Abstract: The accident-tolerant fuel (ATF) system is aimed at improving safety characteristics of the nuclear fuel and cladding in a reactor core where active cooling is lost, and is more preferable compared with the current UO₂-Zr system when the reactor is in normal operation. By the feature of advanced materials with improved properties, the ATF system will obviously slow down the progression of accidents, allowing larger margin of time for implementing the mitigation measures. Specifically, by simulating and analyzing the large break loss of coolant accident (LBLOCA) for both the design basis case and the severe accident case which involved in LBLOCA with completely failed emergency core cooling system (ECCS) for a typical pressurized water reactor (PWR) loaded with ATF, preliminary assessment on the performance of the ATF under severe accident conditions was performed in this paper. The results show that ATF could decrease the peak cladding temperature in the LBLOCA for the design base case and delay core melting in the LBLOCA severe accident case, compared with UO₂-Zr, and be of better accident-tolerance characteristics.