Résumé
Among the numerous scientific challenges pertaining to high-level nuclear waste vitrification and deep geological burial, the alteration of nuclear glass by groundwater combined with the waste package’s self-irradiation are still being studied [1]. Several studies conducted on simplified borosilicate glass compositions (including CJ2: SiO2-AlO2-B2O3-Na2O) have established that reproducing the damage caused by nuclear collision via external irradiation, prior to aqueous alteration, increases the formation rate of the glass’ alteration gel. Its nanometer-scale porosity, which features closed pores as well as open channels, develops faster as well. [2]. This acceleration correlates with higher water mobility across the altered layer, challenging the durability performance of the glass. However, other recent results highlighted the possible collapse of this porous microstructure wen irradiating CJ2 alteration gel with a Xe, 600 keV ion beam, where TEM images demonstrated a complete shrinkage of the observed pores [3]. Due to high vacuum and low temperature in the experimental setup, the influence of certain parameters, such as the presence or absence of pore water, remains unclear. Further research is required to rationalize this possible competing process.<br/>To allow some degree of fundamental understanding and experimental practicality, hexagonal mesoporous silica can serve as model materials to perform ion irradiation experiments assessing on nanometer-scale porous structures. X-ray scattering measurement techniques have already been proved appropriate to monitor the pore collapse of SBA-15 and 170 MCM-41 thin films and powders in several irradiation regimes [4], [5]. Exploratory ion irradiation experiments (Xe, 92 MeV and Ne, 20 MeV) were performed in the past year on SBA-15 and MCM-41 thin films derivatives immersed in water, leading to an overall reduction of pore collapse compared to the dry ones, according to the available analysis tools. (see excerpt on Figure 1) Figure 1 - total thickness reduction of MCM-41 derived thin film irradiated under Ne and Xe ion beams, comparing between dry samples and samples immersed in water prior to irradiation.<br/>In this work, we set out to further study this process and assess the comparability between model materials and alteration gels in various irradiation conditions. Dedicated analysis tools are improved to describe the microstructural evolution in both types of materials. Furthermore, radiation-induced displacement cascades are replicated in molecular dynamics simulations in the ballistic regime and compared to the literature [6]. Finally, in comparative experiments, mesoporous silica thin films and alteration gels are irradiated in an environmental TEM apparatus for a more comprehensive description.<br/>*****<br/>[1] S. Gin, P. Jollivet, M. Tribet, S. Peuget, et S. Schuller, « Radionuclides containment in nuclear glasses: an overview », Radiochim. Acta, vol. 105, no 11, p. 927‑959, nov. 2017, doi: 10.1515/ract-2016-2658.<br/>[2] A. Jan et al., « Radiation effects on the structure and alteration behavior of an SiO 2 –Al 2 O 3 –B 2 O 3 –Na 2 O glass », Int. J. Appl. Glass Sci., vol. 14, no 1, p. 113‑132, janv. 2023, doi: 10.1111/ijag.16618.<br/>[3] A. H. Mir, A. Jan, J.-M. Delaye, S. Donnelly, J. Hinks, et S. Gin, « Effect of decades of corrosion on the microstructure of altered glasses and their radiation stability », Npj Mater. Degrad., vol. 4, no 1, p. 11, déc. 2020, doi: 10.1038/s41529-020-0115-0.<br/>[4] Y. Lou et al., « Structure evolution of mesoporous silica SBA-15 and MCM-41 under swift heavy ion irradiation », Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. At., vol. 365, p. 336‑341, déc. 2015, doi: 10.1016/j.nimb.2015.08.009.<br/>[5] J. Lin et al., « A multiparametric study on the behavior of mesoporous silica under electron irradiation », Materialia, vol. 32, p. 101903, déc. 2023, doi: 10.1016/j.mtla.2023.101903.<br/>[6] Y. Lou, B. Siboulet, S. Dourdain, M. R. Rafiuddin, X. Deschanels, et J.-M. Delaye, « Molecular dynamics simulation of ballistic effects in mesoporous silica », J. Non-Cryst. Solids, vol. 549, p. 120346, déc. 2020, doi: 10.1016/j.jnoncrysol.2020.120346.