RELAP5 one-dimensional two-phase flow code is thermally coupled with ACE-3D multi-dimensional two-phase flow code for analyses of thermal-hydraulic behavior of a heat exchanger. RELAP5 code is suitable for analysis of one-dimensional flow in heat exchanger condenser tubes of interest, but is inappropriate for multi-dimensional flow analysis required to simulate flows in a large volume secondary water pool. Therefore, ACE-3D code is coupled with RELAP5 code as if it works as a subroutine of RELAP5 code. RELAP5 code gives the thermal boundary condition to ACE-3D code and takes the ACE-3D calculation results as the boundary conditions. This paper introduces the coupled code with some calculation results. Key Words: PCCS, RELAP5, ACE-3D, thermal-coupling, ROSA-V, LSTF
