bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulating Radio Element Release and Water-Rock Interactions During Dissolution of Borosilicate Glass
Authors: Chambers A V , Heath T G , Linklater C M , Thompson A M , Wiggin R M 
Published: April 2011

ABSTRACTA model has been developed that can simulate in some detail the chemistry of the glass dissolution process. To test the performance of the model, calculations were carried out to predict the dissolution behaviour of a commercial borosilicate glass. The model could reproduce accurately the behaviour of major elements released from the glass, although in the case of silica, ‘sorption’ at the glass surface was required in order to achieve good agreement with experimental data. Secondary reaction products sepiolite, montmorillonite, analcime and goethite were predicted to form. Further calculations were carried out to simulate the release of radioelements (caesium, strontium, uranium, plutonium) from within the dissolving glass. The precipitation of insoluble solids was the only mechanism included in the model to retain the radioelements at the glass surface. For plutonium, there was good agreement between model predictions and available experimental data. For caesium and strontium, the model underestimated the amount of retention at the glass surface and additional retention mechanisms, such as coprecipitation or ion exchange reactions involving newly-formed clay-type minerals at the glass surface must be invoked to explain experimental observation.
Binding Force Between Clay Mineral and Water Molecules by Semiempirical Molecular Orbital Calculation
Authors: Nagasaki S. , Umemura Y. , Todoriki M. , Tanaka S. , Suzuki A. 
Published: April 2011

ABSTRACTWe evaluate the charge distribution on the surface of a model cluster which simulates a 2:1 type clay mineral and the binding forces between the model cluster surface and water molecules with semi-empirical molecular orbital method (MOPAC). It is found that the negative charge is not localized on the oxygen atoms of the model cluster surface. We calculate the binding forces acting on the water molecules in model cluster-water system and compare them with the binding forces of solid and liquid phases of water. We qualitatively discuss the binding force acting on the water molecule directly sorbed on the model cluster surface and the binding force acting on the water molecule which is not sorbed on the model cluster surface.
Transport Phenomena in Smectite Clay Explained by Considering Microstructural Features
Authors: Pusch Roland 
Published: April 2011

ABSTRACTThe microstructure of clays controls their transport properties. This is concluded from comparing microstructural parameter data with the hydraulic conductivity and the ion diffusive transport capacity. Illitic clays contain a number of interacting open voids with a high flow capacity while natural smectite-rich clays are more homogeneous with smaller voids and a lower hydraulic conductivity than illitic clays with the same density. Artificially prepared smectitic clays, like those proposed for embedding canisters with highly radioactive waste, have a higher conductivity than natural clays with the same smectite content because the microstructural homogeneity of the artificial clays is less good.The anion diffusive transport capacity of smectite-rich clays with high density is much lower than that of clays with low density in contrast to the cation diffusive capacity. This is explained by using quantitative microstructural data.
Predictive Numerical Modeling of Artificial Tracers Migration in the Large-Scale Heating and Hydration Experiments of the FEBEX Project
Authors: Samper J. , Delgado J. , Molinero J. , Juncosa R. 
Published: April 2011

ABSTRACTFEBEX (Full-scale Engineered Barrier EXperiment) is a demonstration and research project dealing with the bentonite engineered barrier designed for sealing and containment of waste in a high level radioactive waste repository. In the FEBEX experiment the bentonite barrier will be subject to heating and hydration during at least three years. One of the novel aspects of FEBEX is the use of artificial tracers, which are intended to provide additional insight into the hydrodynamic and geochemical behavior of the bentonite buffer. Here the results of the numerical prediction of tracers migration are presented. Numerical modeling of the experiments has allowed the identification of the most relevant parameters and will be useful for the design of post-morten analyses.
Determination of the Structure and Porosity of Rock in the Disturbed Zone Around Experimental Full-Scale Deposition Holes Using the 14C-PMMA Method
Authors: Autio J. , Slltari-Kauppi M. 
Published: April 2011

