The objective of the CNFWMP is to develop a disposal concept that will protect human health and the natural environment far into the future. Assessments of the conceptual vault designs are based on system theory in which an attempt is made to correlate experiences with theoretical concepts of planned systems in such a way that the resulting coordination is sound and convincing. By necessity, since experiments with a total disposal system can never be performed, both the design and the performance assessment rely on experiments performed on physical models of vault elements over relatively short times and on information inferred from calculations (mathematical models) that simulate the probable behaviour of the system in the space-time domainof interest. For a simulation model to be successful, that is applied within a real world situation, the model must provide information regarding the behaviour of the system of interest that is clearly better, in some way, than the mental image or other abstract model that would be used instead. The results of a series of tests performed within the activity known as validation serve as tangible evidence regarding the success of a model in representing the system of interest.
This paper focusses on the validation of the models that describe the hygro-thermo-mechanical behaviour of the engineered clay-barriers proposed for application in the Canadian disposal system concept. The strategy being used to address the key issues in modelling to minimize the model error and to maximize the usefulness of the simulation model, based on testing procedures, is reviewed. Finally, a concept of the validation of codes/models that describe the unsaturated behaviour of engineered clay barriers, is described. 相似文献
Sweden is geologically located in the Fennoscandian shield which is dominated by gneisses and granitoids of Precambrian age. The Swedish reference repository concept thus considers an excavated vault at ca. 500 m depth in crystalline rocks. In this concept (KBS-3), copper canisters with high level waste will be emplaced in deposition holes from a system of tunnels. Blocks of highly compacted swelling bentonite clay are placed in the holes leaving ample space for the canisters. At the final closure of the repository, the galleries are backfilled with a mixture of sand and bentonite. This repository design aims to make the disposal system as redundant as possible. Although the KBS-3 concept is the reference concept, alternative concepts and/or repository lay-outs are also studied. The main alternative, currently under development at SKB, is disposal in boreholes with depths of 4–5 km. The geoscientific research will to a great extent be guided by the demands posed by the performance and safety assessments, as well as the constuctability issues. Some main functions of the geological barrier are fundamental for the long-term safety of a repository. These are: bedrock mechanical stability, a chemically stable environment as well as a slow and stable groundwater flux. The main time-table for the final disposal of long-lived radioactive waste in Sweden foresees the final selection of the disposal system and site during the beginning of next decade. 相似文献
The safety of the waste disposal is based on a multibarrier concept including waste packages, concrete disposal modules, site and closure operations.
Under normal conditions, confinement is guaranteed by the waste packages and the disposal modules, as they prevent the waste from being leached by rainfall or underground water over a certain period of time.
The site must bring an additional guarantee concerning the isolation of waste from water. Consequently, the chosen site must be located in an area where no natural disasters (landslides, earthquakes, etc.) can harm the isolating barriers. The geological, hydrogeological and chemical characteristics must allow us to minimize and control the transport of radionuclides within the ground. Finally, the chosen site must be in an area where it is easy to implement a system to monitor the environment.
A set of criteria guides the choice of site. The criteria include such factors as low seismicity, geotechnical stability, a hydrogeology that is simple to model, a location sufficiently above the water table and safe from the threat of flooding, good radionuclide sorption and the absence of any mineral or other natural resources of economic interest.
At the time of the closure of the disposal facility, the entire collection of modules will be covered by an impervious cap composed of clayey layers interbedded by sandy layers and overlain by humus to promote the growth of grass. The facility will then look like a succession of undulating green mounds.
A 300-year monitoring period will follow the closure. During this period, the water collecting networks and cap will be maintained and radioactivity in underground and stream water will be controlled.
We have selected the AUBE site as a case study to illustrate the French waste management experience. We will report on how the site characterization program has been calTied out, including the hydrogeological modelling which is being applied to both the operating and post-closure periods. 相似文献
The experimental programme was developed in collaboration with the CEA/DRDD; the main objective was to build a comprehensive methodology of characterization, applied to the French Ca-smectite clay, ldFo-Card clay selected from several French deposits.
