1.0 Background
Two initiatives for the deep geological disposal of radioactive wastes [1, 2] are currently being proposed for Canada, and are being evaluated and investigated by the CNSC. The proposed repositories rely on both the surrounding host rock and engineered barriers to contain and isolate waste from the biosphere for hundreds of thousands to millions of years. The success of both projects depends largely on the long term performance of these barriers. CNSC staff needs to acquire and maintain independent scientific knowledge to support informed licensing decisions and to disseminate objective information to stakeholders.
A Coordinated Assessment and Research Program (CARP) is currently being funded by the Research and Support Program to examine the long term performance of both the geological and engineered barriers. Within the CARP, the CNSC collaborates with different Canadian and international organizations to obtain experimental data on Thermal (T)-Hydraulic(H)-Mechanical (M)-Chemical (C) processes in both types of barriers. The understanding of those coupled processes is important to assess the long term performance of the barriers and its implication on long term safety of the repository. The experiments are performed either at the laboratory scale, or at a larger scale in underground research facilities in Europe. The CNSC has access to these data from collaborative agreements with international organizations. The development of mathematical models to interpret the experimental data is a crucial step in achieving an understanding of coupled THMC processes. This project aims to develop those models in a stepwise manner:
1. Models based on best available information will be used to perform scoping calculations for a Deep Geological Repository (DGR) for Low and Intermediate Level Wastes (LILW) being proposed in sedimentary rock formations of the Michigan Basin, in order to identify key issues that would affect its long term evolution. The model will assess the stability of shaft and galleries, the formation of excavation damage around them, and the HM response of the rock mass to excavation. It will also assess the long term interaction of bentonite seals with the rock formations. The background information for the DGR is found in: http://www.nwmo.ca/dgrsubmission
2. The model will be refined by validating it using laboratory and in-situ experiments from international projects, and experimental works being conducted by the CNSC.
3. A final analysis will be performed for the LILW DGR.
2.0 Objective
To improve the understanding of coupled THMC processes in bentonite seal materials and sedimentary rocks in order to assess their implications on long term safety of geological repositories.
3.0 Scope of Work
Develop mathematical models to interpret coupled THMC processes in laboratory and in-situ experiments in bentonite seal materials and sedimentary rocks. The COMSOL Multiphysics finite element software available from the CNSC will be used as the modelling tool.
4.0 Tasks to be Performed
4.1 Perform scoping HM calculations of a DGR in sedimentary rocks and identify the major features of the host rock and sealing materials that can influence safety. Those calculations will assess the long term stability of emplacement rooms and shafts under the effects of excavation, gas generation, earthquake and future glaciation. Report on findings.
4.2 Perform THM calculations to simulate the HE-E experiments at the Mont Terri Underground Research Facility [3]. Report on findings.
4.3 Perform simulation of laboratory triaxial tests on Tournemire shale and Cobourg limestone using data provided by CNSC staff. In those tests, the stress-strain behaviour of cylindrical samples would be monitored. In addition, the permeability evolution of the samples would also be monitored, in order to assess the effects of mechanical processes on the permeability. Report on findings.
4.4 Develop models from laboratory experiments on bentonite/sand seals using data provided by the
4.4.1 Model characterization tests (water retention characteristics, swelling potential, etc.) performed using brine as porewater. Report on findings.
4.4.2 Model “mockup” tests that simulate a gap between the seal and the host rock. During the mock-up tests, water, followed by gas will be infiltrated into the assembly, and the evolution of the relative humidity at salient points, swelling pressure, gas flow rates and the evolution of the microstructure would be monitored. Report on findings.
4.4.3 It is expected that macro-scale models would be used in the previous tasks. Using laboratory microstructural information (such as determined from X-ray diffraction) provided by the CNSC, the contractor will develop micro-scale models to interpret the experimental data and verify the validity of assumptions used in macro-scale models. Report on findings.
4.5 Perform revised HM calculations of a DGR in the Michigan Basin using the knowledge gained from task 4.2 to 4.4. Report on findings.
4.6 Draft Final Report on project
