The use of stable lead isotopes for the identification of the sources and transport processes leading to the release of radioactive contaminants downstream of former uranium mine sites - IRSN - Institut de radioprotection et de sûreté nucléaire Accéder directement au contenu
Communication Dans Un Congrès Année : 2022

The use of stable lead isotopes for the identification of the sources and transport processes leading to the release of radioactive contaminants downstream of former uranium mine sites

Résumé

Radioactive-enriched material produced during past uranium mining activities,such as tailings and mine drainage water, potentially releases radioactive contaminants into the surrounding soils and sediments. Activities of U and its decay products could be therefore significantly higher than those of the local geochemical background. Moreover, weathering and erosion of the local bedrock could also lead to a high level of uranium up to 4000 mg.kg-1 [1]. Thus, highlighting the potential sources and mechanisms driving radioactive elements dissemination in the vicinity of former U mines is a key element for the decision-making process, the effective management and remediation of contaminated sediments and soils. This research aims to identify the sources of radioactive contaminants and their transport mechanism by using stable Pb isotopes and radioactive disequilibrium of the 238U-decay series. The study area is a wetland located downstream of U mine tailings, Rophin (France), considered a uranium territory workshop (ZATU). The exploited uranium mineral is parsonsite Pb2(UO2)(PO4)2, rich in common Pb [2]. High U concentration up to 3147 mg.kg-1 (34 mg.kg-1 in local bedrock) was observed in a soil core extracted in the wetland. The results of stable Pb isotopic analysis indicate that U accumulation is linked with a whitish clay soil layer below the organic topsoil layer. The 206Pb/207Pb ratio of this layer reveals a radiogenic signature ~1.73 (local background ~1.20), which means it probably originates from previous mining activities. The alignments of Pb isotope ratio data in three isotope diagrams highlight the mining impact on the soils. Many studies have evaluated the percentage of mining contamination by Pb binary isotope mixing models [3]. We remark here the high content of common Pb in parsonsite could lead to an underestimation of mining impacts. So, the evaluation needs more cautious in this context. Moreover, our results show the mobility of U in the soil core. However, more studies are needed in order to better understand the processes governing the mobility of U and its decay products and to shed new light on their codispersion or not with the radiogenic lead of the U-ore
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Dates et versions

irsn-03881271 , version 1 (24-07-2023)

Identifiants

  • HAL Id : irsn-03881271 , version 1

Citer

Tingting Geng, Olivier Peron, Karine David, Arnaud Mangeret, Mireille del Nero, et al.. The use of stable lead isotopes for the identification of the sources and transport processes leading to the release of radioactive contaminants downstream of former uranium mine sites. 6th International Nuclear Chemistry Congres, Aug 2022, Lanzhou, China. ⟨irsn-03881271⟩
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