共查询到20条相似文献，搜索用时 78 毫秒
1.
N. P. Laverov V. I. Velichkin V. I. Malkovsky N. N. Tarasov Yu. P. Dikov 《Geology of Ore Deposits》2010,52(1):5-13
The spread of radioactive contamination in the subsurface medium near Lake Karachai is considered. The complexity of this
process requires a comprehensive approach to its study. The source of radioactive contamination is overviewed. The map of
faults in subsurface medium is considered in order to determine the prevailing direction of contaminated groundwater flow.
Photometry in observation wells has been used for structural geological estimation of transport properties of the shallow
aquifer, where contaminated groundwater is moving. This study was carried out along with hydrochemical logging, which makes
it possible to estimate the dynamics of contamination of subsurface medium and vertical distribution of groundwater contamination.
Special attention is paid to transport of radionuclides in the form of radiocolloid particles. Groundwater samples were taken
from various depths corresponding to different contamination levels near Lake Karachai. The depth intervals of sampling were
determined from the data of hydrochemical logging. Ultrafiltration through membranes with a specific pore size in combination
with gamma spectrometry was used to characterize radionuclide transfer with colloidal particles differing in size. The local
elemental composition of the radiocolloid surface was studied by Auger spectroscopy. The chemical composition and structure
of radiocolloid particles were determined by X-ray photoelectron spectroscopy with consecutive etching of the particle surface
by argon ions for a certain depth. The data obtained indicate that radiocolloid particles are heterogeneous and an organic
shell consisting of humic and fulvic acids and technogenic organic compounds coat their surface. 相似文献
2.
Current designs for nuclear-waste repositories rely primarily upon subsurface geologic barriers for long-term containment. Because water and air are generally considered to be the mechanisms most likely to transport radioactivity to the surface environment, flow and transport models are important tools in repository assessment. Most models assume that the geologic medium can be treated as a continuum. A substantial body of recent work has focused on applying these models to difficult-to-solve problems, such as the simulation of variably dense or variably saturated flow and transport, large and complex flow systems, sharp solute concentration fronts, and fractured rock systems. The complex chemical interactions between the transport fluid and solid particles within the system have been analyzed using geochemical flow models, most of which assume that the system is at chemical equilibrium. The role of colloids in contaminant transport is a relatively new area of research. The large-scale effects of small-scale variability within the geologic system have been the subject of intense investigation. Inherent limitations of the continuum approach have prompted the design of models in which the flow occurs in discrete fractures. The difficulty and complexity of simulating transport has led to the development of network transport models, which represent the flow field as a series of 1-D path segments. The widespread use of models for prediction and analysis has prompted investigations of their reliability and relative merits. 相似文献
3.
The convective transfer of radionuclides by subsurface water from a geological repository of solidified high-level radioactive wastes (HLW) is considered. The repository is a cluster of wells of large diameter with HLW disposed of in the lower portions of the wells. The safe distance between wells as a function of rock properties and parameters of well loading with wastes has been estimated from mathematical modeling. A maximum permissible concentration of radionuclides in subsurface water near the ground surface above the repository is regarded as a necessary condition of safety. The estimates obtained show that well repositories allow for a higher density of solid HLW disposal than shaft storage facilities. Advantages and disadvantages of both types of storage facilities are considered in order to estimate the prospects for their use for underground disposal of solid HLW. 相似文献
4.
