In case of Main Steam Line Break scenarios, several thermal hydraulics phenomena, such as two-phase critical flow, wall condensation, and stratification of the atmosphere of the containment are involved. The RIVA facility is devoted to the study of such phenomena by means of a fast blowdown of a vessel discharging in a containment. A valve near the inlet of the containment vessel with a fast opening actuator is used to simulate the sudden break of the secondary loop of a nuclear reactor. The entire device is highly instrumented, especially the containment with more than 200 thermocouples. Moreover, two instrumentation sections on the connection pipe allows us to measure local pressure, pressure drop and local temperature before the inlet of the vessel. At first, some experiments are realized by replacing steam by nitrogen, to understand the behavior of the fluid during a very fast blowdown, changing the outlet section of the line. These experiments indicate that a chocked flow is present and allow us to study the influence of temperature, mass flow rate and pressure at the injection section on the jet plume in the vessel. Subsequently, experimental tests with steam and then with some structures in the containment vessel have been realized. They have allowed a better understanding of the wall condensation phenomenon and the effects of the volume occupation rate. The analyses of the results are not presented in the document but will in coming articles. In the same way, further experiments with a steam blowdown have been performed to take into account the wall condensation and will be the subject of a future article.