bluuebunny/crossref_metadata_2025_split huggingface dataset:
Age Structure of Groundwaters Determined by Isotope Methods
Authors: Loosli H.H. , Lehmann B.E. , Mattle N. , Scholtis A. , Heidinger M. , Eichinger L. 
Published: April 2011

ABSTRACTFor the calibration of flow models, isotope methods play an important role. It is possible to deduce time information from radionuclides and therefore information about groundwater ages or flow velocities. Usually a flow system has not one single age (which is also called piston flow age) but an age distribution. In addition, groundwater may be a mixture of different components. For waste disposal investigations it is especially important to know if a small fast flowing water component is admixed. Therefore, one isotope method alone does not allow to answer all questions and a combination of isotope methods is advantageous. The results of such isotope combinations are presented. Possible isotopes are 3H, 85Kr (in combination also with Freon measurements) for a young component; 39Ar allows dating up to about 1000 years and 14C (together with δ13C and carbonate chemistry) reaches back to about 35‘000 years. Qualitative time indicators for very old waters are 4He, 40Ar/36Ar ratios, stable isotopes δ2H and δ8O and special chemical concentrations. In the first part of the poster the input functions of some isotope methods are given for the last decades. A combination is especially successful if the input functions have a totally different shape and therefore the isotope ratio a strong time dependence. In the second part, two to four examples of a successful combination of isotope methods are given. Main area is the Wellenberg site of the NAGRA investigations. Various combinations are demonstrated with time ranges from a few decades to palaeowaters. The conclusions illustrate the possibilities and limits of isotope combinations.
Local Structure of Simplified Waste Glass: Complementarity of XAS and MD Calculations
Authors: Galoisy L , Delaye J.M. , Ghaleb D. , Calas G. , Grand M. Le , Morin G. , Ramos A. , Pacaud F. 
Published: April 2011

ABSTRACTX-ray Absorption Spectroscopy (XAS) together with x-ray diffraction methods were used in inactive analogues of the French nuclear waste glass to analyze Pd-Te precipitates and the peculiarity of the sites occupied by some structural probe elements such as Mo, Zn, Zr and Si in the glassy part of the material. The influence of the precipitates on the structure of the glassy matrix around these structural probes was investigated by comparing noble metal bearing compositions together with noble metal free glasses.In noble metal bearing glasses, Pd is associated to Te as (Pd90Te10) precipitates. Pd K-edge EXAFS shows the presence of Te in the Pd coordination shell and is in accordance with a non-metallic character of the Pd-Te bond. Mo K-edge EXAFS shows that Mo occurs as molybdate groups non connected to the glassy matrix, which may be related to the occasional separation of Mo-rich phases in some compositions. Zr is located in an octahedron with d(Zr-O)=2.08Å 0.01Å whereas Zn is 4-fold coordinated with d(Zn-0)=-1.95 Å± 0.01Å. Beyond this well defined first coordination shell, XAS detects some degree of medium range order which gives insight on the bonding of the site to the polymeric borosilicate network. The interatomic Zn-Si and Zr-Si EXAFS-determined distances agree with a ZnO4and Si04tetrahedra sharing corners geometry and Zr-Si octahedra sharing corner with Si04tetrahedra. A third shell of neighbors around Zr was evidenced in the noble metal bearing glasses and in a four oxide glass, indicating that Zr is an element useful for detecting subtle changes in the local structure of complex borosilicate glasses. Si K XANES shows modifications in the connection between Si04tetrahedra when noble metals are present. To obtain accurate and precise structural interpretations, a direct comparison between EXAFS data and Molecular Dynamic (M.D.) calculations on simplified nuclear glass comprising six oxides has been performed. MD calculations show that the distribution of the Zr-O distances is harmonic in the k-range accessible with EXAFS in glasses.
Vitrification of High-Level Radioactive Waste by Sintering Under Pressure
Authors: Lutze W. , Gong W. , Abdelouas A. , Ewing R. C. , Scales C. 
Published: April 2011

