Butler-based thermodynamic modelling of interfacial energies for in-vessel corium systems
Résumé
The modelling of transient phase segregation phenomena in corium multicomponent thermodynamic systems is limited especially in the miscibility gap at liquid state that leads to a phase separation (stratification of the liquid phases for corium) which is of tremendous importance. The modelling of the associated phase separation transients in corium stratification is limited by deficiency in the interfacial energy data which are difficult to measure experimentally for these high-temperature systems. The limitations of summarizing the interfacial energies as constant coefficients were observed in a recent work on simulation of the stratification kinetics for a corium pool and the necessity to improve the estimation of interfacial energies. This work tests the efficacy of a thermodynamic approach to evaluate the interfacial tensions, initially proposed for metallic systems. This method is based on the Butler equation and makes use of existing thermodynamic databases for multicomponent systems constructed by the CALPHAD method. In practice, the application of this method to corium systems was performed using the open-source code openIEC. To do so, this code was modified to suit our requirements both functionally and methodically. In particular, the OpenCalphad Gibbs energy minimizer has been interfaced in this framework and code verification against previous results was carried out. Then, interfacial energies were calculated for two relevant corium systems (U-O and U-O-Zr-Fe) using two different existing databases (TAF-ID, NUCLEA). The first results thus obtained were analyzed in terms of general trends and compared with existing theoretical aspects. Large differences observed depending on the thermodynamic database were also investigated.
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