Estimation of melt oxidation kinetics

The analysis of the viscous melt behavior in the CORA and QUENCH bundles and the image analysis of the frozen melt show the formation of ceramic precipitates in the melt even in the molten state. The driving mechanism for the formation of precipitates in the melt is the temperature gradient at the oxide-melt interface. The high temperature Prater-Courtright correlation, used usually in computer codes to simulate the oxidation of Zr melt, was obtained based on the oxidation of very thin samples, which does not allow taking into account processes in the bulk melt. Simulation of the melt oxidation by the mechanistic SVECHA code, verified on the basis of many crucible tests, gives more correct result. This takes into account not only the formation of an external oxide layer around the molten pool, but also the formation of ceramic precipitation inside the melt. A numerical calculation carried out for the case with an operating temperature of 2473 K and a temperature gradient at the melt boundary of 50 K showed that the oxidation process occurs parabolically and three times faster than predicted by the Prater-Courtright correlation. The estimated activation energy for the melt oxidation correlation of Arrhenius-type proposed on the basis of SVECHA calculations is 85.9 kJ/mol, which is noticeably lower than the Prater-Courtright activation energy of about 110 kJ/mol.