Treatment of UO2 pellets used for preparing fuel elements of HTR-10 followed by supercritical fluid extraction

International interest in high temperature gas-cooled reactor (HTGR) has been increasing in recent years. It is important to study on reprocessing of spent nuclear fuel from HTGR for recovery of nuclear resource and reduction of nuclear waste. Treatment of UO2 pellets used for preparing fuel elements of the 10 MW high temperature gas-cooled reactor (HTR-10) followed by supercritical fluid extraction was investigated. When UO2 pellets were dissolved and extracted with tri-n-butyl phosphate (TBP)–HNO3 complex in supercritical CO2 (SC-CO2), the extraction efficiency was less than 7% under experimental conditions. After UO2 pellets were ground into UO2 fine powders, the extraction efficiency of the UO2 fine powders with TBP–HNO3 complex in SC-CO2 could reach 92%. After UO2 pellets broke spontaneously into U3O8 powders under O2 flow and 600 °C, the extraction efficiency of the U3O8 powder with TBP–HNO3 complex in SC-CO2 could reach more than 98%.