J Am Ceram Soc. 2020;00:1–10. wileyonlinelibrary.com/journal/jace | 1 © 2020 The American Ceramic Society 1 | INTRODUCTION High-level wastes (HLWs) arising from the reprocessing of spent nuclear fuels (SNFs) contain some fission products and transuranium minor actinides with long half-lives, and safe storage and disposal of these HLWs have become an urgent global issue. 1-3 It is essential to adopt a proper conditioning process to convert HLWs to physically stable and chemically durable solid waste forms, suitable for further waste manage- ment such as transportation, interim storage, and final geo- logical disposal. 1-4 While borosilicate glass has been widely investigated as the most popular medium for the immobilization of HLWs from the reprocessing of civilian SNFs, 2-4 synthetic rock (ab- breviated as synroc, which contains a group of stable titanate mineral phases such as zirconolite, pyrochlore, brannerite, hollandite, perovskite etc) as a representative for ceramic waste forms has also been developed, originally for the immo- bilization of HLWs from Purex-type reprocessing of SNFs. 5-9 Subsequently, synroc formulations based on zirconolite and pyrochlore have been tailored for the immobilization of var- ious actinide-rich radioactive wastes including excess weap- ons plutonium. 10-15 The obvious advantages for synroc-type ceramic waste forms over the conventional borosilicate Received: 27 December 2019 | Revised: 27 February 2020 | Accepted: 12 March 2020 DOI: 10.1111/jace.17119 SPECIAL ISSUE ARTICLE Pyrochlore glass-ceramics fabricated via both sintering and hot isostatic pressing for minor actinide immobilization Yingjie Zhang | Zhaoming Zhang | Tao Wei | Linggen Kong | Young J. Kim | Daniel J. Gregg In commemeration of Dr Eric R. Vance (1942-2019) Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia Correspondence Yingjie Zhang, Australian Nuclear Science and Technology Organisation, Kirrawee DC, NSW, Australia. Email: yzx@ansto.gov.au Abstract Pyrochlore glass-ceramics (GCs) have been investigated with samples fabricated via both sintering and hot isostatic pressing (HIPing) of a mixed oxide precursor. It has been demonstrated that sintering at 1200°C in air is necessary to obtain well-crystal- lized pyrochlore crystals in a sodium aluminoborosilicate glass through a one-step controlled cooling. The crystallization, structure, and microstructure of Eu 2 Ti 2 O 7 py- rochlore as the major phases in residual glass were confirmed with X-ray diffraction (XRD), scanning electron microscopy-energy dispersive spectroscopy, transmission electron microscopy, and Raman spectroscopy. The structures of major Eu 2 Ti 2 O 7 pyrochlore and minor [Eu 4.67 O(SiO 4 ) 3 ] apatite in both sintered and HIPed samples were refined using synchrotron XRD data. While the processing atmosphere did not appear to affect the cell parameter of the main pyrochlore phase, very small volume expansion (~0.3%) was observed for the minor apatite phase in the HIPed sample. In addition, static leaching of the HIPed sample confirmed that pyrochlore GCs are chemically durable. Overall, pyrochlore GCs prepared via both sintering and HIPing with the Eu partitioning factor of ~23 between ceramics and the residual glass are suitable waste forms for minor actinides with processing chemicals. KEYWORDS europium, glass-ceramics, nuclear waste, pyrochlore, titanates