Published: March 2011

ABSTRACTIanthinite, UO2.86·1.5H2O, is a weathering product of uraninite, UO2+x, and has been reported as a corrosion product of UO2. Ianthinite alters to schoepite, UO3·2H2O, or studtite, UO4·2-4H2O, in water. The structures of ianthinite, schoepite and studtite are unknown, but their unit cell parameters differ significantly, and transformations are likely reconstructive.XRD powder data for ianthinite and becquerelite are similar, and they are probably iso-structural; U4+, as U(OH)22+, replaces Ca2+in the interlayer. The proposed formula isU(OH)22+[(UO2)6O4(OH)6]·6H2O.Oxidation in air, has been reported to form schoepite; however, in the absence of water, the oxidation of ianthinite,U(OH)22+[(UO2)6O4(OH)6]·6H2O + 1/2 O2=> (UO2)2+[(UO2)6O4(OH)6]·7H2O ,shows that epi-ianthinite is structurally distinct from schoepite. The oxidation of fine-grained material is rapid, and the color change — from dark purple to yellow — is dramatic. The acicular habit of ianthinite is preserved during oxidation, and acicular “schoepite” is observed in nature, as well as in leaching experiments on spent fuel. Possible substitution of Pu4+for U4+suggests that Pu-ianthinite may control Pu solubility in oxidizing, U-saturated solutions.
Formation of Secondary Uranium Minerals in the Koongarra Deposit, Australia
Authors: Isobe Hiroshi , Ewing Rodney C. , Murakami Takashi 
Published: March 2011

ABSTRACTSecondary uranium minerals from the Koongarra deposit, Northern Territory of Australia, were examined in order to understand the formation and alteration processes of the uranium minerals and their relevance to the migration behavior of uranium, lead, calcium and rare earth elements in the weathered zone. In most of the secondary ore zone, the only stable uranium mineral was saléeite (Mg(UO2)2(PO4)2·10H20), occurring as euhedral platy crystals up to 1 mm in length in veins and at surfaces. Apatite (Ca5(PO4)3F), an accessory mineral of the host rock, has saléeite reaction rims, suggesting formation at the expense of apatite. Ca-uranyl phosphates, such as autunite (Ca(UO2)2(PO4)2·10H2O), were not identified, and Ca-rich uranyl silicates are also absent in the primary ore zone. Pb-bearing uranyl phosphates were found only in the graphite layer cross-cutting the secondary ore zone. In the graphite layer, the local low oxidation condition and high hydrocarbonate content of ground water have affected the formation of uranium minerals and the migration behavior of uranium.
Results From Simulated Contact-Handled Transuranic Waste Experiments at the Waste Isolation Pilot Plant
Authors: Molecke Martin A. , Rob Sorensen N. , Krumhansl James L. 
Published: March 2011

ABSTRACTWe conducted in situ experiments with simulated, i.e., nonradioactive, contact-handled trans-uranic (CH TRU) waste drums at the Waste Isolation Pilot Plant (WIPP) facility for a period of about four years. We performed these tests in two rooms in rock salt, at WIPP, with drums surrounded by crushed salt or 70 wt. % salt/30 wt. % bentonite clay backfills, or partially submerged in a NaCl brine pool. Air and brine temperatures were maintained at ~40°C. These full-scale (210-L drum) experiments provided in situ data on: backfill material moisture-sorption and physical properties in the presence of brine; waste container corrosion adequacy; and, migration of chemical tracers (nonradioactive actinide and fission product simulants) in the near-field vicinity, all as a function of time. Individual drums, backfill, and brine samples were removed periodically for laboratory evaluations. Waste container testing in the presence of brine and brine-moistened backfill materials served as a severe overtest of long-term conditions that could be anticipated in an actual salt waste repository. We also obtained relevant operational-test emplacement and retrieval experience. All test results are intended to support both the acceptance of actual TRU wastes at the WIPP and performance assessment data needs. We provide an overview and technical data summary focusing on the WIPP CH TRU environmental overtests involving ] 74 waste drums in the presence of backfill materials and the brine pool, with posttest laboratory materials analyses of backfill sorbed-moisture content, CH TRU drum corrosion, tracer migration, and associated test observations.
Formation of Vivianite During Microbiologically Influenced Corrosion of Steels
Authors: McNeil Michael , McKay Jennifer 
Published: March 2011

