The Study On The Radionuclide Migration And Simulation In Groundwater Of A Project Area

This paper takes the main radionuclide⁹⁰Sr of a project repository in the northernpart of Sichuan as the research object,focusing on the On-site hydrogeologic testingand using hydrogeological、engineering geological mapping、Hydrogeochemical、drilling and computer simulation techniques.According to the structural features of thehydrogeology of the project area, establishing the hydrogeological conceptual modelof radionuclide migration. Though analyzing its main migration mechanisms andinfluencing factors of migration,predicting and stimulating the transfer law ofradionuclide⁹⁰Sr after it goes into the groundwater,and predicting the migrationcharacteristics and range of pollutants of the different concentrations of⁹⁰Sr in timeand space,in order to provide reference for groundwater environmental impactassessment and the development of preventive measures.The main achievements asfollows:（1） Though the site reconnaissance and survey,to identify the geological andhydrogeological conditions of the project area. There is Yanziyang fracture、Caishichang fracture and Piaocaowan fracture near the project area.The developmentdirection of Cracks are NNW、NWW、NEE.The groundwater types are loose rocks ofthe pore water、bedrock weathering fracture water and structural-fissure water whosemain supply source is atmospheric precipitation and excretion by the gullies andfracture aisles of decelopment in the back mountain to the Wangjiahe,groundwater isslightly alkaline.（2） According to drilling data, to identify the distribution characteristics of thestratigraphic and lithologic: The Quaternary loose sediment types are slope eluvialand blunt flood product layers and the underlying original rock of S1lm⁵is gray- green、gray-yellow shale.The bedrock is divided into strong weathering zone、in-weakweathering zone and weak-breeze weathering zone. The formation occurrence is330°～345°∠36°～48and it is a reverse slope.（3） Though water injection test、packer test、pumping test to derive permeabilitycoefficient of the project area which providing reference data for the migration andsimulation.The permeability coefficient of the Quaternary system is10^-5≤k＜10^-4cm/sand10^-4≤k＜10^-2cm/s and of the bedrock is between0.001and0.12m/d. Permeabilitycoefficient average of strata is mostly10^-4cm/s and it is a medium permeable range.（4） Though establishing conceptual hydrogeological model of radionuclidemigration to draw a conclusion that groundwater level is higher than the underside ofthe repository and the Radionuclide⁹⁰Sr once release from the nuclear wasterepository will directly enter into groundwater.The main factors affecting radionuclidemigration are geochemical characteristics of strontium isotopes,such as the form ofstrontium in groundwater、pH value、ionic strength,and the actual hydrogeologicalconditions of the project area,such as variation of permeability coefficient、Directionand velocity of groundwater.（5） Though NaCl tracer tests and pumping tests to ascertain the velocity,directionand connectivity of groundwater.The velocity are all sizes along the differentdirections and it is higher when there are caacks channel.The velocity of groundwaterfrom ZK44to ZK50is5.12m/d and between other drills is about2m/d. Direction ofgroundwater of project area is from ZK44to ZK57and ZK59and it excretes toWangjiahe,but the latter is the main direction.（6） Using modflow software to simulate and forecast the migration of nuclide⁹⁰Sr in groundwater and drawing the general laws of the radionuclides⁹⁰Sr:The size ofsource strength makes a big difference to migration of⁹⁰Sr，the source strength isgreater，and the concentration and range of pollutants are greater, the time is shorter toreach the Wangjiahe near the project area when radionuclide enters into the ground-water.With time going on,the range of pollutants is gradually larger in the plane,but itwill not increase in the vertical.