• boundary control
• code coupling
• computational fluid dynamics
• Galerkin projection
• Proper Orthogonal Decomposition (POD)
• reduced order modeling

The present thesis work has been developed during a six-months internship period at the Belgian Nuclear Research Centre SCK CEN; it aimed at gaining a deeper insight into the coupling methodology between System Thermal-Hydraulic and Computational Fluid-Dynamics codes, into the Reduced Order Model techniques and its possible applications in the nuclear field. In this work, a computational tool has been developed coupling the System Thermal-Hydraulic code RELAP5/mode3.3 and the ITHACA-FV code as Reduced Order Computational Fluid-Dynamic Model. ITHACA-FV code (In real Time Highly Advanced Computational Applications for Finite Volumes), is a C++ library based on the finite volume solver OpenFOAM currently developed and maintained at SISSA (International School for Advanced Studies, Trieste, Italy). To demonstrate the capabilities of the new computational tool, a series of case has been set up and the obtained results were verified against the predictions of the coupled tool RELAP5-OpenFOAM 6.0. Firstly, the simple pipe flow has been tested and, subsequently, the flow reversal and to the closed loop system were also investigated. Afterwards, the heat transport equation for temperature has been introduced in the Reduced Order Model, applying the coupling procedure to the non-isothermal test case. The analysis conducted have demonstrated the reliability of the Reduced Order Model: it was successfully used in the frame of the coupled calculations.