ABSTRACTSintered silicate glass waste forms with a continuous glass phase and embedded but not completely dissolved waste particles were prepared by powder technology. We used a typical defense waste compositions, containing 38 wt.% of ZrO2 and prepared sinter glass samples with 30, 35, and 40 wt.% waste loading at 830°C and 27.6 MPa, by hot isostatic pressing. The glass former was amorphous silica powder. Simulated waste was added as calcine. Samples were characterized using scanning and transmission electron microscopy. The results show that extensive sintering took place, particularly with the 40 wt.% samples. Waste components, such as Na2O, CaO, MnO2, La203, Fe2O3, NiO, Cr2O3, and P2O5, dissolved completely in the continuous glass phase. ZrO2 was partly dissolved and occurred as aggregates of tiny baddeleyite crystals. The porosity of the samples was 2-3%, indicating that the optimum sintering conditions have not been met to reach porosities <1%.Chemical durability tests were carried out with sintered glass with 35 wt.% waste loading in deionized water at 90°C under static conditions, showing that the glass is at least as chemically durable as a borosilicate glass with 31 wt.% melted at 1350°C.
Modeling the Evolution of a Soluble Matrix in Various Environments
Authors: Maillard S. , Iracane D. 
Published: April 2011

ABSTRACTWe model the dissolution of a soluble matrix protected by a diffusion barrier. The dissolution, driven by a first order kinetics law, allows the solute to diffuse in the barrier with sorption and precipitation interactions. The dissolved mass evolution and the lifetime of the wasteform can be expressed in a closed form and as a function of relevant length scales, reflecting the phenomenon controlling the dissolution. Application to a nuclear glass in a clay barrier shows that diffusion in the barrier is the main phenomenon unless precipitation of chalcedony occurs or silicon is very strongly sorbed in the barrier. This requires further experimental investigation of silicon/clay interaction.
Study of Glass-Ceramic Waste Forms
Authors: Stefanovsky S.V. , Ioudintsev S.V. , Nikonov B.S. , Omelianenko B.I. , Lashtchenova T.N. 
Published: April 2011

ABSTRACTSince the early of the 1990s the method of inductive melting in a cold crucible (IMCC) has been applied at SIA “Radon” for production of various wasteforms, including glasses and Synroc-type ceramics. Sphene-based glass-ceramics composed of glass and crystalline phases were considered as appropriate wasteform for High Level Waste immobilisation. Investigation of two glass-ceramic specimens prepared with the IMCC has been performed using optical microscopy, XRD, SEM/EDS, and TEM methods. The samples produced consist of vitreous and crystalline phases. The vitreous phase consists of two varieties of glass formed by the immiscibility of the initial melt onto two separate liquids. One of the glasses is observed as spherical microinclusions in the matrix glass. The glass of the microspheres are differed from the matrix glass composition by higher contents of Ca, Ti, Ce, Sr, Zr (or Cr), while the matrix glass contains higher amounts of Si, Al, and alkalies. The crystalline phases with sphene- and perrierite-like structures have been also occurred. Their total quantity reaches up to 50 vol.%. The synthetic perrierite has similar unit-cell parameters with its natural mineral analogs with the only exception in two-fold value of c dimension. Zr, Ce, and Sr are incorporated into synthetic sphene and perrierite, while Cs is hosted by the glass phases.
Surface Characterization of Olivine-Rock by X-ray Photoelectron Spectroscopy (XPS). Leaching and U(VI) Sorption Experiments
Authors: Rodrigues E. , Aamrani F.Z. El , Giménez J. , Casas I. , Torrero M.E. , de Pablo J. , Duro L. , Hellmuth K-H. 
Published: April 2011

ABSTRACTHigh-FeO olivine-rock from Lovasjäarvi intrusion (SE-Finland) has been suggested as redox-active backfill-additive in deep high level nuclear waste repositories. In this w'ork, surface characterization of olivine-rock by X-Ray Photoelectron Spectroscopy (XPS) has been used in order to assess the behavior of this rock during leaching experiments and sorption properties of redox sensitive radionuclides. Uranium (VI) sorption has also been performed. Olivine leaching experiments at basic pH have shown the abundance of Fe and 0 relative to Si and Mg clearly indicating the precipitation of a Fe(III)-oxide secondary phase, probably amorphous FeOOH. At acid pH, the decrease of Mg/Si and Fe/Si ratios can be attributed to the formation of silicon dioxide on the mineral surface. The deconvolution of the 4f7 2 Uranium peak has shown the reduction of U(VI) to U(IV) onto the olivine surface.
New Approach for Predicting the Long-Term Behavior of Bentonite: The Unified Method of Molecular Dynamics and Homogenization Analysis
Authors: Kawamura K. , Ichikawa Y. , Nakano M. , Kitayama K. , Kawamura H. 
Published: April 2011

