U、238Pu在砂质含水层中的迁移机制研究

The adsorption transfer mechanism of U and 238Pu in sandy aquifers

放射性核素在非均质含水层多孔介质中以水流为载体的迁移是一个复杂的物理化学过程,为了准确模拟放射性核素释入环境介质后在潜层地下水中的迁移,必须借助物理试验和数值模拟技术。本试验以干旱地区砂土介质为研究对象,研制了饱和带砂土弥散渗透试验土柱装置,分别将U和^238Pu以液相点源形式布设在土柱入水断面处,试验周期结束后解体测量U、^238Pu在土柱空间内的浓度分布,利用Hydrus-3D建立溶质迁移三维数值模型模拟相关试验参数。试验结果表明:U 14 d内在土柱中沿水流方向向下迁移了24.3 cm,峰值浓度为7.03μg?cm^?3,拟合得到分配系数为35 mL?g^?1,纵向弥散度为22 cm、横向弥散度为25 cm;^238Pu在140 d内沿水流方向向下迁移了2.1 cm,峰值浓度为0.47 ng?cm^?3,拟合得到分配系数为6 500 mL?g^?1,纵向弥散度为2 cm、横向弥散度为25 cm。U、^238Pu在非均质试验土柱中迁移曲线的不同主要与砂土介质和溶质的吸附滞留作用有关,由本试验给出的相关弥散渗透迁移试验方法可为放射性核素在土壤介质中迁移、转化规律研究提供技术支撑及理论支持。

[Background]The migration of radionuclides carried by water flow in aquifer porous media is a complex physical and chemical process.[Purpose]This study aims to accurately and truly reflect the nuclide transportation in the groundwater by physical experiments and numerical simulation techniques.[Methods]First of all,the sand medium in arid area was taken as the research object,and a soil column device for saturated sandy soil dispersion and permeability test was developed for experimental test.Then,the U and^238Pu were arranged in the form of liquid point source in the form of liquid point source in the intake section of the soil column,respectively,and the concentration distribution of nuclides in the space of the soil column was measured after the test cycle.Finally,Hydrus-3D was used to establish a three-dimensional numerical model of nuclide migration and to fit the relevant experimental parameters.[Results]The experimental results showed that U migrated downward 24.3 cm along the water flow direction in soil column after 14 days,the distribution coefficient was 35 mL?g^?1,the longitudinal dispersion was 22 cm,and the transverse dispersion was 25 cm.^238Pu migrated downward 2.1 cm along the water flow direction in soil column after 140 days,the peak concentration was 0.47 ng?cm^?3,the distribution coefficient was 6 500 mL?g^?1,the longitudinal dispersion was 2 cm,and the transverse dispersion was 25 cm.The different migration curves of U and^238Pu in heterogeneous test soil columns are mainly related to the adsorption and retention of sand media and solutes.[Conclusions]The proposed experimental method for nuclide migration in aquifer porous media can provide support for the study of the migration and transformation in soil media.