Structural role of Zr in alteration gels of simplified nuclear glasses
1*Laurence Galoisy, 1Georges Calas, 2Patrick Jollivet, 2Frédéric Angeli and 2Stéphane Gin
1IMPMC (Université Paris Pierre et Marie Curie, UMR CNRS 7590) 4, place Jussieu 75005 Paris, France
2CEA-Marcoule, Valrho, Laboratoire d’étude du Comportement à Long Terme des matrices de conditionnement, 30200 Bagnols-sur-Cèze, France
Vitrification of high-level radioactive waste in borosilicate glasses has received a great attention in several countries since decades. The possible glass leaching by water in geological repository, is an important phenomenon that needs to be understand to better constrain the long-term evolution of the glasses used to store these specific wastes. We will present structural features of the evolution of simplified nuclear glasses under forcing conditions. During the alteration by water, an amorphous gel is formed at the surface of the glass. The durability of the gel and its properties depend on the structural role played by different elements. New generations of spent fuels require higher content of Zr4+ in glasses. Simplified 5-oxides borosilicate glasses taken as analogs for nuclear waste glasses and containing 1 to 8 mol% ZrO2 were leached in basic (pH=9), neutral (pH=7) and acidic conditions (pH=1). The modifications of the Zr4+ environment (Zr-O interatomic distances, number of neighbors and site distortions), has been investigated in the alteration gels by X-ray absorption spectroscopy (XAS) as a function of the increasing ZrO2 content using Zr L2–3 edge and K-edge XANES and by Zr K-edge EXAFS.
Data obtained on the bulk and the surface of the leached glasses are compared at the different pH. The structural evolution of the gel around Zr4+ in two distinct layers illustrates the molecular-scale modification of the material when in contact with water. On the leached glasses, the coordination numbers of Zr (changing coordination number from 6 to 7 and 8 in the gel) as well as the medium range order derived from L2-edge XANES spectra is compared to the pristine glass and to glasses and alteration products of more complex compositions.
 P. Jollivet, G. Calas, L. Galoisy, F. Angeli, B. Bergeron, S. Gin, M. Ruffoni, N. Trcera, J. Non-Cryst. Solids 2013, 381, 40-47
 E. Pelegrin, G. Calas, P. Ildefonse, P. Jollivet, L. Galoisy Non-Cryst. Solids 2010, 356, 44-49, 2497-2508