某铀矿区周边土壤^(238)U和^(226)Ra分布特征及污染评价

Distribution characteristics and pollution assessment of ^(238)U and ^(226)Ra in soils surrounding a uranium mining area

为查清某铀矿区周边土壤污染源项的污染强度及范围,对需要治理的污染源进行量化,对该铀矿周边土壤0.0~0.2,0.2~0.4,0.4~0.6,0.6~0.8,0.8~1.0m土层土壤中放射性核素^(238)U和^(226)Ra活度进行现场调研和统计分析(水平土壤正态分布、箱型图、Q-Q图),其表明放射性核素污染的空间分布特征及有效性影响,利用^(226)Ra/^(238)U反映风化程度.结果表明:在0.0~0.2m土壤深度,^(238)U和^(226)Ra浓度最高,分别为813.44~5059.20,737~4536Bq/kg,随深度增加^(226)Ra和^(238)U浓度呈减小趋势,0.6~1.0m深度^(238)U和^(226)Ra浓度均超美国核管会(NRC)铀矿和水冶设施退役中残存放射性核素的土壤去污标准浓度(370Bq/kg),因此,针对研究区的土壤治理,厚度选取应不小于1m.污染评价结果表明:研究区属重度-极重度污染、强生态风险危害的土壤面积占比最高,随距铀矿区距离增加,^(226)Ra和^(238)U污染程度降低,潜在生态危害减小.

To determine the pollution intensity and range of the soil pollution source surrounding a uranium mining area,and quantify the pollution sources that need to be treated,we carried out a field investigation and statistical analysis of ^(238)U and ^(226)Ra activities in the soil layers of 0.0~0.2,0.2~0.4,0.4~0.6,0.6~0.8,0.8~1.0m around the uranium mine,and thereby determined the spatial distribution of radionuclide contamination and its effectiveness,as well as using ^(226)Ra/^(238)U to reflect weathering degree.The results demonstrated that the highest concentrations of ^(238)U and ^(226)Ra were 813.44~5059.20 and 737~4536Bq/kg respectively at 0.0~0.2m soil depth.The concentrations of ^(226)Ra and ^(238)U decreased with the increase of depth,and the concentrations of ^(238)U and ^(226)Ra at the depth of 0.6~1.0m were still higher than the soil decontamination standard concentration(370Bq/kg)regulated by the United States Nuclear Regulatory Commission(NRC)on the residual radionuclides in the decommissioning of uranium mines and Hydrometallurgical facilities.Therefore,for the soil treatment in the study area,the needed treatment soil depth should not be less than 1m.The results of pollution assessment showed that in the study area,the soil area with severe to extremely severe pollution and strong ecological risk hazards accounted for the highest proportion;with the increase of the distance from uranium mining area,the pollution degree of ^(226)Ra and ^(238)U decreased,and the potential ecological risk decreased as well.