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A comprehensive review of the current advances on titanate glass-ceramic composite materials as waste forms for actinide immobilization is given. Apart from providing a comprehensive summary of earlier works in the field, some technical analysis and perspectives are provided pointing to the potential future studies. [Display omitted] • A comprehensive review on titanate glass-ceramic waste forms for actinide immobilization is provided. • Current advances on the titanate glass-ceramic composite materials are summarised. As the emerging versatile waste forms for immobilizing actinide-rich radioactive wastes, glass-ceramic composite materials based on some durable ceramic phases are being developed. They have apparent advantages over the conventional borosilicate glasses and multi- or single- phase ceramics as they essentially combine the chemical and processing flexibilities of glasses to accommodate processing impurities and excellent chemical durability of ceramic phases to host actinides. More recently, some new advances have been made on scientific and technological aspects including new glass-ceramic systems; improved understanding of ceramic phase evolution in glass; actinide validation studies and simplified processing techniques. This review is intended to cover the current advances on the development of glass-ceramic composite waste forms focusing on titanate ceramic phases (zirconolite, pyrochlore and brannerite) for immobilizing various actinide-rich radioactive wastes arising from the nuclear fuel cycle. [ABSTRACT FROM AUTHOR]

Glass-ceramics (GCs) based on titanate pyrochlores have attracted recent attention as candidate waste forms for actinide immobilization. As zirconate pyrochlore has a superior radiation resistance, it is anticipated that Zr substitution of Ti in titanate pyrochlore GCs would increase their potential for waste form applications. The concept was primarily addressed via the preparation of Gd 2 Ti 2-x Zr x O 7 (x = 0.1–0.3) GCs to determine the effects of sintering temperature, Zr substitution, and pyrochlore content (50–70 wt%) on the properties of the resultant GCs. XRD and SEM analyses were used to reveal the phase assemblages and microstructures while TEM and Raman spectroscopy were used to analyze the local structures. XRD results confirmed the formation of the targeted pyrochlore as the major phase, with Gd 9.33 (SiO 4) 6 O 2 oxyapatite present as a minor phase. SEM analyses revealed that up to 0.2 formula units of Ti could be substituted by Zr under the processing conditions. The pyrochlore crystallite sizes were largely controlled by the sintering temperature and cooling rate and showed little sensitivity to the glass contents. This work has demonstrated successful substitutions of Ti with Zr in Gd 2 Ti 2 O 7 GCs as potential waste forms for actinide wastes owing to their superior radiation resistance. The feasibility of Zr substitution of Ti in Gd 2 Ti 2 O 7 glass-ceramics for improving radiation resistance of titanate pyrochlore glass-ceramics as potential composite waste forms for actinide immobilization has been investigated. It has been demonstrated that up to 0.2 formula units of Zr can replace Ti in Gd 2 Ti 2 O 7 to form titanate-zirconate pyrochlore glass-ceramics with major crystalline pyrochlores and a minor Gd-silicate oxyapatite phase. [Display omitted] • Zr substitution of Ti in Gd 2 Ti 2 O 7 glass-ceramics for better radiation tolerance. • Up to 0.2 formula units of Zr can replace Ti under the experimental conditions. • Phase assemblage, structure and microstructure have been investigated. • The glass-ceramics contain major pyrochlore and minor oxyapatite. [ABSTRACT FROM AUTHOR]