bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ion Exchange Behavior of the Febex Bentonite. 1. Na/K, Na/Mg and Na/Ca Experimental Exchange Isotherms
Authors: Huertas F.J. , Carretero P. , Delgado J. , Linares J. , Samper J. 
Published: May 2011

ABSTRACTNa/K, Na/Mg, and Na/Ca exchange isotherms have been experimentally determined for the FEBEX bentonite. Na-homoionized FEBEXbentonite was reacted at room temperature with mixedsalt dissolution of NaCl/KCl, NaCl/MgCl2, or NaCl/CaCl2, while keeping a total cation normality of 0.5 eq L-1. Isotherm exchange experiments were performed using ten (duplicated)experimental points, which cover the complete range of the corresponding binary equivalent fractions. Results indicate that for the Na/K exchange reaction, Vanselow coefficients are larger than one, what is in agreement with the tendency of the smectite of having greater affinity for K than for Na. The exchange constant decreases as K progressively replaces Na in the smectite. This tendency ends when the equivalent fraction of potassium, EK, reaches a value of around 0.250.3. From this point to higher K contents, it remains nearly constant irrespective of EK but slightly decreasing again at values near one. The Vanselow selectivity coefficient for the Na/Mg isotherm indicates a preference for the divalent cation. It is nearly constant (Kv ≍ 5.6) for EMg < 0.6, but increases up to 10.2 for a nearly Mg-saturated smectite.The Na/Ca exchange resembles that of Na/Mg, although the selectivity coefficients are larger (Kv ≍ 7.0 for ECa < 0.6). The comparison of the selectivity coefficients for the Na/Mg and Na/Ca exchange reactions indicates that the smectite has a slightly higher affinity for Ca than for Mg. This result is consistent with those observed for the Wyoming bentonite.
Laboratory Examination of Microbial Perturbations in a Granitic Environment
Authors: M. West J. , Hama K. , Bateman K. , Coombs P. , Hards V. , Milodowski A. E. , Wetton P. , Yoshida H. 
Published: May 2011

ABSTRACTMicrobial activity can have a significant impact on geochemical processes as it can influence mineral dissolution and precipitation, pH, alkalinity and redox. Experiments were conducted to study the rock-water and microbial interactions, specifically to examine the influence of microbes on the groundwater environment in fractured crystalline rock. These used combinations of crushed Äspö Diorite, Äspö groundwater with iron and sulphate reducing bacteria in columns and continuously stirred tank reactors under both anaerobic and aerobic conditions. Results showed loss (dissolution and/or mobilization) of fine grained crushed material (<50 μm) which had originally adhered to grain surfaces in the starting material. The mobilized fines were subsequently trapped on biofilms developed between grains. There was also evidence for the formation of smectite (not present in the starting materials) which, together with the trapping of translocated fines in intergranular pore throats by biofilms, resulted in blockage of the column experiments. The degree of mineralogical alteration and/or pore blocking was greater in the experiments when bacteria were present and occurred under anaerobic conditions. Little evidence for rock-water interactions was seen in the chemical analysis data for all the experiments. Modelling of the fluids showed them to be saturated with respect to clay minerals. The observed mineralogical changes seem to reflect alteration occurring in microbially mediated microenvironments close to mineral surfaces. Consequently, these changes may be too small to be detected by the chemical analysis of the bulk fluid. These experiments have shown that microbial activity can impact on fluid flow through porous media even in nutrient poor conditions. In addition, the formation of new clay minerals on pore-surfaces is potentially important for ion exchange and sorption reactions.
Behavior of High Performance Concrete Under High Temperature (60-450°C) for Surface Long-Term Storage: Thermo-Hydro-Mechanical Residual Properties
Authors: Gallé C. , Sercombe J. , Pin M. , Arcier G. , Bouniol P. 
Published: May 2011

ABSTRACTAfter various thermal treatments (up to 450°C), residual thermo-hydro-mechanical (T-H-M) properties of two OPC high performance concretes (HPC) were analyzed in the context of surface long-term storage. Materials were prepared with silico-calcareous aggregates (standard HPC) and hematite aggregates (heavy HPC). The initial microstructural (porosity ≈10%) and transport (gas permeability ≈10-19 m2) properties are similar for both concretes. As far as the mechanical aspect is concerned, heavy HPC shows a higher compressive strength and elastic modulus than standard HPC (78 and 63 MPa, 81 and 49 GPa, respectively). Heavy HPC is also characterized by a higher thermal conductivity (7.3 W m-1 K-1 compared to 2.7 W m-1 K-1 for standard concrete). Results analysis show that thermo-hydro-mechanical damages are smaller for heavy HPC. Between 60 and 250°C, the elastic modulus and the compressive strength of standard HPC decrease by 40% and 16%, respectively. For heavy HPC, these parameters respectively decrease by 10% and 4%. A similar trend was observed for thermal conductivity evolution. Gas permeability and porosity data confirm the good behavior of heavy HPC. As a conclusion, hematite HPC seems to provide more interesting T-H-M residual properties than standard HPC. Limited thermal expansion and thermal gradients induced by hematite are probably responsible of this behavior.
The Maralinga Rehabilitation Project
Authors: Perkins C. , Harris J. 
Published: May 2011

