1,3,4- 1Technical University of Darmstadt, Darmstadt, Germany
- 2GFZ Helmholtz Centre for Geosciences, Potsdam, Germany
- 3Federal Company for Radioactive Waste Disposal, Peine, Germany
- 4Clausthal University of Technology, Clausthal-Zellerfeld, Germany
The long-term safety assessment of high-level radioactive waste repositories must account for climate changes over the next million years. During this period, the Earth's surface will undergo up to 10 glacial-interglacial cycles, where glacial activity and permafrost formation/melting will cause repeated phase transitions of water within rock pores and fractures. These freeze-thaw processes induce volumetric expansion and contraction in the geological strata, leading to complex thermal–hydraulic–mechanical coupling effects that can impact both geological and engineered barriers. A comprehensive understanding of these processes is essential for assessing the long-term safety of radioactive waste repositories.
This study utilizes a modified triaxial testing system to investigate the relationship between freeze-thaw-induced volume changes of sandstone and key influencing factors, such as porosity, permeability, temperature, and saturation. Furthermore, this research will be extended to examine the effects of freeze-thaw cycles on consolidated materials (e.g., granite and mudstone) and unconsolidated materials (e.g., clay and sand).
The experimental results will be used for three-dimensional finite element modeling, enabling the simulation of volumetric changes in rock subjected to freeze-thaw cycles by refining thermo-hydro-mechanical (THM) processes within the OpenGeoSys (OGS) framework. In the future, this simulation will be further extended to the hydrogeological scale, where a catchment model will be developed to evaluate the impact of glacial cycles on regional groundwater flow dynamics and assess their cumulative effects.
By integrating experimental analysis, numerical simulations, and hydrogeological modeling, this study proposes a systematic framework for performing safety assessments of glacial-interglacial scenarios. The findings will enhance the scientific understanding of subsurface processes.
Keywords: volume change, permafrost, glaciation, safety assessment, radioactive waste repository, freeze-thaw cycles, finite element modeling, groundwater flow
How to cite: Sheng, H., Schedel, M., Pham, H., Schüth, C., Sass, I., and Rühaak, W.: Evaluation of Volume Change Due to Freeze-Thaw Cycles in Nuclear Waste Repository Safety Assessment, Third interdisciplinary research symposium on the safety of nuclear disposal practices, Berlin, Germany, 17–19 Sep 2025, safeND2025-61, https://doi.org/10.5194/safend2025-61, 2025.