For this programme specific experimental facilities are needed adapted to this kind of material. The main results concerning thermal, hydraulic and radioelement transfer properties are presented for pure Fo-Ca clay, or used in mixtures with different components such as sand, graphite or talc.
Hydraulic properties of Fo-Ca and Na-bentonite MX-80 are compared and discussed. 相似文献
The results from the laboratory tests were used to find a relationship between water content, void ratio, swelling pressure and suction. Two equations for swelling pressure represent the outline of the model.
In the first equation, the swelling pressure developed during water uptake is normalised by a pressure corresponding to the swelling pressure at saturation. This is done in order to be independent of void ratio. A relationship between the normalised swelling pressure and the degree of saturation is suggested.
The second equation describes a relationship between the swelling pressure, the water content and the actual suction (or relative humidity). The equation is based on a thermodynamic relationship and includes the retention curve (i.e. water content vs. suction under free swelling conditions).
The model can be used for a state where two of the four variables; water content, void ratio, swelling pressure and suction are known and can thus be useful to evaluate field measurements and model late stages of the wetting process. An example of an application is given. The equations are mainly based on results from tests with increasing degrees of saturation under constant void ratio but are also suggested for use with increasing void ratio. 相似文献
The paper presents design systems, based on computer programs, where these features are demonstrated. The refrigeration capacity is given as a boundary condition at the freezing pipe, either as temperature or flux.
Two programs are discussed; a one-dimensional (1-D), finite difference program for the analysis of a single pipe, and a two-dimensional (2-D), finite element code, with seepage flow as an option, more suited for real problems.
The programs are used to display the influence of various design parameters, such as refrigeration capacities, material properties and geometries.
A comparison is made between the 2-D program and a simplified method developed by K.R. Khakimov, which shows that the simplified method gives a very conservative estimate of the frozen volume vs. elapsed time.
Finally, the 2-D program computing combined heat and seepage flow is applied to a laboratory model of a soil freezing system, and the agreement between measured and computed values of temperature and water flow is shown to be acceptable. 相似文献
A gel formation of the bentonite was observed to be a dominant process in the erosion of bentonite particles although an intrusion of bentonite into a rock fracture also contributed to the erosion. The concentration of the eroded bentonite particles eroded by a flowing groundwater was increased with an increasing flow rate of the groundwater. It was observed from the experiments that the erosion of the bentonite particles was considerably affected by the ionic strength of a groundwater although the effect of the pH was not great within the studied pH range from 7 to 10. An erosion of the bentonite particles in a natural groundwater was also observed to be considerable and the eroded bentonite particles are expected to be stable at the given groundwater condition.
The erosion of the bentonite particles by a flowing groundwater did not significantly reduce the physical stability and thus the performance of a compacted bentonite buffer. However, it is expected that an erosion of the bentonite particles due to a groundwater flow will generate bentonite particles in a given groundwater condition, which can serve as a source of the colloids facilitating radionuclide migration through rock fractures. 相似文献
The definition of Didymaulichnus miettensis Young as a Terminal Proterozoic trace fossil is questioned, and it may be considered to interpret the ‘bilobate’ structure as the upturned, opposite margins of microbial shrinkage cracks which have been brought back into contact by compaction after burial. 相似文献
The study of a high-level or long-lived nuclear waste disposal concept is necessarily a step-by-step procedure, with two main objectives: on one hand, ensuring a good disposal design, including feasibility of the vaults and their stability during the operating phase with the eventual continuation of the phase of waste retrievability, i.e. on a long period of time not shorter than one hundred years. On the other hand, the objective is to preserve the long-term clay properties with regard to radionuclide behavior, in particular those properties which influence their containment capacity.
Swelling clays as an engineered barrier material have been considered by ANDRA for a long time. Buffer material as an interface between the nuclear waste packages and the geological barrier and tight core of dams in drifts and shafts are the two types of constructions for which the clay conditioning and performance have been investigated. In both of these applications, the understanding of the THM behavior of the swelling clay is required. In the first case the THM load parameters are much more severe and the geochemical imbalances are of greater consequences.
