The siting process of a deep geological nuclear repository is a complex long-term endeavour involving many different stakeholders. Assessing the suitability of a site for a nuclear waste repository requires, among others, robust simulation models of the relevant underground thermal, hydrological, mechanical, and chemical (THMC) processes. Screening such sites for an entire country involves running these simulation models for various parameter sets, on various scales, with various degrees of simplification. The data integration from different sources and post-processing and visualization of results are of equal importance as the models themselves.

The OpenWorkFlow project, funded by the Bundesgesellschaft für Endlagerung (BGE), aims at developing open source, automated, robust, quality assured simulation workflows in the context of the nuclear waste repository siting process in Germany. During the first project phase from 2021 to 2024 several software products emerged from the OpenWorkFlow project, which will be presented on this poster:

• OGSTools, a Python tool suite around OpenGeoSys (OGS), the reference THMC simulator in the OpenWorkFlow project, simplifying model setup, simulation studies and post-processing (https://ogstools.opengeosys.org).
• A FEFLOW to OGS converter, enabling to combine the advantages of both simulators: the convenience and UI features of FEFLOW and the transparency and extensibility of OGS (https://ogstools.opengeosys.org/stable/user-guide/feflowlib.html).
• A fully automated workflow for the thermal dimensioning of a nuclear waste repository—i.e., determining the required area for a repository—for various parameter combinations. This workflow has already been used in the siting process in Germany in practice.
• A set of virtual reality applications have been developed that provide a virtual field trip to the Mont Terri rock laboratory and a serious game in an immersive virtual environment. These applications support the exploration and validation of underground processes. They enable an improved science communication of conducted research as well as training and collaboration on the ongoing experiments.

The second phase of the OpenWorkFlow project has started in January 2025. Until the end of 2029 the existing simulation workflows will be heavily extended to support the safety assessment of nuclear waste repository candidates.