Densification of Mesoporous Silicas Induced by Radiation Damage - New Perspectives for the Treatment of Radioactive Effluents

In recent years, mesoporous silicas (SBA15, MCM41) discovered in the 1990's, synthetized by sol-gel process have been the subject of numerous studies for various applications in the fields of catalysis, CO₂ encapsulation, or treatment of radioactive effluents. More precisely, a new strategy for this treatment is based on the use of a mesoporous silica functionalized by an organic ligand selective of the Radionuclides (RN). This hybrid material would allow at the same time the separation of the RN and their encapsulation after collapsing the porosity. This new concept would result in obtaining a primary wasteform matrix. Several ways are being considered to close the mesoporosity: chemical reactions (sol-gel in particular), thermomechanical treatments, and irradiation effects. The collapse of silica mesoporosity by external irradiation (ion and electron) has been demonstrated in several works. More recently, the possibility of closing the porosity of a mesoporous silica through self-irradiation damage produced by the presence of the short-lived actinide ²³⁸Pu has been studied in our laboratory. The results of this work will be presented in the talk. ^238/239Pu sorption experiments have shown that hybrid silicas grafted with Ac-Phos and Prop-Phos ligands have a loading capacity of around 10% by weight, enabling significant self-irradiation damage, comparable to an external irradiation experiment, to be achieved in around two years. Our findings are in line with previous results. Small-angle X-ray scattering (SAXS), which is accessible on the SOLEIL synchrotron's MARS beamline, was employed for characterization of these Pu-doped materials. After 17 months of ageing, these measurements show a decrease in the interplanar (100) distance of the hexagonal pore network of mesoporous silica, indicating a densification of around 10% of the pore volume. The results obtained will be discussed in the light of the differences observed between external irradiation and self-irradiation