In order to assess the safety of disposal of radioactive waste in salt formations, models for the thermo-mechanical behaviour of rock salt that have been developed in previous programmes have to be verified by in-situ experiments.
The experimental results obtained will be available to predict the behaviour of salt deposits and will give essential information to be used in safety assessment of disposal facilities for radioactive waste in rock salt, especially in the field of elastic behaviour and pressure dependency of creep.
To assess the safety of disposal of radioactive waste in salt formation, models for the thermomechanical behaviour of rock salt that have been developed in previous programmes have to be verified by in situ experiments. In this research programme, in situ measurements are carried out in the Asse II salt mine in Germany. This involves:
determination of in situ elastic behaviour of salt and convergence measurements carried out with the Variable Pressure Device (VPD) in the available 300 m hole at the bottom of the borehole with different pressures;
free convergence measurments of the salt wall at 5 depths in the borehole, ie at different salt pressures, as soon as a 600 m deep borehole becomes available. In order to account for the presence of microcracks and primary creep effects, the in situ elasticity of the rock salt in this set has been assumed to be considerably less (by a factor of 3 to 4) than the values found in laboratory experiments on small salt samples. The VPD experiment, however, shows that the in situ value appears to be significantly higher and does not differ much from values found in the laboratory experiments. This implicates that the set of constitutive parameters needs to be reconsidered and a renewed evaluation of all in situ experiments must be performed.
The following in-situ measurements are carried out in the Asse II salt mine in Germany.
1. Determination of in-situ elastic behaviour of salt and convergence measurements at the bottom of the borehole with different pressures. The measurements will be carried with the Variable Pressure Device (VPD) in the available 300 m hole.
2. Free convergence measurements of the salt wall at five depths in a borehole, i.e. at different salt pressures as soon as a 600 m deep borehole becomes available.
1. Maintenance of installed equipment:
Including the maintenance of the hardware and software required for remote instrument control and data transmission between the Asse salt mine and the ECN in Petten.
2. Execution of the experimental programme:
The VPD measurements require that parameters (pressures) are changed and thus require local operation. The convergence measuring devices have to be installed in the borehole before measuring and removed afterwards.
3. Data collection and interpretation of the results:
The automatically collected experimental data will be validated and interpreted.
4. Evaluation of experimental results:
Consequences for the models used for the description of thermo-mechanical behaviour of rock salt resulting from the measurements will be evaluated taking into account the measurements performed in previous programmes.