摘要
设施选址阶段厂址的适宜性评估以及事故工况下放射性核素的环境风险评估过程中需要开展核素迁移实验研究工作.本工作采用室内静态批式法及动态原状土柱实验,开展了90Sr、241Am在非饱和多孔介质粉质黏土中的迁移转化过程研究,通过实验室精细化物理模拟试验和数值模拟技术分析了不同环境要素对核素迁移过程的影响.结果表明:90Sr、241Am在粉质黏土介质中的吸附、解吸等温线性相关系数r2均大于0.9,表明Freundlich等温吸附模型可较好地描述不同核素在粉质黏土中的吸附和解吸过程,岩土介质对强吸附核素241Am的阻滞能力远大于90Sr,且体系的可逆性好于90Sr.对90Sr而言,动态柱法非平衡吸附模式考虑了溶解相与吸附相之间的一级速率反应系数β,计算的浓度分布曲线与实测浓度点吻合程度较好,通过非平衡模式拟合得到90Sr在非饱和粉质黏土中的吸附分配系数为3.6 mL/g,p为0.55/h;241Am在平衡吸附、非平衡吸附两种模式下得到的核素浓度分布曲线与实测值吻合均较好,表明核素在土壤介质中的吸附特性越强,吸附、解吸速率越快,越接近瞬时吸附时体系更容易达到平衡,两种模型均可以较好地描述核素的迁移反应过程,利用平衡模式拟合得到吸附分配系数为3×103mL/g.
Abstract
The studies on the batch experiments and transport of 90Sr and 241 Am were respectively conducted under unsaturated flow conditions in silty clay column.The results show that the linear correlation coefficient r2 of adsorption and desorption isotherms for 90Sr and 241Am in silty clay medium is greater than 0.9,which indicates that the Freundlich isotherm adsorption model can better describe the adsorption and desorption process of different nuclides in silty clay.The adsorption capacity of strongly adsorbed nuclides 241 Am is much greater than that of 90Sr.As for 90Sr,the first-order rate coefficient(named as β)between the dissolved phase and the adsorbed phase was considered in the non-equilibrium adsorption model by transport column.The calculated concentration distribution curve is good agreement with the measured values.The fitting results show that the distribution coefficient(named as Kd)and β of 90Sr in the fine sand aquifer are 3.6 mL/g and 0.55/h.Respectively,in terms of 241Am,the radionuclides concentration distribution curves in equilibrium adsorption model and non-equilibrium adsorption model are in good agreement with the measured values.It shows that the stronger adsorption capacity of the nuclides have the faster rate of the adsorption-desorption in the soil,meanwhile the shorter time for the system reaction equilibrium.At this time,the fitting results of the equilibrium adsorption mode and the non-equilibrium adsorption model are closer to each other.Meanwhile the calculated Kd value by equilibrium adsorption model is 3× 103 mL/g.
维普
万方数据