Uranium-Series Constraints on Radionuclide Transport and Groundwater Flow at the Nopal I Uranium Deposit, Sierra Pea Blanca, Mexico

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• 作者：Steven J. Goldstein ; Amr I. Abdel-Fattah ; Michael T. Murrell ; Patrick F. Dobson ; Deborah E. Norman ; Ronald S. Amato ; Andrew J. Nunn
• 刊名：Environmental Science & Technology
• 出版年：2010
• 出版时间：March 1, 2010
• 年：2010
• 卷：44
• 期：5
• 页码：1579-1586
• 全文大小：404K
• 年卷期：v.44,no.5(March 1, 2010)
• ISSN：1520-5851

文摘

Uranium-series data for groundwater samples from the Nopal I uranium ore deposit were obtained to place constraints on radionuclide transport and hydrologic processes for a nuclear waste repository located in fractured, unsaturated volcanic tuff. Decreasing uranium concentrations for wells drilled in 2003 are consistent with a simple physical mixing model that indicates that groundwater velocities are low (10 m/y). Uranium isotopic constraints, well productivities, and radon systematics also suggest limited groundwater mixing and slow flow in the saturated zone. Uranium isotopic systematics for seepage water collected in the mine adit show a spatial dependence which is consistent with longer water−rock interaction times and higher uranium dissolution inputs at the front adit where the deposit is located. Uranium-series disequilibria measurements for mostly unsaturated zone samples indicate that ²³⁰Th/²³⁸U activity ratios range from 0.005 to 0.48 and ²²⁶Ra/²³⁸U activity ratios range from 0.006 to 113. ²³⁹Pu/²³⁸U mass ratios for the saturated zone are <2 × 10⁻¹⁴, and Pu mobility in the saturated zone is >1000 times lower than the U mobility. Saturated zone mobility decreases in the order ²³⁸U ≈ ²²⁶Ra > ²³⁰Th ≈ ²³⁹Pu. Radium and thorium appear to have higher mobility in the unsaturated zone based on U-series data from fractures and seepage water near the deposit.