We present preliminary simulation results of coupled thermal-hydraulic-mechanical-chemical processes in saliferous formations in the context of underground disposal of heat-generating nuclear waste in rock salt with crushed salt backfill. The work presented in this paper is the continuation of recent work in which the effects of halite dissolution/precipitation were not considered. The simulations have been performed using TOUGH-FLAC, with an equation-of-state module that effectively considers fluids of variable salinity. The preliminary results presented suggest that the backfill reconsolidation process is not affected noticeably when halite dissolution/precipitation is accounted for (in particular, time for reconsolidation and final porosities reached). Concerning the natural salt, the most important effect is related to the increasing solubility of halite with temperature, which affects the effective porosity. Assuming that porosity changes due to chemical effects influence permeability, our simulation results suggest that the extension of the area affected by a secondary permeability is greater when dissolution/precipitation is considered. These results are preliminary and should be validated based on experimental evidence. The time frame during which chemical effects have a noticeable impact is dependent upon the heat power released by the waste packages, and extends between 10 and 100-200 years in the scenario investigated.
Rock salt is a potential medium for the underground disposal of nuclear waste because of several favorable properties: undisturbed rock salt is water and gas tight, it has very low porosity and high thermal conductivity as compared to other shallow-crustal rock types. In addition, rock salt shows creep behavior and is able to heal technically induced fractures if the stress regime is propitious [1-4]. Moreover, rock salt is usually found underground in large volumes in geologically stable areas and is easy to mine . The run-of-mine salt can be used to backfill the open mined spaces (crushed salt backfill, with average grain size smaller than 50- 60 mm ).