The objective of this research is to establish characterization protocol and obtain accurate chemical speciation of UCl3 and UCl4 for UCl3 synthesis from chlorination of uranium. Uranium trichloride, UCl3, has found great application in spent oxide fuel dissolution for conversion of used commercial fuel to a chloride form, which facilitates further fuel management and disposition options. High purity UCl3 is the key to the spent oxide fuel dissolution technology. However, high purity UCl3 is not available commercially. Consequently, a high grade UCl3 must be synthesized in the laboratory, for which accurate quantification of relative UCl3 and UCl4 concentrations plays pivotal role for quality control.



We propose to use a combined X-ray diffraction (XRD) and transmission electron microscope (TEM) method coupled with energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The XRD and TEM techniques will provide quantitative information for UCl3 and UCl4 for various UCl3/UCl4 samples synthesized at different conditions. This proposed project directly supports our on-going Laboratory-Directed Research and Development(LDRD) project (19A39-059FP- Dissolution Phenomena of Used Nuclear Oxide Fuel in Molten Salt Systems) and will provide a fundamental understanding of UCl3 and UCl4 chemical speciation, which will help optimize both the UCl3 synthesis technology and the used fuel dissolution technology. Thus, it can further impact used fuel management and disposition strategies.

Stockpiles of used nuclear oxide fuel from commercial reactors in the U.S. exceed 70,000 metric tons with an accumulation rate in excess of 2000 metric tons per year, which poses great challenges for used fuel management and disposition. It is ideal to convert used commercial fuel to a chloride form, thereby facilitating multiple options for further use, treatment, storage, and disposal. Uranium trichloride (UCl3) plays an important role in the used fuel dissolution technique as the chlorinating agent. Depleted uranium chloride could be used with a base salt to yield a uranium oxide and noble metal fission product stream that could possibly be contacted handled for further treatment, storage, or disposal. Also, use of depleted uranium chloride in the proposed technique would provide a fertile material for a molten chloride salt reactor fuel. Alternately, low-enriched uranium chloride could be used in this system to produce a contact-handled stream of low-enriched uranium oxide (i.e., 3 - 5% enriched in uranium-235 with noble metal fission products) for possible reuse in a light water reactor (LWR). Furthermore, use of low-enriched uranium chloride would provide an additional fissile content, if needed, in a molten chloride salt reactor fuel.

Uranium trichloride (UCl3) plays an important role in the used fuel dissolution technique as a chlorinating agent. UCl3 can be synthesized by various chlorinating agents including PbCl2, CdCl2, CuCl2, BiCl3 and NH4Cl and ZnCl2.1-6 During the U chlorination process for UCl3 synthesis, a highly reactive UCl4 is formed, which is highly corrosive to the stainless steel container.1, 4 XRD demonstrated successful phase identification for UCl3 and UCl4 because UCl3 is tricapped trigonal prismatic while UCl4 is body centered tetragonal (diteragonal-dipyrmidal).5, 8 However, further quantification for chemical speciation of UCl3/UCl4 has never been done. Thus, there is a knowledge gap and great need for quantifiable UCl3/UCl4 chemical speciation to ensure the selectivity of U(III) in the synthesis of high purity UCl3.