bluuebunny/crossref_metadata_2025_split huggingface dataset:
Adsorption Behavior of I– Ions on Minerals for Geologic Disposal of 129I Wastes
Authors: Sazarashi M. , Ikeda Y. , Seki R. , Yoshikawa H. , Takashima Y. 
Published: April 2011

AbstractThe I– adsorption on a modified mineral, which is prepared by impregnating Ag(l) nitrate complex with thiourea(tu) into montmorillonites, have been studied by batch method. The modified mineral was found to adsorb I– ions selectively even under the coexistence of Cl– ions. The distribution ratio(Kd) is 5000 ml/g under the conditions of initial [I–] = 1.0 × 10−5 M(M = mol/dm3), pH = 6.4, and solution/modified mineral = 100 ml/g. It was found that the [Ag(tu)]I precipitates are formed by mixing Nal solution with Ag(l)-tu complex solution, while any precipitates are not formed in addition of NaCl solution, and that anion exchange property of the modified mineral is low. Furthermore, it was confirmed that the [Ag(tu)]I complexes are present in the modified minerals after adsorbing I– ions. From these results, the I– selective adsorptivity of the modified mineral was considered to be due to the formation of [Ag(tu)]I precipitates within the interlayer region of montmorillonite.
Significance of Electrostatic Sorption in the Retardation of Radionuclides Released from a Repository
Authors: Meier H. , Zimmerhackl E. , Zeitler G. , Menge P. 
Published: April 2011

AbstractResults of zeta potential measurements by electroosmosis with site-specific waters and sedimentary rocks from strata overlying the Gorleben salt dome are given and compared with sorption data of radionuclides obtained in batch experiments. It is shown that zeta potentials of sediment-groundwater systems in spite of being lower than the corresponding surface potentials are a sensitive indicator of interface reactions depending on the type of the sediment, ionic strength of waters, pH and temperature. Moreover, it is demonstrated that sorption data and, additionally, the influence of various parameters can often be understood by taking into account variable electrostatic forces between charged surfaces and nuclide species.
Thermodynamic Modeling of Neptunium(V) Solubility in Concentrated Na-CO3-HCO3-Cl-ClO4-H-OH-H2O Systems
Authors: Novak Craig F. , Roberts Kevin E. 
Published: April 2011

AbstractSafety assessments of nuclear waste repositories often require estimation of actinide solubilities as they vary with groundwater composition. Although a considerable amount of research has been done on the solubility and speciation of actinides,1,2relatively little has been done to unify these data into a model applicable to concentrated brines. Numerous authors report data on the aqueous chemical properties of Np(V) in NaClO4, Na2CO3, and NaCl media, but a consistent thermodynamic model for predicting these properties is not available. To meet this need, a model was developed to describe the solubility of Np(V) in Na-Cl-ClO4-CO3aqueous systems, based on the Pitzer activity coefficient formalism for concentrated electrolytes. Hydrolysis and/or carbonate complexation are the dominant aqueous reactions with the neptunyl ion in these systems. Literature data for neptunyl ion extraction and solubility are used to parameterize an integrated model for Np(V) solubility in the Np(V)-Na-CO3-HCO3-Cl-ClO4-H-OH-H2O system. The resulting model is tested against additional solubility and extraction data, and compared with Np(V) solubility experiments in complex synthetic brines.
Humate Complexation of Neptunium(V) and its Modeling
Authors: Moriyama Hirotake , Nakata Yasuhiro , Higashi Kunio 
Published: April 2011

AbstractThe complexation behavior of Np(V) with humate was investigated by spectrophotometry in the pH range from 5.7 to 10 in 0.01–0.5M NaClO4. The absorption peaks of NpO2+and Np(V) humate were observed at 979.6nm and 989.9nm, respectively, and the apparent complexation constant of the Np(V) humate was found to be pH-dependent. A two-site complexation model was applied to the interpretation of the observed pH-dependence by considering the participation of the two functional groups of carboxylate and phenolate. The dissociation and complexation constants of both functional groups were determined.
The Geochemical Behaviour of Nickel in the Repository Environment
Authors: Savage David 
Published: April 2011