ABSTRACTIn a nuclear waste repository the disturbed rock zone adjacent to the deposition holes of waste canisters is a potential transport pathway of radionuclides. The properties of the disturbed zone may also play an important role in the saturation of the bentonite buffer and in gas release.Three experimental holes of the size of deposition holes (depth 7.5 m and diameter 1.5 m) in a KBS-3 type repository were bored in hard granitic rock in the Research Tunnel at Olkiluoto. The disturbed rock zone caused by the boring was analyzed including determination of the porosity and structure of the disturbed and intact rock. These were studied in the laboratory using core samples by using the novel 14C-polymethylmethacrylate (14C-PMMA) method. In addition the structure of the disturbed zone was also examined using scanning electron and optical microscopy. A distinct zone of disturbance adjacent to the surface of the deposition holes was found. This disturbed zone was further divided into three separate sub-zones with gradual transition between the zones. It was also observed that the machine and tool factors have effect on the properties of the disturbed zone.
SIMS Analysis of Lead Isotopes in the Primary Ore Body of the Koongarra Deposit, Australia: Behavior of Lead in the Alteration of Uranium Minerals
Authors: Isobe H. , Hidaka H. , Ohnuki T. 
Published: April 2011

ABSTRACTLead, the final decay product of uranium, is found in natural uranium ore deposits. The isotope composition of lead in uranium-bearing minerals reflects their age and the migration behavior of lead. Secondary Ion Mass Spectroscopy (SIMS) can be used to analyze the isotopic composition of minerals. SIMS analysis of lead contained in the Koongarra uranium deposit, Australia, revealed that uraninite and uranyl minerals with different chemical composition in the primary ore region have homogeneous lead isotope, from the highest grade area to a uranyl silicate zone at a distance of 6.1m. Uranyl minerals, which have good crystallinity and retain stoichiometric composition, have “old” lead isotope composition identical to that of uraninite. Uranyl minerals keep exchanging lead with ground water in the primary ore region through metamictization and recrystallization by alpha-decay damage. Sulfide minerals just outside the primary ore body contain only radiogenic lead with an isotopic composition different from that of uranium minerals. Lead that migrated from the primary ore body formed sulfide minerals in a specific geological event. Since then, lead produced from uranium decay has been retained in the primary ore body, in spite of recrystallization of uranyl minerals and exchange and homogenization of lead isotopes. Uranium minerals may retain minor elements despite intense alpha-decay dose.
Solubility of Radionuclides in Fresh and Leached Cementitious Systems at 22°C and 50°C
Authors: Ochs M. , Hager D. , Helfer S. , Lothenbach B. 
Published: April 2011

ABSTRACTThe solubility of Ni, Sn, Pb, Eu, and Sr was investigated at 22°C and 50°C in simulated cement porewaters corresponding to fresh cement (‘FPW’, pH 13.2) and cement leached of soluble alkalis, whose porewater chemistry is dominated by equilibrium with portlandite (‘APW’, pH 12.5). Solubility limits were approached from undersaturation, using Ni(OH)2(c), SnO2(c) (cassiterite), PbO(red), and Eu(OH)3(c) as solids. For Sr, no solubility experiments were carried out since the cement contains enough Sr to reach equilibrium with strontianite and celestite. Solubilities generally increase with increasing pH and temperature. The measured solubility of Pb ranges from about 4× 10−3 to 1×1O−2M and is within thermodynamically predicted values. The measured solubility of Ni is <O.5-1.3×10−7M in APW and about 3-4×10−7M in FPW, which is lower than predicted by most thermodynamic data. The measured solubility of Eu ranges from <6.6×10−10M in APW to 1.8-2.7×10−9M in FPW, which agrees well with thermodynamic calculations. The solubility of cassiterite is low, with dissolved Sn concentrations ranging from 3.5× 10−8M in APW to 3.3× 10−6M in FPW. Thermodynamic calculations predict much higher solubilities, presumably for less crystalline phases. However, oversaturation measurements in APW reproduced the solubility limits obtained by undersaturation within a factor of two. To our knowledge, no relevant thermodynamic data are available.
Data Reduction for Radionuclide Transport Codes Used in Performance Assessments: An Example of Simplification Process
Authors: Dverstorp B. , Mendes B. , Pereira A. , Sundström B. 
Published: April 2011

