Unveiling the origins and transport processes of radioactive pollutants downstream from a former U-mine site using isotopic tracers and U-238 series disequilibrium

Tingting Geng (1, 2) , Arnaud Mangeret (2) , Olivier Péron (1) , David Suhard (3) , Josselin Gorny (2) , Louise Darricau (2) , Mathieu Le Coz (2) , Nicolas Ait-Ouabbas (4) , Karine David (1) , Christophe Debayle (5) , Pascale Blanchart (6) , Gilles Montavon (1) , Alkiviadis Gourgiotis (2)

1 SUBATECH - Laboratoire de physique subatomique et des technologies associées
2 IRSN/PSE-ENV/SPDR/LT2S - Laboratoire de recherche sur les transferts dans les sites et sols pollués
3 IRSN/PSE-SANTE/SESANE/LRSI - Laboratoire de recherche en Radiochimie, Spéciation et Imagerie
4 IRSN/PSE-ENV/SPDR/LETIS - Laboratoire d'étude et de recherche sur les transferts et les interactions dans les sous-sols
5 IRSN/PSE-ENV/SPDR - Service des Pollutions et des Déchets Radioactifs
6 IRSN/PSE-ENV/SERPEN/BERAD - Bureau d'étude et d'expertise du radon

High U concentrations (reaching up to 14,850 mg ⋅ kg−1), were determined in soils and sediments of a wetland downstream of a former U mine in France. This study aims to identify the origin of radioactive contaminants in the wetland by employing Pb isotope fingerprinting, (234U/238U) disequilibrium, SEM, and SIMS observations. Additionally, information about U and 226Ra transport processes was studied using U-238 series disequilibrium. The results of Pb fingerprinting highlighted inherited material inputs of different U-mines with mainly two types of U-ores: i) pitchblende (UO2), and ii) parsonsite (Pb2(UO2)(PO4)2). Moreover, significant disequilibrium of (230Th/238U) and (226Ra/230Th) activity ratios highlighted the mobility of 238U and 226Ra in the wetland, primarily driven by the water table fluctuations. Finally, this work uncovered a limitation of Pb isotope fingerprinting in the case of parsonsite materials, as the high natural Pb content of this mineral may hide the uranogenic Pb signature in the samples.

Mots clés: U-series disequilibrium; Pb stable isotopes; Uranium mines; U-contaminated environment

Domaines: Physique [physics]

Tingting Geng, Arnaud Mangeret, Olivier Péron, David Suhard, Josselin Gorny, et al.. Unveiling the origins and transport processes of radioactive pollutants downstream from a former U-mine site using isotopic tracers and U-238 series disequilibrium. Journal of Hazardous Materials, 2024, 472, pp.134416. ⟨10.1016/j.jhazmat.2024.134416⟩. ⟨hal-04574503⟩