Malov A I
Institute of Environmental Problems of the North at the Ural Branch of the Russian Academy of Sciences, 23 Severnoy Dviny Emb., Arkhangelsk, 163061, Russia.
J Environ Radioact. 2016 Mar;153:61-67. doi: 10.1016/j.jenvrad.2015.11.006. Epub 2015 Dec 22.
The chemical composition and isotopes of carbon and uranium were investigated in groundwater samples that were collected from 16 wells and 2 sources in the Northern Dvina Basin, Northwest Russia. Across the dataset, the temperatures in the groundwater ranged from 3.6 to 6.9 °C, the pH ranged from 7.6 to 9.0, the Eh ranged from -137 to +128 mV, the total dissolved solids (TDS) ranged from 209 to 22,000 mg L(-1), and the dissolved oxygen (DO) ranged from 0 to 9.9 ppm. The (14)C activity ranged from 0 to 69.96 ± 0.69 percent modern carbon (pmC). The uranium content in the groundwater ranged from 0.006 to 16 ppb, and the (234)U:(238)U activity ratio ranged from 1.35 ± 0.21 to 8.61 ± 1.35. The uranium concentration and (234)U:(238)U activity ratio increased from the recharge area to the redox barrier; behind the barrier, the uranium content is minimal. The results were systematized by creating a conceptual model of the Northern Dvina Basin's hydrogeological system. The use of uranium isotope dating in conjunction with radiocarbon dating allowed the determination of important water-rock interaction parameters, such as the dissolution rate:recoil loss factor ratio Rd:p (a(-1)) and the uranium retardation factor:recoil loss factor ratio R:p in the aquifer. The (14)C age of the water was estimated to be between modern and >35,000 years. The (234)U-(238)U age of the water was estimated to be between 260 and 582,000 years. The Rd:p ratio decreases with increasing groundwater residence time in the aquifer from n × 10(-5) to n × 10(-7) a(-1). This finding is observed because the TDS increases in that direction from 0.2 to 9 g L(-1), and accordingly, the mineral saturation indices increase. Relatively high values of R:p (200-1000) characterize aquifers in sandy-clayey sediments from the Late Pleistocene and the deepest parts of the Vendian strata. In samples from the sandstones of the upper part of the Vendian strata, the R:p value is ∼ 24, i.e., sorption processes are expressed more weakly, and uranium is possibly desorbed from the sediments. Overall, these results provide a better understanding of the evolution of uranium isotopes in groundwater systems.
对从俄罗斯西北部北德维纳河流域的16口井和2个水源采集的地下水样本中的化学成分以及碳和铀的同位素进行了研究。在整个数据集中，地下水温度范围为3.6至6.9°C，pH值范围为7.6至9.0，氧化还原电位（Eh）范围为-137至+128 mV，总溶解固体（TDS）范围为209至22,000 mg L⁻¹，溶解氧（DO）范围为0至9.9 ppm。¹⁴C活度范围为0至69.96±0.69现代碳百分比（pmC）。地下水中铀含量范围为0.006至16 ppb，²³⁴U:²³⁸U活度比范围为1.35±0.2至8.61±1.35。从补给区到氧化还原屏障，铀浓度和²³⁴U:²³⁸U活度比升高；在屏障之后，铀含量最低。通过创建北德维纳河流域水文地质系统的概念模型，对结果进行了系统化整理。结合放射性碳测年使用铀同位素测年，可以确定重要的水岩相互作用参数，如含水层中的溶解速率:反冲损失因子比Rd:p（a⁻¹）以及铀延迟因子:反冲损失因子比R:p。水¹⁴C年龄估计在现代到大于35,000年之间。水²³⁴U - ²³⁸U年龄估计在260至582,000年之间。随着地下水在含水层中停留时间从n×10⁻⁵增加到n×10⁻⁷ a⁻¹，Rd:p比降低。出现这一发现是因为在该方向上TDS从0.2增加到9 g L⁻¹，相应地，矿物饱和指数增加。相对较高的R:p值（200 - 1000）表征了晚更新世砂质粘土沉积物和文德系地层最深处含水层的特征。在文德系地层上部砂岩的样本中，R:p值约为24，即吸附过程表现得较弱，铀可能从沉积物中解吸出来。总体而言，这些结果有助于更好地理解地下水系统中铀同位素的演化。
