共查询到20条相似文献，搜索用时 484 毫秒
1.
The kinetics of radionuclide desorption from bentonite colloids and subsequent sorption onto fracture filling material can influence colloid-facilitated radionuclide migration in ground water. To shed light on the significance of these issues batch-type experiments using a cocktail of strong and weak sorbing radionuclides as well as FEBEX bentonite colloids in the presence of fracture filling material from Grimsel (Switzerland) under Grimsel ground water conditions have been conducted. Results show that tri- and tetravalent radionuclides, 232Th(IV), 242Pu(IV) and 243Am(III) are clearly colloid associated in contrast to 233U(VI), 237Np(V) and 99Tc(VII). Concentrations of colloid-borne 232Th(IV), 242Pu(IV) and 243Am(III) decrease after ∼100 h showing desorption from bentonite colloids while 233U(VI) and 99Tc(VII) concentrations remain constant over the entire experimental time of 7500 h thus showing no interaction either to colloids or to the fracture filling material. 232Th(IV) and 242Pu(IV) data yield a slower dissociation from colloids compared to 243Am(III) indicating stronger RN–colloid interaction. In the case of 237Np(V), a decrease in concentration after ∼300 h is observed which can be explained either by slow reduction to Np(IV) and subsequent sorption to mineral surfaces in accordance with the evolution of pe/pH and/or by a slow sorption onto the fracture filling material. No influence of the different fracture filling material size fractions (0.25–0.5 mm, 0.5–1 mm and 1–2 mm) can be observed implying reaction independence of the mineral surface area and mineralogical composition. The driving force of the observed metal ion desorption from colloids is binding to fracture filling material surfaces being in excess of the available colloid surface area (76:1, 55:1 and 44:1 for the 0.25–0.5 mm, 0.5–1 mm and 1–2 mm size fraction of the FFM, respectively). 相似文献
2.
A. P. Novikov Yu. I. Fabelinskii E. A. Lavrinovich T. A. Goryachenkova A. A. Grechnikov 《Geochemistry International》2016,54(13):1196-1209
Researchers of the Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences created a luminescence photometer of a new generation for the determination of trace amounts of uranium and transuranium elements (TUE). The limits of detection for actinides vary from 0.3 pg for uranium and neptunium to 2.0 pg for plutonium. For 237Np, the relative limit of detection is 0.008 Bq/L. The photometer was tested in the radioecological monitoring of a number of polluted zones in Russia. The dynamics of actinide migration in all of the studied zones enhanced in the series 239Pu < 241Am < 237Np. In this series, concentrations of radionuclides in water-soluble and exchange forms that are most mobile and determine the migration mobility of chemical elements increased in all of the studied soil types. In the group of fulvic acids, concentrations of radionuclides decreased in the series 237Np > 241Am > 239Pu irrespectively of the soil. In the group of humic acids, concentrations of radionuclides increased in the series 237Np < 239Pu < 241Am. The sorption coefficients of radionuclides by bottom sediments of the Markha River (Kraton-3 underground nuclear explosion site) and Lake Kyzyltash (East Urals Radioactive Trace) were calculated. Bioaccumulation factors of radionuclides by different plants in the impact area of the Kraton underground nuclear explosion were determined depending on the plant type. 相似文献
3.
Pihong Zhao Mavrik Zavarin Roald N. LeifBrian A. Powell Michael J. SingletonRachel E. Lindvall Annie B. Kersting 《Applied Geochemistry》2011,26(3):308-318
The effect of dissolved organic matter (DOM) on Am(III), Pu(IV), Np(V), and U(VI) sorption was investigated with natural water (pH ∼8) and zeolitized tuff samples collected from the Rainier Mesa tunnel system, Nevada Test Site, where the USA detonated underground nuclear tests prior to 1992. Perched vadose zone water at Rainier Mesa has high levels of DOM as a result of microbial degradation of mining debris (diesel, wood, etc.). The Am and Pu sorption Kds were up to two orders of magnitude lower in water with high DOM (15-19 mg C/L) compared to the same water with DOM removed (<0.4 mg C/L) or in naturally low DOM (0.2 mg C/L) groundwater. In contrast, Kds of Np and U were less affected by DOM at these solution conditions. Uranium sorption decreased as a result of high dissolved inorganic C (DIC) resulting from microbial degradation of DOM. Thermodynamic model predictions, based on actinide-humic acid stability constants available in the literature, are in general agreement with measured Kd data, correctly predicting the effects of DIC and DOM on actinide retardation. This agreement is encouraging to future modeling efforts and suggests that effects of DOM and DIC can be incorporated into reactive transport modeling predictions. The Am and Pu transport rates in Rainier Mesa tunnel waters will be substantially faster as a result of the elevated DOM levels. Low diffusion rates of actinide-DOM macromolecular complexes may focus Pu and Am transport into fractures and minimize retardation via matrix diffusion. The resulting transport behavior will affect actinide distribution patterns and associated risk estimates. 相似文献
4.
