Thermo-Hydro-Mechanical Processes in Evolving Multi-Phasic Geomaterials, Interfaces and Geoenvironmental Endeavours

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Developing feasible techniques for disposal of hazardous, heat emitting nuclear fuel waste is a critical environmental concern to many countries that store their waste at reactor sites, which, as they age, become increasingly unsuitable for safely storing the waste. Events in Fukushima have emphasized the vulnerability of temporary storage sites; safe disposal strategies must address the cradle-to-grave cycle and restore nuclear energy as a viable option to reduce reliance on fossil fuels. Many countries favour the creation of a Deep Geologic Repository (DGR) in stable geologic formations to contain the stored waste and prevent release to the geosphere and the biosphere. The favoured geologic media varies by country; clay deposits in Belgium, argillaceous rocks in France, granitic rock masses in Canada, Finland, Japan, Sweden and Switzerland, salt formations in Germany, arid geologic media in China, sedimentary rock formations in the UK and Spain and porous tuff in the USA. Since the 1960's Canada has considered locating a DGR for high-level nuclear waste in the Canadian Shield and possibly a DGR for short-lived low- to intermediate-level nuclear waste in the argillaceous rock formations of southern Ontario. Developing a DGR is not routine; strict environmental controls must be in place with a series of engineered barriers to minimize both short- and long-term release of radionuclides to the environment. Any rock mass that houses a DGR is a key element in a disposal concept and should act as a natural geologic barrier to retard radionuclide migration in the long term. The Thermo-Hydro-Mechanical (THM) behaviour of intact rocks and defects such as fractures are critical factors that will decide the efficacy of a DGR concept. The mechanical, fluid flow and thermal properties of rocks can be altered by the creation of a storage vault and by the thermal loading by the stored waste. The long-term impacts on the DGR, ranging from groundwater flow alterations due to climate change, glacial advance and other processes such as induced earthquakes, need to be accounted for in the safety assessment. Most importantly, the performance of the DGR needs to be investigated for time scales that transcend conventional engineering endeavours. Suitable mathematical models of THM processes and experimental techniques, have to be developed to evaluate the parameters characterizing the multi-physics processes. The mathematical models have to be implemented in computational procedures to predict the performance of a DGR at time scales of interest to long-lived radioactive wastes. These important research components will lead to the implementation of a successful deep geologic disposal strategy in Canada. The over-arching findings related to THM research examined in this proposal can also enhance our understanding of both leakage of sequestered greenhouse gases and methane from defective interfaces and ground subsidence due to water and resource extraction.