A computer program is developed to simulate the fluid and thermal mixing of the Electric Power Research Institute/Creare one-fifth-scale tests. The mass-flow-weighted skew-upwind differencing scheme (SUDS), as well as the upwind differencing scheme, and the k-∈ two-equation model of turbulence in cylindrical coordinates are employed in the numerical simulation. The computational results are compared with experimental data of test numbers 42, 46, and 51 and COMMIX results. The numerical diffusion is significantly reduced by SUDS, and a satisfactory prediction is achieved.