The understanding of the thermo-hydro-mechanical behaviour of a clay barrier is needed for the prediction of its final in situ properties after the hydration and thermal transient in a radioactive waste repository.
As part of the CEC 1990–1994 R&D programme on radioactive waste management and storage, the CEA (Fr), CIEMAT (Sp), ENRESA (Sp), SCK · CEN (B), UPC (Sp) and UWCC (UK) have carried out a joint project on unsaturated clay behaviour (Volckaert et al., 1996). The aim of the study is to analyse and model the behaviour of a clay-based engineered barrier during its hydration phase under real repository conditions. The hydro-mechanical and thermo-hydraulic models developed in this project have been coupled to describe stress/strain behaviour, moisture migration and heat transfer. A thermo-hydraulic model has also been coupled to a geochemical code to describe the migration and formation of chemical species.
In this project, suction-controlled experiments have been performed on Boom clay (B), FoCa clay (Fr) and Almeria bentonite (Sp). The aim of these experiments is to test the validity of the interpretive model developed by Alonso and Gens (Alonso et al., 1990), and to build a database of unsaturated clay thermo-hydro-mechanical parameters. Such a database can then be used for validation exercises in which in situ experiments are simulated.
The Boom clay is a moderately swelling clay of Rupellian age. It is studied at the SCK · CEN in Belgium as a potential host rock for a radioactive waste repository. In this paper, suction-controlled experiments carried out on Boom clay by SCK · CEN are described. SCK · CEN has performed experiments to measure the relation between suction, water content and temperature and the relation between suction, stress and deformation. The applied suction-control techniques and experimental setups are detailed. The results of these experiments are discussed in the perspective of the model of Alonso and Gens. The influence of temperature on water uptake was rather small. The measured swelling-collapse behaviour can be explained by the Alonso and Gens model. 相似文献
5.
《Applied Geochemistry》2000,15(5):667-686
Interstitial water from the Boom clay Formation around the HADES (high activity disposal experimental site, an underground research facility belonging to the Nuclear research centre, SCK·CEN, at Mol-Dessel, Belgium.) underground research facility at Mol, Belgium, and waters sampled at different locations in the Rupelian aquifer, underlying the clay formation, have been studied. The Boom clay is a Tertiary mudrock containing about 55 % clay and the Rupelian aquifer is located in a silty layer. Special care was taken to adapt or improve measurement, sampling, conservation and analysis methods to get a reliable regional and local database, for the purpose of testing a general model describing the regulation and acquisition of the composition of these fluids. The isotopic and chemical composition of the waters allows them to be assigned to a common origin, namely mixing between a marine endmember and the clay interstitial water, followed by reequilibration with the host rock through dissolution–precipitation reactions involving identified secondary minerals. Oxidation–reduction state and trace element behavior are also discussed and the limits of the model are outlined. 相似文献
6.
Summary The mechanical behaviour of reconstituted normally consolidated Boom clay was examined in a series of laboratory triaxial stress path tests. The aim was to establish some basic characteristics of this soil. The compressibility of the reconstituted Boom clay was found to be moderate, corresponding to the soils of the same plasticity. The results indicated also that the destructured Boom clay exhibited a brittle behaviour. The undrained secant stiffness was found to vary with strain level and also to be dependent on the consolidation pressure. 相似文献
7.
8.
