In order to control oss of coolant accident accidents, the reactors of Generation III + (e.g. AP1000, CAP1000) hold back the melt in the reactor pressure vessel instead of an external core catcher. For this purpose, the reactor pressure vessel is covered with baffles, which are intended to control the flow around the vessel. The inlet is located at the bottom so that the flow can flow to the lowest point of the reactor pressure vessel. There the water heats up and the water-steam mixture is guided upwards through the baffles directly on the reactor pressure vessel. In the upper area of ​​the reactor pressure vessel, the steam is released in order to flow into the containment. The failure criterion for the passive IVR concept is the occurrence of film boiling when the critical heat flux is reached. As part of the SIMA project, a test-section was developed to be integrated into the experimental COSMOS-L system. Based on previous studies on the flow behaviour in the IVR concept, these are simulated in the new test arrangement and the phenomenon of the boiling crisis is investigated.