The thermal simulation of drift storage (TSS) full-scale test is being performed in the Asse salt mine in Germany to study the thermomechanical effects of the direct disposal of spent-fuel elements in a nuclear salt repository. The test field comprises two parallel test drifts, in each of which three dummy casks are deposited. The remaining volume of the drifts is backfilled with crushed salt. The casks are equipped with electrical heaters with a thermal power output of 6.4 kW each. The test has been in operation since September 1990. A design temperature of ~210°C at the surface of the heater casks was reached after 5 months. Because the thermal conductivity of the backfill increases with its compaction, the temperature at the surface of the casks subsequently decreased, reaching ~170°C after 5 yr of heating. The drift closure, which causes increasing compaction of the backfill, was considerably accelerated by heating. However, the initial backfill porosity of 35% decreased more slowly than predicted, to ~27% in the heated area at the end of 1995. The average backfill pressure has currently reached 18% of the initial vertical stress in the test field area, which has been estimated at ~12 MPa. Studies of water and gas releases from the backfill material reveal significant increases of carbon dioxide, methane, and hydrogen concentrations due to heating. In situ measurements will be continued in the coming years to study further thermomechanical reactions of the backfill and the surrounding rock salt to the heat input.