Modelling of the external cooling circuits of the E-SCAPE scale facility in forced and natural circulation mode using CFD tools

The present work presents an internship which was performed in collaboration with the SCKCEN staff in the frame of the research project leading to the design, the building and the commissioning of the MYRRHA reactor (Multi-purpose hYbrid Research Reactor for High-tech Applications). MYRRHA is a multi-purpose pool-type fast neutrons reactor where the cooling medium used is a Lead Bismuth Eutectic Alloy (LBE). Moreover, it is an "Accelerator Driven System" prototype whose subcritical core will be "fed" by spallation neutrons. This kind of reactor is highly economical, enhances safety and has minimal waste production. In particular, the present work focuses on the thermal-hydraulic behaviour of the E-SCAPE facility (European SCAled Pool Experiment) which was built to provide designers and safety experts with an experimental tool that would mimic the circulation of the coolant in MYRRHA during forced and natural circulation and that would validate the CFD and system codes that are being used in the design of the MYRRHA reactor. E-SCAPE was designed with a scale factor close to 6, working with the same cooling fluid (LBE) and using an electrical core that emulates a 100 kW nuclear core. However, unlike MYRRHA’s configuration, the primary cooling circuits, the pumps and the heat exchangers have been placed outside the vessel due to geometrical constraints. During this internship, a CFD model of the E-SCAPE external loops has been developed, in order to complete the existing model of the vessel. The goal was to analyse steady-state and transient conditions during operational conditions and accidents and to investigate flows (especially complex 3-D flow phenomena). The external circuits model should guarantee a good compromise between the number of nodes (and thus the number of meshing elements) and the amount of details, especially to limit the extra computing time of the complete model in transient. Various modules emulating E-SCAPE components (pumps, heat exchangers, valves,...) needed to be added in order to increase the efficiency of the model, especially to simulate heat transfer for low molecular Prandtl number fluids such as LBE. The validation of each component was done using manufacturers data, theoretical analysis and first experimental data (even if a full experimental data set will only be available from the end of the year 2016). Moreover, the implementation of this model was necessary in order to validate and assess the limitations of the existing system codes of the facility (with regards to the CFD model and experimental data). Those system codes are less accurate (and inadequate to simulate three dimensional flows) but faster and easier to run. The final goal is to be able to use both validated models for the simulation of MYRRHA’s behaviour and to know when system codes can be used or when their accuracy is too limited and CFD tools have to take over. The results of this study will be presented in the final report of the project following this internship.