Flow analysis in the upper plenum of the micas model in support of the astrid reactor program

The sodium cooled reactor ASTRID project (Advanced Sodium Technological Reactor for Industrial Demonstration) led by the CEA has entered the basic design phase. Current developments are focused on the large equipment such as the vessels. Even if France has a great experience in the SFR technology because of the 90's EFR program, new experiments are needed both to qualify the design options and to validate the code calculations. Since experiments with sodium are more complex to carry out, most tests are conducted in models using water as simulant fluid. According to the dimensionless analysis, experiments can be designed to be representative of the phenomenology to study. The MICAS mock-up of the ASTRID upper plenum was designed regarding this methodology using the Froude number for the free surface flow issues and the Richardson number for the thermal studies. It was built at a 1/6 scale in transparent polymer for optical measurements.First experiments were dedicated to study the free surface flow and the gas entrainment. Experimental conditions, such as the water flow rate, were calculated to get the representative Froude number. From those operating conditions and the MICAS geometry, calculations were led using TRIO_CFD at CEA and Adapco StarCCM+ at AREVA. This article is devoted to present the methodology and the results of the velocity measurements in the MICAS model dedicated to validate the code calculations. A PIV system was used to measure the velocity. As this technique is based on an optical access to two perpendicular planes, its implementation on the MICAS mock-up was complex. Indeed, many immerged components, such as the pump pits and the decay heat exchangers, prevent any optical access in specific areas. Most measurements were performed around the core, the Intermediate Heat Exchanger (IHX) and the Above Core Structure (ACS). The integration of the velocity around the ACS allows calculating the flow rate crossing this structure. As the control rods in the ACS are modeled by porous media, it is an important result to fit the pressure drop coefficient in the code.