The thermal-hydraulics challenges of a nuclear reactor are numerous and their investigation is crucial for the design and safety of new reactors. Numerical simulation through CFD codes or System thermal hydraulics codes can address a lot of the different challenges; nevertheless the use of water modeling for the study and validation of the thermal hydraulic behavior of a new primary system remains a valuable tool. A water model of the pooltype liquid metal-cooled MYRRHA reactor has been developed at the von Karman Institute in collaboration with SCK•CEN. It is a full Plexiglas model at a geometrical scale 1/5 of the design version 1.2 of MYRRHA. The scaling was performed by respecting as much as possible the Richardson, Euler, Reynolds and Péclet numbers’ similarity with MYRRHA. This transparent water model allows the application of optical measurement techniques for the flow characterization. Different transient tests relevant for MYRRHA have been defined by SCK•CEN. These test cases have been studied using the water model facility. They include the study of the transient thermal hydraulic behavior when switching from forced to Loss-of-Flow (LOF), the failure of a single pump, the failure of one of the four heat exchangers and the loss of coolant inventory (LOC). Results of phenomenological behavior are presented as well as the time–dependent variation of temperatures recorded with different arrays of thermocouples immersed inside the upper plenum.