不同喷淋强度对核素Sr-90在土壤中迁移的影响

Effect of Spraying Intensity on Migration of Sr-90 in Soil

基于室内土柱法,建立120 ml d^(-1)、60 ml d^(-1)、30 ml d^(-1)三种不同喷淋强度下放射性核素Sr-90在砂土介质中的动态土柱迁移试验,试验时间分别为51 d、102 d、204 d,研究不同喷淋强度对Sr-90迁移规律的影响。结果表明,三种不同喷淋强度下Sr-90的浓度峰在土柱体中的迁移距离分别为42.3 cm、46.2 cm、44.4 cm,迁移距离基本一致,与喷淋强度和时间成正比。此外,Sr-90在土柱体剖面的浓度分布曲线均存在明显的不对称性和拖尾,即Sr-90从源层上洗脱下来后,受到砂土介质的吸附作用,待浓度峰值通过后,更多的Sr-90从之前的砂土介质中解吸出来,使得很长时间段内土柱体中保持相对较高的浓度。应用Hydrus-1d软件建立平衡吸附、非平衡吸附两种模式下的核素迁移数值模型,发现在非平衡吸附模式中考虑一级速率系数β能更好地描述浓度分布曲线的拖尾,通过与实测浓度值拟合得到Sr-90的分配系数为0.73 ml g^(-1)、0.70 ml g^(-1)、0.72 ml g^(-1),喷淋强度对分配系数影响不大。

Based on the dynamic soil column method in laboratory, experiment was conducted on studying the migration of radionuclide Sr-90 in Sand relative to different spraying intensity（spraying intensity was designed to 120 ml d^-1, 60 ml d^-1, 30 ml d^-1,and the corresponding experimental time were 51, 102 204 day respectively）.Results showed that migration distance of Sr-90 concentration peak in the soil columns more or less the same, were 42.3 cm、46.2 cm、44.4 cm, Which was positively related to intensity and duration of the spraying. In addition, the concentration distribution curves of Sr-90 in soil column section all exhibited asymmetry and “tailing” phenomena under the three different spray intensity, i.e. After Sr-90 was leached down from the source layer, it was adsorbed to the Sand, thus lagging behind and getting desorbed after the peak concentration passing the observation point, hence Sr-90 concentration remained to be quite high in soil columns for a long time. With the aid of HYDRUS-1D software, two numerical models were established for radionuclide migration, one based on equilibrium adsorption and the other on non-equilibrium adsorption. It was found that the non-equilibrium sorption model, which took into account the first-order rate coefficients β, could be used to better explain the asymmetry and tailing phenomena. Based on fitting the measurements of Sr-90 concentrations in the soil columns, distribution coefficient of Sr-90 in the Sand was figured out to be 0.73 ml g-1, 0.70 ml g-1 and 0.72 ml g-1 relative to intensity of the spraying, which shows that intensity of the spraying did not have much effect on distribution coefficient of Sr-90.