| The safe disposal of high-level radioactive waste?HLW?is one of the outstanding problems in the development of nuclear energy and the utilization of nuclear technology.With the development of nuclear power,the public and the society pay more attention to the safe disposal of high-level radioactive waste,and the problem of safe disposal of HLW in China is more urgent.At present,the geological disposal of HLW is regarded as the most promising disposal scheme.The primary and most basic of the HLW geological disposal scheme is the site selection of the disposal depot,and the site conditions are one of the most critical factors affecting the long-term safety of the HLW disposal repository.In view of the importance of the disposal site,the IAEA has established safety requirements for geological disposal.Many countries have been very careful in determining the site of the disposal depot,and have called for a multi-faceted comparison of the surrounding rock type,geological conditions,hydro-geological conditions,economic and social conditions,construction and transportation conditions of the disposal repository.The selection of clay rock sites is an important choice for the research and development of the geological disposal of HLW in major nuclear countries.The study of pre-selected site construction and engineering conditions is an indispensable part of site selection.It is of great practical significance not only to evaluate the feasibility and suitability of engineering geological conditions,hydro-geological conditions and external construction environment of pre-selected sites,but also to provide reference for the design of the proposed buildings in pre-selected sites.In this paper,a comprehensive study on the construction and engineering conditions of HLW disposal repository in the pre-selected areas is carried out.The main research work and results are as follows:?1?The safety requirements and technical guidelines for site selection of nuclear waste disposal depots in relevant international and regional organizations and nuclear countries are investigated in detail.Combining with the safety requirements and site selection criteria,the paper further refines and supplements the specific site selection criteria for the clay rock disposal sites in China.?2?Data collection and engineering geological survey on natural geography,economy,transportation,climate,electricity utilization,water use,source and supply of construction materials,regional structures,earthquakes,strata,lithology,hydrogeology,surface soil and bad geology were carried out.The results show that the study area basically meets the requirements of site selection for HLW disposal repository.?3?Data on drilling,cataloguing and geophysical tests were collected.Physical mechanical tests have been carried out on the macroscopic characteristics of rock mass,mineral composition analysis as well as moisture content,density,permeability,free expansion rate,thermal properties,wave velocity,uniaxial compression and triaxial compression.Through the analysis of experimental data and data,the characteristics,physical and mechanical properties and engineering geological characteristics of the clay rock in the study area were preliminarily identified.?4?Combined with the results of laboratory tests,the rock mass in the borehole area of Tamusu was divided into surrounding rock grade.Based on the size of the conceptual design model of the underground disposal reservoir in Belgium,the excavation stability of the key cavern group structure of the proposed underground disposal reservoir is numerically simulated based on the engineering background of the Tamusu.The TZK-1borehole in the study area is the???grade rock mass in the 393.5?432.5m region,and the proportion of the?grade rock mass in the 437.4?467.2m region is the largest,while the main?grade rock mass in the 468.9?478.8m range.During the simulation excavation,the structure stability of the cavern group is good,the deformation mainly appears in the shaft side wall,the main,branch roadway top,bottom plate,two sides position,in addition,the surrounding rock deformation produced in the cross part is also more obvious.The axis direction of the main roadway tunnel should be at a certain angle with the maximum horizontal principal stress direction,and the stability is the best when the angle is about 45°to 60°.?5?Based on the concept design of the HLW disposal depot in china and the design ideas of the disposal depot in france and belgium,this paper simulates and studies the near-field environmental change process of the barrier failure of the disposal depot after receiving the waste.The process is essentially a force-thermal sequential coupling process without considering the seepage field.The temperature field shows a rapid growth-peak-continue-slow-down-fast-down-rebalancing process.At about 100 days,the temperature of the disposal depot reaches its peak,and the maximum temperature can reach about 100°C.The temperature field shows the concentric ellipse distribution with the center waste tank as the center.The closer the center is,the higher the temperature is.The influence of temperature field on the force field is very significant,which has little effect on the overall stability of the structure formed after excavation.?6?Based on the mathematical model of porous medium groundwater and solute transport,the migration process of groundwater and nuclides in surrounding rock was studied.The activity of nuclides decreases gradually with the increase of migration distance,but the difference is large in different media,which may be related to the flow rate of groundwater in different media.79Se migration rate was the fastest,135Cs followed by 99Tc.As a geological barrier,clay rock can effectively control the migration rate of groundwater,thus controlling the time and activity of nuclide reaching biosphere.?7?Through the research,combined with the current site safety requirements and technical guidelines,it is considered that the Tamusu area is suitable for construction and engineering conditions. |
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