Thermal-hydraulic characterization of the CIRCE-THETIS facility key components by means of CFD and STH codes

This work is conceived to make a further step in the pre-test analysis of the CIRCE-THETIS facility, which employs LBE as primary coolant, by conducting detailed numerical simulations of the fitting volume and of the helical coil steam generator. The new fitting volume double-wall configuration was simulated through a CFD code to estimate the reduction in the heat loss with respect to the previous geometry. Concerning the heat exchanger, both STH and CFD codes are used to properly study the two-phase water behaviour and the LBE flow in the shell side of the steam generator. Density wave oscillations were observed and investigated in the STH simulation. Turbulence and other 3D phenomena were studied in the CFD environment. The steam generator was tested with different CFD turbulence models to choose the most appropriate one for the present study. The agreement between the two codes, specifically tuned for the heat exchanger analysis, was investigated by conducting several simulations with different boundary conditions. Limitations and capabilities of STH and CFD codes in dealing with complex systems, such a helical coil steam generator, were discussed as well. Eventually, a new steady state CFD simulation of the entire CIRCE-THETIS facility was conducted after the update of the models for the fitting volume and steam generator relevant developed in the frame of this work.