Radionuclide Transport in Fracture-Granite Interface Zones
In situ radionuclide migration experiments, followed by excavation and sample characterization, were conducted in a water-conducting shear zone at the Grimsel Test Site (GTS) in Switzerland to study diffusion paths of radionuclides in fractured granite. In this work, we employed a micro-scale mapping technique that interfaces laser ablation sampling with inductively coupled plasma-mass spectrometry (LA/ICP-MS) to measure the fine-scale (micron-range) distribution of actinides ({sup 234}U, {sup 235}U, and {sup 237}Np) in the fracture-granite interface zones. Long-lived {sup 234}U, {sup 235}U, and {sup 237}Np were detected in flow channels, as well as in the adjacent rock matrix, using the sensitive, feature-based mapping of the LA/ICP-MS technique. The injected sorbing actinides are mainly located within the advective flowing fractures and the immediately adjacent regions. The water-conducting fracture studied in this work is bounded on one side by mylonite and the other by granitic matrix regions. These actinides did not penetrate into the mylonite side as much as the relatively higher-porosity granite matrix, most likely due to the low porosity, hydraulic conductivity, and diffusivity of the fracture wall (a thickness of about 0.4 mm separates the mylonite region from the fracture) and the mylonite region itself. Overall, the maximum penetration depth detected with this technique for the more diffusive {sup 237}Np over the field experimental time scale of about 60 days was about 10 mm in the granitic matrix, illustrating the importance of matrix diffusion in retarding radionuclide transport from the advective fractures. Laboratory tests and numerical modeling of radionuclide diffusion into granitic matrix was conducted to complement and help interpret the field results. Measured apparent diffusivity of multiple tracers in granite provided consistent predictions for radionuclide transport in the fractured granitic rock.
- Research Organization:
- Lawrence Livermore National Laboratory (LLNL), Livermore, CA
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 984938
- Report Number(s):
- UCRL-JRNL-234653
- Journal Information:
- Physics and Chemistry of the Earth, vol. 33, no. 14-16, April 1, 2008, pp. 1042-1049, Journal Name: Physics and Chemistry of the Earth, vol. 33, no. 14-16, April 1, 2008, pp. 1042-1049 Journal Issue: 14-16 Vol. 33
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
54 ENVIRONMENTAL SCIENCES
58 GEOSCIENCES
ABLATION
ACTINIDES
DIFFUSION
DISTRIBUTION
EXCAVATION
FRACTURES
GRANITES
HYDRAULIC CONDUCTIVITY
LASERS
PENETRATION DEPTH
POROSITY
RADIOISOTOPES
RADIONUCLIDE MIGRATION
SAMPLING
SHEAR
SPECTROSCOPY
THICKNESS
TRANSPORT