Abstract: To avoid dead pipe segment and thermal stratification hazard, the dead pipe segment and thermal stratification hazards among primary loop related pipes for new type PWR based on experience and nuclear island system design features were analyzed in the paper. Having screened out those pipes in which the hazard could occur, the residual heat removal pipe CFX simulation was carried out typically. Final results show thermal stratification temperature distribution and downstream pipe segment temperature rising between two isolation valves filled with coolant originally. In conclusion, the residual heat removal pipe meets the requirements of thermal stratification criteria generally, and the dead pipe segment hazard may occur in pipe segment between two isolation valves, but could be prevented by means of layout adjustment. Besides, results show the characteristics of buoyancy recirculation and vortex impingement from primary loop flow on residual heat removal pipe.