ABSTRACTFor predicting the long-term behavior of bentonite, we present a new and unified simulation procedure of Molecular Dynamics Method (MD) and Homogenization Analysis (HA). The MD is applied to establish molecular-scale bentonite properties and the HA is introduced to extrapolate the molecular model to the bulk-scale continuum model.
Evolution of the Porewater Chemistry in Compacted Bentonite
Authors: Muurinen Arto , Lehikoinen Jarmo 
Published: April 2011

ABSTRACTThe evolution of porewater chemistry in bentonite was studied in solution-bentonite interaction experiments under anaerobic conditions at room temperature. The parameters varied were the bentonite density, bentonite-to-water ratio (b/w), ionic strength of the solution, and the composition of bentonite. At the end of the experiment, the equilibrating solution and the porewater squeezed out of the bentonite samples were analysed. This paper presents the preliminary experimental results of these ongoing studies. The evolution of porewater chemistry was determined by the dissolving components initially present in the bentonite together with the ions coming with water from the surroundings. Ion-exchange processes occured between the exchangeable cations of montmorillonite and the cations in the water. The obtained concentrations in the external solution and porewater strongly depended on the b/w used. The concentrations in the squeezed porewaters were clearly lower than in the external waters and decreased with increasing density during squeezing.
Application of Electrochemical Acceleration Test Method to Changes in Cementitious Barrier Performances by Leaching Degradation
Authors: Saito H. , Tajima T. , Fujiwara A. , Tsuji Y. 
Published: April 2011

ABSTRACTSince cementitious materials used in repositories will be in contact with water, one of the most important tasks is to assess their long-term performance while they are being degraded very slowly by leaching. The authors have proposed an electrochemical acceleration test method and clarified its applicability. In this method, a specimen is placed between two glass vessels containing water. An anode and a cathode connected to a DC power source provide a potential gradient across the specimen. Ca2+ ions in the pore solution move rapidly to the cathode side, and thus hasten cement hydrate dissolution.In this study, we obtained two types of almost homogeneously degraded specimens by controlling cumulative quantity of dissolved Ca2+ ions. In the first type, there was no Ca(OH)2and the C-S-H phases underwent insignificant alteration, whereas in the second type, degradation of the C-S-H phases occurred.As a preliminary evaluation of cementitious materials, diffusion coefficients of tritiated water were measured for nondegraded and degraded specimens. Diffusion coefficients were increased by degradation and closely corresponded to changes in porosity.
Experimental Investigation of Passivation Behavior and Corrosion Rate of Carbon Steel in Compacted Bentonite
Authors: Taniguchi N. , Honda A. , Ishikawa H. 
Published: April 2011

ABSTRACTCarbon steel is one of the candidate materials for overpacks for high-level radioactive waste disposal in Japan. Passivation behavior and corrosion rate of carbon steel were investigated by electrochemical measurements under simulated repository conditions. The results of the anodic polarization measurements showed that carbon steel was hard to passivate in highly compacted bentonite. Therefore, general corrosion seems to be most probable in repository conditions. In order to monitor the in-situ general corrosion rate in compacted bentonite, the AC impedance of carbon steel was measured under aerated conditions. It was confirmed that the corrosion rate in saturated bentonite decreased with time and it was almost the same as that observed in deaerated aqueous conditions. The corrosion rate did not increase in the presence of corrosion products formed by external current supply.
Microstructure of a Slag-Cement Paste Determined by Small-Angle Neutron Scattering
Authors: Aldridge L.P. , Bertram W.K. , Sabine T.M. , Ioffe A 
Published: April 2011

ABSTRACTSmall angle neutron scattering from hydrating cement paste was compared to that from a paste made of a blend of cement and ground granulated blast furnace slag. The scattering measurements were used to determine the average size of the scattering particles during hydration. Their rate of growth was monitored in-situ over the first 40 hours of hydration. There was little difference in the scattering spectra, showing that the scattering particles in paste containing slag blend or cement were of similar size. At the beginning of hydration the particle radii were about 250 nn and after 14 days they had grown to over 600nm.Estimates of particle sizes are critically dependent on the amount of multiple scattering. Therefore the amount of multiple scattering of the sample must be taken into account before making comparisons between the sizes of particles of different matrices.
Chlorination Reactions Applied to Reprocessing of Aluminum-Uranium Spent Nuclear Fuels
Authors: Bohel A.E. , Nassini H.E. , Bevilacqua A.M. , Pasquevich D.M. 
Published: April 2011

