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

摘要

Zirconolite (CaZrTi_2O_7) 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 TiO_2, ZrO_2, CaO and Al_2O_3 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 + ZrO_2 + TiO_2) and Al_2O_3 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 ZrO_2 by HfO_2 in parent glass composition was also studied in order to prepare Ca(Zr_(1-x)Hf_x)Ti_2O_7 (0 < x ≤ 1) based glass-ceramics which could be interesting in order to minimize criticality problems.