Nathalie VALLE oral presentation (OA2-Mon4-3-4)
ISOTOPIC TRACING OF GLASS ALTERATION MECHANISMS
1 Luxembourg Institute of Science and Technology, Materials Research and Technology Department, 41 rue du Brill, 4422 Belvaux, Luxembourg
2 Centre de Recherches Pétrographiques et Géochimiques, UMR 5873 CNRS - Université de Lorraine, BP 20, 54501 Vandoeuvre les Nancy, France
3 Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR 7583, CNRS,, Université Paris-Est Créteil, 94010 Créteil, France
Throughout the world, glass has been chosen to confine highly radioactive waste because it can accommodate a large number of different elements in its microstructure and has high durability. Today, the presence of medieval stained glass on cathedral bears testament to this durability. Nevertheless, glass in contact with water is not inert. Different reactions occur and lead to the formation of an alteration layer on the surface of pristine glass. It is essential to assess the capability of this layer to retain hazardous elements. In the case of nuclear waste glass, the quantification of the release of radionuclides over periods as long as several million years (physical radioactive period of the most radioactive elements) is of great importance, but very challenging. Such a long-term prediction requires the understanding of alteration mechanisms in order to establish a solid basis for a geochemical modeling of the long-term behavior of nuclear glass.
In spite of the numerous investigations focused on glass alteration during the last thirty years, the involved mechanisms have not yet been clearly understood as evidenced by recent works , , .
In our study, we have used Si and O isotopic tracing to gain new insights in our understanding of glass alteration. With this aim, alteration experiments were carried out in dynamic mode in an 29Si (and also 18O) doped solution to discriminate between the silicon from glass (mainly 28Si) and from solution (mainly 29Si). The isotopic signatures obtained from the altered glass pieces as well as from the contacting solution were determined by SIMS. The comparison of these different signatures enabled us to highlight inward and outward silicon diffusion as well as the different mechanisms involved in the formation of the altered glass layer.