To utilize the Northern Sea Route as a future commercial maritime transport route, a container ship with nuclear power and icebreaking capability was considered as an alternative to fossil fuel engines due to better reliability and reduce greenhouse gas emission. SMART was selected due to the possibility of near-term deployment and a high degree of safety, and a trans-critical CO2 cycle was considered for its power conversion system because of its expected good performance under the selected sailing environment. In part 1, major components and passive systems were designed based on thermodynamic cycle optimization. In part 2, GAMMA + code is modified to simulate CO2 two-phase flow, and the code is validated with experimental data. SMART with trans-critical CO2 cycle is modeled with the modified GAMMA + code to check the controllability of the system under icebreaking conditions, and evaluate safety after an accident event with CO2 Passive Residual Heat Removal System (PRHRS), using a natural circulation loop.