ABSTRACTThe $108 million Maralinga Rehabilitation Project to clean-up the former British atomic test site in South Australia, the largest remediation of this type, was completed in 2000. The rehabilitation was agreed by the Commonwealth and South Australian Governments and the Maralinga Tjarujta traditional owners, following methods identified by technical experts. The rehabilitation permits unrestricted access to about 90% of the former restricted area, but excludes full time occupation of the remaining 120 square kilometers.The clean-up has largely been directed at remediating plutonium contamination caused by minor trials. The clean-up involved two components, the removal of surface soil from the more contaminated areas, and the treatment of contaminated debris pits. Over 350,000 cubic meters of soil and debris was removed over about 2 square kilometers of land, and was buried in 10-15 meter deep trenches under a capping of clean soil of at least 5 meters. Treatment of contaminated pit debris at various sites has involved in situ vitrification, a process which involves application of an electric current to heat and melt debris encasing the contaminated material in a vitric/ceramic block, and exhumation of the contaminated debris and at depths of at least 5 meters.The independent regulator to the project, the Australian Radiation Protection and Nuclear Safety Agency, has indicated that the clean-up of the test sites has met the radiological criteria laid down in the original plan. Discussions are progressing with the South Australian Government and the Maralinga Tjarujta traditional owners as to the long-term management of the site, and the possible hand back of the land from the Commonwealth to South Australia for addition to the Maralinga Tjarutja freehold lands.
Radionuclide Transport Calculations in the Safety Assessment SR 97
Authors: Lindgren M. , Lindström F. 
Published: May 2011

ABSTRACTThis study treats radionuclide transport calculations for a canister defect scenario in the safety assessment SR 97, which concerns a deep repository for spent nuclear fuel of the KBS-3 type in Sweden. The aims of the calculations are to:Quantitatively describe the radionuclide transport.Show the impact of uncertainty in input data and show which parameters govern the calculated release rates.Compare three different real sites in Sweden (Aberg, Beberg and Ceberg) with each other and with dose limits given in Swedish regulations (none of the sites is considered in the on-going localization process). Only briefly described in this paper.Illustrate the impact of the different barriers in the system.Deterministic calculations illustrate the radionuclide transport for reasonable conditions. Uncertainty cases show the influence of the uncertainty for data related to different parts of the repository system by systematically giving them pessimistic values while all others are reasonable. Simplified probabilistic calculations have also been performed.The analysis shows that the most important parameters in the near field are the number of defective canisters and the instant release fraction. In the far field the most important uncertainties affecting release and retention are connected to permeability and connectivity of the fractures in the rock. The dose rate in the biosphere is essentially controlled by the possibilities of dilution.The calculated maximum doses for the hypothetical repositories are well below the dose limits, and hence they meet the acceptance criteria for a deep repository for spent fuel.
Using Results from Tru Experiments for WIPP to Determine Model Development and Needed Experimental Programs
Authors: Silva M. K. , Oversby V. M. 
Published: May 2011

ABSTRACTThe Waste Isolation Pilot Plant (WIPP) is located at a depth of 655 m in bedded salt at a site about 40 km east of Carlsbad, New Mexico.The 1996 U. S. Department of Energy (DOE) application for certification by the U. S. Environmental Protection Agency (EPA) included results of a performance assessment (PA) for the planned repository.After the EPA certified the facility in May, 1998, emplacement of contact handled transuranic waste (CHTRU) began in March, 1999.The WIPP facility must undergo a recertification by EPA every 5 years to demonstrate compliance with disposal regulations.Performance assessment is expected to be a key part of the recertification process.The PA will include probabilistic calculations to predict the release of actinides to the accessible environment over a 10,000 year period using a variety of plausible scenarios.The 1996 PA used a model for Pu(IV) solubility based on Th data and the assumption of analogous behavior for all actinides in the (IV) oxidation state.That model did not allow for mobility between the various possible oxidation states of Pu.The possible effects of increases in solubility of Pu through complexation with organic ligands was also not included in the PA because it was argued by DOE that such complexation would be insignificant. Subsequent data from tests using actual TRU wastes show strong evidence that the importance of organic ligands and the potential for multiple oxidation states must be carefully considered in estimating the expected solution concentrations of Pu in WIPP brines.This paper reviews the present state of knowledge of the behavior of Pu-containing wastes in contact with brines similar to those expected to be important for the WIPP repository, recent advances in understanding of the nature of Pu-oxide phases, and analytical methods that have high sensitivity for Pu speciation. A conceptual model for Pu in TRU wastes is presented and a series of steps - including experiments and calculations - that could led to an improved basis for the PA calculations to be done during the WIPP recertification process is outlined.
Modeling of Near Field Actinide Concentrations in Radioactive Waste Repositories in Salt Formations: Effect of Buffer Materials
Authors: Schuessler W. , Kienzler B. , Wilhelm S. , Neck V. , Kim J.I. 
Published: May 2011