Abstract:Exposure of carbon and HY-80 high strength low alloy (HSLA) steels to anaerobic Postgate cultures containing sulfate reducing bacteria leads to production of mackinawite, Fe9S8, and vivianite, Fe3(PO4)2.8H2O, with minor amounts of other minerals, the vivianite being sometimes accompanied by siderite, FeCO3. The vivianite and mackinawite persist on exposure to air or oxygenated water. Green rust is a significant alteration product on some steels. The implications of these findings are discussed in light of present and possible future nuclear waste containers.
The Sorption of Niobium, Tin, Iodine and Chlorine onto Nirex Reference Vault Backfill
Authors: Baker S. , McCrohon R. , Oliver P. , Pilkington N.J. 
Published: March 2011

ABSTRACTUK Nirex Ltd is proposing to develop a deep underground repository for the disposal of solid low- and intermediate-level radioactive wastes in the UK, and is currently investigating Sellafield in Cumbria as a possible site. The Nirex Safety Assessment Research Programme (NSARP) comprises scientific research to support the post-closure performance assessment of the repository. One of the investigations carried out by AEA Technology under the NSARP is the study of the sorption of radionuclides onto the backfill. Sorption is one of the key parameters determining the rate of release of radionuclides from the repository. The radionuclides present in the waste include 94Nb, 126Sn, 129I and 36Cl. This paper reports the measurement of the sorption of niobium, tin, iodine and chlorine onto the Nirex reference vault backfill at 20±5°C by the batch sorption method. The temperature dependence of tin sorption was investigated by carrying out additional experiments at 77±5°C. Experiments on niobium solubility and sorption were carried out under saline conditions to reflect the nature of the groundwater at Sellafield. Sorption coefficients (Rd) for niobium are within the range measured in other work, whereas for tin the results are a factor of ten lower than literature values. For iodine and chlorine, the results are consistent with the literature; they also show an increase in Rd with decreasing initial inventory. The Rd values for niobium and tin are significantly higher than those for chlorine and iodine.
Effects of Nonequilibrium Adsorption on Nuclide Transport in a Porous Rock
Authors: Teng Shi-Ping , Lee Ching-Hor 
Published: March 2011

ABSTRACTAn analytical solution covering the entire range of adsorption properties of rock has been derived for the migration of radiionuclide in a porous rock matrix. The analysis takes into account the advective transport, hydrodynamic dispersion, adsorption between solid phase and liquid phase, and the radioactive decay. For adsorption of nuclide within the rock, the effects of no adsorption, linear nonequilibrium adsorption, and linear equilibrium adsorption are integrated into a generic transient analytical solution. The results indicate that the assumption of equilibrium adsorption can result in underestimation of the concentration profile in the early stages of migration. However, both the equilibrium and nonequilibrium profiles eventually approach the same value. It is also noted that for the case of nonequilibrium adsorption, plateaus appear in the concentration profile of the breakthrough curves. The effects of different adsorption rates are also analyzed.
Preliminary Analysis of Potential Chemical Environments Inside Failed Waste Containers at the Proposed Yucca Mountain Repository
Authors: Colten-Bradley Virginia , Walton John C. 
Published: March 2011

ABSTRACTPrediction of radionuclide release rates for high-level waste requires estimates of the rates of waste form alteration and formation of secondary minerals inside the failed canister. Unsaturated repository sites may promote development of a variety of chemical environments related to two phase (liquid/ vapor) transport and temperature gradients caused by radiogenic decay. A mass balance (shell balance) approach is used to estimate the effects of dripping water, evaporation, and condensation on the waste canister and the presence of saline water inside the failed waste canister. The simplified calculations predict large variability of water chemistry over spatial scales of a few centimeters. The effects of the predicted aqueous chemistry on waste form alteration, secondary mineral formation, and radionuclide solubility are examined.
Preliminary Results for the Experimental Evaluation of a Radwaste Repository Near-Field Model
Authors: Kang C. H. , Lee J. O. , Hahn P. S. , Park H. H. 
Published: March 2011

ABSTRACTA series of experiments for a simplified system has been performed to evaluate a near-field model of radioactive waste repository developed by the University of California, Berkeley. In the experiments, iodine as nonsorbing species and cesium as sorbing species were employed. This paper presents the initial 200-day results of these experiments. Good agreement is found between the model and the experimental results. The results of this work will give basic ideas on the design of the near field of a repository.
Introduced Materials and Colloid Formation: a Report on the Current State of Knowledge
Authors: Meike A. , Wittwer C. 
Published: March 2011