Abstract59Ni may make significant contributions to calculated doses in performance assessment (PA) studies of geological repositories for radioactive waste, due principally to the adoption of relatively high near-field solubilities. Ni concentration values used in PA are typically 1–6 orders of magnitude greater than those measured in natural groundwaters. This difference is a result of the utilisation in PA of solubility data for pure nickeliferous solids, and in some instances, the selection of solids chemically incompatible with the disposal environment. The geochemical behaviour of Ni is reviewed. It is considered highly unlikely that Ni will form discrete pure solids in the repository near-field, so that partition as a trace element into solid solutions should be considered. Henry’s law behaviour of trace elements is discussed and geochemically-realistic Ni solubility values for HLW and L/ILW disposal scenarios calculated. It is concluded that Ni will behave according to the chemical conditions of the disposal environment, which should be reflected in the choice of solubility data for PA. The adoption of solid solution modelling for other elements of interest to PA should be considered.
Illite in the Oklo Natural Fission Reactors in Gabon: Considerations for Cs Containment
Authors: Szabó Gyula , Guczi Judit , Nagy Bartholomew , Janeczek Janusz , Ewing Rodney C. 
Published: April 2011

AbstractThe ∼2 Ga old Oklo, Okelobondo and Bangombé natural reactors in the Republic of Gabon contain solid graphitic bitumens and clay minerals, both of which have effected the containment, or partial containment, of 235U and several fission products. In laboratory experiments, sorption of 134Cs by illite, and illite coated with petroleum was measured in aqueous NaCl solutions to simulate subsurface (connate) waters in sedimentary rocks. Elevated temperatures and increasing salinity of the NaCl solutions facilitated the removal of sorbed cesium from illite.
Uranium Fixation During Uranium Migration Under an Oxidizing Condition
Authors: Murakami Takashi , Tsuzuki Katsuyuki , Sato Tsutomu , Isobe Hiroshi , Ohnuki Toshihiko 
Published: April 2011

AbstractA rock specimen, collected downstream of the Koongarra uranium ore deposit, Australia, was examined mainly by high resolution transmission electron microscopy in order to understand the uranium fixation mechanism. Uranium was found to exist as saleeite (Mg(UO2)2(PO4)2.10H2O) microcrystals of 1 – 20 nm scattered between iron minerals (mainly goethite and hematite) of 2 – 50 nm. The microtextural relationship between saléeite and the iron minerals revealed that the iron minerals function as catalyst for the formation of saléeite. The intermediate metamict microstructures of the saléeite microcrystals are consistent with the estimated formation age of saléeite, 1 to 3 × 106 years. Uranium has been, thus, fixed as saléeite downstream as well as in the secondary ore deposit. Saléeite in the secondary ore deposit showed completely periodic to fully metamict microstructures, suggesting that saléeite, a major uranium mineral in the secondary ore deposit, probably began to form a few million years ago and continued to form for the next million years.
Temperature Dependence of Amorphization for Zirconolite and Perovskite Irradiated with 1 Mev Krypton Ions
Authors: White T. J. , Ewing R. C. , Wang L. M. , Forrester J. S. , Montross C. 
Published: April 2011

AbstractA transmission electron microscope investigation was made of zirconolites and perovskites irradiated to amorphization with 1 MeV krypton ions using the HVEM-Tandem Facility at Argonne National Laboratory. Three specimens were examined - a prototype zirconolite CaZrTi2O7, a gadolinium doped zirconolite Ca0.75Gd0.50Zr0.75Ti2O7and a uranium doped zirconolite Ca0.75U0.50Zr0.75Ti2O7. The critical amorphization dose Dc was determined at several temperatures between 20K to 675K. Dc was inversely proportional with temperature. For example, pure zirconolite requiring 10x the dose for amorphization at 475K compared with gadolinium zirconolite. Using an Arrhenius plot, the activation energy Ea for annealing in these compounds was found to be 0.129 eV and 0.067 eV respectively. The greater ease of amorphization for the gadolinium sample is probably a reflection of this element’s large cross section for interaction with heavy ions. Uranium zirconolite was very susceptible to damage and amorphised under 4 keV argon ions during the preparation of microscope specimens. In each sample, zirconolite coexisted with minor perovskite, reduced rutile (Magneli phases) and zirconia. These phases were more resistant to ion irradiation than zirconolite. Even for high gadolinium loadings, perovskite (Ca0.8Gd0.2TiO3) was 3-4 times more stable to ion irradiation than the surrounding zirconolite crystals.
The Microbiology of The Maqarin Site, Jordan - A Natural Analogue for Cementitious Radioactive Waste Repositories
Authors: West Julia M , Coombs Patricia , Gardner Susan J , Rochelle Christopher A 
Published: April 2011