ABSTRACTAn innovative dry method for reprocessing highly enriched Al-U spent fuel is presented. It is based on the use of hot chlorine gas to chemically attack the irradiated fuels, converting aluminum, uranium and fission products into their respective chlorides. Separation of the large amounts of non-radioactive species, basically aluminum and its impurities, can be further accomplished by exploiting the significant differences between relative volatilities of metallic chlorides and also by selectivity of chlorination reactions. The technical feasibility of the method proposed is theoretically demonstrated by performing a case study on the highly enriched Al-U fuels of the RA-3 Argentine research and test reactor.
Numerical Modeling and Column Experiments to Simulate the Alkaline Disturbed Zone Around a Cementitious Radioactive Waste Repository
Authors: Bateman K. , Coombs P. , Noy D. J. , Pearce J. M. , Wetton P. D. 
Published: April 2011

ABSTRACTIn order to be able to describe the migration of an alkaline plume, coupled chemistry and flow computer models may be employed. A series of laboratory column experiments were conducted to test the capabilities of currently available coupled models to predict product solids and output fluid compositions as a function of time. The predictions did not replicate all the variations of Ca:Si observed during mineralogical analysis, probably due the unavailability of sufficient kinetic and thermodynamic data for the range of calcium silicate hydrates (CSH) phases of interest. However, the predictions do reproduce the variation of Ca:Si ratios with time and distance along the columns. A better understanding of the above processes will lead to greater confidence in predictive modelling of the migration of alkaline plumes away from the cementitious barriers of radioactive waste disposal facilities.
Borosilicate Nuclear Waste Glass Alteration Kinetics: Chemical Inhibition and Affinity Control
Authors: Advocat T. , Chouchan J. L. , Crovisier J. L. , Guy C. , Daux V. , Jegou C. , Gin S. , Vernaz E. 
Published: April 2011

ABSTRACTThe objective of this work was to develop a more representative mathematical formulation of the alteration kinetics of the borosilicate SON68 glass by combining three approaches: (1) Compare extensive prior experimental static leaching results for SON68 glass with the first-order kinetic law in which silica is the predominant element, (2) Assess the exact role of dissolved silica on the alteration rate under conditions near and far from saturation, by means of dynamic leach tests and, (3) Compare the new data with the general kinetic law for silicates in which the reaction affinity, catalysis and inhibition are the three influencing factors.
The Excavation Project in the Grimsel Test Site: In Situ High-Resolution Gamma and Alpha Spectrometry of 60Co, 75Se, 113Sn, 152Eu, 235U, and 237Np/233Pa
Authors: Eikenberg J. , Ruethi M. , Alexander W.R. , Frieg B. , Fierz T. 
Published: April 2011

ABSTRACTFull excavation of a water-conducting shear zone used for radionuclide migration experiments is part of a comprehensive study to physically determine the sites of in-situ radionuclide retardation. Prior to the excavation, multi-tracer solutions containing strongly sorbing y- and αemitting nuclides were injected into the shear zone and the water extracted was analyzed on-line using in situ, high-resolution y-spectrometry. In addition, water samples were collected to compare quantitatively the on-line data with subsequent laboratory measurements α- and γ- spectrometry) and also to analyze samples with activities below the detection limits of the in-situ analysis. The breakthrough curves indicate that Se had passed through the fracture with a velocity comparable to a conservatively behaving dye (uranine), but very strong retardation of Co. Eu and Sn was observed. The recoveries of these nuclides were found to be in the order of only a few percent when the dipole flow-field was interrupted about one month after radionuclide injection and the fracture was sealed off for excavation. Significant retardation was also obtained for the oxemitters U, Np and Pa. Almost identical breakthrough curves for these actinides were measured, suggesting a similar spatial distribution in the fracture at any given time.
Progress in Physical Rock Matrix Characterization: Structure of the Pore Space
Authors: Sütari-Kauppi M. , Flitsiyan E.S. , Klobes P. , Meyer K. , Hellmuth K-H. 
Published: April 2011