ABSTRACTEngineered barrier systems are designed to reduce the near field actinide concentrations in case of water penetration into a repository. In this paper, the influence of buffer materials, such as MgO/CaO and clays, on the solubilities of Am, Np, Pu, and U is studied. The analysis is performed for low level cemented waste forms in a rock salt formation in contact with MgCl2 saturated salt brine (Q-brine).The evolution of the geochemical milieu by cement corrosion is calculated using reaction path modeling supported by the code EQ3/6. The influence of different buffer materials is analyzed with respect to their impact on the solution chemistry and corresponding actinide concentrations.
Status of the Pangea International Repository Feasibility Studies
Authors: Mccombie C. , Kurzeme M. 
Published: May 2011

ABSTRACTThe potential technical, scientific, safety, security, environmental and economic advantages of implementation of deep geologic repositories for the disposal of nuclear waste within an international framework were outlined in papers from the IAEA and from the Pangea organization over the past three years. Of increasing importance are the security and non-proliferation benefits which could result from having closely supervised centralized repositories for declared surplus fissile materials resulting from disarmament activities in nuclear weapon states.The Pangea concept is for repositories sited on technical and safety grounds independent of national boundaries. The sites would be in geologic formations situated in flat, stable, arid regions, where the convincing demonstration of long-term safety should be easier to achieve. Pangea identified several potential host regions of the world which warrant further investigation of their suitability for an international repository. As yet a formal feasibility study has been initiated only in Australia. This was allocated first priority due to the vastness of the region with potentially suitable geology, also because of its stable governmental system, its strong environmental record and non-proliferation credentials. Australia also has a strong anti-nuclear movement, no nuclear power plants, but an important uranium mining industry.Hence progress to date in Australia has been mixed. Political resistance has culminated in legislation in Western Australia prohibiting the construction and operation of a repository for the disposal of imported nuclear waste, unless approved by both houses of the WA Parliament. Within the scientific, technical and business communities, there has been much greater readiness to objectively weigh up the pros and cons of hosting an international disposal facility. The public reaction has been mixed, with some individuals and communities strongly opposing the concept whilst others are prepared to seek information before judging the case on its merits.Meanwhile, on the world stage, the generic concept of international disposal facilities continues to be elaborated - including defining better the roles which such facilities could play in management and disposition of surplus weapons material. In addition contacts are being strengthened with potential users of such facilities and actions being taken to intensify Pangea's activities in other countries identified as having potential host regions for a high-isolation repository of the type proposed by Pangea.
Simulation of the Waste Glass Behavior in a Loamy Soil of the Wet Repository Site
Authors: Ojovan M.I. , Ojovan N.V. , Startceva I.V. , Chuikova G.N. , Barinov A.S. 
Published: May 2011

ABSTRACTA model developed for description of waste glass corrosion has been applied to assess the radionuclide release from real radioactive (intermediate level) vitrified material over extended storage periods. Field data generated during the long-term testing of the prototype waste glass packages were mathematically processed and the derived parameters used in model calculations. Regardless of the corrosive saturated conditions of the wet near-surface repository, the fairly high safety of trench disposal has been demonstrated for borosilicate glass containing real NPP- operational waste.
Scenarios Selection for a Simple Concept Landfill
Authors: Badie Olivier-Moana , Goldschmidt Frédéric , Besnus François , Péres Jean-Marc 
Published: May 2011

ABSTRACTScenarios are used to deal with uncertainty on the evolution of complex systems. The scenario selection methodologies also have to provide a basis for reflexion and traceability of the reasoning. In the case of a simple concept landfill, a methodology that fulfils these requirements has been developed. It distinguishes on the one hand the landfill evolution, and on the other hand, the human behavior evolution. It is based on three steps: (i) characterization of the landfill itself, in order to define situations leading to releases of radionuclides, (ii) characterization of the human behavior in order to define situations leading to intrusions, and (iii) characterization of the interfaces between the two subsystems, in order to identify situations which could lead to a radiological risk for man. The method has been applied to performance assessment for landfill of uranium mill tailings. It has led to one reference scenario, and five altered scenarios taking into account specific landfill evolutions such as loss of covering or loss of integrity of the dike, and human intrusions such as housing on the site of landfill or excavation of the site.
Development and Analysis of Scenarios for a Permanent Repository for Radioactive Wastes in Salt Rock
Authors: Keller S. 
Published: May 2011