In this study the effect of the temperature increase on the hydro-mechanical properties of sheared Boom clay samples is investigated. Two samples of Boom clay are resaturated in a new hollow cylinder triaxial cell with a short drainage path and then sheared by performing an axisymmetric triaxial loading. The effect of the undrained heating under deviatoric stress is studied on the first sample. It is shown that undrained temperature increase leads to an increase of pore water pressure and consequently to a decrease of the effective mean stress which brings the sample to failure. For an initially sheared sample, the failure occurs along the existing shear band which behaves as a weakness plane in the sample. The responses of the local strain measurement transducers clearly show the sliding of rigid blocks when failure occurs in the sample.The effect of the presence of a shear band on the permeability of the other Boom clay sample is investigated at ambient temperature and at 80 °C. It is shown that the presence of a shear band does not affect significantly the permeability. These results confirm the good self sealing properties of Boom clay at ambient and at high temperature. 相似文献
9.
《Applied Geochemistry》2002,17(6):837-853
This study presents the characterization of Pu-bearing precipitates and the results from uptake studies of Np and Pu on inorganic colloidal particulates in J-13 water from the Yucca Mountain site. Plutonium solubilities determined experimentally at pH values of 6, 7, and 8.5 are about two orders of magnitude higher than those calculated using the existing thermodynamic database indicating the influence of colloidal Pu(IV) species. Solid phase characterization using X-ray diffraction revealed primarily Pu(IV) in all precipitates formed at pH 6, 7, and 8.5. The solubility controlling Pu-bearing solids precipitated at ambient temperature consisted of amorphous Pu(OH)4(s) with several Pu–O distances between 2.3 and 2.7 Å that are characteristic for Pu(IV) colloids. High temperature (90 °C) increased solid phase crystallinity and produced Pu(IV) solids that contained Pu oxidation state impurities. X-ray absorption spectroscopic studies revealed diminished Pu–O and Pu–Pu distances that were slightly different from those in crystalline PuO2(s). A Pu–O bond of 1.86 Å was identified that is consistent with the plutonyl(V) distance of 1.81 Å in PuO2+(aq). Hematite, montmorillonite, and silica colloids were used for uptake experiments with 239Pu(V) and 237Np(V). The capacity of hematite to sorb Pu significantly exceeded that of montmorillonite and silica. A low desorption rate was indicative of highly stable Pu-hematite colloids, which may facilitate Pu transport to the accessible environment. Neptunium uptake on all mineral phases was far less than Pu(V) uptake suggesting that a potential Pu(V)–Pu(IV) reductive sorption process was involved. The temperature effect on Pu solubility and pseudocolloid formation is also discussed. 相似文献
10.
黏土岩温度-渗流-应力耦合特性试验与本构模型研究进展 总被引：2，自引：0，他引：2
高放废物处置库、垃圾填埋场等工程中常常涉及到温度场（T）、渗流场（H）和应力场（M）的耦合作用的问题。从试验和理论模型两个角度综述国内外黏土岩温度-渗流-应力耦合特性的研究进展,主要包括其传热特性、温度影响下的渗流特性、变形、强度、蠕变特性。在此基础上,重点分析了黏土岩水-热迁移模型以及热-力耦合本构模型的适应性。基于上述认识,通过试验研究了比利时Boom clay在温度作用下的强度、渗透性、蠕变性等特征。结果表明：随着温度升高,Boom clay的强度有所降低,渗透性显著增强,蠕变速率明显加快。提出了适用于Boom clay的THM耦合弹塑性损伤模型,计算结果验证了模型能合理反映温度的影响。最后,探讨了黏土岩THM耦合机理研究的不足和今后的研究方向。 相似文献
11.
The HADES project (High Activity Disposal Experimental Site) aims at demonstrating the technical feasibility and the long-term safety of geological disposal of reprocessed HLW (High-Level Wastes) radioactive wastes. This disposal could be realised in the Tertiary Boom clay formation below the Mol/Dessel nuclear site. Previous studies in the 80's on the geomechanical behaviour of Boom clay, at host rock temperature (15°C), have demonstrated the mining capabilities of this clay. European partners have collaborated to increase the number of in-situ tests to be developed and operated from the Underground Research Facility (URF). Integrated large-scale experiments have been developed during the last four years, within the framework of the Commission of the European Communities (CEC) research contracts, in order to gain more insight into the thermal influence of heat-emiting wastes on the clay behaviour in the near field.
