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Title: Radionuclide Transport in Fracture-Granite Interface Zones

Abstract

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 withmore » 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.« less

Authors:
;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
984938
Report Number(s):
UCRL-JRNL-234653
TRN: US1006061
DOE Contract Number:  
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics and Chemistry of the Earth, vol. 33, no. 14-16, April 1, 2008, pp. 1042-1049; Journal Volume: 33; Journal Issue: 14-16
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 12 MANAGEMENT OF RADIOACTIVE WASTES AND NON-RACIOACTIVE WASTER FROM NUCLEAR FACILITIES; 54 ENVIRONMENTAL SCIENCES; ABLATION; ACTINIDES; DIFFUSION; DISTRIBUTION; EXCAVATION; FRACTURES; GRANITES; HYDRAULIC CONDUCTIVITY; LASERS; PENETRATION DEPTH; POROSITY; RADIOISOTOPES; RADIONUCLIDE MIGRATION; SAMPLING; SHEAR; SPECTROSCOPY; THICKNESS; TRANSPORT

Citation Formats

Hu, Q, and Mori, A. Radionuclide Transport in Fracture-Granite Interface Zones. United States: N. p., 2007. Web.
Hu, Q, & Mori, A. Radionuclide Transport in Fracture-Granite Interface Zones. United States.
Hu, Q, and Mori, A. Wed . "Radionuclide Transport in Fracture-Granite Interface Zones". United States. https://www.osti.gov/servlets/purl/984938.
@article{osti_984938,
title = {Radionuclide Transport in Fracture-Granite Interface Zones},
author = {Hu, Q and Mori, A},
abstractNote = {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.},
doi = {},
journal = {Physics and Chemistry of the Earth, vol. 33, no. 14-16, April 1, 2008, pp. 1042-1049},
number = 14-16,
volume = 33,
place = {United States},
year = {Wed Sep 12 00:00:00 EDT 2007},
month = {Wed Sep 12 00:00:00 EDT 2007}
}