Butler‐based thermodynamic modeling of interfacial energies for in‐vessel corium systems

Abstract

The modeling of transient phase segregation phenomena in corium multicomponent thermodynamic systems is complicated especially in the liquid miscibility gap which can lead to phase separation (stratification of the liquid phases for corium) and is of tremendous importance. The modeling of the associated phase separation transients in corium stratification is limited by a 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 of a corium pool and the necessity to improve the estimation of interfacial energies [1,2]. This work tests the efficacy of a thermodynamic approach to evaluate the interfacial tensions, initially proposed for metallic systems by Kaptay [3]. 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 [4]. To do so, this code was modified to enable required features, both functionally and methodically. In particular, the OpenCalphad Gibbs energy minimizer has been interfaced in this framework and benchmarked against previous results. Then, interfacial energies were calculated for two relevant corium systems (U-O and U-O-Zr-Fe) using two different existing databases (TAF-ID and NUCLEA). The first results obtained were analyzed in terms of general trends and compared to existing theoretical aspects. Large differences were observed depending on the thermodynamic database that was used.