Vitreous and crystalline phosphate high level waste matrices: Present status and future challenges

Vitrification is currently the most effective process for immobilization of nuclear waste. However, ubiquitous borosilicate glass is not suitable for immobilization of nuclear waste from advanced reactors such as Fast Breeder Reactors (FBR) because solubility of many compounds/elements existing in the spent fuel in borosilicate glasses is quite poor. In order to possess a viable immobilization strategy for wastes arising from advanced reactors, alternatives to borosilicate glasses such as phosphate glasses, glass-ceramics and crystalline waste forms are being investigated. This review aims to provide an overview of nuclear waste immobilization employing phosphate-based glasses, glass-ceramics and crystalline ceramic hosts, focusing on structure and properties that make these new matrices suitable for the challenging task of waste immobilization.