Thermohydrological conditions and silica redistribution near high‐level nuclear wastes emplaced in saturated geological formations

Evaluation of the thermohydrological conditions near high‐level nuclear waste packages is needed for the design of the waste canister and for overall repository design and performance assessment. Most available studies in this area have assumed that the hydrologic properties of the host rock are not changed in response to the thermal, mechanical, or chemical effects caused by waste emplacement. However, the ramifications of this simplifying assumption have not been substantiated. We have studied dissolution and precipitation of silica in liquid‐saturated hydrothermal flow systems, including changes in formation porosity and permeability. Using numerical simulation, we compare predictions of thermohydrological conditions with and without inclusion of silica redistribution effects. Two cases were studied, namely, a canister‐scale problem, and a repository‐wide thermal convection problem and different pore models were employed for the permeable medium (fractures with uniform or nonuniform cross sections). We find that silica redistribution in water‐saturated conditions does not have a sizeable effect on host rock and canister temperatures, pore pressures, or flow velocities.