R & D programmes are necessarily integrated into the design process of the disposal concept. The results will allow selection between technical solutions estimated as valuable candidates for validation within the project duration, i.e. 13 years, and those solutions which cannot be. In return the design process indicates what are the more profitable axis for the future R & D efforts. 相似文献
The ERASE association planned to build a landfill for both solid waste and contaminated soil/sediments disposal. In order to determine more accurately the volume of material to be disposed of in the landfill, a site investigation was carried out during September/November 1998. The site investigation consisted mainly of systematic soil sampling at shallow depths, both within the industrial area and along the natural water streams.
The site investigation results revealed high concentrations of toxic pollutants, mainly heavy metals (namely As, Hg, Pb and Zn), in the soil of the industrial area. Much higher concentrations were found in the sediments of the water streams, several kilometres away from the industrial complex (the pollution source area).
In most cases, concentration increases with depth, reaching groundwater. Therefore the site investigation programme carried out could not determine the full extent of the contamination. Consequently, further studies were strongly recommended, which should include a wider and deeper investigation area and groundwater sampling. 相似文献
The material model is based on the Drucker-Prager Plasticity model and a Porous Elastic Model. The effective stress concept and Darcy's law are applied and the swelling/consolidation and thermomechanical processes are coupled according to the separate mechanical properties of the pore water, the solids and the clay skeleton. The model can be used by the finite-element program ABAQUS.
The model has been tested in several laboratory and field verification tests. Comparison between measured and calculated behaviour shows that the general behaviour is described properly and several calculations of different scenarios have been made for the Swedish KBS 3 concept. However, certain processes, like the hysteresis effect at consolidation/swelling, the curved stress-strain relation at shearing, and the curved failure envelope, are not modelled in a perfectly accurate way and an improved material model is proposed here. It combines the behaviour of the Cam-clay model on the wet side with the more relevant plastic behaviour of a modified Drucker-Prager model with a curved failure envelope and the possibility to introduce strain softening after failure.
The paper presents some laboratory results that are the basis of the first model. It also shows the application of the model to finite-element calculations of some laboratory tests. Comparisons between the calculations and measured results expose some disadvantages of the model and a concept for an improved model is suggested. 相似文献
The results indicate parallel hardening lines at systematically lower values of specific volume at elevated temperatures. In shear, increased temperatures produced lower values of maximum deviator stressqf, and higher pore water pressure changesΔuf. The net result is curved peak strength envelops in plots ofqf versuspf′ that are higher at elevated temperatures, even though the strengths,qf of individual specimens are lower. The critical state strength envelope is curved inq, p′-planes.
The effect of drained heating on buffer to 100°C is not marked. Compressibilities, stiffnesses, strengths, and pore water pressure generation are all affected, but none of the changes are great. 相似文献
The experimental field is located at a depth of 520 m where two major tests have been carried out since 1987. The first test (1987–1989) tested the backfilling by heating different types of crushed salt (max. 130°C) emplaced in large-diameter boreholes. One hole remained empty as a control. The second experiment started in 1989 with the opening of a gallery and the boring of three different boreholes (7 m depth, 250 mm diameter) where the annulus between the cylindrical heating cell and the salt mass differs fundamentally in configuration: as tight as possible, empty, or backfilled with crushed salt. The first configuration was tested at the end of 1991.
In both test fields, a complete series of measurements has been carried out to record temperatures, pressures and deformations on the heating devices, as well as in the surrounding media. Backfill and host rock are monitored with sensors placed in different boreholes. High-resolution tiltmeters and accurate levelling complete the field of investigations. Thermo-mechanical behavior and the properties of the materials have been considered in detail using laboratory test results. Calculations showed how thermo-mechanical interactions behave and generally agreed in a satisfactory manner with the measurements of the test field.
Finally, after cooling and dismantling of the experiment, the microscopic change of the different crushed salts used for the backfilling is analysed. 相似文献