《Applied Geochemistry》2004,19(1):119-135
Colloid-facilitated transport of contaminants could enhance the release rate of radionuclides from the cementitious near field of a repository for radioactive waste. In the current design of the planned Swiss repository for intermediate-level radioactive waste, a gas-permeable mortar is employed as backfill material for the engineered barrier. The main components of the material are hardened cement paste (HCP) and quartz aggregates. The chemical condition in the backfill mortar is controlled by the highly alkaline cement pore water present in the large pore space. The interaction of pore water with the quartz aggregates is expected to be the main source for colloids. Colloid transport is facilitated due to the high porosity of the backfill mortar. Batch-type studies have been performed to generate colloidal material in systems containing crushed backfill mortar or quartz in contact with artificial cement pore water (ACW) at pH 13.3. The chemical composition of the colloidal material corresponds to that of calcium silicate hydrates (CSH). Batch flocculation tests show that, after about 20 days reaction time, the concentration of the CSH-type colloids is typically below 0.1 mg l−1 due to reduced colloid stability in ACW. Uptake studies with Cs(I), Sr(II) and Th(IV) on a CSH phase (initial C:S ratio=1.09) have been carried out to assess the sorption properties of the colloidal material. The influence of uptake by colloids on radionuclide mobilisation is expressed in terms of sorption reduction on the immobile phase (HCP). Sorption reduction factors can be estimated on the assumption that the sorption properties of the colloidal material are either similar to those of the CSH phase or HCP, and that sorption is linear and reversible. A scaling factor accounts for the higher specific surface area of the colloidal material compared to the CSH phase and HCP. At colloid concentration levels typically encountered in highly alkaline cement pore waters, colloid-induced sorption reduction is predicted to be negligibly small even for strongly sorbing radionuclides, such as Th(IV). Thus, no significant impact of cementitious colloids on radionuclide mobilisation in the porous backfill mortar is anticipated. 相似文献
5.
V. I. Mal’kovskii 《Doklady Earth Sciences》2011,436(1):39-41
A model of precipitation of radiocolloid particles on enclosing rocks at colloid-facilitated transport of radionuclides by
groundwater is considered. The model proposed is based on probabilistic analysis of deposition of heterogeneous colloidal
particles on fixed sites of groundwater filtration channels, which are formed by connected systems of pore_ and fracture voids
in enclosing rocks. The model takes into account heterogeneity of the system of colloidal particles and competition of different
particles for the same potential deposition sites. Theoretical analysis is based on the solution of the system of Kolmogorov-Feller
equations. The limit values of the obtained solutions correspond to the equilibrium distribution of radiocolloid particles
of different sizes between the groundwater and the enclosing rocks. In the case of a homogeneous system of particles, the
obtained distribution is reduced to the Langmuir isotherm. 相似文献
6.
The transportation of colloidal radionuclides by groundwater was subject to theoretical analysis. The far field of radioactive contamination of the underground environment (liquid waste pumping sites or storage of solidified waste) is dominated by pseudocolloids, i.e., colloidal particles of natural origin contaminated with radionuclides upon contact of groundwater with radioactive materials. Properties of real pseudocolloids were analyzed at sites of radioactive contamination of the underground environment. Based on a probabilistic approach, we developed a mathematical model of pseudocolloid transportation by groundwater, taking into account the difference in size of colloidal particles and the occurrence of nonradioactive natural particles with a similar composition in the groundwater. It is proved that nonuniform dimensions of the particles considerably affect the water transportation rate. 相似文献
7.
Comprehensive GC/MS analysis was applied to both the mobile liquid phase (seepage water) and the immobile solid matter of discrete layers derived from a waste deposit landfill. The vertical distribution of organic compounds supports information on the transport, transfer and transformation processes with depth and, consequently, with time.Numerous low molecular weight organic contaminants of natural and xenobiotic origin were identified and partially quantified. Several were selected to act as molecular indicators for different processes. Interpretation of their occurrence and concentration profiles (considering possible waste sources) and their molecular properties allowed us to (i) differentiate immobile and mobile fractions, (ii) reveal restrictions in the vertical transport by transfer processes between particulate and water phase, (iii) identify dynamic accumulations of individual contaminants and (iv) estimate approximate residence times. In addition, intensive degradation processes were pointed out for the natural fraction of the organic matter by way of determination of specific transformation products. Besides the transformation of natural components, transformation of numerous xenobiotics was recognised. In particular, with respect to an important group of contaminants, the phthalate-based plasticisers, a detailed view of (i) the influence of transfer and transport phenomena on transformation processes as well as (ii) the consecutive appearance of different degradation steps in both seepage water and solid waste was pointed out. The information provides a valuable base for the prediction of the long term behaviour of organic contaminants in waste deposit landfills. 相似文献
8.