ABSTRACTThe input data required for transport models for use in long-term risk assessments of repositories for radioactive waste, in geological media, are intrinsic to the performance of the models. The flow parameters utilized in these models typically come from 2 or 3D hydro-geological calculations done in a prior phase of an assessment. This paper examines some of the standard simplifications introduced when hydrogeological data are reduced to ID as is often required for radionuclide transport models. Two key aspects of data reduction are the determination of average properties of fractured media between and along transport pathways. To quantify possible errors associated with these reduction procedures, two computer experiments have been done. We show that the use of effective flow parameters, representing the average properties of a set of independent transport pathways, in a 1 D radionuclide transport model can result in an underestimation of peak releases by one order of magnitude or more. This result is valid for short-lived nuclides whenever retardation is an important factor. On the other hand, averaging of spatially varying transport properties along a transport pathway may lead to unjustified conservatism. A simple calculation example using Monte Carlo technique, shows that a model that does not take into account spatially varying retardation properties along the transport pathways may overestimate peak release rates by several orders of magnitude. We conclude that more sophisticated transport models taking into account available hydrogeological information on spatial variability are needed to fully understand the potential errors associated with consequence calculations in the performance assessment
Novel and Practicable Approach to Modeling Radionuclide Transport Through Heterogenous Geological Media
Authors: Schneider J.W. , Zuidema P. , Smith P.A. , Gribi P. , Hugi M. , Niemeyer M. 
Published: April 2011

ABSTRACTThis paper describes a novel approach to modelling radionuclide transport through a heterogeneous geological medium. It is assumed that a statistical description of the heterogeneity can be formulated. The approach then essentially consists of three steps: (i) sampling of a large number of potential transport pathways (15‘000 in this example), covering the ranges of properties; (ii) grouping of these pathways in a manner which reflects their importance for radionuclide transport into a small number of “legs” with appropriately averaged properties; (iii) modelling geosphere transport processes in these legs. It is demonstrated that the number of legs required to represent conservatively, but without excessive conservatism, all the transport pathways is small (5 in this example). This result is important for safety assessment, where many different parameter variations may need to be considered and where computational efficiency is often a vital issue.
Gas Threshold Pressure Tests in Deep Boreholes for Determining Two-Phase Flow Properties of the Host Rock at the Proposed L/ILW Repository, Switzerland
Authors: Senger Rainer , Marschall Paul , Lavanchy Jean-Marc 
Published: April 2011

