Study of XeF2 fluorination potential against Rh2O3, RuO2, ZrO2, and U3O8 for use in reactive gas recycle of used nuclear fuel

Abstract

Triuranium octoxide (U3O8) and stable surrogate oxides of selected fission product species representative of a Used Nuclear Fuel (UNF) matrix typical of Light Water Reactor (LWR) service were fluorinated using an alternate, solid-phase fluorinating agent, XeF2. This fluorination reaction formed volatile and non-volatile compounds and demonstrated the possibility of chemical and thermal separations of the UNF matrix based on this approach. A series of experiments was conducted at the milligram quantity scale using a Shimadzu DTG-60 TG/DTA for testing of all non-radioactive samples and a Netzsch STA 409 TGA for testing of all radioactive samples. The fluorination and subsequent volatilization potentials were analyzed by mixing excess fluorinating agent with an oxide form of the UNF material and then heating to elevated temperatures for analysis. Thermogravimetric and differential thermal analysis allowed reaction pathways to be analyzed and suggested windows both thermally and chemically for separations of these various components. The differences in thermophysical properties of these products can be utilized as a starting point to effectively separate, isolate, and collect product streams with different compositions for further processing. The study of these chemistries could be incorporated into advanced separations methods to provide another possible solution for the long-term sustainability of nuclear energy applications.