This paper aims to verify the applicability of open source code, OpenFOAM, to internal flows for the use of nuclear power plant flow simulation. For the verification, several representative flow cases are selected (Plain Couette flow ith Pressure Gradient, Cavitation over a sharp-edged circular orifice, Converging-Diverging Nozzle). the simulation results are compared with experimental or theoretical result. Result from Plain Couette flow is similar with analytical solution. And for the Cavitation over a sharp-edged circular orifice, the coefficient of discharge, Cd, is evaluated by experimental result. The Converging-Diverging Nozzle is compressible flow simulation from subsonic to supersonic flow fields. It shows that the flow fiedls are similar with analytical solution and the location of shock are well predicted. Based on this research, future study using OpenFoam is proposed.