Far-field analysis of shear slip potential and ground uplift by high-level radioactive waste repositories with single- and multi-canister and multi-layer disposal concepts

This study analyzes the shear slip potential and ground uplift around high-level radioactive waste (HLW) repositories using coupled thermo-hydro-mechanical (THM) numerical models at a far-field scale. Alternative disposal concepts with multi canisters or layers to increase disposal efficiency, which is inversely proportional to the disposal area, are considered. The change in the coulomb failure stress (CFS) is used to evaluate the shear slip potential around the geological repository, assuming hypothetical faults with specific orientations are critically stressed. Initially, the CFS dominantly increased inside the repository and near the lateral boundary of the system, and it gradually dissipated as decay heat from the HLW significantly diminished. The maximum Delta CFS outside the reference, double-canister, triple-canister, double-layer, and triple-layer disposal concepts is calculated as 1.9 MPa, 2.33 MPa, 2.39 MPa, 2.63 MPa, and 2.77 MPa, respectively, near the boundary of the repositories. However, Delta CFS is lower than the shear slip criterion if a fault is located more than 2 km away from the all disposal repositories. The influence of fault orientation is evaluated by plotting Delta CFS on a stereonet for each disposal concept. The maximum Delta CFSs of the reference and double-canister disposal concepts are calculated if the approximate dip angle of a fault is 30 degrees, whereas that of other disposal concepts is determined at a dip angle of 20 degrees. The double-layer disposal concept exhibits the largest amount of ground uplift among all disposal concepts, but the effect of ground uplift on the surface facilities can be deemed insignificant considering the rate and slope of ground uplift. Parametric studies on the fault friction coefficient, elastic modulus, and thermal expansion coefficient of rock mass suggest that the shear slip potential and ground uplift are largely dependent on those parameters. Thus, site characterization is essential for designing a deep geological repository to maintain a sufficient distance from a fault.