ABSTRACTScenarios were developed and analyzed as part of a long-term safety analysis of a permanent repository for radioactive wastes. A procedure is described by which features, events, and processes (FEP) at a specific site can be evaluated for the long-term safety assessment of a permanent repository for radioactive waste. These FEPs can be weighted according to selected criteria and combined to scenarios using a conceptual model of the site.
Application of Supplementary Safety Indicators for H12 Performance Assessment
Authors: Takasu A. , Naito M. , Umeki H. , Masuda S. 
Published: May 2011

ABSTRACTThe safety of a geological disposal system can be assessed using defined indicators such as risk and dose level, which directly measure radiological effects on human beings. Since the safety assessment of a geological disposal system covers a very long period of time, there are inherent uncertainties involved in assumptions about future human activities and environmental conditions, which increase the longer the time frame becomes.To allow for some of these uncertainties, it has been proposed to supplement assessment results based on dose levels (or equivalent risks) by other independent indicators, without relying on assumptions made in the biosphere model. Safety indicators such as nuclide concentration, flux and radiotoxicity can usefully supplement dose calculations in the evaluation of overall system performance. In particular, they may be more indicative of the isolation capability of a disposal system and the potential risks of radioactive waste disposal over the very long timescales of safety assessment.In the H12 study, which is the project aimed at establishing a technical basis for HLW disposal in Japan, supplementary safety indicators have been applied to increase confidence in the safety assessment. The nuclide concentrations evaluated in the geosphere and biosphere in the H12 repository system were compared with measurements of naturally occurring nuclides. The comparison indicated that the concentration of radionuclides released from the repository would be several orders of magnitude lower than that of natural radionuclides. This suggests that application of supplementary safety indicators could increase the reliability of long-term safety by more rigorous measurements of concentrations of naturally occurring radionuclides in the characterization phase at a specific site, which will be compared with concentrations of relevant nuclides predicted by site-specific performance assessment models.
Alteration of Uranium-Rich Microlite
Authors: Gieré R. , Buck E. C. , Guggenheim R. , Mathys D. , Reusser E. , Marques J. 
Published: May 2011

ABSTRACTMicrolite, a Ta-rich member of the pyrochlore group, occurs in 440 Ma old lithium pegmatites in Mozambique and exhibits a pronounced growth zoning, with a U-free core surrounded by a U-rich rim (UO2≤ 17 wt%). Subsequent to the uplift of the host rock, microlite was subjected to intense low-temperature alteration during which Na, Ca and F were leached from the microlite crystals. This alteration, resulting from exposure to tropical conditions, also led to localized redistribution of radiogenic Pb (formation of plumbomicrolite) and to hydration of microlite, but U remained immobile. The low-temperature alteration effects are only observed in the U-rich rim, which is characterized by abundant microfractures. As demonstrated by electron diffraction images and powder X-ray patterns, the U-rich rim is largely metamict. Our investigation illustrates the importance of natural analogues in evaluating the durability of pyrochlore-based nuclear waste-form materials over geologic time.
Field and Laboratory Examination of Uranium Microcrystallization and Its Role in Uranium Transport
Authors: Murakami Takashi , Ohnuki Toshihiko , Isobe Hiroshi , Sato Tsutomu 
Published: May 2011

ABSTRACTAdsorption is believed to be a dominant mechanism of uranium distribution between solid and solution, and thus, to play a major role in uranium transport. Because iron oxides and hydroxides are abundant at the Earth's surface and are great adsorbents of uranium, we have examined natural rocks that contain iron minerals along with uranium, and also carried out Fe-U coprecipitation and aging experiments to find how uranium is distributed between Fe minerals. Transmission and scanning electron microscopy reveals that microcrystals (10-50 nm) of metatorbernite (Cu(UO2)2(PO4)28H2O) are scattered within nodules consisting of fine-grained (2-50 nm) goethite and hematite, where the ground water is undersaturated with respect to metatorbernite, for the natural rocks from the Koongarra ore deposit, Australia. The microscopy also reveals that microcrystals (a few nm) of dehydrated schoepite ((UO2)O0.25(OH)1.5) are formed among fine-grained hematite after aging coprecipitated Fe-U in the laboratory, and the solution is undersaturated with respect to schoepite. The beam size of microscopes is found to be important for the chemical analysis of such microcrystals. We detect a strong signal of uranium for a beam size < 40 nm; whereas a weak uranium signal is obtained for a beam size > 150 nm. Our results indicate that such a weak uranium signal should not be taken as a result of homogeneously distributed uranium over goethite and hematite surfaces by, for instance, adsorption. The micrcrystallization observed in both the field and laboratory suggests that fine grained uranyl minerals play a major role in uranium transport and migration.