This paper summarizes the knowledge gained from the in-situ hydro-thermo-mechanical experiments realised from the URF. The objectives and main issues of the tests are described. Information regarding selection of parameters and representativeness of their measurements is discussed. Despite their different aims and designs, three hydro-thermo-mechanical experiments are compared in order to emphasize similarities in the general behaviour of the clay massif submitted to a thermal load. It is observed that its behaviour is qualitatively similar to the reaction upon a constant total stress increase. With the information now available, it is not obvious to draw conclusions with respect to the irreversibility of some phenomena.
Simple in-house analytical codes are able to simulate with a good accuracy the hydro-thermo-mechanical behaviour of clay. Nevertheless, these codes are not sufficient to describe the complexity of the phenomena that are involved in hydro-thermo-mechanical processes as pointed out by field data. In order to validate more complex models, the possibilities to improve the representativeness of the measurements are investigated. 相似文献
12.
Rodney C. Ewing 《Comptes Rendus Geoscience》2011,343(2-3):219-229
During the past 60 years, more than 1800 metric tonnes of Pu, and substantial quantities of the “minor” actinides, such as Np, Am and Cm, have been generated in nuclear reactors. Some of these transuranium elements can be a source of energy in fission reactions (e.g., 239Pu), a source of fissile material for nuclear weapons (e.g., 239Pu and 237Np), and of environmental concern because of their long-half lives and radiotoxicity (e.g., 239Pu and 237Np). There are two basic strategies for the disposition of these heavy elements: (1) to “burn” or transmute the actinides using nuclear reactors or accelerators; (2) to “sequester” the actinides in chemically durable, radiation-resistant materials that are suitable for geologic disposal. There has been substantial interest in the use of actinide-bearing minerals, especially isometric pyrochlore, A2B2O7 (A = rare earths; B = Ti, Zr, Sn, Hf), for the immobilization of actinides, particularly plutonium, both as inert matrix fuels and nuclear waste forms. Systematic studies of rare-earth pyrochlores have led to the discovery that certain compositions (B = Zr, Hf) are stable to very high doses of alpha-decay event damage. Recent developments in our understanding of the properties of heavy element solids have opened up new possibilities for the design of advanced nuclear fuels and waste forms. 相似文献
13.
《Applied Geochemistry》1996,11(4):555-565
Organic material is present at low concentrations, typically 1–2 mg/l in terms of dissolved organic carbon (DOC), in groundwaters deep in granitic rock. Hydrophobic and hydrophilic acids may complex inorganic contaminants and change their sorption behaviour on geological materials. This report describes a series of experiments performed under aerobic conditions to investigate the effects of fulvic acid over a concentration range of 0–5 mg/I DOC on the sorption of85Sr,137Cs,233U,238Pu and241'Am by crushed granite, biotite, goethite, montmorillonite and quartz. In addition, similar solutions were used to study the effects of dissolved fulvic acid on the sorption of99Tc and125I on each of the above solids except quartz. The fulvic acid was extracted from groundwater collected at a depth of 240 m in the granitic rock of the Underground Research Laboratory near Lac du Bonnet, Manitoba.In all experiments, the sorption of the fulvic acid by the geological materials was in the order goethite montmorillonite > biotite > granite > quartz. No sorption of Tc was observed from any of the solutions on any of the solids. Low sorption of I on montmorillonite occurred in the presence of the dissolved organic material. No sorption of I was observed with the other solids used. Only montmorillonite sorbed any appreciable amount of Sr in this study with the fulvic acid having no effect on this sorption. All the solids except quartz sorbed substantial amounts of Cs, but sorption was not affected by the organic material in solution. Each of the solids sorbed U with no difference in sorption observed due to the dissolved organic. In general, Pu sorption decreased as the concentration of dissolved fulvic acid increased. However, sorption of Pu on quartz remained at approximately the same levels regardless of the concentration of organic in solution. Generally high sorption of Am was found. Lowest sorption of Am on all solids occurred from the solution with the highest concentration of fulvic acid. Sorption of Am on granite decreased as the concentration of the organic in solution increased.This study indicated that, under aerobic conditions, the effect of dissolved organic material on sorption of radioisotopes depends on the radioisotope in question and the concentration of the organic in solution. 相似文献
14.
