Competition Between Internal and Surface Crystallization in Glass-ceramics Developed for Actinides Immobilization
- PDF / 1,171,993 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 57 Downloads / 164 Views
&RPSHWLWLRQ%HWZHHQ,QWHUQDODQG6XUIDFH&U\VWDOOL]DWLRQLQ*ODVVFHUDPLFV 'HYHORSHGIRU$FWLQLGHV,PPRELOL]DWLRQ Pascal Loiseau1, Daniel Caurant1, Odile Majerus1, Nöel Baffier1, Catherine Fillet2 Laboratoire de Chimie Appliquée de l’Etat Solide (UMR CNRS 7574) , ENSCP, 11 rue P. et M. Curie, 75231 Paris (France) 2 CEA/DEN/DIEC/SCDV/LEBM), 30207 Bagnols sur Cèze (France)
1
$%675$&7 Glass-ceramic matrices containing zirconolite (nominally CaZrTi2O7) as the only crystalline phase in their bulk can be considered as good candidates for actinide-rich nuclear wastes (containing minor actinides or Pu) immobilization. In this study, three different methods are envisaged and compared to prepare such waste forms using neodymium as trivalent actinides surrogate. Independently on the preparation method, zirconolite is shown to be the only crystalline phase to nucleate in the bulk. However, crystallization of silicate phases (titanite CaTiSiO5 + anorthite CaAl2Si2O8) can occur from samples surface and can compete with zirconolite crystallization. The effect of the crystal growth thermal treatment duration (2-300 h) at high temperature (1050-1200°C) on glass-ceramics structure and microstructure is studied. In the oxides system studied here, it appears that zirconolite is not thermodynamically stable in comparison with titanite but, for kinetics reasons, such transformation will not occur during waste forms disposal. ,1752'8&7,21 Investigations of the enhanced separation of the long-lived α-particle emitting radionuclides (minor actinides) from high-level nuclear wastes and their immobilization in specific highly durable host matrices are currently in progress in several countries. Highly durable matrices are also developed for Pu-rich wastes immobilization. Among the different waste forms investigated, ceramics and more particularly the ones containing high amounts of titanium and zirconium such as zirconolite (nominally CaZrTi2O7) exhibit very high chemical durability [1]. In spite of their higher long-term performances in comparison with glasses, single-phase ceramic waste forms remain more difficult to prepare than glasses. Thus, glass-ceramics – such as zirconolite-based ones – appear as good alternative waste forms because they combine the ease of glass preparation (melting + casting) and the properties of ceramics (very high chemical durability and actinides incorporation capacity). Moreover, due to the existence of a residual glassy phase embedding the crystals, glass-ceramics can accommodate more easily waste composition fluctuations and impurities than ceramics. In comparison with glassy and ceramic waste forms, the amount of works reported on glassceramic matrices is very limited and concerns only non separated wastes immobilization [1,2]. The possibility to prepare zirconolite-based glass-ceramics containing small zirconolite crystals as the only crystalline phase in the bulk of a glassy matrix (after internal and probably homogeneous nucleation) and able to incorporate trivalent and tetravalent actinide surrog
Data Loading...
