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Gas migration experiments in bentonite: implications for numerical modelling

Published online by Cambridge University Press:  05 July 2018

C. C. Graham,
J. F. Harrington,
R. J. Cuss and
P. Sellin
C. C. Graham*
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
J. F. Harrington
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
R. J. Cuss
Affiliation:
British Geological Survey, Keyworth, Nottingham NG12 5GG, UK
P. Sellin
Affiliation:
SKB, Stockholm, Sweden
*
*E-mail: caro5@bgs.ac.uk
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Abstract

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In the Swedish KBS-3 repository concept, there is potential for gas to be generated from corrosion of ferrous materials under anoxic conditions, combined with the radioactive decay of the waste and radiolysis of water. A full understanding of the probable behaviour of this gas phase within the engineered barrier system (EBS) is therefore required for performance assessment. We demonstrate key features from gas transport experiments on pre-compacted Mx80 bentonite, under laboratory and field conditions, and discuss their implications in terms of a conceptual model for gas migration behaviour. On both scales, major gas entry is seen to occur close to the sum of the porewater and swelling pressures of the bentonite. In addition, gas pressure at breakthrough is profoundly sensitive to the number and location of available sinks for gas escape. Observations of breakthrough can be explained by the creation of dilatational pathways, resulting in localized changes in the monitored porewater pressures and total stresses. These pathways are highly unstable, evolving spatially and temporally, and must consequently influence the gas permeability as their distribution/geometry develops.

Such observations are poorly embodied by conventional concepts of two-phase flow, which do not fully represent the key processes involved. Although dilatancy based models provide a better description of these processes, the paucity of data limits further development and validation of these models at present.

Keywords

bentoniteengineered barrier systemsgas migrationgeological disposalpathway dilationradioactive waste

Information

Type
Research Article
Information
Mineralogical Magazine , Volume 76 , Issue 8 , December 2012, pp. 3279 - 3292
Creative Commons
Creative Common License - CCCreative Common License - BY
© [2012] The Mineralogical Society of Great Britain and Ireland. This is an open access article distributed under the terms of the Creative Commons Attribution (CC BY) licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2012

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