Chemical transformations of UF4 under controlled temperature and relative humidity

JOURNAL OF NUCLEAR MATERIALS

卷:557

Article

Pastoor, Kevin J.¹  Dzara, Michael J.¹  Pylypenko, Svitlana¹  Shafer, Jenifer C.^1,2  Jensen, Mark P.^1,2 

[1] Colorado Sch Mines, Dept Chem, Golden, CO 80401 USA

[2] Colorado Sch Mines, Nucl Sci & Engn Program, Golden, CO 80401 USA

关键词: Uranium tetrafluoride;    Nuclear fuel cycle;    Nuclear forensics;    Powder X-ray diffraction;    X-ray photoelectron spectroscopy;   

DOI  :  10.1016/j.jnucmat.2021.153260

来源: Elsevier

【 摘 要 】

Uranium tetrafluoride (UF4) is a critical compound in the nuclear fuel cycle, particularly as an intermediate in uranium hexafluoride (UF6) and uranium metal production, and as a fuel for fluoride-based molten salt reactors. Changes to UF4 in humid air were investigated by aging anhydrous UF4 under various temperature and relative humidity (RH) conditions for up to 9 months. Powder X-ray diffraction (pXRD) and thermogravimetric analysis revealed UF 4 remained largely unchanged during the aging study for most of the conditions investigated (293 and 308 K, and <= 75% RH), consistent with the conventional consideration that UF4 is stable under ambient conditions. However, aging under high RH conditions (>90%) resulted in chemical speciation changes and formation of UF 4 and UF4 hydrate mixtures. Specifically, UF4 . 2.5H(2)O was formed within 30 days for UF4 aged at 293 K and 95% RH. Uranium tetrafluoride hydrates with less than 2.5 waters of hydration were formed within 180 days for UF4 aged at 308 K and 91% RH. These findings represent the first report of UF4 hydrates forming from the reaction of UF4 with atmospheric water vapor at ambient temperatures. Investigation of the surface composition of unaged and aged UF4 samples with X-ray photoelectron spectroscopy revealed degradation of the UF4 surface, consistent with the degradation observed for the bulk UF4 from the pXRD measurements. From a nuclear forensics perspective, these short timeline aging studies suggest that the presence of UF4 hydrate in UF4 materials may indicate it was stored under high humidity conditions. (C) 2021 Elsevier B.V. All rights reserved.

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