Abstract
Under humid conditions, uranyl fluoride ([(UO2F2)(H2O)]7·4H2O) undergoes a loss of fluorine to form a uranyl hydroxide species, which can be further hydrated to form a uranyl peroxide species. X-ray diffraction data of the uranyl peroxide product is presented for the first time. In addition, the temperature and humidity conditions under which these reactions occur have been clarified by a 220-day experiment using microRaman spectroscopy to track chemical changes in individual particles of uranyl fluoride. At 25 and 35∘C, uranyl fluoride is found to be stable at 32% relative humidity but not stable at and above 59% relative humidity. We show that water vapor pressure is the driving factor in formation of both the hydroxide and peroxide products. The kinetics of the transformation from uranyl fluoride into uranyl hydroxide is consistent with a denucleation reaction following the absorption of water molecules.
Original language | English |
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Article number | 151889 |
Journal | Journal of Nuclear Materials |
Volume | 529 |
DOIs | |
State | Published - Feb 2020 |
Funding
In conclusion, the degradation of uranyl fluoride ([(UO 2 F 2 )(H 2 O)] 7 ·4H 2 O) in humid conditions has been more fully characterized with complementary XRD and microRaman hydration experiments. As demonstrated previously, uranyl fluoride is unstable in humid conditions ( ≥ 59% RH at 25 ∘ C and ≥ 50% RH at 35 ∘ C), transforming into a uranyl hydroxide hydrate that can be converted into a uranyl peroxide species. Structural confirmation of the production of uranyl peroxide in this degradation pathway is shown for the first time. Transformation of uranyl fluoride to uranyl hydroxide is proposed to occur in a denucleation reaction, which is consistent with the kinetics of the observed reaction. Additional work is required to better characterize the second observed reaction, from the uranyl hydroxide product to the uranyl peroxide product, which remains more elusive. This material is based upon work supported by the US Department of Homeland Security under grant award number 2012-DN-130-NF0001 . The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the US Department of Homeland Security.
Keywords
- Degradation
- Raman spectroscopy
- Relative humidity
- Uranium
- Uranyl fluoride
- Uranyl hydroxide
- Uranyl peroxide
- X-ray diffraction