The International DECOVALEX Model Comparison Project: Recent Advances in Simulating Coupled Thermal-Hydrological-Mechanical and Chemical Processes

This presentation provides an overview of an international research collaboration for advancing the understanding and modeling of coupled thermo-hydro-mechanical-chemical (THMC) processes in the subsurface. The creation of the international DECOVALEX Project, now running for almost three decades, was motivated by the recognition that prediction of these coupled effects is an essential part of the performance and safety assessment of geologic disposal systems for radioactive waste and spent nuclear fuel. The main characteristic of DECOVALEX is the close collaboration on analyzing and simulating state-of-the-art field and laboratory experiments, which provides a wide range of experiences, perspectives and solutions to these complex problems and allows for detailed comparison of analysis and modeling results.

Over the past decades, the project has tackled many of the key THMC processes relevant to radioactive waste disposal, with an emphasis on the perturbations occurring during the earlier repository stages, and it has done so for all the major rock types considered for hosting geologic repositories. This presentation provides examples of research contributions made to date, selected from the most recent research phase referred to as DECOVALEX-2019. These examples range from the modeling of large-scale in situ heater tests representing mock-ups of nuclear waste disposal tunnels, to analysis of gas transport tests in the engineered barrier system, and the numerical analysis of controlled-injection fault slip experiments to understand thermal stress impacts. The presentation ends with concluding remarks about the value of the collaborative DECOVALEX Project, summarizing the significant impact of DECOVALEX on the current state-of-the-art of understanding and modeling of coupled THMC processes, and illustrating that the insight and scientific knowledge gained would not have been possible if individual groups had studied these data alone rather than within a truly collaborative setting.