Coupled Simulation of the NACIE Facility using the RELAP5 Thermal System Code and the CFD Ansys FLUENT Code

Since the Lead-cooled Fast Reactor (LFR) has been conceptualized in the frame of GEN IV International Forum (GIF), ENEA and Pisa University are strongly involved on the HLM technology development. In the present work is presented the activity carried out at the DICI (Dipartimento di Ingegneria Civile e Industriale) of the Pisa University in collaboration with ENEA Brasimone Research Centre, concerning the coupling between thermal Hydraulics system code and Computational Fluid Dynamics (CFD) codes applied to LBE loop facility. In particular this work concern with the application to the NACIE (Natural Circulation Experiment) LBE experimental loop (built and located at the ENEA Brasimone research centre) of the in-house developed coupling tool between a modified version of RELAP5/Mod3.3 and Fluent commercial CFD codes. The first part of the documents deals with the description of the NACIE loop type facility, while in the second part of the work the coupling toll is presented and obtained results are compared to stand alone RELAP5 results and data obtained from the NACIE experimental campaign. Specifically, the set up numerical model is based on a two-way explicit coupling scheme. RELAP5 nodalization of the whole NACIE primary circuit is re-arranged in such a way to split the overall domain into two regions, one to be simulated by RELAP5 system code and one to be simulated using the Fluent CFD code (non overlapping domains); pressure temperature and LBE mass flow rate are exchanged at the boundaries of the two simulation domains. The region simulated by Fluent code is schematized both as 2D axis symmetric domain and as 3D symmetric domain. Comparative analyses among the simulations performed by RELAP5-Fluent coupled codes and by RELAP5 stand-alone code showed good agreement among them, giving positive feedback on the feasibility and capability of the developed coupling methodology.