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Uranium remobilisation in anoxic deep rock-groundwater system in response to late Quaternary climate changes – Results from Forsmark, Sweden

Suksi, Juhani; Tullborg, Eva-Lena; Pidchenko, Ivan; Krall, Lindsay; Sandström, Björn; Kaksonen, Kai; Vitova, Tonya; Kvashnina, Kristina O.; Göttlicher, Jörg

Unusually high uranium (U) concentrations (up to 175 μg/L) have been measured in groundwater at depths between 400 and 650 m at the Forsmark site, eastern Sweden. Since it is unlikely that such high concentrations formed under the stagnant and low redox groundwater conditions that currently prevail, this study employs U-series isotopes to understand how the recent evolution (<1 Ma) of the flow system has influenced the observed U distribution. Material from fractures as deep as 700 m along the assumed flow route was subject to U-series disequilibrium (USD) measurements, as well as sequential extractions (SE) and U redox-state analyses that revealed the U-series activity ratios in the bulk and soluble fraction of the fracture precipitates. Uranium isotope data collected over several years of annual groundwater monitoring were scrutinized to evaluate the U sources and U exchange in fractures located in high-U groundwater sections. Numerical simulations with the experimental data were used to study evolution of U-series isotope composition in a fracture in the highest U section at ~500 m depth under various U mobility scenarios. The results show that U redistribution in fractures with certain dissolution/deposition flux ratios during periodic water intrusions, driven by glaciation and deglaciation events during the last 120 ka, can explain the U anomaly in the groundwater.

Verlagsausgabe §
DOI: 10.5445/IR/1000139160
Veröffentlicht am 22.10.2021
Cover der Publikation
Zugehörige Institution(en) am KIT Institut für Nukleare Entsorgung (INE)
Institut für Photonenforschung und Synchrotronstrahlung (IPS)
Publikationstyp Zeitschriftenaufsatz
Publikationsdatum 05.12.2021
Sprache Englisch
Identifikator ISSN: 0009-2541, 1872-6836
KITopen-ID: 1000139160
HGF-Programm 32.11.03 (POF IV, LK 01) Fundamental Scientific Aspects
Weitere HGF-Programme 54.11.11 (POF IV, LK 01) Accelerator Operation, Research and Development
Erschienen in Chemical Geology
Verlag Elsevier
Band 584
Seiten Art.-Nr.: 120551
Vorab online veröffentlicht am 27.09.2021
Nachgewiesen in Scopus
Web of Science
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