The sodium oxidation reaction and suppression effect of sodium with suspended nanoparticles – growth behavior of dendritic oxide during oxidation

Abstract

Liquid sodium is used as coolant in fast reactors (FRs), because of its high thermal conductivity and wide temperature range of liquid phase. It has superior thermal medium properties but its chemical reactivity with water and oxygen is very high. Hence, FR plants have to take safety measures regarding these reactions. To develop FR systems for practical use, a better physical and chemical understanding of reaction phenomena and more mechanistic analyses for accidents are desired. Oxidation in the early stage of sodium combustion is especially important regarding the aspect of reaction continuity. The purpose of this study is to understand the sodium reaction precisely in order to apply the knowledge of the sodium reaction to promoting further safety of FRs. In the authors' previous study, it was recognized that dendritic oxide had an important role in the sodium oxidation reaction such as supplying unreacted sodium to the reaction interface. In this study, a mechanistic model for supplying sodium through the dendritic oxide, which is influenced by physical properties and environmental factors, was proposed from the observation results of growth of the dendritic oxide. This mechanistic model provides an explanation of the oxidation behavior, which is consistent with the observation results from the oxidation reaction of sodium with suspended nanoparticles, that sodium with suspended nanoparticles showed a suppression effect on the oxidation reaction due to the difference of dendritic oxide growth behavior.