In many countries, geological disposal facility is considered as an option for the long-term management of radioactive waste. In the French, Swiss, and Belgian concepts, clays have been selected as suitable host formations. Considerable amounts of gas can be generated within geological disposal facilities – mainly hydrogen from corrosion of metallic elements of the repository or of the waste themselves. Although gas production will be slow, it is important to assess how gas will accumulate, migrate, and be released within the disposal system and what could be the potential system perturbations caused by gas production and pressurisation in order to properly evaluate the functioning of a geological disposal facility. To address this question, the EURAD-GAS project under the umbrella of the European Joint Programme EURAD (2019–2024) studied gas transport mechanisms in clays. The project aimed to enhance understanding of gas movement through low-permeability materials and assess its implications for barrier integrity and repository performance. This paper provides an overview of the state of knowledge on gas transport processes collected within this project and illustrates how this knowledge can be used to assess gas transport at the scale of a geological repository in clay formations.
Levasseur et al. (2026) studied this question.