Investigating microstructural evolution during the electroreduction of UO2 to U in LiCl-KCl eutectic using focused ion beam tomography
Investigating microstructural evolution during the electroreduction of UO2 to U in LiCl-KCl eutectic using focused ion beam tomography
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DOI：
10.1016/j.jnucmat.2016.07.036
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发表时间：
2016-11-01
影响因子：
3.1
通讯作者：
Shearing, P. R.
中科院分区：
文献类型：
--
作者：
Brown, L. D.;Abdulaziz, R.;Shearing, P. R.
使用熔盐介质对乏核燃料进行后处理是液-液萃取技术的一种有吸引力的替代方法。热电化学法利用二氧化铀的直接、选择性的电化学还原，然后选择性地电镀铀金属。LiLi-KCI共晶中UO2电化学还原为U的热力学预测表明是氧离子活度的函数。UO2电极的微观结构可能会影响盐的Po(2-)。在熔融的氯化锂-氯化钾共晶体系中，填充二氧化铀的“微桶”电极被部分电还原为金属铀。这种部分电还原导致了两种不同的微结构：致密的UO2和多孔的U金属结构，用能量色散X-射线能谱表征。对该电极的五个区域进行了聚焦离子束断层扫描，显示出总孔隙率从外边缘的17.36%到中心的3.91%，与每个位置的预期反应程度相称。在相同的区域，孔的连接性也从88.32%下降到17.86%，并且沿着电还原的传播轴模拟了穿过样品的曲折度，从4.42的值增加到无穷大的值(断开的孔)。这些微结构特征可能会阻碍O2-离子的传输，导致局部Po(2-)的变化，从而导致无法进行电还原。(C)2016年，由爱思唯尔出版。
Reprocessing of spent nuclear fuels using molten salt media is an attractive alternative to liquid-liquid extraction techniques. Pyroelectrochemical processing utilizes direct, selective, electrochemical reduction of uranium dioxide, followed by selective electroplating of a uranium metal. Thermodynamic prediction of the electrochemical reduction of UO2 to U in LiCI-KCI eutectic has shown to be a function of the oxide ion activity. The pO(2-) of the salt may be affected by the microstructure of the UO2 electrode. A uranium dioxide filled "micro-bucket" electrode has been partially electroreduced to uranium metal in molten lithium chloride-potassium chloride eutectic. This partial electroreduction resulted in two distinct microstructures: a dense UO2 and a porous U metal structure were characterised by energy dispersive X-ray spectroscopy. Focused ion beam tomography was performed on five regions of this electrode which revealed an overall porosity ranging from 17.36% at the outer edge to 3.91% towards the centre, commensurate with the expected extent of reaction in each location. The pore connectivity was also seen to reduce from 88.32% to 17.86% in the same regions and the tortuosity through the sample was modelled along the axis of propagation of the electroreduction, which was seen to increase from a value of 4.42 to a value of infinity (disconnected pores). These microstructural characteristics could impede the transport of O2- ions resulting in a change in the local pO(2-) which could result in the inability to perform the electroreduction. (C) 2016 Published by Elsevier B.V.