Abstract: In order to carry out transient safety analysis of PWR cores used for long-lived fission product (LLFP) transmutation, a code system was developed based on CASMO-4, RSIM and modified NLSANMT/COBRA-4. Using this system, the safety feature of LLFP transmuting PWR in rod ejection accidents was studied and the power evolution and maximum fuel center temperature variation were analyzed at both BOL and EOL. The numerical results show that loading ⁹⁹Tc leads to lower peaking power because of more negative moderator temperature coefficient, while loading ¹²⁹I results in higher peaking power. Also, loading ⁹⁹Tc and ¹²⁹I will make fuel center temperature rise up about 127-157 ℃, which is still within the melting point of UO₂ fuel.