Simulation of operational conditions of HX-HERO in the CIRCE facility with CFD/STH coupled codes

The paper describes the application of a coupled methodology between Fluent CFD code and RELAP5 System Thermal-Hydraulic code developed at the DICI (Dipartimento di Ingegneria Civile e Industriale) of the University of Pisa. The methodology was applied specifically to the LBE-water heat exchanger HERO located inside the S100 vessel of the CIRCE facility, built at ENEA Brasimone Research Centre, to investigate the capabilities of this component. In the proposed methodology, the primary side of the HX-HERO, containing LBE, is simulated by the CFD code, while the secondary side, containing a two phase mixture of water and vapour, is reproduced by the System Thermal-Hydraulic code. During the calculation the two codes exchange, at the coupled boundaries: the bulk temperature and heat transfer coefficient of the ascending water (RELAP5 to Fluent) and the wall temperature at the water side surface of the pipes (Fluent to RELAP5). The coupling technique was tested by comparing the numerical results with the experimental data recently obtained by ENEA; the numerical results predicted well the qualitative trend of the temperature and provided an overall good prediction of the temperature also from a quantitative point of view. It is worth noticing that this good performance remained reliable for all the cases simulated, proving the general applicability of the methodology.