ABSTRACTSafety assessment of potential gas release from the L/ILW requires information on two-phase flow behavior of the host rock. To determine the relevant formation properties for gas flow through the host rock, a combination of hydrotest and gas-injection sequences were designed and subsequently implemented in the Nagra field testing program at Wellenberg. The results of the design caculations indicate that the gas threshold pressure can be estimated from a gas injection test followed by a shut-in test using the log-log diagnostic plot of the gas injection sequence and the Homer plot of the recovery sequence. For a composite well-aquifer model, the gas threshold pressure of the outer zone, when estimated from the gas injection sequence, is increased, because water is displaced from the inner zone into the outer zone as gas is injected into the inner zone. This results in the overestimation the gas threshold pressure of the outer zone, and in turn, of the air-entry pressures in the corresponding capillary pressure models. The pressure response during the gas injection sequence in a composite well-aquifer model can be drastically different for different relative permeability models. For a Brooks-Corey model, the pressure indicates a distinct increase when gas flow starts into the outer zone. For a Grant model, the pressures can actually decrease during a constant-rate gas injection sequence. A decrease in interval pressure during gas injection was observed in two different field tests in the Palfris Formation at Wellenberg. In borehole WLB-SB4as, the gas injection test in interval VM16 was analyzed with the inverse code ITOUGH2 to determine the two-phase flow parameters for two different conceptual models. The simulations indicated that the particular pressure response, characterized by a sudden decrease during gas injection, could not be reproduced with a Brooks-Corey relative permeability model. However, assuming a Grant model, a sudden pressure decrease during the gas injection sequence could be simulated. The results indicate the importance in determining the hydraulic properties and the well-aquifer model from a combined analysis of hydro- and gas injection tests, in order to accurately determine the two-phase flow parameters.
The “FEBEX” Project: A Demonstration and Testbench of the Spanish Concept for Crystalline Rock Repositories
Authors: Fuentes-Cantillana J.L. , Huertas F. , Santiago J.L. 
Published: April 2011

ABSTRACTA full-scale “In situ” test is currently being conducted as part of the FEBEX project. This test is being carried out at the Grimsel Test Site in Switzerland and reproduces the “AGP-Granite” concept of the Spanish agency ENRESA for HLW repositories. Two heaters, of the same dimensions and weight as the canisters in the reference concept, have been placed in a horizontal drift of 2,28 m diameter and backfilled with a total of 115.7 t of highly compacted bentonite blocks, up to a total test length of 17 m. More than 600 sensors have been installed in the experiment, which runs basically in an automatic mode and is being remotely controlled and monitored from Spain. This paper addresses the engineering, installation and instrumentation aspects of this test. In addition, some preliminary results are shown
Synthesis of Actinide-Doped Zirconia by Plasma Calcination
Authors: Burakov B.E. , Helean K.B. , Korolev V.A. , Ewing R.C. , Anderson E.B. , Shpunt L.B. , Strykanova E.E. 
Published: April 2011

ABSTRACTZirconia containing actinides in solid solution, (Zr, An)Ox, where An = U, Pu, Am, Np, Cm is considered as a starting material for the synthesis of two durable crystalline host-phases for actinide immobilization: zircon (Zr, An)SiO4 and cubic zirconia (Zr,An)O2. The use of this starting material is necessary in order to provide for total actinide incorporation into the structures of the final phases, zircon and cubic zirconia, while avoiding the presence of unincorporated actinides. Difficulties arise when the chemically inert pure oxides, ZrO2 and AnOx are used as precursor materials. Melting techniques, which are commonly used to provide solid solution of inert oxides are not acceptable for ceramic preparation, particularly the synthesis of ceramic Pufuels. This paper presents a new approach utilizing plasma calcination. Solids containing both zirconium and actinides are calcined in a plasma. This allows the use of intermediate, stabilized actinide forms, for example, co-precipitated actinide-zirconium oxalates which have a low solubility level or a solid sol-gel precursor, such as (Zr, An)SiOx.Calcination was completed using an induction plasma in an argon gas mredium. Two types of material were used: co-precipitated oxalates of Zr and Ce with 10 wt.% Ce and a solidified sol-gel (Zr, Ce)SiOx with 10 wt.% Ce. Weakly milled material with a particle size of 0.34 mm was dropped through the plasma at a speed of 40-60 grams per hour. The final product was examined by high resolution transmission electron microscopy (HRTEM). The calcined oxalate material consisted of aggregates of globular particles (tens to hundreds of nm) of monoclinic and tetragonal (Zr,Ce)O2. The calcined sol-gel consisted of globular particles (50 to 100s nm) of monoclinic and tetragonal (or pseudo-cubic) (Zr, Ce)O2 in an amorphous silica matrix. This paper discusses the application of plasma calcination to the immobilization of excess weapons Pu and other actinides. The plasma calcination of solid materials would be used for ceramic Pu-fuel fabrication, as well as for the final disposal in geological formations.
Aspects Concerning Retrievability in the Planned Swiss Low- and Intermediate-Level Waste Repository
Authors: Nold A. L. , Fritschi M. , Kowalski E. 
Published: April 2011

