Radium-226 is one of the main radionuclides remaining in uranium mining residues. However, its direct descendant, radon-222, is a noble gas with a half-life of 3.8 days, which is potentially dangerous to humans if inhaled. In order to minimize the release of this element into the air, mining residues are placed under barriers that limit the diffusive transport of Rn-222 to the surface. The design of these barriers (thickness, materials, water saturation, etc.) should be based on experimental data that quantitatively describe the mobility of radon within them. However, due to the many experimental difficulties associated with studying this radioactive gas, this type of data is rare and often specific to a particular study site, making it difficult to generalize (Fournier et al., 2005; Furhman et al., 2023). However, new investigation techniques have recently emerged that should enable us to deepen our understanding of the diffusive behavior of radon. For example, new devices have been developed to study the diffusion of radionuclides through materials that are partially saturated with water (Savoye et al., 2018; 2024). In addition, spectroscopic autoradiography has recently made it possible to quantify and map alpha emitters present in materials, particularly those in the 238U decay chain and therefore 222Rn (Lefeuvre et al., 2024).
The objective of this doctoral project is therefore to combine these two new approaches to investigate how the diffusion of radon through materials considered as barriers (laterites, bentonite, etc.) can be impacted by the key parameters used to design barriers, namely their degree of water saturation, their level of aging, and their intrinsic heterogeneity.