Zirconolite-based glass-ceramics for actinides immobilization: Effects of glass composition and of actinides simulant na

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II6.8.1

Zirconolite-based glass-ceramics for actinides immobilization: Effects of glass composition and of actinides simulant nature Pascal Loiseau1, Daniel Caurant1, Isabelle Bardez1, Odile Majerus1, Noël Baffier1 and Catherine Fillet2 1 LCAES (UMR 7574), ENSCP, 11 rue Pierre et Marie Curie 75231 Paris Cedex 05, FRANCE 2 CEA, DEN/DIEC/SCDV/LEBM, 30207 Bagnols-sur-Cèze, FRANCE ABSTRACT Zirconolite (CaZrTi2O7) based glass-ceramics, in which the crystalline phase (aimed at preferentially incorporating minor actinides or Pu) is embedded in a durable calcium aluminosilicate glassy matrix, can be envisaged as good waste form candidates. In this study, the effect of parent glass composition – and particularly of TiO2, ZrO2, CaO and Al2O3 amounts on the microstructure and the structure of the glass-ceramics obtained after controlled devitrification (nucleation + crystal growth) is reported. It clearly appears that the volume percentage of zirconolite crystals and their nucleation rate in the bulk of the glass strongly depends both on (CaO + ZrO2 + TiO2) and Al2O3 amounts in parent glass. Neodymium is mainly used to simulate trivalent minor actinides whereas several samples were also prepared with other lanthanides (Ce, Eu, Gd, Yb) in order to investigate the effect of simulant field strength in glass on the nature and the composition of the crystals formed. The effect of partial or total molar substitution of ZrO2 by HfO2 in parent glass composition was also studied in order to prepare Ca(Zr1-xHfx)Ti2O7 (0 < x ≤ 1) based glass-ceramics which could be interesting in order to minimize criticality problems. INTRODUCTION As the contribution of minor actinides (Np, Am, Cm) to long term radiotoxicity (time > 300 years) of high-level nuclear wastes (HLW) is the most important, their separation from other fission products and their immobilization in specific highly durable host materials are searched. Such waste forms can also be envisaged for incorporation of excess weapons Pu. Zirconolite (nominally CaZrTi2O7) is a titanate ceramic well-known for its high capacity to incorporate lanthanides (considered as good actinide surrogates) and actinides into the Ca and Zr sites of its structure and for its very good chemical durability in spite of its tendency to amorphization due to radiation damages from α-decays [1]. Different methods have been developed to prepare zirconolite either by sintering alkoxides/nitrates precursors or by melting [2]. However, glass remains the only waste form developed industrially for HLW immobilization . Development of zirconolite-based glass-ceramics appears as an interesting alternative because it combines the ease of glass preparation and the properties of zirconolite ceramic. Indeed, zirconolite-based glass ceramics which are constituted of small zirconolite crystals homogeneously dispersed in a durable glassy matrix can be obtained by controlled devitrification of a melt or of a parent glass prepared using classical glass technology [3,4]. In the ideal case, long-lived radionuclides would be mainly

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