[en] The thermal-hydraulic analysis was conducted on the research reactor core for improvement on the primary cooling system of GRR(Greece Research Reactor)-1. In order to design a primary cooling system, key data were provided by the thermal-hydraulic analysis. The COOLOD code was employed to carry out the thermal-hydraulic analysis, but it was for one-dimensional calculation and single channel analysis. It can't reproduce the three-dimensional flow in complex geometries. Although pressure drop through the fuel assembly was one of the most important values to design the primary cooling system, there was no data of it from an experiment or an estimation. It should be certain that the flow distribution between coolant channels was even, since all coolant channels of a plate type fuel assembly were completely separated from each other. However, those can be obtained by conducting an experiment, a quite long time and financial resources contribute to preventing an experiment. Regarding these, the CFD (Computational Fluid Dynamics) method was a very useful alternative to reach a solution to these problems. The CFD method provide reliable and useful predictions instead of experiments due to its applicability to complex shapes which were as real as possible. This is a summary report of CFD analysis for a plate type fuel assembly of GRR-1. In this study, flow distribution between each coolant channel of the fuel assembly was predicted. In order to estimate the pressure drop through the fuel assembly, many calculations were done for various flow rate conditions. A correlation between pressure drop to flow rate was yielded from those calculation results. Temperature distribution was estimated on the fuel plates of assembly at normal operation, and was compared with the prediction results obtained by the COOLOD code. Finally, it was predicted whether or not the uncovered core can be maintained under the core melting point only by air cooling of natural circulation, when the loss of reactor pool water occurs