Study On Transport Of Tracers In Groundwater At A Radionuclide Influenced Site

In some industrial activities of energy exploitation,artificial radionuclides may be released into water and soil environment,causing radioactive pollution of air,soil or groundwater.At present,the main method to deal with radioactive waste is to separate it into different depths of landfill storage,its leakage may cause groundwater pollution.Aiming at a site affected by radionuclides,this paper collected the observation data of tracer elements in groundwater,and studied the migration characteristics of radioactive solute in groundwater by using numerical model method,so as to provide services for the traceability and treatment of pollutants.Using the research field of hydrogeological exploration data and underground water level observation data,combined with meteorological data,this paper involves the site of the unconfined aquifer groundwater flow field is analyzed,based on GMS software MODFLOW model with 6layer structure is constructed,the determined by the steady flow to simulate the groundwater flow field of the control parameters and boundary conditions.On this basis,the seasonal dynamic unsteady flow simulation is carried out,which serves as the basis for the simulation of radioactive solute transport in groundwater.There are 30 groundwater observation wells at the study site,and the sampling indicators include total α and β radiation intensity and some typical radioactive elements.In this paper,the dynamic characteristics of tritium（³H）and strontium(⁹⁰Sr)isotopes were studied.It was found that in some observation wells,the concentration of ³H exceeded the background value for a long time,but the enrichment center had obvious seasonal variation,and the concentration of ⁹⁰Sr had relatively stable enrichment center.It was preliminarily speculated that there were 3 release sources for ³H and only 1 release source for ⁹⁰Sr.Based on MT3DMS,the leaching release and transport processes of radioactive solutes in groundwater under various scenarios were simulated.The results show that the migration rate of ³H is higher than that of ⁹⁰Sr,and it takes at least 1200days for a stable leaching source to form a steady pollution plume.The pollution plume mainly starts from the release source and extends to the downstream of the groundwater flow,and the extension distance of ³H can be more than 600 m,while the extension distance of ⁹⁰Sr is generally less than 400 m,and the extension distance of the pollution plume to the upstream is generally less than 50 m.Considering the seasonal variation of precipitation,the solute transport simulation based on unsteady flow shows the periodic fluctuation of trace element concentration with time,which is in good agreement with the observed results.Through simulation comparison,the prespeculated release source location of ³H is generally reliable,while the release source of ⁹⁰Sr needs to be adjusted.Through the analysis of this paper,basic mastered the research field of spatial and temporal variations of groundwater tracer element.Different source for ³H and ⁹⁰Sr speculate,numerical simulation method is used to estimate the radioactive solute diffusion from the source to the surrounding groundwater migration behavior,to guide the evaluation of groundwater contamination and prevention and control.