潜流带是河流地表水和地下水交混区域,是河流中重要的物质能量交换和水生生物栖息的场所,而胶体颗粒在潜流带中沉积,会改变潜流带中的水动力结构和生态环境。本文利用室内循环水槽实验和多物理场耦合的数值模拟方法,旨在研究胶体颗粒在河流上覆水与潜流带中的迁移过程和胶体颗粒在潜流带中沉积分布特征及其对不同因素的响应规律。结果表明:河流上覆水中胶体会逐渐被河床截留且截留胶体集中于河床浅层;沙波水平方向截留量呈现出迎水面较高、背水面较低的趋势;胶体在潜流带沉积的主要机制是潜流交换、颗粒沉降与河床截留作用。本文能为胶体颗粒在潜流带中的生态环境作用研究提供科学依据,并为河流生态环境修复、河流健康管理提供理论支持。 相似文献
9.
It occurs worldwide that the organic components of non-aqueous phase liquid (NAPL) enter the porous medium and become the source of contaminants in the subsurface. The transport of the organic components through NAPL interphase into the aqueous phase and the subsurface determines the extent of contamination, the persistence of residual NAPL phases and the techniques of remediation. During the transport process the NAPL interphase may experience "aging", a physical and chemical change when NAPL is exposed to aqueous and or gaseous phases. This aging process alters vice versa the mass transfer behaviour of the organic contaminants in the porous medium. 相似文献
10.
Gour-Tsyh Yeh Yilin Fang Fan Zhang Jiangtao Sun Yuan Li Ming-Hsu Li Malcolm D. Siegel 《Computational Geosciences》2010,14(1):149-170
Subsurface contamination problems of metals and radionuclides are ubiquitous. Metals and radionuclides may exist in the solute
phase or may be bound to soil particles and interstitial portions of the geologic matrix. Accurate tools to reliably predict
the migration and transformation of these metals and radionuclides in the subsurface environment enhance the ability of environmental
scientists, engineers, and decision makers to analyze their impact and to evaluate the efficacy of alternative remediation
techniques prior to incurring expense in the field. A mechanistic-based numerical model could provide such a tool. This paper
communicates the development and verification of a mechanistically coupled fluid-flow thermal-reactive biogeochemical-transport
model where both fast and slow reactions occur in porous and fractured media. Theoretical bases, numerical implementations,
and numerical experiments using the model are described. A definition of the “rates” of fast/equilibrium reactions is presented
to come up with a consistent set of governing equations. Two example problems are presented. The first one is a reactive transport
problem which elucidates the non-isothermal effects on heterogeneous reactions. It also demonstrates that the rates of fast/equilibrium
reactions are not necessarily greater than that of slow/kinetic reactions in the context of reactive transport. The second
example focuses on a complicated but realistic advective–dispersive–reactive transport problem. This example exemplifies the
need for innovative numerical algorithms to solve problems involving stiff geochemical reactions. It also demonstrates that
rates of all fast/equilibrium reactions are finite and definite. Furthermore, it is noted that a species-versus-time curve
cannot be used to characterize the rate of homogeneous fast/equilibrium reaction in a reactive transport system even if one
and only one such reaction is responsible for the production of this species. 相似文献
11.
岩溶区地下水数值模拟研究进展 总被引：2，自引：2，他引：0
岩溶含水介质的不均一性导致岩溶地下水流动、溶质运移和热量迁移的数学模拟研究成为地下水模拟的难点。本文综述了岩溶区地下水流模拟的几种方法,重点阐述了等效多孔介质法、双重连续介质法和三重介质法的定义、发展过程和适用范围,并回顾了这几种方法的研究成果。从等效多孔介质法到三重介质法,模拟精度不断提高,适用范围也逐渐由大区域实际问题向小区域理论研究过渡。介绍了溶质运移模拟和热迁移模拟的研究方法及实例。溶质运移模拟以对流弥散方程为基础,其中尺度效应是溶质运移模拟的重点研究问题;热量迁移模拟应考虑地下热水密度变化对地下热水运动的影响。溶质运移模拟和热量迁移模拟往往是将迁移模型和已经调试成功的地下水流动模型相耦合,从而达到模拟溶质及热量迁移的目的。由于溶质运移和热量迁移的复杂性,现阶段水流模型多数处于等效多孔介质模型阶段。综合理论及实际应用,指出精确刻画裂隙及管道和注重基础数学算法是岩溶水数值模拟进步的关键。 相似文献
12.
