Study of Chemical Changes in Uranium Oxyfluoride Particles Progress Report November 2009 - July 2010

Progress in Uranium Chemistry: Driving Advances in Front-End Nuclear Fuel Cycle Forensics

“…For the two samples stored in less than 33% RH, their MRS spectra remained unchanged, which indicates that UO 2 F 2 particles are relatively stable when stored under these conditions. This result seems to contrast the earlier-discussed observations of Kips et al for samples stored in dry conditions (<15% RH); however, Kips et al reported that, following the initial fluorine loss during the first several weeks of storage in dry air, the fluorine loss for UO 2 F 2 was minimal on a yearlong time scale, indicating that the decomposition had stabilized or occurred at a very slow rate . The p-XRD pattern of the initial bulk material matched favorably with the expected hydrated UO 2 F 2 pattern.…”

“…There have been a few recent vibrational spectroscopy studies of UO 2 F 2 particulate created by hydrolysis of UF 6 (eq ), primarily using MRS. Kips et al studied UO 2 F 2 created in an aerosol deposition chamber, ranging in size from 0.1 to 1 μm diameter, deposited on graphite planchets. , They observed the intense uranyl stretching peak at either 865 or 863 cm –1 and the weaker U–O bending peak around 180 cm –1 . For reference, the range of symmetric uranyl stretching frequencies is approximately 800–900 cm –1 for various uranyl compounds .…”

“…Next, Kips et al investigated fluorine loss during storage under varying levels of humidity. , Using SIMS and MRS, they analyzed UO 2 F 2 particles stored in an inert atmosphere, dry air (<15% RH), moderately humid air (30–43% RH), and high-humidity air (70–76% RH). Using SIMS, they measured the 19 F + / 238 U + ratio for the particles, and while there was large variability of the measured ratio for each storage condition, their results demonstrate a general trend that increasing humidity tends to increase fluorine loss.…”

“…Using SIMS, they measured the 19 F + / 238 U + ratio for the particles, and while there was large variability of the measured ratio for each storage condition, their results demonstrate a general trend that increasing humidity tends to increase fluorine loss. Using MRS, they observed the strong uranyl stretching peak at 865 or 863 cm –1 for samples stored in an inert atmosphere. , The MRS spectrum for particles stored in dry air showed the uranyl stretching peak at around 863 cm –1 and an additional peak around 845 cm –1 , likely also from uranyl stretching. The spectrum for samples stored in moderately humid air also showed uranyl stretching peaks at around 863 cm –1 and 845 cm –1 .…”

“…Recent research has also investigated elemental and chemical impurities present in process samples of uranium compounds, also with a focus of discerning process history as well as the origin of the uranium. − ,,,− For example, the concentrations of rare-earth elements (REEs) have been found to be potentially useful for identifying the origin of UOCs . Other research has focused on understanding the degradation of uranium compounds, particularly under environmental conditions. − These efforts are important for nuclear forensics investigations of aged materials or samples exposed to the environment. For instance, various UOCs stored in controlled relative humidity (RH) and temperature conditions have undergone chemical reactions, converting them to different uranium compounds. ,− One final focus area has been developing improved or new analytical techniques for probing various key uranium compounds. − For example, laser-induced breakdown spectroscopy (LIBS), which can be packaged in a field-deployable form factor, has been studied as a possible technique to rapidly identify various uranium oxides and UO 2 F 2 . , Overall, the significance of the recent research and the growing importance of nuclear forensics is evident in the proposal and establishment of Nuclear Proliferomics, a field of study focused on building comprehensive databases of nuclear materials’ properties that could be leveraged through various data analytics and machine-learning techniques to advance nuclear forensics analyses …”