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Title: Measurement and modelling of reactive transport in geological barriers for nuclear waste containment

Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. Here, this balances the insufficient characterisation information and provides the means for future mechanical–physical–chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(VI) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexesmore » are diffusing as neutral species in OPA. In the case of U(VI) diffusion the method is extended to account for sorption and convection. Finally, rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1]
  1. Univ. of Manchester (United Kingdom). Research Centre for Radwaste & Decommissioning and Modelling & Simulation Centre, Dalton Nuclear Inst.
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Glenn T. Seaborg Inst., Physical & Life Sciences Directorate
  3. Helmholtz-Zentrum Dresden-Rossendorf, Dresden (Germany). Inst. of Resource Ecology
Publication Date:
Report Number(s):
LLNL-JRNL-676844
Journal ID: ISSN 1463-9076; PPCPFQ
Grant/Contract Number:
AC52-07NA27344; EP/ K016946/1
Type:
Accepted Manuscript
Journal Name:
Physical Chemistry Chemical Physics. PCCP (Print)
Additional Journal Information:
Journal Name: Physical Chemistry Chemical Physics. PCCP (Print); Journal Volume: 17; Journal Issue: 45; Journal ID: ISSN 1463-9076
Publisher:
Royal Society of Chemistry
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND RUEL MATERIALS; 38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
OSTI Identifier:
1234576

Xiong, Qingrong, Joseph, Claudia, Schmeide, Katja, and Jivkov, Andrey P. Measurement and modelling of reactive transport in geological barriers for nuclear waste containment. United States: N. p., Web. doi:10.1039/c5cp05243b.
Xiong, Qingrong, Joseph, Claudia, Schmeide, Katja, & Jivkov, Andrey P. Measurement and modelling of reactive transport in geological barriers for nuclear waste containment. United States. doi:10.1039/c5cp05243b.
Xiong, Qingrong, Joseph, Claudia, Schmeide, Katja, and Jivkov, Andrey P. 2015. "Measurement and modelling of reactive transport in geological barriers for nuclear waste containment". United States. doi:10.1039/c5cp05243b. https://www.osti.gov/servlets/purl/1234576.
@article{osti_1234576,
title = {Measurement and modelling of reactive transport in geological barriers for nuclear waste containment},
author = {Xiong, Qingrong and Joseph, Claudia and Schmeide, Katja and Jivkov, Andrey P.},
abstractNote = {Compacted clays are considered as excellent candidates for barriers to radionuclide transport in future repositories for nuclear waste due to their very low hydraulic permeability. Diffusion is the dominant transport mechanism, controlled by a nano-scale pore system. Assessment of the clays' long-term containment function requires adequate modelling of such pore systems and their evolution. Existing characterisation techniques do not provide complete pore space information for effective modelling, such as pore and throat size distributions and connectivity. Special network models for reactive transport are proposed here using the complimentary character of the pore space and the solid phase. Here, this balances the insufficient characterisation information and provides the means for future mechanical–physical–chemical coupling. The anisotropy and heterogeneity of clays is represented using different length parameters and percentage of pores in different directions. Resulting networks are described as mathematical graphs with efficient discrete calculus formulation of transport. Opalinus Clay (OPA) is chosen as an example. Experimental data for the tritiated water (HTO) and U(VI) diffusion through OPA are presented. Calculated diffusion coefficients of HTO and uranium species are within the ranges of the experimentally determined data in different clay directions. This verifies the proposed pore network model and validates that uranium complexes are diffusing as neutral species in OPA. In the case of U(VI) diffusion the method is extended to account for sorption and convection. Finally, rather than changing pore radii by coarse grained mathematical formula, physical sorption is simulated in each pore, which is more accurate and realistic.},
doi = {10.1039/c5cp05243b},
journal = {Physical Chemistry Chemical Physics. PCCP (Print)},
number = 45,
volume = 17,
place = {United States},
year = {2015},
month = {10}
}