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Elucidating the Composition and Structure of Uranium Oxide Powders Produced via NO2 Voloxidation
ACS Omega ( IF 3.7 ) Pub Date : 2024-02-23 , DOI: 10.1021/acsomega.4c00029
Kathryn M Peruski 1 , Tyler L Spano 1 , Matthew C Vick 1 , Chase Cobble 1 , Allison T Greaney 1 , Joanna McFarlane 1
Affiliation  

Voloxidation is a potential alternative reprocessing scheme for spent nuclear fuel that uses gas–solid reactions to minimize aqueous wastes and to separate volatile fission products from the desired actinide phase. The process uses NO2(g) as an oxidant for uranium dioxide (UO2) fuel, ideally producing soluble uranium powders which can then be processed for full recycle. To continue development of the process flowsheet for voloxidation, ongoing examination of the process chemistry and associated process materials is required: discrepancies in the proposed chemical reactions that occur when spent nuclear fuel is exposed to NO2(g) atmospheres must be addressed. The objective of this work is to analyze the intermediate solid phases produced during voloxidation to support verification of the proposed NO2(g) voloxidation reaction mechanisms. This objective was achieved through using (1) powder X-ray diffraction and Raman spectroscopy to identify bulk uranium phases and (2) scanning electron microscopy to describe the morphology and microstructure of the powders at each reaction stage. The initial oxidation of UO2 under NO2(g) reactions produced ε-UO3. Further exposure to NO2(g) did not nitrate the solid to produce uranyl nitrate, as reported in some literature. However, after the powder was hydrated with steam and then further exposed to NO2(g), some traces of uranyl nitrate hexahydrate were found. The results of this study suggest that surface hydration of powders plays a vital role in uranyl nitrate formation under voloxidation conditions and raises questions about the kinetics of the oxide-to-nitrate voloxidation conversion process. Future chemical and engineering design decisions for the voloxidation process may benefit from an improved understanding of these chemical mechanisms.

中文翻译:


阐明 NO2 挥发氧化产生的氧化铀粉末的成分和结构



挥发氧化是乏核燃料的一种潜在的替代后处理方案,它利用气固反应来最大限度地减少含水废物,并将挥发性裂变产物与所需的锕系元素相分离。该工艺使用 NO 2 (g) 作为二氧化铀 (UO 2 ) 燃料的氧化剂,理想地生产可溶性铀粉末,然后可对其进行加工以实现完全回收。为了继续开发挥发氧化工艺流程,需要对工艺化学和相关工艺材料进行持续检查:必须解决当乏核燃料暴露于 NO 2 (g) 气氛时所发生的拟议化学反应的差异。这项工作的目的是分析挥发氧化过程中产生的中间固相,以支持验证所提出的 NO 2 (g) 挥发氧化反应机制。这一目标是通过使用 (1) 粉末 X 射线衍射和拉曼光谱来识别块状铀相,以及 (2) 扫描电子显微镜来描述每个反应阶段粉末的形态和微观结构来实现的。 UO 2在NO 2 (g) 反应下的初始氧化产生ε-UO 3 。如一些文献中报道的,进一步暴露于NO 2 (g)不会使固体硝酸化以产生硝酸铀酰。然而,当粉末用蒸汽水合,然后进一步暴露于NO 2 (g)后,发现了一些痕量的六水合硝酸铀酰。 这项研究的结果表明,粉末的表面水合在挥发氧化条件下硝酸铀酰的形成中起着至关重要的作用,并提出了关于氧化物至硝酸盐挥发氧化转化过程的动力学问题。未来对于挥发氧化过程的化学和工程设计决策可能会受益于对这些化学机制的更好的理解。
更新日期:2024-02-24
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