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241Am migration in a sandy aquifer studied by long-term column experiments.
Robert Artinger1, Wolfram Schuessler, Franz Scherbaum
1Forschungszentrum Karlsruhe, Institut für Nukleare Entsorgung, P.O. Box 3640, 76021 Karlsruhe, Germany. artinger@ine.fzk.de
Environmental Science & Technology
|December 19, 2002
Summary
Americium-241 (Am) migration in sandy aquifers is slow, with most Am binding to iron sites, resulting in a high retardation factor of 10^4. This indicates limited Am transport over long periods.
Area of Science:
- Environmental Science
- Geochemistry
- Radiochemistry
Background:
- Understanding radionuclide migration is crucial for nuclear waste management.
- Americium-241 (Am) is a key radionuclide of concern in radioactive waste.
Purpose of the Study:
- To investigate the long-term migration behavior of Am(III) in a sandy aquifer under realistic conditions.
- To determine the retardation factor of Am in quartz sand.
Main Methods:
- Long-term column experiments (over 1 year) using aeolian quartz sand.
- Equilibration with two groundwaters of differing dissolved organic carbon (DOC) concentrations.
- Injection of Am-spiked groundwater and monitoring of Am elution with a non-sorbing tracer (tritiated water).
- Selective dissolution analysis to identify Am binding sites on sand surfaces.
Main Results:
- A small fraction of Am eluted with tritiated water, indicating colloid-borne transport.
- The maximum Am activity was detected within the first 40 mm of the column, despite tracer travel of ~350 m.
- Am was preferentially bound to iron hydroxide/oxide sites on the sand surface.
- A high retardation factor (R) of approximately 10^4 was determined.
Conclusions:
- Am migration in sandy aquifers is significantly retarded, primarily due to strong sorption to iron oxides.
- The determined retardation factor suggests limited Am transport over extended timescales.
- Column experiments provide valuable data for predicting radionuclide behavior in subsurface environments.