A multi-scale approach for the investigation of crushed salt as long-term barrier in a rock salt repository (MEASURES)

In the concept for a high-level nuclear waste (HLW) repository in rock salt, crushed salt fulfils the crucial role as long-term barrier together with the surrounding geological barrier rock salt. Crushed salt is a long-term stable material which guarantees a maximum of compatibility with the host rock, and which is easily available (mined-off material). The sealing effect of crushed salt evolves by porosity/permeability reduction due to compaction driven by the convergence of the surrounding rock salt. The compaction process of crushed salt is influenced by environmental conditions (e.g., temperature, stress state, convergence rate) and internal properties (e.g., grain size/grain size distribution, moisture content), therefore, comprises thermal-hydraulic-mechanical (THM) coupled processes.

Comprehensive knowledge of the sealing effect evolution as required for the long-term safety analysis for a HLW repository, includes full process understanding of the porosity/permeability reduction during ongoing compaction and a reliable prediction of the compaction process in long-term.

The project MEASURES is initiated by an international group of organizations with wide ranges of experience in the field of repository research and crushed salt compaction (Friedenberg et al., 2025). The aim of the project is to be able to predict real behavior based on the entire process chain from laboratory tests, the microstructural analysis of these tests, and material models that take these test and analysed results into account, and also to be able to demonstrate this in-situ.

The MEASURES project is based on a strong interaction between experimental and microstructural studies, and numerical methods. The following main areas are addressed:

• Sensitivity of long-term compaction to mean stress, water content and initial porosity;
• Quantification of contributions from individual microstructural mechanisms;
• Permeability measurements over a range of relevant porosities;
• Calibration of constitutive models against generated experimental data;
• Quantification of uncertainties both in laboratory and numerical simulations;
• Addressing sample-to-sample variability and lab-to-lab variability.

The outcomes of the MEASURES project will improve the process understanding of crushed salt and help to reduce uncertainties in the prediction of the evolution of crushed salt’s barrier properties. Thus, the project helps to strengthen the long-term safety case for a HLW repository in rock salt.

 Acknowledgements

Thanks go to the MEASURES family for the fruitful collaboration and constant support.

The project partner GRS, BGE-TEC, IfG and TUC greatly acknowledge the project funding received by the German Federal Ministry for the Environment, Nature Conservation, Nuclear Safety and Consumer Protection (BMUV), represented by the Project Management Agency Karlsruhe (PTKA) under the contract FKZ 02 E 12214 A-D.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

References

Friedenberg, L., Bartol, J., Beese, S., Coulibaly, J. B., Düsterloh, U., Gartzke, A.‑K., Hangx, S., Jantschik, K., Kirby, M., Laurich, B., Lerch, C., Lerche, S., Li, L., Lüdeling, C., Mills, M. M., Naumann, D., Norris, S., Oosterhout, B. van, Rahmig, M., . . . Zemke, K. (2025). Multi-Scale Experimental and Numerical Analysis of Crushed Salt Used as Engineered Backfill in a Rock Salt Repository - 25062. In I. N. WM SYMPOSIA (Chair), Waste Management Symposia 2025, Phoenix.