放射性核素在包气带中的迁移模拟

为研究核素在包气带中的迁移特征及包气带厚度和泄漏持续时间对核素迁移的影响,通过原位土-水特征曲线测试等获取参数,选用Hydrus-1D模拟不吸附的H-3和吸附的Sr-90在包气带中的迁移。结果表明:包气带对核素迁移存在迟滞作用,Sr-90和H-3到达饱和带时间延长;Sr-90流入饱和带浓度峰值远小于泄漏浓度;小部分(3.8%)H-3和几乎所有Sr-90滞留在包气带;包气带厚度增大,核素到达潜水面时间非线性增大,Sr-90流入饱和带的总量呈数量级递减;泄漏时长增大,流入饱和带的H-3总量呈线性增大、Sr-90总量呈数量级递增。建议如下:不考虑包气带的环评过于保守,建议补充该项工作;应加强监测,一旦发生放射性液体泄漏,应立即采取措施切断补给源来缩短泄漏持续时间,并可采取降低地下水位增大包气带厚度的应急措施降低放射性核素对地下水的污染。

Simulation study on the migration of radionuclides in the vadose zone

In order to study the migration characteristics of radionuclides in vadose zone as well as the effects of vadose zone thickness and leakage duration on the nuclides migration, in situ soil-water characteristic curve tests were carried, moreover, the migration behavior of not adsorbed H-3 and adsorbed Sr-90 was studied by simulation using Hydrus-1D. The results show that: (1) Vadose zone has obvious hysteresis effect on nuclides migration: The time of Sr-90 (0.9 d) and H-3 (0.35 d) reaching saturated zone is extended, the peak concentration (9.71×10-11 Bq/L) of Sr-90 is far less than the leaked liquid (0.178 Bq/L), a small amount (3.8 %) of H-3 and almost all Sr-90 was traped in vadose zone.(2) With the increase of vadose zone thickness, the time of nuclides arriving at water table increases non-linearly and the amount of Sr-90 flowing into the saturated zone decreases by order of magnitude. (3) With the increase of leakage time, the amount of H-3 flowing into the saturated zone increase linearly and the amount of Sr-90 flowing into the saturated zone increase by order of magnitude. The above research results show: (1) The environmental impact assessment that did not consider the vadose zone was too conservative. (2)Once radionuclides have leaked, emergency measures of cutting off the supply source and lowering water level should be taken to shorten the leakage duration and increase vadose zone thickness.