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Enhanced radionuclide immobilization and flow path modifications by dissolution and secondary precipitates
Wooyong Um1, R Jeffrey Serne, Steven B Yabusaki
1Pacific Northwest National Laboratory, P.O. Box 999, MS P7-22, Richland, WA 99354, USA. wooyong.um@pnl.gov
Journal of Environmental Quality
|July 7, 2005
Summary
Radioactive waste leaks at Hanford Site cause mineral changes, altering contaminant pathways and enhancing radionuclide immobilization. Secondary precipitates shift migration from vertical to horizontal, improving waste containment.
Area of Science:
- Environmental Science
- Geochemistry
- Nuclear Waste Management
Background:
- Caustic radioactive waste leaks at Hanford Site cause mineral dissolution and secondary precipitation.
- These reactions impact contaminant fate and transport in the vadose zone.
Purpose of the Study:
- Investigate how secondary mineral precipitates affect contaminant flow paths.
- Determine the influence of these precipitates on radionuclide immobilization.
Main Methods:
- Reacting quartz, quartz-biotite mixture, and Hanford sediment with simulated caustic waste.
- Utilizing batch and flow-through tests.
- Analyzing mineral precipitation and pore geometry changes using X-ray microtomography.
Main Results:
- Continuous silica dissolution and secondary mineral precipitation (primarily nitrate-cancrinite) were observed.
- Secondary precipitates cemented quartz grains, modifying pore geometry and potentially shifting flow paths horizontally.
- Precipitates enhanced sediment sorption capacity for key radionuclides (iodine-129, selenium-79, technetium-99, strontium-90).
Conclusions:
- Secondary mineral precipitation alters Hanford Site contaminant migration pathways, favoring horizontal movement.
- Cancrinite precipitates improve radionuclide immobilization in Hanford sediments, aiding in waste containment strategies.