ABSTRACTQuantitative autoradiography for the investigation of rock matrices has been further developed by use of tritium-labeled polymethylmethacrylate (3H-PMMA), the use of thin sections and image analysis functions allowing correlations of mineralogic-petrographical and analytical or porosity information. The autoradiographic system was studied experimentally and theoretically. The autoradiography could achieve a resolution down to 10 and 20 μm for3H and14C, respectively. Possible candidates for intact, low-porous rock standard materials were studied and the measurement of their transport properties discussed. Porosities and diffusivities measured in rock types dominated by very small pores were depending on the probe molecule used. The effect was most pronounced in flint which gave low porosities for MMA, Hg and He and no diffusivities at all for He.
Crystal Chemistry and Microstructures of Uranyl Phosphates
Authors: Suzuki Y. , Murakami T. , Kogure T. , Isobe H. , Sato T. 
Published: April 2011

ABSTRACTThe crystal chemistry and microstructures of saleeite (Mg(UO2PO4)2•10H2O) and metatorbernite (Cu(UO2PO4)2•8H2O), from Koongarra, Australia and Shinkolobwe, Congo, were examined by X-ray diffraction analysis, infrared spectroscopy (IR), scanning electron microscopy (SEM) equipped with energy dispersive X-ray analysis, transmission electron microscopy (TEM) and analytical electron microscopy. The uranyl phosphates consist of uranyl phosphate layers with cations and waters in the interlayers. The IR spectra of saleeite and metatorbernite show the presence of hydroxyls in the interlayers in addition to water molecules. The d002 spacings of the hydrated phases of saleeite and metatorbernite up to 300°C reveal that the uranyl phosphate layers themselves are quite stable in the temperature range although the interlayer water molecules are lost easily. The presence of a mixed phase of saleeite and metatorbernite is confirmed in the micrometer and nanometer scales. However, SEM and TEM examination suggest saleeite and metatorbemite generally grow separately, and rarely form solid solution or interstratification. The results imply that U is retained in uranyl phosphate minerals even when the temperature at around repositories increases, and that saleeite and metatorbernite precipitate independently from solution according to their solubilities even when Mg2+ and Cu2+ coexist in solution.
Modeling of Groundwater Flow at Wellenberg Using Monte Carlo Simulations
Authors: Jaquet O. , Schindler M. , Voborny O. , Vinard P. 
Published: April 2011

ABSTRACTWellenberg is the proposed candidate site for LLW/ILW repository in Switzerland (Figure 1). The performance assessment of the planned repository calls for a thorough hydrogeological characterization of the site. The spatial distribution of the hydraulic conductivity within the host rock is a key input for the evaluation of the host rock performances. The spatially variable conductivity field is modelled geostatistically in 3 dimensions using a conditional simulation method. In order to account for the possible range of spatial variability, several simulations of the conductivity are generated. The conditional simulation of the conductivity - representing possible versions of the unknown reality - are used as input for numerical modelling. For each simulated conductivity field, the groundwater flow is numerically modelled using finite elements. This Monte Carlo approach allows the propagation of the input uncertainty due to spatial variability of the conductivity onto the predictions delivered by the flow model. With the help of this approach several specified performance criteria - together with their uncertainty - were estimated for the evaluation of storage capabilities of the Wellenberg host rock.
Retention of Neptunium in Uranyl Alteration Phases Formed During Spent Fuel Corrosion
Authors: Buck E. C. , Finch R. J. , Finn P. A. , Bates J. K. 
Published: April 2011

ABSTRACTUranyl oxide hydrate phases are known to form during contact of oxide spent nuclear fuel with water under oxidizing conditions; however, less is known about the fate of fission and neutron capture products during this alteration. We describe, for the first time, evidence that neptunium can become incorporated into the uranyl secondary phase, dehydrated schoepite (UO3•0.8H2O). Based on the long-term durability of natural schoepite, the retention of neptunium in this alteration phase may be significant during spent fuel corrosion in an unsaturated geologic repository.
Glass Waste Form Performance for Disposal of the Cesium and Strontium Concentrate Resulting From the Partitioning of HLW
Authors: Aloy A.S. , Iskhakova O.A. , Kol‘tsova T.I. , Trofimenko A.V. 
Published: April 2011

ABSTRACTThe recent advances in HLW partitioning indicate that cesium–137 and strontium–90 can be separated in the form of a pure concentrate. Based on this concentrate the glass RT2–1 containing 4.7 wt.% Cs2O and 2.7 wt.% SrO was selected for more intensive and wider studies to predict long-term performance of this waste form under repository conditions.Leach tests were made in distilled and mineralized water before and after crystallization at 20, 90 and 130°C.Fully devitrified glass contained only one crystalline phase corresponding to the pollucite structure.