The TAPIRO (TAratura Pila Rapida a Potenza zerO, Fast Pile Calibration at 0 Power) is a fast neutron source reactor located in the Centre of ENEA Casaccia, Italy. This research reactor has been operated since 1971 for investigation on neutron propagation in fast reactors components, fast neutron irradiation damage analysis supporting fusion energy program and aerospace applications, testing of innovative detectors for Large Hadron Collider programs, training and education. In the present paper a thermal-hydraulic analysis is carried out with different approaches to characterize the core cooling system of the TAPIRO reactor in order to compare the results obtained with the present methods and calculation tools, with those evaluated during the reactor project phase. Two different methods have been used for such analysis, one by TIESTE-MINOSSE code for a preliminary analysis and one by RELAP5-3D code for a best estimate analysis. Calculations concern the steady state at nominal power and two kinds of transients (loss of flow and a reactivity insertion). Comparison with experimental data has been performed.