Japan's Toshiba Energy Systems & Solutions Corporation said on 19 March that it has established redox treatment technology for metal-oxide to minimise secondary radioactive wastes from nuclear power plants.

The technology that enables certain useful elements to be extracted from vitrified high-level radioactive waste. Those elements can then be reused, and the volume of residual high-level waste is reduced. Toshiba said the technology uses molten to isolate four elements containing long-lived fission products (LLFPs) into metal from vitrified radioactive waste.

The research was conducted under the Impulsing Paradigm Change through Disruptive Technologies (ImPACT) Programme led by the Council for Science, Technology and Innovation, Cabinet Office for the “Reduction and Resource Recycling of High-Level Radioactive Wastes through Nuclear Transmutation.  

Under the programme, led by manager Dr Reiko Fujita, the reduction of LLFPs and recycling of resources from radioactive waste are being investigated along with the conversion of LLFPs into stable or short-lived nuclides. The vitrified radioactive wastes contain palladium, selenium, caesium, zirconium and other LLFPs, which have a half-life of around one million years. The LLFPs must be separated from high-level radioactive wastes to reuse them and minimise the wastes.

This raises the issue of reversibility and retrievability in the context of long-term geological disposal. The research team demonstrated that reusable elements could be separated from vitrified wastes by using molten salt technology. This technology, when combined with other technologies being developed under the ImPACT programme, could decrease the size and depth of a proposed repository.

The research team has retrieved dummy LLFP nuclides as solids, molten salts and gasses by reducing dummy vitrified waste in the molten salt. The radiation-tolerant molten salt can be used repeatedly resulting in decreased amounts of secondary wastes, and the team will continue research to provide a practical system to reuse and minimise high-level radioactive waste. The glass structures were dissolved using a special chemical treatment as vitrified wastes stored at disposal sites will never dissolve naturally. The research team also includes the Japan Science and Technology Agency.