The Reactor Cavity Cooling System (RCCS) is one of the new safety features that will be incorporated in the High Temperature Gas-Cooled Reactors design (HTGR). The system was designed to remove the heat from the reactor cavity and maintain the temperature of structures and concrete walls under desired limits during normal operation (steady-state) and accident scenarios. A small scale water-cooled experimental facility was built in order to study the complex thermohydraulic phenomena taking place in the RCCS. The facility consists of a stainless steel vessel with electric radiant heaters and a set of nine riser pipes where water, driven by natural circulation, flows upward removing the heat from the cavity. Lower and upper manifolds connect the nine risers from and to a water tank located on top of the cavity. A steady-state run was performed to study the thermal-hydraulic behavior of the system, to observe the onset of natural circulation of the coolant in the loop and to better understand the complex heat transfer mechanisms through the reactor cavity. The present paper describes the procedure adopted to reach the steady-state conditions at a give working temperature. Coolant and pipe walls temperature profiles were recorded during the experiment as well as coolant flow rate. A detailed description of the experimental facility, instrumentation installed and procedures will be provided. The data collected during the experimental activity showed interesting behavior of the water through the nine risers and asymmetries in the temperature profiles of water and risers walls. The data produced are of importance in the system codes and computational fluid dynamics codes validation.