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Radionuclide transport in fractured chalk under abrupt changes in salinity
Tuvia Turkeltaub1, Noam Weisbrod1, Mavrik Zavarin2
1The Zuckerburg Institute for Water Research, The Jacob Blaustein Institutes for Desert Research, Ben Gurion University of the Negev, Midreshet Ben Gurion 8499000, Israel.
The Science of the Total Environment
|November 19, 2023
Summary
Salinity changes significantly impact uranium and strontium mobility in fractured chalk, a potential nuclear waste repository. Higher salinity enhances their movement, while lower salinity reduces it, crucial for repository safety assessments.
Area of Science:
- Geochemistry
- Hydrogeology
- Nuclear Waste Management
Background:
- Geologic repositories are the agreed solution for nuclear waste disposal.
- Chalk, a low permeability rock, is studied as an alternative host rock where traditional options are unavailable.
- Fractures in chalk and changing groundwater salinity in arid regions can affect radionuclide transport.
Purpose of the Study:
- To assess the viability of chalk as a host rock for radioactive waste disposal.
- To investigate the impact of seasonal salinity variations on radionuclide mobility in fractured chalk.
- To understand the behavior of Uranium (U(VI)), Strontium (Sr), Cerium (Ce), and Rhenium (Re) under changing salinity conditions.
Main Methods:
- Experiments using naturally fractured chalk cores.
- Injection of radioactive U(VI) and simulant tracers (Sr, Ce, Re).
- Exposure to varying salinity solutions: artificial rainwater (ARW) and artificial groundwater (AGW), coupled with reactive transport modeling.
Main Results:
- Rhenium (Re) behaved as a conservative tracer, and Cerium (Ce) showed mobility only in colloidal form, with neither affected by salinity changes.
- Uranium (U(VI)) and Strontium (Sr) exhibited increased mobility with high salinity (AGW) and decreased mobility with low salinity (ARW).
- Saline groundwater solutions promote U and Sr release through ion-exchange, enhancing their migration in fractured chalk.
Conclusions:
- Chalk's suitability as a repository host rock is influenced by groundwater salinity.
- Salinity variations near geologic repositories can significantly impact the mobility of key radionuclides like U and Sr.
- Ion-exchange processes in saline conditions are critical factors in radionuclide migration within fractured chalk.
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