Evaluation of potential radiation doses and health risk to future populations is the primary goal of post-closure performance assessments. This article summarizes current methods used to estimate radiation doses and health risks following emplacement of high-level waste in a geologic repository. The methods described use the radionuclide concentrations in groundwater, surface water, or the atmosphere estimated by the release and transport analyses methods described in previous articles. Methods are described here to estimate (1) transfer of radionuclides from water or air to humans by various exposure pathways, (2) radiation dose received by individuals and populations from each exposure pathway, and (3) population health risks. 相似文献
13.
Stability assessment and characterization of colloids in coastal groundwater aquifer system at Kalpakkam 总被引：1，自引：0，他引：1
Natural colloids have a potential role in facilitating the transport of radionuclides in groundwater. To assess the role of
mobile colloidal phases in radionuclide transport, characterization of colloids for size, size distribution, zeta potential,
surface charge and elemental composition is required. Groundwater samples were collected from 12 borewells in the study area
and were characterized with respect to physicochemical parameters. Water quality parameters such as pH, temperature, specific
conductance, TDS and dissolved O2 were measured in situ. Based on salinity, two groundwater types were identified in the study area: (1) freshwater type and
(2) brackish type. Laboratory and field-scale turbidity measurements in addition to quantitative analysis of major ions were
carried out. It was observed that the colloid concentrations are reduced at higher salinity. Zetasizer, particle size analyzer,
scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction techniques were used to characterize
the colloidal particles in groundwater. Colloids were present in all the groundwater samples, the concentration varying between
0.05 and 6 mg/L. Colloid concentration was greater in wells with low ionic strength and the number of colloidal particles
varied between 3 × 109 and 4 × 1011 particles/L. The average colloid size varied between 200 and 350 nm for various samples. The zeta potential of the colloidal
particles varied between −25.5 and –34.0 mV. SEM analysis of colloidal particles revealed the presence of clays particularly
kaolinite and that the mineral composition of colloids reflects the mineralogy of the aquifer. For proper risk assessment
and remediation studies, the role of colloids in radionuclide transport assumes greater importance. This study highlights
the need for, and relevance of, detailed colloid characterization to assess its role in the migration of radionuclides from
near surface disposal facilities. 相似文献
14.
O. Hieke Merlin L. Menegazzo Vittori E. Molinaroli A. Morani L. Tassi Pelati 《地学学报》1992,4(4):434-442
The artificial radionuclides 137 Cs, 134 Cs and 106 Ru have been determined up to 16 cm deep in two sediment cores collected in March 1988 at the River Adige estuary in the northern Adriatic Sea. Interdependent relations between the properties of the sediment levels and the activity of radionuclides have been investigated using multivariate statistical analysis. The interactions between radiocontaminants and the particulate matter or water phase are discussed during their transfer processes from the river to the estuary and the marine environment. Diffusion phenomena within the sedimentary column have also been considered. The vertical distribution of the artificial radionuclides due to Chemobyl fallout in sediment cores from the River Adige mouth, compared to those from similar estuarine environments in the Adriatic Sea, point out a general rapid accumulation of river-borne solid material in coastal zones of the North Adriatic Sea. 相似文献
15.
土壤中污染物迁移转化规律的数值模拟研究 总被引：2，自引：0，他引：2
考虑到田间土壤的结构性以及运移其中的污染物的化学反应特征,建立了两区双点平衡/动力学吸附溶质运移模型。用拟交替显隐式有限差分格式对模型进行了离散,通过编制的相应程序,对一施药期的水田进行了模拟。研究了土壤中污染物的迁移转化规律,分析了不可动水和非平衡吸附相对浓度分布的影响。结果表明：不可动区水相和非平衡吸附相的浓度具有的滞后现象,在污染前期一定程度上起到了延缓污染作用,而在污染后期又在一定程度上加重了污染。二者的存在均对溶质的迁移转化具有重要的影响,进行数值模拟时应充分考虑二者的存在。模拟及分析结果为土壤环境质量评价提供了定量依据,同时对环境污染的治理与控制具有理论和现实意义。 相似文献
16.
