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Thermal cycling: impact on bentonite permeability

Published online by Cambridge University Press:  02 January 2018

S. G. Zihms  and
J. F. Harrington
S. G. Zihms*
Affiliation:
British Geological Survey, Transport Properties Research Laboratory, Nicker Hill, Keyworth NG12 5GG, UK
J. F. Harrington*
Affiliation:
British Geological Survey, Transport Properties Research Laboratory, Nicker Hill, Keyworth NG12 5GG, UK
*
# Current Address: The Institute for Petroleum Engineering, Heriot-Watt University, Edinburgh EH14 4AS, UK
*E-mail: [email protected]
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Abstract

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Due to its favourable properties, in particular, low permeability and swelling capacity, bentonite has been favoured as an engineered-barrier and backfill material for the geological storage of radioactive waste. To ensure its safe long-term performance it is important to understand any changes in these properties when the material is subject to heat-emitting waste. As such, this study investigates the hydraulic response of bentonite under multi-step thermal loading subject to a constant-volume boundary condition, to represent a barrier system used in a crystalline or other hard-rock host rock. The experimental set up allows continuous measurement of the hydraulic and mechanical responses during each phase of the thermal cycle. After the initial hydration of the bentonite, the temperature was raised in 20°C increments from 20 to 80°C followed by a final step to reach 120°C. Each temperature was held constant for at least 7–10 days to allow the hydraulic transients to equilibrate. The data suggest that the permeability of bentonite appears to be sensitive to changes in temperature which may extend beyond those explained by simple changes in water viscosity. However, permeability may be boundary-condition dependent and this should be considered when designing experiments or applying these results to other repository host rocks. Either way, the magnitude of the change in permeability observed in this study is minor and its impact on the hydraulic performance of the barrier is negligible.

Keywords

bentonitepermeabilitythermal cyclingtemperaturehydraulic
Type
Research Article
Information
Mineralogical Magazine , Volume 79 , Issue 6 , November 2015 , pp. 1543 - 1550
Creative Commons
Creative Common License - CCCreative Common License - BY
Copyright © The Mineralogical Society of Great Britain and Ireland 2015. This is an open access article, distributed under the terms of the Creative Commons Attribution (CC BY) license (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 2015

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