Mangeret Arnaud, Blanchart Pascale, Alcalde Gilles, Amet Xavier, Cazala Charlotte, Gallerand Marie-Odile
Institut de Radioprotection et de Sureté Nucléaire (IRSN), PSE-ENV. BP 17, Fontenay-aux-Roses, 92262, France.
Institut de Radioprotection et de Sureté Nucléaire (IRSN), PSE-ENV. BP 17, Fontenay-aux-Roses, 92262, France.
J Environ Radioact. 2018 Dec;195:67-71. doi: 10.1016/j.jenvrad.2018.08.018. Epub 2018 Oct 4.
The present study reports the evidence of a radioactive contamination in a wetland located downstream from a former French U mine in Brittany. This situation is demonstrated according to the measurements of gamma dose rates and activity ratios of U and Th-decay series nuclides, which give the justification regarding the accumulation of significant amounts of U, Th and Ra in this wetland. The dose rate map highlights an increase of radiation level along the former mine water pathway compared to the background value, with a maximum value of 1500 nSv.h reached in the wetland. Activities of U, Th and Ra and Th/U ratios measured in surface wetland soils are significantly higher than the geochemical background. Th/U ratios less than unity suggest a preferential accumulation of U in the wetland, compared to its daughter isotopes. Moreover, the loss of Ra compared to Th raises its higher mobility compared to its parent isotope. In far-field sediments, Ra/U ratio of 1.76 implies a different geochemical behavior of U, which could be explained by the occurrence of mobile U species. The results suggest that contamination of wetland soils and far-field sediments could result from discharges of underground mine waters.
本研究报告了位于布列塔尼一座前法国铀矿下游湿地存在放射性污染的证据。根据γ剂量率以及铀和钍衰变系列核素的活度比测量结果证实了这种情况，这些测量结果为该湿地中大量铀、钍和镭的积累提供了依据。剂量率图显示，与背景值相比，沿前矿井水路径辐射水平有所增加，在湿地中达到了1500 nSv·h的最大值。在湿地表层土壤中测得的铀、钍和镭活度以及钍/铀比显著高于地球化学背景值。小于1的钍/铀比表明，与子同位素相比，湿地中铀的积累更为优先。此外，与钍相比镭的损失表明其相对于母体同位素具有更高的迁移率。在远场沉积物中，1.76的镭/铀比意味着铀具有不同的地球化学行为，这可以由可移动铀物种的存在来解释。结果表明，湿地土壤和远场沉积物的污染可能源于地下矿井水的排放。
