Modeling of groundwater flow and radionuclide transport in a high-level radioactive waste repository with multiple canisters

A two-dimensional numerical model incorporating a multiple-canister configuration and a non-uniform flow field of the host rock is developed for more reliable performance assessment of a water-saturated high-level radioactive waste repository. A space-dependent flow velocity distribution is established numerically using the finite-element method. Transport of Cs-135 is simulated using the random-walk method. Numerical results for a source condition of instantaneous-pulse-input show that (i) migration of Cs-135 is influenced significantly not only by the canister configurations but also by flow boundary conditions, ii) effect of applied hydraulic gradient direction on Cs-135 migration becomes more significant as the number of canisters increases, while the effect is negligible for a single-canister configuration, (iii) the direction of the hydraulic gradient orthogonal to the orientation of the disposal tunnel is most advantageous with respect to the isolation of the radionuclide, and (iv) the single-canister configuration yields conservative results compared with multiple-canister configurations.