Review of high temperature thermochemical properties and application in phase-field modelling of incipient melting in defective fuel

In a defective fuel element, fuel oxidation may occur that may affect the thermal performance of the fuel element thereby increasing the potential for centreline melting. A review of UO2+x material properties is presented, and methods of extrapolation to melting conditions are, where necessary, recommended based on mechanistic considerations and self-consistency among the properties. These properties are implemented in a phase-field model derived through the theory of irreversible processes to simulate coupled heat and mass transport in the presence of a dynamic, non-congruent phase change. Simulation results are presented for centreline melting in operational, defective nuclear fuel showing that centreline melting is a self-regulating process.