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In this paper, a CFD analysis of the Fuel Pin Simulator (FPS) of the CIRCE-HERO facility built at the ENEA research centre in Brasimone was performed. STAR-CCM+ code was used with the purpose of reproducing steady-state and transient experimental conditions adopting LBE as working fluid. RANS and URANS simulations were performed comparing the calculated temperature trends with the experimental data. In particular, the FPS average outlet temperature was monitored for the transient case and an exhaustive study of the heat transfer between the FPS and the pool during the transient was carried out. The impact of the involved heat transfer phenomena on the FPS energy balance was studied from a quantitative point of view and the relevant difference in terms of thermal inertia between pool and FPS component was pointed out.

With the aim of finding efficient solutions for cross flow turbine (CFT) bi-directional diffusers able to harvest non perfectly rectilinear tidal currents, a 2D CFD analysis of ducted CFTs was carried out with focus on the effects of diffuser shape and yaw angle. The HARVEST hydrofoil shaped diffuser, equipped with a pair of counter-rotating turbines, and a bi-directional symmetrical diffuser were compared in terms of coefficient of power (CP), torque ripple, overall thrust on diffuser and wake characteristics. Slightly better CP were predicted for the symmetrical diffuser, due to the convergent walls that address the flow towards the blade with a greater attack angle during early and late upwind and to the viscous interactions between the turbine wakes and strong vortices shed by the diffuser. A CP’s extraordinary improving resulted when yaw increased up to 22.5° for the hydrofoil shaped and up to 30° for the symmetrical diffuser. Similar behaviour in yawed flows also occurred in case of a ducted single rotor, demonstrating that it is a characteristic of CFTs. The insertion of a straight throat in the diffuser design proved to be an effective way to mitigate torque ripple, but a CP loss is expected.