Hydrogeological modeling of radionuclide transport in low permeability media: a comparison between Boom Clay and Ypresian Clay 总被引：1，自引：0，他引：1
Deep low-permeability clay layers are considered as suitable environments for disposal of high-level radioactive waste. In Belgium, the Boom Clay is the reference host formation and the Ypresian Clay an alternative host formation for research and safety and feasibility assessment of deep disposal of nuclear waste. In this study, two hydrogeological models are built to calculate the radionuclide fluxes that would migrate from a potential repository through these two clay formations. Transport parameter heterogeneity is incorporated in the models using geostatistical co-simulations of hydraulic conductivity, diffusion coefficient and diffusion accessible porosity. The calculated radionuclide fluxes in the two clay formations are compared. The results show that in the Ypresian Clay larger differences between the fluxes through the lower and the upper clay boundary occur, larger total output radionuclide amounts are calculated and a larger effect of parameter heterogeneity on the calculated fluxes is observed, compared to the Boom Clay. 相似文献
15.
M. Honty M. De Craen L. Wang J. Madejová A. Czímerová M. Pentrák I. Stríček M. Van Geet 《Applied Geochemistry》2010
Boom Clay is currently viewed as a reference host formation for studies on deep geological disposal of radioactive waste in Belgium. The interactions between bulk rock Boom Clay and 0.1 M KOH, 0.1 M NaOH, 0.1 M Ca(OH)2, young cement water and evolved cement water solutions, ranging in pH from 12.5 to 13.2, were examined as static batch experiments at 60 °C to simulate alkaline plume perturbations, which are expected to occur in the repository due to the presence of concrete. Both liquids and solids were investigated at specific times between 90 and 510 days in order to control the elemental budget and to search for potential mineralogical alterations. Also, the clay fraction was separated from the whole-rock Boom Clay at the end of each run and characterized for its mineralogical composition. Thereby, the importance of the mineral matrix to buffer the alkaline attack and the role of organic matter to protect clay minerals were also addressed. The results indicate that the degree of geochemical perturbation in Boom Clay is dependent on the initial pH of the applied solution together with the nature of the major cation in the reactant fluids. The higher the initial pH of the media, the stronger its interaction with Boom Clay. No major non-clay mineralogical alteration of the Boom Clay was detected, but dissolution of kaolinite, smectite and illite occurred within the studied experimental conditions. The dissolution of clays is accompanied by the decrease in the layer charge, followed by a decrease in the cation-exchange capacity. The highest TOC values coincide with the highest total elemental concentrations in the leachates, and correspondingly, the highest dissolution degree. However, no quantitative link could be established between the degree of organic matter decomposition and clay dissolution. 相似文献
16.
The Boom Clay formation (Oligocene) is studied as a reference host rock for methodological studies on deep geological disposal of radioactive waste. During excavation of galleries within the Clay formation (HADES underground research facility, Mol, Belgium), the physico-chemical conditions are significantly modified as an air–clay interface is created. In order to study the long-term impact of the air–clay contact on the organic matter contained in the Boom Clay, two types of samples were studied: (1) a reference series of clay samples having been in contact with the atmosphere of the HADES gallery for increasing times up to several years and (2) unaltered clay samples submitted to artificial oxidation in a ventilated oven at 80 °C. The evolution of geochemical data of the two series was compared using Rock-Eval pyrolysis, GC–MS and size exclusion chromatography. The organic matter of the unaltered clays sampled in the HADES galleries is dominated by type III kerogen (terrestrial) with some contribution of type II (marine) and is thermally immature. The evolution of geochemical parameters during air alteration for the two series are very similar. They show progressive oxidation of kerogen accompanied by the release of bitumen enriched in low molecular weight constituents. Molecular analysis evidences the presence of a complex mixture of aliphatic and aromatic O-bearing compounds, inherited from the degradation of kerogen as well as from the clay catalyzed oxidation of the bitumen. These results show that (1) air oxidation is a major process in the in situ alteration of the organic matter of Boom Clay within the HADES galleries, (2) laboratory oxidation experiments at 80 °C yield similar results as in situ air alteration of Boom Clay and (3) artificial air oxidation may be used to assess the long term exposure of the organic matter to air. 相似文献
17.