ABSTRACTSwiss legislation requires the safe final disposal of radioactive wastes. Final disposal is defined by the safety authority guidelines as follows: ‘After a repository has been sealed, no further measures shall be necessary to ensure safety. The repository must be designed in such a way that it can be sealed within a few years.’ The time for repository sealing is not specified.In Switzerland, the Wellenberg site was selected for the LIILW repository after an extensive site evaluation process and, in June 1994, the application for the general licence was submitted to the Swiss Federal Government. In addition to the federal licence, a mining concession has to be granted by the canton in a public referendum. The decisive cantonal vote in June 95 was negative (52%) and led to a temporary set-back in the project.Among the reasons for this negative result was the proposed repository emplacement concept. It was planned to successively backfill the voids between the emplaced disposal containers in the caverns layer by layer. Retrieval of the waste would therefore involve high expenditure and effort. The concept therefore implies closing part of the repository at a very early stage. The outcome of the referendum reflected an unwillingness on the part of the population either to accept this situation or to make a decision today on final disposal. In many discussions, a stepwise implementation of the repository was requested, not only from the point of view of technical feasibility but also to allow political and legal aspects to be taken into consideration. A final decision - particularly regarding closure of the repository - could then be taken in the future, after giving the coming generation an opportunity to think over our proposed solution.To meet this requirement, GNW/Nagra studied modified repository emplacement concepts within the framework of Swiss legislation. In the proposed new project, concrete containers are emplaced in the caverns without any backfill, allowing easy retrieval until the decision is taken to close the facility. This decision may be taken only after completion of container emplacement, allowing for further monitoring of the filled repository caverns. A decision on how to proceed is currently being prepared by a federal working group with representatives from the canton, the safety authorities and GNW/Nagra.Studies have shown that, with an appropriate design, drainage and ventilation system, the required stability of the modified repository cavern can be achieved also under seismic loading and that the requirements of operational safety can be met. The potential long opening times of the repository caverns show some minor effects on certain repository components, such as e.g. slight carbonatisation of the container backfill. Overall, it can nevertheless be demonstrated that the long-term safety is not adversely affected.
Process Model of Gas-Related Phenomena Associated With a Proposed L/ILW Repository in Switzerland
Authors: Senger Rainer , Gribi Peter , Hugi Markus , Zuidema Piet 
Published: April 2011

ABSTRACTNAGRA (National Cooperative for the Disposal of Radioactive Waste) has been investigating the feasibility for siting a low- and intermediate-level radioactive waste (L/ILW) repository in subsurface geologic environments. The design of the L/ILW repository consists of a horizontally accessed cavern system located beneath Wellenberg in the low-permeability unit of Valanginian marl. One of the concerns for the safety analysis is the effect of gas generation (primarily hydrogen) from anaerobic corrosion and degradation of waste material. The development of a free gas phase and the concomitant pressure buildup can result in the displacement of contaminated pore waters from the repository. Moreover, excess buildup of pressures in the repository can impact the structural integrity of the engineered barrier and of the surrounding host rock. For the investigation of the gas-related phenomena in a proposed L/ILW repository, a process model was developed to simulate the different performance periods of the repository which include: (1) construction/operation period of the repository resulting in desaturation of the host rock caused by pressure decline and ventilation in the cavern, and (2) post-closure period after backfilling and sealing of the caverns resulting in resaturation of the host rock and of the cavern, and in the release of waste-generated gas. Period (1) takes into account degassing of dissolved gas (methane) in the formation water due to the pressure decline around the cavern, and period (2) considers dissolution of free gas caused by the pressure increase associated with the resaturation and with the gas production in the cavern.