This disclosure describes systems and methods for treating nuclear fuel with supercritical fluids, such as supercritical carbon dioxide. The addition of various ligands to the supercritical fluids is disclosed, where one or more ligands can be chosen to selectively remove one or more fission products from the nuclear fuel. The nuclear fuel may be treated either within the nuclear reactor or may be removed from the reactor before treatment. This disclosure also presents methods and systems for liquid nuclear fuel treatment with supercritical fluids in, for example, a molten salt fast reactor, a traveling wave reactor, and a containerized molten salt reactor.