About Gas Permeability and Diffusion through Concrete

Abstract

Gas production is expected in radioactive-waste storage structures. This will induce a slow increase in gas pressure, which necessitates the study of gas transfer at a low pressure. In this special case, calculations of the flow through storing materials while solely using permeability and Darcy’s law are likely to be inadequate, as diffusion may play a crucial role in the process. The gas permeability and gas diffusion coefficient of industrial concrete have then been measured on the dry material. Diffusion tests were performed with a new device, specially designed for this study. The diffusion coefficient was directly measured with the use of the first Fick’s law, as the test was analyzed under a steady state. Using some simplified hypotheses, it was then possible to compare the proportion of flow occurring due to diffusion with the one occurring due to permeation. The tendency is very clear and unambiguously shows that diffusion is predominant at a very low injection pressure but becomes negligible as soon as the gas pressure exceeds a moderate value.

Keywords

• gas permeability
• gas diffusion
• dry concrete
• injection pressure