An interdisciplinary approach in Zone-Atelier Territoires Uranifères (ZATU) to highlight the trace of uranium mining heritage (ZA Territoire Uranifères)

5ecolloque des Zones Ateliers – CNRS 

2000-2020, 20 ans de recherche du Réseau des Zones Ateliers

SESSION 6 - Des observatoires pour suivre les évolutions des socio-écosystèmes

An interdisciplinary approach in Zone-Atelier Territoires Uranifères (ZATU) to highlight the trace of uranium mining heritage (ZA Territoire Uranifères)

Gilles Montavon ∗ 1,2, Alexis Martin 2, Hassan-LoniYahya 2, Andreas Fichtner 2, Olivier Péron†  2, Karine David 2,Patrick Chardon 3, Sebastien Larrue 4, Alkiviadis Gourgiotis 5, Susanne Sachs6, Thuro Arnold 6, Bernd Grambow 2, Thorsten Stumpf 6

1  LTSER  "Zone Atelier TerritoiresUranifères" –  CNRS INEE –  France

2  LaboratoireSubatech  UMR6457 –  add new organisation : IN2P3/CNRS/IMTAtlantique/Université de Nantes –  France

3  Laboratoire dePhysique  de Clermont  – Institut National de Physique Nucléaire et de Physique  des Particules  du CNRS, Université Clermont  Auvergne :UMR6533,  Centre National de la RechercheScientifique : UMR6533 –  France

4  GEOLAB  UMR6042 – add new organisation : UCA/ Université de Limoges –  4 rue Ledru 63057 Clermont-Ferrandcedex,  France

5  Institut deRadioprotection et de Sûreté Nucléaire (IRSN) –  PRP-DGE-SRTG-LT2S –  France

6  Helmholt-ZentrumDresden-Rossendorf,  Institute ofRessource Ecology –  Allemagne

Résumé

Uranium mining and millingactivities  as well as mineral processing plants raise environ- mental concerns due to the possiblerelease of radioactive and other potentially toxic elements. Therefore,  their long-term  management  requires knowledge of past events  and a good under- standing of the geochemicalmechanisms regulating the mobility of residualradionuclides.  This work presents the resultson the traces and footprints of anthropic activity,  linked to past U mining activities,  within  the vicinity of Rophin  tailings storage site (Puy  de Dôme, France). An interdisciplinary approach was developed based on a study of the history and records of the site,  on the radiological and chemicalcharacterization of soil cores and on dendrochronology. Gamma survey  measurements  on the wetland about 200m downstream  of Rophin reach 1050 nSv.h-1 that is 3 times the geological background radiationlevels.  Soil cores taken in the wet- land showed U concentrations up to 1855 mg.kg-1that appears to be associated with the presence of a whitish silt loam (WSL)  soil layer located at around 10-30 cm depth below an organictop soil layer.  Records (regulatory documents, inspection reports, letters) supported by former aerial photographs suggest the discharge of U mineral particles during the operation of the site between 1949 and 1957, due to malfunction of the ore washingplant process and the sedimentation step. In accordance with previous findings, analysis of 137Cs and 14C activities date the WSL  layer back to the beginning of the 1950s.  Moreover, lead isotope ratios indicates that contaminationin the WSL  layer can be discriminated by an enrichment  signature with a larger contributionof radiogenic lead to total lead (k = 8.6 ± 0.07 %). The dendroanalysis permits to link the U emissionsfrom Rophin with the site history using oak tree rings as a suitablebioindicator of changes in bioavailable U concentrations.  Oak tree rings (Quercus petraea ) located downstreamof the site contain uranium concentrations up to 50 µg.kg-1, which is up to ten times higher than values measured from unaffected trees located upstream.   Moreover, highest U concentrationswererecorded for the exploitation period but also, more surprisingly,  for the recent makeovers of the Rophinsite (2002  and 2010).  This  interdisciplinary  investigation give clear insights of whathappened in the vicinity of Rophin tailings storage site.  Allcomplementary fields ofstudy corroborate that U mineral particleswere transported by turbidwaters in Rophin’s watershed. While initially transported as mineral particles, at least the majority of the deposited uraniumin WSL  layer appears to be trapped in the top soil layer with a high organic mattercontent. However it evolution shouldbe monitored to understand the the overall dynamicsoccurring at the site.

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Programme et recueil des résumés à télécharger dans l'onglet documents ci-dessus.

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https://20ans-rza.sciencesconf.org/resource/page/id/5