Analysis of thermal stratification phenomena in the CIRCE-HERO facility

Analysis of the temperature distribution in the pin bundle of the CIRCE facility

“…This results in a relevant temperature difference between the fluid inside the FPS and the one in the pool leading to heat transfer phenomena that cannot be neglected in the energy balance of the FPS component. Consequently, calculations considering an imposed temperature or convective conditions were performed; in particular, a heat transfer coefficient of 2000 W/(m 2 K) was selected since it granted the best results for the starting steady-state condition and it was found as a suitable value in agreement with what obtained in the previous work of Buzzi et al (2020). In both cases, the external temperature is the one measured in the pool at the beginning of the transient, maintained constant during the calculation.…”

“…In this work a Prt of 1.5 was set in accordance with the other previous CFD studies on heat transfer in liquid metals (e.g. Martelli et al, 2017 andBuzzi et al, 2020) where a Prt in a range of 1< Prt<3 was considered.…”

“…Four simulations with different thermal boundary conditions imposed at the FPS external walls were performed for the reference case in order to assess the best predicting capabilities. The imposed conditions are adiabatic condition (no heat exchange with the pool) and convective conditions adopting three different heat transfer coefficients, 1000, 2000 and 5000 W/(m 2 K) in similarity with the previous work Buzzi et al (2020). For the cases in which a convective condition was considered, the environmental temperature was set in accordance with the measured pool axial temperature.…”

“…In particular, the temperature distributions inside the fuel pin simulator of the CIRCE-HERO facility were analysed. In addition, the information gained in previous work (Buzzi et al, 2020) regarding the heat transfer between pool and FPS was taken into account. Indeed, in the present paper, the impact of different imposed thermal boundary conditions on the FPS fluid temperature distribution was evaluated, underlining relevant differences between the steady and transient conditions.…”

STH/CFD Coupled Simulation of the Protected Loss of Flow Accident in the CIRCE-HERO Facility

“…This operation was performed in order to provide the coupled code with the capability to simulate the thermal stratification phenomena observed in the experimental results inside the pool. In particular, considering the results of a parallel work performed at the University of Pisa focusing on the prediction of this phenomenon in a CFD stand-alone application [22], heat transfer was assumed occurring through the thermal structures of the FPS and of the Fitting volume providing interesting results, the same surfaces are thus again considered for the present coupled calculation. During nominal operation conditions, the pool is in fact heated through these surfaces by the hot fluid flowing inside the CIRCE-loop; during the simulated accident, instead, more complex phenomena occur and heat transfer in both directions may be obtained as clearly highlighted later in this paper.…”