Neodymium Incorporation in Zirconolite-Based Glass-Ceramics
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Neodymium Incorporation in Zirconolite-Based Glass-Ceramics P. Loiseau1, D. Caurant1, N. Baffier1 and C. Fillet2 1 Laboratoire de Chimie Appliquée de l’Etat Solide (UMR CNRS 7574), ENSCP, 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France 2 Commissariat à l’Energie Atomique (CEA), Centre d’Etudes de la Vallée du Rhône, DCC/DRRV/SCD/LEBM, BP 171, 30207 Bagnols sur Cèze, France ABSTRACT The investigations on enhanced reprocessing of nuclear spent fuel, and notably on separating the long-lived minor actinides, such as Am and Cm, from the other fission products have led to the development of highly durable specific matrices such as glass-ceramics for their immobilization. This study deals with the characterization of zirconolite (CaZrTi2O7) based glass-ceramics synthesized by devitrification of an aluminosilicate parent glass. Trivalent actinide ions were simulated by neodymium, which is a paramagnetic local probe. Glass-ceramics with Nd2O3 contents ranging from 0 to 10 weight % were prepared by heat treatment of a parent glass at two different growth temperatures: 1050° and 1200°C. X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and electron spin resonance (ESR) measurements clearly indicate that Nd3+ ions are partly incorporated in zirconolite crystals formed in the bulk of the glass-ceramic samples. The amount of neodymium in the crystalline phase was estimated using ESR results and was found to decrease with increasing either heat treatment temperature or total Nd2O3 content. INTRODUCTION Research on enhanced reprocessing of nuclear spent fuel for the separation of minor actinides (Np, Am, Cm) has led to the development of new matrices for their specific immobilization. Zirconolite (CaZrTi2O7) is a crystalline phase that was extensively studied within the framework of SYNROC [1] (titanate-based polyphase ceramics) for the immobilization of high-level radioactive wastes (HLW). It exhibits a good capacity to incorporate a wide range of actinide and lanthanide elements, as well as an excellent long term behavior (chemical durability and self-radiation resistance). The work discussed here concerns the characterization of zirconolite-based glassceramics synthesized by devitrification of an aluminosilicate parent glass [2,3]. A strong enrichment of actinides in zirconolite crystals is required in order to provide an efficient immobilization. Such a pattern provides a double containment barrier: the radionuclides are incorporated in crystals, which are themselves embedded in a durable residual glassy phase. For this study, Nd3+ ion was selected to simulate Am3+ and Cm3+ actinide ions because of their identical charge and their very similar ionic radii: in an eight-coordinated site (coordination of the largest site of zirconolite structure), the ionic radii of Nd3+ and Am3+ are 1.109 Å and 1.09 Å respectively [4]. Neodymium cannot be considered as a simulant of neptunium since the oxidizing state of this actinide in zirconolite is generally Np4+ [5]. Furthermore, the study of neodymium incorporation
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