17.
T. Kuppusamy 《国际地质力学数值与分析法杂志》1993,17(7):457-469
Aquifer contamination by organic chemicals in subsurface flow through soils due to leaking underground storage tanks filled with organic fluids is an important groundwater pollution problem. The problem involves transport of a chemical pollutant through soils via flow of three immiscible fluid phases: namely air, water and an organic fluid. In this paper, assuming the air phase is under constant atmospheric pressure, the flow field is described by two coupled equations for the water and the organic fluid flow taking interphase mass transfer into account. The transport equations for the contaminant in all the three phases are derived and assuming partition equilibrium coefficients, a single convective – dispersive mass transport equation is obtained. A finite element formulation corresponding to the coupled differential equations governing flow and mass transport in the three fluid phase porous medium system with constant air phase pressure is presented. Relevant constitutive relationships for fluid conductivities and saturations as function of fluid pressures lead to non-linear material coefficients in the formulation. A general time-integration scheme and iteration by a modified Picard method to handle the non-linear properties are used to solve the resulting finite element equations. Laboratory tests were conducted on a soil column initially saturated with water and displaced by p-cymene (a benzene-derivative hydrocarbon) under constant pressure. The same experimental procedure is simulated by the finite element programme to observe the numerical model behaviour and compare the results with those obtained in the tests. The numerical data agreed well with the observed outflow data, and thus validating the formulation. A hypothetical field case involving leakage of organic fluid in a buried underground storage tank and the subsequent transport of an organic compound (benzene) is analysed and the nature of the plume spread is discussed. 相似文献
18.
19.
M. D. Sharma 《Journal of Earth System Science》2007,116(4):357-367
Anisotropic wave propagation is studied in a fluid-saturated porous medium, using two different approaches. One is the dynamic
approach of Biot’s theories. The other approach known as homogenisation theory, is based on the averaging process to derive
macroscopic equations from the microscopic equations of motion. The medium considered is a general anisotropic poroelastic
(APE) solid with a viscous fluid saturating its pores of anisotropic permeability. The wave propagation phenomenon in a saturated
porous medium is explained through two relations. One defines modified Christoffel equations for the propagation of plane
harmonic waves in the medium. The other defines a matrix to relate the relative displacement of fluid particles to the displacement
of solid particles. The modified Christoffel equations are solved further to get a quartic equation whose roots represent
complex velocities of the four attenuating quasi-waves in the medium. These complex velocities define the phase velocities
of propagation and quality factors for attenuation of all the quasi-waves propagating along a given phase direction in three-dimensional
space. The derivations in the mathematical models from different theories are compared in order to work out the equivalence
between them. The variations of phase velocities and attenuation factors with the direction of phase propagation are computed,
for a realistic numerical model. Differences between the velocities and attenuations of quasi-waves from the two approaches
are exhibited numerically. 相似文献
20.
轻非水相液体（light non-aqueous phase liquid,LNPAL）在地下介质中的运移分布与残余捕获受多种因素影响和控制。LNAPL污染场地概念模型中一般视LNAPL从地表泄漏后穿过包气带至潜水面。然而地下介质的非均质性与包气带含水量的空间变异分布可形成复杂的LNAPL污染源区结构,LNAPL可能无法到达潜水面,而在毛细水带蓄积。文章基于数值模型综合分析了LNAPL泄漏量、介质非均质性与含水量空间变异分布、潜水面周期性变化等多种因素对LNAPL污染源区结构的影响。研究表明:（1）当泄漏量较大时,LNAPL可运移至潜水面;（2）当泄漏量较小时,对于上粗下细的层状非均质条件,LNAPL可能在毛细水带边缘发生蓄积,无法到达潜水面;（3）包气带中黏土透镜体并非都是LNAPL运移的阻碍,LNAPL可以穿透低含水量的黏土透镜体,只有高含水量的黏土透镜体才对LNAPL的入渗有阻碍作用;（4）潜水面周期性变化将导致污染范围扩大。 相似文献