452685 Route to Separation of Actinide Metals from Rare Earth Metals Via Conversion to Chlorides
Parker Okabe1, Devin Rappleye2, and Michael F. Simpson1
1University of Utah, Department of Metallurgical Engineering
2Lawrence Livermore National Laboratory
Separation of actinides from rare earths has important applications both related to rare earth metal extraction and closing the nuclear fuel cycle. Rare earths are often found in mineral deposits along with thorium, which can complicate their extraction and purification. Rare earths are also formed as fission products in spent nuclear fuel. Nuclear fuel recycling technologies aim to separate the actinides and use them as feed for fabrication of new fuel, while keeping the actinides out of the waste streams that are destined for permanent disposal in geologic repositories. Pyroprocessing of spent fuel can be used to electrochemically separate actinides from rare earths and generate rare earth-rich metallic waste forms. But the proximity of the reduction potentials for actinides and rare earths make it very difficult to eliminate carryover of actinides into the rare earth waste forms. The rare earth waste forms will be much simpler and cheaper to dispose if the actinides can be completely removed. It is, thus, important to develop a process to reduce actinide contamination in rare earth metals. While aqueous separations methods involving acid dissolution followed by extraction into an organic phase have been scaled up and implemented commercially in several countries, this approach is widely viewed as unattractive due to actinide proliferation and environmental concerns. There is, thus, increasing interest in pyrochemical separations approaches that eliminate liquid wastes and demonstrate low selectivity for actinide separation. One such pyrochemical approach that we are investigating is based on physical property differences between actinide and rare earth chlorides. In order to develop this approach, experiments have been run with cerium and cerium+uranium metal. Metallic samples were made by melting cerium and uranium together into a small bead. In a batch reactor, these metal beads were first hydrided with pure H2 to form metal hydride powders and then were chlorinated with anhydrous chlorine gas. Pressure readings were used to monitor the extent of reaction versus time. Hydriding was pursued to reduce the particle size and facilitate rapid and complete chlorination. Complete hydriding could be accomplished in 3 hrs at 300oC, provided the starting size of the metal beads was approximately 5 mm in diameter or smaller. Otherwise, unreacted metal cores were present.
This work performed under the auspices of the U.S. Department of Energy for Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344