(608f) TRISO SNF Deconsolidation – Summary of Pnnl’s 3-Year Program

Staff at the Pacific Northwest National Laboratory have progressed several projects for the Department of Energy’s Nuclear Energy Office, Office of Materials and Chemical Technologies (NE-43) related to processing Tri-structural ISOtropic (TRISO) spent nuclear fuel (SNF). TRISO nuclear fuel is to be used in several commercially proposed advanced High Temperature Gas Reactors (HTGRs). In contrast to light water reactors (LWRs), HTGRs use either helium gas or liquid salt as coolant and are moderated by graphite. The quantities of graphite and the way the material is integral to the fuel means the volume of disposed SNF is significantly larger than that discharged from LWRs. Therefore, there are waste management benefits to separating the fuel from the graphite and potentially disposing of the latter as low level waste. TRISO nuclear fuel itself consists of uranium oxycarbide coated with pyrolytic carbon and silicon carbide, which complicates reprocessing the SNF. PNNL’s 3-year program started with reviewing technologies applicable to deconsolidating the graphite to expose the coated fuel particles and fracturing the coatings to expose the fuel. A deep dive on the most promising technology was then conducted to evaluate its feasibility in a process plant. Finally, a flowsheet was developed incorporating the selected technology and the fuel’s dissolution in nitric acid. Further research and development needs were identified throughout the program.