The PRORIA code and its recent modifications are described here. The PRORIA code analyzes the transient response of the core against the reactivity increase caused by the control rod rapid withdrawal. The code solves and analyzes neutronic and thermal–hydraulic equations simultaneously. The code is designed for western PWR-type reactor performance. The equations representing thermal–hydraulic and neutronic should be modified to use the code to analyze VVER-1000 reactor core transients, because The VVER-1000 reactor fuel has a central hole in the fuel pellet. In a cylindrical solid fuel pellet, operation of an oxide fuel material at high temperature alters its morphology and the inner region is restructured to form a void at the center surrounded by a dense fuel region. Most of the restructuring occurs within the first few days of operation with slow changes afterward. Hence, the effects of a central hole in mathematical equations and in the transient are investigated. After the code modification, three accident scenarios with control rod ejection are simulated. The results are in good agreement with those reported in the plant’s FSAR. The results show that the peak fuel temperature in the hot fuel pin is lower than what the original code predicts by 150–500°C. Furthermore, the Doppler reactivity effect, when the fuel pellet has a central hole, is higher than the solid fuel pellet.