Gas transfer and mechanical incidence on storage barriers

Abstract In deep geological repositories, the hydrogen produced by the corrosion of the steel container protecting the nuclear waste represents a risk of damage for the surrounding engineered and geological barriers, due to a gas pressure accumulation with time and, finally, of a potential breakthrough of the barrier. Such a prediction relies on the existence of a clear modelling of the transfer and coupling phenomena. The situation described in our study is made of liquid water and dissolved gas, making a perfect liquid mixture (solution). Both of the two components of the mixture (namely: the water and the dissolved hydrogen) migrate through the barriers under diffusive and convective flow. At the same time, the constitutive equations describing the mechanical interaction of the solution (water+dissolved gas) with the solid phase (engineered barrier or rock) are derived from simple physical assumptions. The mechanical influence of the dissolved gas proves to be a simple osmotic pressure leading, in practical cases, to a very low increase of the total pressure and of the correspondent mechanical stress, highly smaller than described by previous authors. On the other hand, the often neglected consumption of water with corrosion seems, on a mechanical point of view, the dominant and major phenomenon, creating an important decrease of water and total pressure. On the basis of these phenomena and the associated parameters (permeability and diffusion coefficient), a sensitive analysis is carried out. Finally, a first unsaturated extension is proposed as a perspective for future research and future evaluations.