Initial Nucleation and Growth Morphology of Uranium Electrodeposited in LiCl-KCl Eutectic

Abstract

In molten salt electrodeposition, a clear understanding of the initial nucleation and growth of nuclei formed on a substrate/electrode is critical to determining the morphology and structure of deposits in order to produce devices and products in various scientific fields. Typically, in the widely researched and demonstrated electrorefining process, most of uranium (U) from the spent nuclear fuel (SNF) are selectively recovered on a solid metallic electrode excluding other fission products. However, the troublesome dendritic structure of uranium deposit has a drastic impact on the entire electrochemical conditions and process efficiency. Thus, a clear understanding in the electrodeposition process and mechanisms of uranium on the electrode/substrate will ascertain the fundamental behind dendritic formation process to guarantee effective separation and extraction. However, up to now, most works has been restrained to explain the fundamental nucleation mechanism using electrochemical methods such as chronoamperometry[1-3]. Currently, B. Pesic took an important first step to reveal the initial morphology of uranium electrocrystallization[4]. However, its nuclei morphology and growth evolution are still not well clarified in molten salt. It is a challenge to obtain and characterize the micro or nanosized nuclei, especially for the very active element as uranium, which is very sensitive to water and oxygen and worse accompany larger amount of solid salts. Therefore, we have designed a detachable disk electrode (DDE) which can easily replace the disk substrate with inessential salt adhering, highly reduce the complexity of experiment operation and enhance the effectiveness and facticity of the visual characterization of initial nucleation[5]. Figure 1 presents the representative SEM image of morphology of U electrodeposited on a GC disk electrode in LiCl-KCl-0.905wt%UCl3 at -50mA for 5s. The highly informative image shows the distinct sites and unique distribution of uranium nucleation. In this work, the nucleation mechanism, morphologies of initial nuclei, growth and evolution of uranium electrodeposited on different substrates (W and GC) will be comprehensively presented and discussed.