article posted 21 March 2016
Olivier Bouty PhD, is a physicist in atomic physics, currently working at the French Atomic Energy Commission (CEA), in the field of borosilicate glasses for nuclear waste confinement.
One of his skills centers on the combination of Wide Angle X-ray Diffraction (WAXS) technique (lab-based diffractometer or large X-ray facilities), neutron diffraction, with atomistic Reverse Monte Carlo simulations. He already published several results on europium-doped borosilicate glasses.
Combined XAS investigation and atomistic simulations of a borosilicate Cm-doped glass related to nuclear waste confinement
Olivier Bouty*, Pier L. Solari1 & S. Cammelli1
*Commissariat à l’Energie Atomique, DEN/DTCD/SECM/LMPA, 30207 Bagnols / Cèze, France
1 Synchrotron SOLEIL, L'Orme des Merisiers, Saint Aubin, BP 48, F-91192 Gif-sur-Yvette Cedex, France
In the context of a better characterization of borosilicate glasses for nuclear waste confinement, we present an X-ray Absorption Spectroscopy (XAS) study of two borosilicate curium-doped glasses (based on the International Simplified Glass (ISG) composition: ISGC), combined with Reverse Monte Carlo (RMC) simulations. The first sample is an eight-year ISGC damaged glass (D-ISGC), which has already accumulated an a-decay dose greater than 6.1018 a.g-1
, a value corresponding to a damaged but stabilized structural state. The second sample results from annealing of the latter D-ISGC damaged glass (A-ISGC).
Cm, Pu and Zr species were probed by XAS technique at L3
-edge and K-edge respectively. From the XANES region, we show that Cm and Pu species appear respectively in +3 and +4 oxidation state in both glasses. No Cm local environment changes are observed. In contrast, a small variation in Pu local environment appears between the damaged and annealed glass, reflecting a possible coordination variation or Pu–Zr substitution. A more drastic effect appears for Zr local environment, where a seven-fold coordinated site grows over time under a-self irradiation effects, at the expense of the initial major six-folded symmetry site (fig. 1).
Furthermore, based on former Wide Angle X-ray Scattering (WAXS) and neutron diffraction experiments, combined with RMC simulations on ISG, an atomistic configuration was built for this glass. The inferred scattering paths were afterwards used to try modelling the EXAFS region of the Zr K-edge D-ISGC spectrum.
An attempt to interpret the fits results in terms of structural effects, and also with the help of new available literature information, is done.
References: O. Bouty, L. Ramond, P. L. Solari, S. Cammelli: XANES investigation of a borosilicate Cm-doped glass related to nuclear waste confinement (2016, under review).
Fig. 1: Comparison of XANES spectra at Zr K-edge for D-ISGC (red curve), A-ISGC (blue curve), ISG (black curve) with cristalline references catapleite (green curve) and m-ZrO2