Phase identification, microstructural characterization, phase microanalyses and leaching performance evaluation of SYNROC-FA crystalline ceramic waste form

Abstract

SYNROC-FA, a crystalline ceramic waste form designed to contain 50 wt% Amine process, uranium-rich, high-level, radioactive waste for ultimate deep-geologic disposal, has been characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Phase identification was carried out using XRD, electron diffraction in TEM, and backscattered electron imaging in SEM. Phase microanalyses were carried out using energy-dispersive X-ray analyzers (EDX) during SEM and TEM examinations. X-ray diffraction and grain microanalyses using EDX revealed the existence of a pyrochlore-structured phase CaU(Ti 3+, Ti 4+) 2O 7, perovskite (Ca, U)(Ti 3+, Ti 4+)O 3 and uraninite (U, Ca, Ti)O 2, while Ba-hollandite Ba(Al 3+, Ti 3+) 2Ti 5O 14 was identified using only XRD. The leaching resistance of SYNROC-FA was determined by carrying out a modified MCC-1 leach test in a simulated Canadian Shield groundwater at 90°C for 120 days. The normalized leach rate of Ba was 6 × 10 −3 g · m −2 · d −1 while the concentrations of U and other simulated fission products in the leachants were below the detection limits of inductively coupled plasma spectrometry and atomic absorption techniques. The leach rates of U and Ti were estimated to be less than 6 × 10 −5 and 3 × 10 −5 g · m −2 , respectively.