Crystal chemistry of immobilization of fast breeder reactor (FBR) simulated waste in sodium zirconium phosphate (NZP) ceramic matrix

Fuel from the fast breeder reactor waste is reprocessed and subjected to cooling for a period of about one year. Fission and activation products of the fuel are the major constituents of this waste. Sodium zirconium phosphate (hereafter NZP) has been identified as a potential material for immobilization of long lived heat generating radio nuclides. It was found that most of the elements present in the radioactive waste could be immobilized in this ceramic matrix without significant changes of the three-dimensional framework of the host material. Simulated NZP waste forms synthesized by ceramic route at 1200 °C crystallize in the rhombohedral system (space group R−3c). The crystal chemistry of 0–35 wt.% waste loaded NZP waste forms have been investigated using General Structure Analysis System (GSAS) programming of the step analysis powder diffraction data. Rietveld refinement of crystal data on the waste oxide (WOx) loaded waste forms gives a satisfactory convergence of R-factors. The particle size along prominent reflecting planes ranges between 68 and 141 nm. The polyhedral distortions and effective valence calculations from bond strength data are also reported. Morphological examination by scanning electron microscopy (SEM) reveals that the size of almost rectangular parallelepiped shaped grains varies between 0.2 and 5 μm. The EDX analysis provides analytical evidence of immobilization of effluent cations in the matrix.