Investigation of the effects of thawing/freezing processes on rock integrity in the context of nuclear waste repository safety
Motivation
During the assessment period of one million years, starting after the closure of the repository for high-level radioactive waste in Germany, future climate developments have to be considered. Based on the concept of uniformitarianism (or actualism), taking the Quaternary period (the last 2.6 million years) into account, up to 10 glacial/interglacial cycles have to be expected for the next one million years.
This cyclicity and the accompanying effects, such as glaciations and the formation of permafrost, may have an impact on the geological barriers of the repository.
Aim and Methods
Due to the physics of water, freezing leads to an expansion coupled with stresses that occur in the pore-space and fractures of rocks, respectively. During the subsequent thawing compaction can occur. This happens cyclically, on variable time scales.
The process of expansion and compaction will be investigated in this project numerically and experimentally as a thermal-mechanical (TM) coupled process on relevant rocks. Respective constitutive relations for a general numerical consideration will be derived.
By means of an integrated hydrogeological model, the described process of expansion and compaction will be modeled on the scale of a groundwater catchment area. Permafrost data from CatchNet will be used for this purpose. The results will be finally evaluated with regard to the relevance for the repository safety.
Corresponding preliminary work has been developed in another international project (INTERFROST). Amongst others, volume changes during thawing/freezing turned out to be relevant in the INTEFROST study.
The code to be used for the numerical study is OpenGeo-Sys (OGS), an open source software for numerical modeling of coupled thermal, hydraulic, mechanical and chemical (THMC) processes.
The work carried out and the planned doctorate are related to research package 2 of the international research network CatchNet “Permafrost in transition impact on groundwater-surface water interactions.”
Team
PhD student (to be announced)
Wolfram Rühaak, supervisor, habilitated adjunct professor (Privatdozent), Technische Universität Darmstadt (TUDA)
Eva Schill, co-supervisor, Professor, Technische Universität Darmstadt (TUDA)
Leonie Peti, contact at Bundesgesellschaft für Endlagerung (BGE)
Marc Wengler, contact at Bundesgesellschaft für Endlagerung (BGE)
Publications
The project is currently in its infancy. Check back later!