Thermal cycling: impact on bentonite permeability

Stephanie Zihms, J. F. Harrington

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

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 degrees C increments from 20 to 80 degrees C followed by a final step to reach 120 degrees 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.

Original languageEnglish
Pages (from-to)1543-1550
Number of pages8
JournalMineralogical Magazine
Volume79
Issue number6
DOIs
Publication statusPublished - Nov 2015
Event1st IGD-TP Geodisposal Conference 2014 - Manchester
Duration: 24 Jun 201426 Jun 2014

Keywords

  • bentonite
  • permeability
  • thermal cycling
  • temperature
  • hydraulic
  • BOOM CLAY
  • COMPACTED BENTONITE
  • BEHAVIOR
  • TEMPERATURE

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