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A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories

Abstract

This paper presents an international, multiple-code, simulation study of coupled thermal, hydrological, and mechanical (THM) processes and their effect on permeability and fluid flow in fractured rock around heated underground nuclear waste emplacement drifts. Simulations were conducted considering two types of repository settings (1) open emplacement drifts in relatively shallow unsaturated volcanic rock, and (2) backfilled emplacement drifts in deeper saturated crystalline rock. The results showed that for the two assumed repository settings, the dominant mechanism of changes in rock permeability was thermal–mechanically induced closure (reduced aperture) of vertical fractures, caused by thermal stress resulting from repository-wide heating of the rock mass. The magnitude of thermal–mechanically induced changes in permeability was more substantial in the case of an emplacement drift located in a relatively shallow, low-stress environment where the rock is more compliant, allowing more substantial fracture closure during thermal stressing. However, in both of the assumed repository settings in this study, the thermal–mechanically induced changes in permeability caused relatively small changes in the flow field, with most changes occurring in the vicinity of the emplacement drifts.

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Acknowledgments

Review comments by Ki-Bok Min, University of Adelaide, Australia and Dan Hawkes at the Lawrence Berkeley National Laboratory are greatly appreciated. Funding to LBNL for the work done by the LBNL authors was provided by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. Funding for modeling work by other research teams was provided by Japan Atomic Energy Agency (JAEA), the Federal Institute for Geosciences and Natural Resources (BGR), and the National Nature Science Foundation of China under Grant No. 50709036, 40520130315. It is emphasized that the views expressed in this paper are solely those of the authors and cannot necessarily be taken to represent the views of any of the organizations or individuals listed above.

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Correspondence to Jonny Rutqvist.

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Rutqvist, J., Barr, D., Birkholzer, J.T. et al. A comparative simulation study of coupled THM processes and their effect on fractured rock permeability around nuclear waste repositories. Environ Geol 57, 1347–1360 (2009). https://doi.org/10.1007/s00254-008-1552-1

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  • DOI: https://doi.org/10.1007/s00254-008-1552-1

Keywords

  • Coupled processes
  • Nuclear waste repository
  • Temperature
  • Stress
  • Permeability