In the context of nuclear waste disposal in clay formations, laboratory experiments were performed to study at reduced scale the excavation damaged zone (EDZ) induced by the construction of galleries in the Boom clay formation. For this purpose, thick-walled hollow cylindrical samples were subjected (after recovery of in situ stress conditions) to a decrease in the inner confining pressure aiming at mimicking a gallery excavation. X-ray computed tomography (XRCT) scans of the specimens were carried out through the testing cell before and after the mechanical unloading and allowed to quantify the displacements undergone by the clay as a result of the mechanical unloading. The deformation of the hollow cylinders and the inferred extent of the damaged zone around the central hole are found to depend on the orientation of the specimen with respect to the bedding planes and show a great similarity with in situ observations around galleries and boreholes at Mol URL in the Boom clay formation. In the experiments performed on samples cored parallel to the bedding, the damaged zone is not symmetrical with respect to the hole axis and extends more in the direction parallel to the bedding. It is the same for the radial convergence of the hole walls which is larger in the direction parallel to bedding than in the perpendicular one. In contrast, a test on a sample cored perpendicularly to the bedding did not show any ovalisation of the central hole after the mechanical unloading. These observations confirm the significance of the pre-existing planes of weakness (bedding planes) in Boom clay and the need for a correct consideration of the related mechanical anisotropy. 相似文献
18.
《Applied Geochemistry》2000,15(7):975-1001
The modelling of metal-humate interactions has been a field of active research for more than 3 decades but despite all efforts there is still far from a consensus concerning humic binding models. The authors demonstrate that a synopsis of large sets of reliable experimental data for Ca, Co, Ni, Eu, Am, Cm, Np(V) and U(VI) reveals a consistent picture of the influence of metal concentration, pH and ionic strength on metal-humate interactions. However, this consistent behaviour cannot be interpreted with high numerical accuracy by simple binding models, the need for more adjustable parameters increases proportional to the width of the experimental parameter range to be fitted. This experience triggered the proposal of a pragmatic approach for performance assessment purposes. The “conservative roof” approach does not aim to accurately model all experimental data but rather allows estimates to be made of the maximum effects on metal complexation to be expected from humic substances. A specific “conservative roof” model is applied to situations generally to be expected in deep groundwater and selected cases of interest for planned Swiss repositories of radioactive waste are discussed in detail. 相似文献
19.
20.
《Applied Geochemistry》1998,13(1):105-126
Leaching experiments in aqueous media were carried out on non-radioactive and radioactive nuclear waste glasses to investigate the release behaviour of 4 actinides (Th, U, Np and Pu) and 3 lanthanides (La, Ce and Nd) from the solid into solution. The experiments were conducted under flowing conditions using synthetic aqueous solutions. The lanthanide and actinide concentrations were measured in the leachates before and after filtration to 0.45 μm and 1.8 nm.Over 98.5% of the lanthanides and Th released from the glass were retained in the alteration products on the glass surface, probably coprecipitated with a siliceous gel. The retention was enhanced by the presence in the gel of 20 wt% P oxides from the initial 5 × 10−3 M PO4 solution. In the leachates, more than 90% of the lanthanides and Th were associated with colloidal particles.Uranium and Np retention varied from 40% in a 5 × 10−3 M CO3 medium to 95% in a 5 × 10−3 M PO4 medium. In the CO3 medium, U and Np formed stable CO3 complexes that diminished the formation of precipitates; in the PO4 medium, precipitation of PO4 or more complex phases may have occurred.Pu exhibited atypical behaviour to the extent that it was strongly bonded to colloidal particles in solution, concentrated in the fraction exceeding 0.45 μm, and modifyed the calculated Pu leach rates. These particles may be the result of limited disaggregation of the alteration film. As most of the Pu was found at valence IV, it may be strongly retained in the alteration layer by precipitation or coprecipitation.Under oxidizing conditions, Np and U are found at high valences as Np(V) and U(VI), yielding charged forms in solution (NpO2+ and UO2+). The lanthanides, Th and Pu were present at lower valences as Ln(III), Th(IV) and Pu(IV), yielding Ln3+, Th4+ and Pu4+ in oxidizing media. The different behaviour of U and Np compared with the lanthanides, Th or Pu, observed during these experiments shows that the valence is the determining factor, and must be taken into account in assessing the evolution of radionuclides during the alteration of nuclear waste glass. 相似文献