AbstractThe Maqarin site, Jordan is being studied as a natural analogue of a cementitious radioactive waste repository. The microbiology has been studied and diverse microbial populations capable of tolerating alkaline pH were detected at all sampling localities. Dissolved organic carbon was identified as the potentially most important reductant with sulphate identified as the main oxidant, both supplying energy for microbial life. Calculations on upper limits of microbial numbers were made with a microbiology code (MGSE) using existing information but the results are overestimates when compared with field observations. This indicates that the model is very conservative and that more information on, for example, carbon sources is required.
Formation of Actinide(III)-Humate and its Influence on Adsorption on Kaolinite
Authors: Takahashi Yoshio , Minai Yoshitaka , Kimura Takaumi , Meguro Yoshihiro , Tominaga Takeshi 
Published: April 2011

AbstractApparent stability constants of Eu(III)- and Am(III)-humates determined at various pH (4.8 to 8) and supporting electrolyte concentration (0.02 to 1 mol/1), indicate that the humate complexes may be dominant species in the aquifer. Distribution coefficients of Eu(III) and Am(III) between kaolinite and solution phase were affected strongly by the presence of humic acid in the solution. Adsorption of humic acid may be an important factor controlling fixation of actinides(III) on mineral surfaces.
Effects of Smectite Illitization on Transport of Actinides Through Engineered Barriers of HLW Repositories
Authors: Ahn Joonhong , Nagasaki S. , Tanaka S. , Suzuki A. 
Published: April 2011

AbstractEffect of smectite illitization on mass release rate from the bentonite-filled buffer of the engineered barriers is analyzed based on experimental results of sorption of americium and neptunium onto illite-smectite mixtures, and on mathematical models for smectite illitization by K+diffusion, water flow through the engineered barriers, waste glass dissolution, and transport of americium and neptunium including solubility sharing with two major americium isotopes and moving boundary effect of the neptunium precipitation region. Numerical results for mass release rates of americium and neptunium as well as time-dependent pore velocity and glass dissolution rate are shown. Illitization effect is negligible with parameter values assumed here.
Experimental Study of Cation Diffusivities in Homoionized Montmorillonite by Electrical Conductance Method
Authors: Okamoto Masahide , Takase Toshio , Higashi Kunio 
Published: April 2011

AbstractMontmorillonite purified from bentonite was homoionized by leaching with a chloride solution of sodium, potassium, cobalt or strontium, and then leaching with ethanol until the leachate contained only a negligible amount of the cation.The electrical conductances of thus obtained Na-, K-, Co- and Sr- homoionized montmorillonite were measured. Applying the Nernst- Einstein equation to the electrical conductance, the diffusion coefficient for cations attached to the solid phase (montmorillonite) Ds, and that for cations in the bulk water phase Dw, were evaluated independently. As predicted, Ds was almost independent of the solid/liquid ratio, while Dw increased rapidly with the decrease of the ratio towards the diffusion coefficient in free water.
Hydraulic and Diffusive Properties of Clay-Based Backfill Material for a Low-and Intermediate-Level Waste Repository
Authors: Cho W.J. , Lee J.O. , Hahn P.S. , Park H.H. 
Published: April 2011

AbstractThe results of experimental studies performed to determine the radionuclide diffusion coefficients in a compacted clay and the hydraulic conductivities of clay/crushed granite mixtures with various clay contents are presented. Clay used in the experiments is a natural clay from the southeastern part of Korea, and it contains mainly calcium bentonite. The hydraulic conductivities of clay/crushed granite mixtures decreased with increasing clay content. In case of clay content of 50 wt.%, they maintain the considerably lower values even at the dry density of 1.5 Mg/m3. The diffusion coefficients for 90Sr, 137Cs, 60Co and 125I in water saturated clay at a dry density of 1.4 Mg/m3 were measured at room temperature. The average apparent diffusion coefficients obtained are 4.5 × 10−12 m2/s, 9.0 ×10−13 m2/s, 3.4 × 10−13 m2/s and 6.7 × 10−11 m2/s for 90Sr, 137Cs, 60Co, and 125I, respectively.
Mechanical Properties of Bentonite-Sand Mixtures Under Triaxial Stress Condition
Authors: Umedera M. , Fujiwara A. , Yasufuku N. , Hyodo M. , Murata H. 
Published: April 2011

