Full-scale 3D modelling of a nuclear waste repository in the Callovo-Oxfordian clay. Part 1: thermo-hydraulic two-phase transport of water and hydrogen

Abstract

AbstractThe development of deep geological repositories for nuclear waste requires a sound system understanding, to which performance analyses by means of numerical flow and transport simulations form an important contribution. In this context, we present modelling studies of the thermo-hydraulic two-phase transport of water and hydrogen in the planned French repository in this paper, part 1. Part 2 of this paper uses the same modelling concept extended to include radionuclide transport. The numerical TOUGH2-MP-model encompasses the host rock from cap to bed rock, including the repository in full 3D. We compare two repository layouts and assess their robustness through sensitivity simulations with varied key parameters and hydrogen generation regimes, and a coupling of hydrogen generation to water availability. The results show that a continuous gas phase functions as balancing system between connected waste areas. Its extension and continuity depend on the permeability and diffusion parameters, and the amount and temporal regime of hydrogen production. Naturally, the available storage volumes have an impact as well. The layout with larger storage volume behaves more benevolenty towards parameter variations. Overall, both layouts perform satisfactorily. Our methodology enables detailed studies of the global system behaviour and helps to compare different repository layouts.