Nitrate conversion and supercritical fluid extraction of UO2-CeO2 solid solution prepared by an electrolytic reduction-coprecipitation method.

A low-waste technology for the reprocessing of spent nuclear fuel (SNF) has been developed recently, which involves the conversion of actinide and lanthanide oxides with liquid N₂O₄ into their nitrates followed by supercritical fluid extraction of the nitrates. The possibility of the reprocessing of SNF from high-temperature gas-cooled reactors (HTGRs) with nitrate conversion and supercritical fluid extraction is a current area of research in China. Here, a UO₂-CeO₂ solid solution was prepared as a surrogate for a UO₂-PuO₂ solid solution, and the recovery of U and Ce from the UO₂-CeO₂ solid solution with liquid N₂O₄ and supercritical CO₂ containing tri-n-butyl phosphate (TBP) was investigated. The UO₂-CeO₂ solid solution prepared by electrolytic reduction-coprecipitation method had square plate microstructures. The solid solution after heat treatment was completely converted into nitrates with liquid N₂O₄. The XRD pattern of the nitrates was similar to that of UO₂(NO₃)₂ ·3H₂O. After 120 min of online extraction at 25 MPa and 50 ℃, 99.98% of the U and 98.74% of the Ce were recovered from the nitrates with supercritical CO₂ containing TBP. The results suggest a promising potential technology for the reprocessing of SNF from HTGRs. [ABSTRACT FROM AUTHOR]