Variations in ²³⁴U/²³⁸U activity ratios in groundwater—A key to flow system characterisation?

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• 作者：J. Suksi ; K. Rasilainen and P. Pitkä ; nen
• 关键词：²³⁴U/²³⁸U activity ratio ; A-recoil ; Groundwater ; U-series disequilibrium ; Glacial processes
• 刊名：Physics and Chemistry of the Earth ; Parts A/B/C
• 出版年：2006
• 期刊代码：96_14747065
• 类别：ear
• 出版时间：2006
• 卷：31
• 期：10-14
• 页码：556-571
• 文件大小：306 K

摘要

Two key questions concerning geological disposal of high-level radioactive waste are (i) how robust is the barrier system during long term disturbances and (ii) do we know the possible disturbances well enough? One step towards answers is to study how groundwater flow systems have behaved in the past. Studying naturally occurring radioactive tracers in groundwater offers useful information. Uranium isotopes ²³⁴U and ²³⁸U are oft-used tracers. A characteristic of the ²³⁴U/²³⁸U activity ratio (AR) is its considerable variation in groundwater. It is known that the reason for variation is isotopic fractionation at the rock–water interface. However, the reason why AR varies in groundwater is not clear. We tried to answer this question by carefully examining the geochemical and nuclear chemical origins of U isotopic fractionation and by studying a large body of U data from Finnish and Swedish investigation sites. We found that despite large variations in AR and U concentrations, the respective ²³⁴U and ²³⁸U activities show a correlation which contains useful information of the flow system behaviour which is in line with other hydrochemical data.