The advanced validation of a CFD code for containment applications requires the investigation of water steam in the different flow types like jets or buoyant plumes. This paper addresses therefore the simulation of two “HYJET ” experiments from the former Battelle Model Containment by CFX. These experiments involve jet releases into the multi-compartment geometry of the test facility accompanied by condensation of steam at walls and in the bulk gas. In both experiments mixtures of helium and steam are injected. Helium is used to simulate hydrogen. One experiment represents a fast jet whereas in the second test a slow helium-steam release is investigated. CFX was earlier extended by bulk and wall condensation models and is able to model all relevant phenomena observed during the experiments. The paper focuses on the simulation of the two experiments employing an identical model set-up. This provides information on how well a wider range of flowing conditions in case of a full containment simulation can be covered. Some aspects related to numerical and modelling uncertainties of CFD calculations are included in the paper by investigating different turbulence models together with the modelling errors of the differencing schemes applied.