Iron-based alloys have been considered as promising candidate material to replace zirconium-based alloys as fuel cladding based on the previous experience of the first generation of pressurized water reactors (PWR). Moreover, the safety margins of nuclear fuels can be improved by means of additives in the fuel pellet, as beryllium oxide (BeO), due to the increase of the fuel thermal conductivity. These efforts are part of the accident tolerant fuel (ATF) program which aims to develop nuclear fuel systems with enhanced performance under normal operation, design-basis accident and severe-accident conditions. This paper addresses the combined effects on the fuel performance considering the BeO additive in the fuel pellet and stainless steel 348 as cladding material under steady-state and loss-of-coolant-accident (LOCA) scenario. The fuel performance simulation and assessment are conducted using modified versions of well-known fuel performance codes (FRAPCON/FRAPTRAN). The obtained results have shown that the studied fuel system (stainless steel cladding and UO2-BeO) enables an improvement in the main parameters associated to the fuel safety margins under steady-state irradiation as well as LOCA scenario.