Studies of Helium Behavior in Uranium Hexafluoride

Technical Report · Sun Sep 01 04:00:00 EDT 2024

DOI:https://doi.org/10.2172/2498446· OSTI ID:2498446

Richards, Jason M. ^[1]; Trowbridge, Lee D. ^[1]; Jennings, Harold ^[1]; Davis, Tara A. ^[1]; Singleton, Michael ^[2]; Fugate, Glenn A. ^[3]

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1. Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
3. Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)

Several issues have arisen from experimental observations and/or theoretical postulation related to the behavior of helium in uranium hexafluoride (UF₆) matrices and how it may impact the ability to use this noble gas to quantify the fill date of the cylinder. A series of experiments was conducted to address several such issues, and the results and implications are reported here. Two issues relate to bias in the helium measurement due to ambient air from extraneous sources such as atmospheric air or from potential holdup in a large, activated alumina chemical trap. These issues are really a question of differential retention of helium versus three other inert gas isotopes (representative of other noble gases found in air) used as a calibration for air in leakage. Discernable bias was not detected in either case. Another issue had to do with helium potentially brought into the cylinder by a liquid UF₆ fill and subsequently released as the material solidifies and/or during storage. The solubility of helium in liquid UF₆ was measured to investigate this theory. The experiment quantified the potential magnitude of the initial helium contribution if present. The final issue was that of retention of helium in solid UF₆. Investigation of this theory necessitated quantifying both the solubility and the diffusivity of helium in UF₆. In one experiment, the solubility was measured at cryogenic temperature, allowing quantification of helium in solid UF₆ such as would be found in a cold trap. In a second experiment, transport of helium into and through a macroscopic plug of solid UF₆ was examined. The transport was very slight although apparently detectible. Effectively, only an upper limit to the transport could be determined, but that limit implied that helium holdup in solid UF₆ is a real possibility.

• Research Organization: Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-00OR22725
• OSTI ID: 2498446
• Report Number(s): ORNL/TM--2024/3613
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY