An Analysis of Possible Mechanisms of Lead Oxide Vapor Formation in the Vapor Bubble Volume

A kinetic model is presented describing the formation of lead oxide vapor in the volume of a vapor bubble in the lead melt with its subsequent dissolution in the lead melt and crystallization in the bubble. The model is implemented in the approximation of homogeneous distribution of reagents and oxidation reaction products in the bubble volume. It is shown that vapor bubbles in the lead melt volume may be considered as chemical “microreactors” producing lead oxide vapor and nanoparticles in the bubble volume. The paper presents the results of calculation by a homogeneous model of the lead oxide vapor concentration in the bubble volume as a function of time and of the conditions for the possible formation of a soluble oxide shell on the bubble surface. The model includes mechanisms controlling lead evaporation and oxidation of lead vapor as it interacts with water vapor in the bubble volume and crystallization of lead vapor on the bubble inside surface with formation of a solid phase shell. Partial transformation of vapor bubbles into gas–vapor bubbles with an oxide shell could potentially affect their further behavior in the lead coolant. However, subsequent transport of the bubbles in the coolant circuit will lead to the dissolution of the oxide shell in the sections with the coolant at a higher temperature that will neutralize this negative effect. Moreover, formation of an oxide shell around the vapor bubbles can cause temporary trapping of hydrogen in the bubble volume.