ABSTRACTThis paper reviews potential sources of colloids and enhanced adsorption of radionuclides that may stem from materials introduced into a repository setting. Three major sources of colloids are examined: metals, cements, and organics. The sensitivity of colloids to chemical species, pH, time, temperature, radiolysis, redox state, gradients of the aforementioned variables, and microbial activity is shown. We consider these influences on colloid formation and sorption with respect to introduced materials. We also discuss areas that have not been addressed but may have consequences in a repository setting.
A Preliminary Investigation of the Applicability of Surface Complexation Modeling to the Understanding of Transportation Cask Weeping
Authors: Granstaff Victoria E. , Chambers William B. , Doughty Daniel H. 
Published: March 2011

ABSTRACTA new application for surface complexation modeling is described. These models, which describe chemical equilibria among aqueous and adsorbed species, have typically been used for predicting groundwater transport of contaminants by modeling the natural adsorbents as various metal oxides. Our experiments suggest that this type of modeling can also explain stainless steel surface contamination and decontamination mechanisms.Stainless steel transportation casks, when submerged in a spent fuel storage pool at nuclear power stations, can become contaminated with radionuclides such as 137Cs, 134Cs, and 60Co. Subsequent release or desorption of these contaminants under varying environmental conditions occasionally results in the phenomenon known as “cask weeping.” We have postulated that contaminants in the storage pool adsorb onto the hydrous metal oxide surface of the passivated stainless steel and are subsequently released (by conversion from a fixed to a removable form) during transportation, due to varying environmental factors, such as humidity, road salt, dirt, and acid rain. It is well known that 304 stainless steel has a chromium enriched passive surface layer; thus its adsorption behavior should be similar to that of a mixed chromium / iron oxide.To help us interpret our studies of reversible binding of dissolved metals on stainless steel surfaces, we have studied the adsorption of Co+2 on Cr2O3. The data are interpreted using electrostatic surface complexation models. The FITEQL computer program was used to obtain the model binding constants and site densities from the experimental data. The MINTEQA2 computer speciation model was used, with the fitted constants, in an attempt to validate this approach.
Intrusion of Seawater into a Porous Fracture zone a Coupled Geohydrochemical Modelling Exercise
Authors: Pirhonen Veijo O. 
Published: March 2011

ABSTRACTA coupled geochemical transport program PHREEQM2D has been tested in order to examine intrusion of seawater into fracture zones which can be connected to tunnels, such as nuclear-waste repositories on the sea shores. The code consists of a flow and transport program HST2D and a chemical equilibrium program PHREEQE. It uses a mixing cell approach, where chemistry and transport are solved separately. Ion exchange is calculated by means of a simple surface complexation model.In the present artificial exercise, replacement of groundwater by seawater in a connecting porous fracture zone was modelled without comparing the results to observed data. Dilution, mixing, ion exchange, and dissolution/precipitation reactions were examined.The results of modeling showed that the sulphate front of seawater moved some distance towards the tunnel during the simulations. The characteristic solutes of dilute groundwater were assumed to enter the tunnel in a short period of time. Amounts of sulphates decreased due to dilution and mixing. The chemical contents of waters were also affected by dissolution, precipitation, and ion exchange. Calcite dissolved and oxyhydroxides precipitated in oxidizing water. The strongest exchangeable ions in water, Ca and Na, were retarded due to ion exchange in the mixing zones. This caused an increase in dissolution of calcite in the mixing zones. Calcite would, however, start to precipitate in the mixing zone when the ion exchange capacity of rock would be consumed.Some important factors, such as retardation on oxide surfaces (adsorption models) and microbial activity (organic complexation models) have not been tested in the present exercise. Otherwise, the PHREEQM2D showed its applicability to modelling of chemical equilibrium, dilution, mixing, ion exchange, and elution/precipitation in discrete porous zones in transient conditions. It could be used to model temperature-enchanced, coupled geohyd-Γochemical, processes in porous zones consisting of densely fractured or crushed crystalline rock.
Further Development and Studies of Gas Methods in Matrix Diffusion
Authors: Hartikainen Kari , Väätäinen K. , Hautojärvi A. , Timonen J. 
Published: March 2011

ABSTRACTThe present status of the recently introduced gas method equipment for migration studies of fractured and porous media is briefly reviewed together with advances in the experimental techniques. The conditions under which matrix diffusion can be observed in both gas flow and water flow experiments are discussed in some detail. Results for a gas flow experiment are shown, and explained with a numerical model which incorporates the effects of hydrodynamic dispersion and matrix diffusion. The necessary parameters for a corresponding water flow experiment are also briefly discussed.