According to the characteristics of reactor types for present 1 000 MW level nuclear power units in China

two types of exhaust pipe for direct air cooling system applied for different reactor types were put forward. Focusing on the steam flow distribution and flow resistance problem

the hydraulic characteristics for the two different pipe layouts were simulated by using the computational fluid dynamics(CFD) method. The results show that

the branches flow symmetrically distributes about the upper central tee joint

with the maximum flow at the two branches in the middle. The flow distribution of each branch is uniform

and the flow deviation is controlled at about 5%. The system flow resistance is strongly related to the back pressure

the lower the back pressure

the greater the system flow resistance. The system flow resistance increases with the steam flow under the same back pressure condition

the order of the system flow resistance value was: EPR1000(quadruple-flow)AP1000 EPR1000(sextuple-flow)CPR1000. The results can provide technical support for further engineering practice.