Modification of FROBA code and its application in Thermal-Mechanical analysis of the Single-Cell thermionic fuel element

In view of the high temperature of the single-cell Thermionic Fuel Element (TFE), the fuel mass transfer model was developed and the mechanical model was modified by considering fuel creep and fuel cracks in this paper. Afterwards, implemented models were verified by comparing with the results in the reference or calculated by Matlab or BEEs (a fuel performance analysis code developed upon the open-source MOOSE framework). Further, the thermal–mechanical performance simulation of the single-cell TFE under the normal operation was carried out. The results indicate that the fuel pellet gets in contact with the emitter due to radial mass transfer. Driven by axial mass transfer, the axial distribution of power and temperature are flattened, and the maximum temperature is decreased. Although the single-cell TFE is safe at normal power, once the power is raised due to unfavorable factors, the central channel may be blocked, leading to excessive emitter deformation and increasing the risk of short circuit of the fuel element.