AbstractA series of triaxial compression tests is being conducted under the drained condition on bentonite and sand mixtures, known as buffer, in saturated and optimum water content states to clarify the mechanical properties of the buffer.It was found that the mechanical properties of bentonite and sand mixtures are strongly influenced by water and bentonite contents: shear strength in a saturated state is less than that in an optimum water content state; shear strength decreases rapidly with increasing bentonite content. Strength properties are much dependent on confining pressure.
Experimental Studies on the Interaction of Groundwater with Bentonite
Authors: Sasaki Y. , Shibata M. , Yui M. , Ishikawa H. 
Published: April 2011

AbstractInteractions of sodium bentonite with distilled water and two types of synthetic groundwater were studied by batch experiments. In the experiments, clay and pure minerals were reacted at room temperature under aerobic and anaerobic condition as a function of time and liquid/solid ratio. The clay and pure minerals used in the experiments were Kunigel-VI (crude Na-bentonite), Kunipia F(purified Na-bentonite), purified Na-smectite(purified from Kunipia F), calcite and pyrite as accessory minerals. The chemical composition in the liquid phase was analyzed through centrifugation and ultra filtration. Alteration of the distribution of exchangeable cation in the bentonite was analyzed by NH4Ac and XRD. The results indicated that the interaction between bentonite(Kunigel-Vl) and groundwater under aerobic condition was described by ion exchange reaction of smectite, dissolution of calcite and oxidation of pyrite.From these experimental studies, the model of the interaction of groundwater with bentonite proposed by Wanner was modified. The comparison between calculation and experimental results showed good agreement and indicated that this model could be adopted to predict porewater chemistry of bentonite for performance assessment of geological isolation system of high level waste.
The Importance of Thermal Loading Conditions to Waste Package Performance at Yucca Mountain
Authors: Buscheck Thomas A. , Nitao John J. 
Published: April 2011

AbstractTemperature and relative humidity are primary environmental factors affecting waste package corrosion rates for the potential repository in the unsaturated zone at Yucca Mountain, Nevada. Under ambient conditions, the repository environment is quite humid. If relative humidity is low enough (<70%), corrosion will be minimal. Under humid conditions, corrosion is reduced if the temperature is low (<60°C). Using the V-TOUGH code, we model thermo-hydrological flow to investigate the effect of repository heat on temperature and relative humidity in the repository for a wide range of thermal loads. These calculations indicate that repository heat may substantially reduce relative humidity on the waste package, over hundreds of years for low thermal loads and over tens of thousands of years for high thermal loads. Temperatures associated with a given relative humidity decrease with increasing thermal load. Thermal load distributions can be optimized to yield a more uniform reduction in relative humidity during the boiling period.
Contributions of Thermodynamic and Mass Transport Modeling to Evaluation of Groundwater Flow and Groundwater Travel Time at Yucca Mountain, Nevada
Authors: Murphy William M 
Published: April 2011

AbstractConstraints on groundwater flow and groundwater travel time (GWTT) at the proposed HLW repository site at Yucca Mountain, Nevada, U.S.A., can be provided through thermodynamic modeling of relations between gas, liquid, and solid phases, and mass transport modeling. In the unsaturated zone at Yucca Mountain the observed distribution of 14C can be reasonably represented by a mass transport and mass transfer model representing diffusion of 14C02 in the gas phase from the ground surface and equilibrium between aqueous and gas phases, in the absence of net advective flow. This mechanism could also account for aqueous phase 14C activities in the unsaturated zone. Thermodynamic interpretations indicate that groundwaters extracted from boreholes in the water saturated tuffaceous aquifer at Yucca Mountain are undersaturated with respect to calcite, providing evidence that groundwater flow bypasses zones of rock containing calcite and therefore must be channelized. This conclusion is supported by published isotopic data for calcites and groundwaters.
The Nagra/Pnc Grimsel test site Radionuclide Migration Experiment: Rigorous Field Testing of Transport Models
Authors: Umeki H. , Hatanaka K. , Alexander W.R. , Mckinley I.G. , Frick U. 
Published: April 2011

