Durable oxyfluoride waste forms for salt wastes from molten salt reactors

Abstract Molten salt reactors (MSRs) are promising technology to replace traditional light and heavy water reactors in the near future. Waste management for MSRs, however, remains a pressing concern that needs to be resolved prior to realizing deployment of MSRs. Specifically, the generated salt waste needs to be safely sequestered, a task made difficult by the high solubility of the salt waste that can cause the release of radionuclides into the environment. This work demonstrates a new approach to immobilize multiple fluoride salts into a single waste form by converting highly-soluble fluorides to durable and stable oxyfluorides. Notably, we report a method of conversion of CsF, a very problematic salt, into a pyrochlore structure CsNb 2 O 5 F. Multiphase assemblages of oxyfluoride phases are prepared in a single step synthesis. Subsequent leach testing of the as prepared oxyfluorides indicate release rates orders of magnitude lower than standard reference glasses. Graphical abstract