The coupling of thermal, hydraulic, mechanical and chemical (THMC) processes for fractured rocks is an extremely complex area of scientific research that may have a significant bearing on the potential design and performance of radioactive waste disposal facilities. The purpose of Task C1 under DECOVALEX-2015 is to:
The emphasis of this work is to gain understanding of possible physical processes that can be used to explain the results of the experiments. It is expected that the different teams will adopt different approaches but that in all cases the different approaches should all provide insight into the development of robust, predictive THMC analysis for fractured systems.
The two sets of experiments each consider an artificially induced axial fracture within small cylindrical samples (one ~50 mm x ~90 mm sample for the novaculite and three ~30mm x ~60mm samples for the granite). The samples were contained with a test cell through which a confining mechanical load was applied, deionised water flow through the sample was maintained at different rates and pressures, and the whole apparatus could be heated. Flow rates, differential pressures and effluent geochemical time series data were collected as different experimental conditions were applied, allowing key aspects of the geochemical, mechanical and hydraulic evolution of the samples to be observed under different environmental conditions.
To gain insights on how the aperture distribution changed for the novaculite, both fracture surfaces were scanned using a laser profilometery technique at a horizontal resolution of 0.05 mm, prior to the start of the experiment. Post-experimental aperture data was obtained via Wood’s metal injection and X-ray Computerised Tomography (CT) scanning. For the granite, no direct fracture surface or aperture data were collected, however post-experimental imaging of the fracture surfaces using Scanning Electron Microscopy with Energy-Dispersive X-ray spectroscopy (SEM-EDX) was conducted in order to investigate mineral precipitation dynamics.
The current plan of the task includes 7 distinct steps, the focus being initially on the novaculite experiment where the simpler geochemistry and more comprehensive fracture topography data make for a more natural starting point. It is also hoped that the understanding from the novaculite data can inform the more complex granite experiments.
For further information, please contact the task leader, Dr Alex Bond (firstname.lastname@example.org)