AbstractThe long-term programme of in-situ radionuclide migration experiments in the underground test site at Grimsel (GTS) involves the development and testing of radionuclide transport models with their associated databases. The field experiments are carried out in a water-bearing shear zone in crystalline rock utilising a suite of tracers of differing geochemical behaviour. A rigorous model testing procedure has been developed for the GTS radionuclide migration experiment. This paper describes application of this testing procedure to a solute transport code developed by PNC.
Diffusion Measurements on Crystalline Rock Matrix
Authors: Hartikainen Kari , HautojÄrvi A. , Pietarila H. , Timonen J. 
Published: April 2011

AbstractA new gas flow technique is introduced such that experiments on very long samples are possible. This new technique together with increased accuracy of the measurements, allows the observation of power law tails in the break-through curves. Dispersion in these experiments can be controlled in great detail, and therefore the power law tails can be used to determine very accurately the parameters relevant in matrix diffusion. Results for rock and metal samples are shown, and they are fitted with model calculations which include both dispersion and matrix diffusion. The introduced technique, which is designed for ordinary drill cores, is suitable for scanning a large number of samples in a very short time.
U Series Concentration Distributions Around Rock Fractures—Qualitative Indication of Matrix Diffusion
Authors: Suksi Juhani , Saarinen Leena , Ruskeeniemi Timo , Rasilainen Kari , Siitari-Kauppi Marja 
Published: April 2011

AbstractConcentrations of U series nuclides (238U, 234U, 230Th, 226Ra and 231Pa) across secondary U accumulations in rock matrix around water-carrying fractures were examined to find records of radionuclide movement. The accumulations, loaded in rock pores, were separated without dissolving the host rock. The concentration profiles observed, form patterns which point to both “old” and “young” U accumulations and, moreover, post accumulation movement of certain radionuclides. In the case of the young U accumulation, shown to have occurred between 10,000 and 33,000 years ago, the apparent diffusivity of Da=6.10-15 m2/s for U could be calculated.
Conditioning Stochastic Groundwater Flow Models on Head Data
Authors: Jackson K. Andrew 
Published: April 2011

AbstractWe present a new method for conditioning realizations of the logarithm Y of transmissivity on head data. Each realization is conditioned by subtracting a linear combination of certain basis functions, each corresponding to a measurement, obtained by a process based on co-kriging. The required cross covariance between head and Y can be numerically computed very efficiently using the adjoint method. The coefficients in the linear combination are chosen to try to rninimise the differences between computed and measured heads. The most efficient methods for such non-linear optimisation problems are those that exploit information about the second derivatives of the function being minimised. We show how these second derivatives can be computed very efficiendy using the adjoint method for certain classes of finite-element schemes. We illustrate our method by application to the WIPP-2 test case of the international INTRAVAL project. We show that the match between computed and measured heads is greatly improved. We compare our method with approaches that use pilot points. Our method is exact if the variability of the Y field and the deviations of the measured heads from the values computed for the mean of the Y field are both small, whereas pilot-point methods are only approximate. However, our method may be more expensive computationally. Finally, we discuss the extension of our method to conditioning on transient head data and to dealing with boundary conditions.
Performance Assessment of a Repository for Intermediate-Level Radioactive Waste Using the Probabilistic System Assessment Program Mascot
Authors: Sinclair J. E. , Agg P.J. 
Published: April 2011

AbstractUK Nirex Ltd is planning the deep geological disposal of intermediate- and low-level radioactive wastes. A site close to Sellafield in Cumbria in the north-west of England has been selected for evaluation, and an extensive programme of site characterization is underway. In support of this programme of characterization, and in preparation for presentation of a post-closure radiological safety case, performance assessment using mathematical modelling has been carried out by the Disposal Safety Assessment Team at AEA Technology, on behalf of UK Nirex Ltd. This paper describes recent developments of the assessment models relating to the groundwater pathway for return of radionuclides to the environment.