Analysis of stress measurements in the TSDE test at the ASSE salt mine

The German concept for the direct disposal of spent fuel rods comprises their emplacement in Pollux casks in backfilled drifts of a repository in salt rock. To demonstrate the suitability of this concept, a large-scale test 'Thermal Simulation of Drift Emplacement (TSDE)' is being carried out in the Asse salt mine. The objective of this test is to determine the thermomechanical behavior of the host rock and of the crushed salt used for backfilling of the drifts. To this end, two parallel drifts were excavated, each containing three heater casks to simulate the heat output of high-level radioactive waste. The geotechnical test program includes the measurement of temperature, deformation, stress, density, compaction, and permeability in the host rock and the backfill. The rock stress mesurements carried out by the BGR include measurement of the initial stress, of the secondary stress around the test drifts, and of stress change. Typical measured data, in particular data of the current long-term measurements are presented. To analyze the data, model calculations concerning the time-dependent stress change around the test drifts were made. Comparing experimental and theoretical data, good agreement can be obtained if the interpretation reflects the time-dependent stress conditions around the test drifts and around the measurement boreholes.