Numerical research on the thermal-hydraulic characteristics of the large sodium-cooled fast reactor roof slab

The roof slab of a large sodium-cooled fast reactor is a structure subjected to bottom heating and external cooling. Preserving the roof slab's integrity is paramount for ensuring the safety of the fast reactor, which is profoundly influenced by the temperature distribution. However, owing to its intricate internal configuration, obtaining a detailed and comprehensive temperature distribution of the roof slab is challenging. To address this, a refined and comprehensive 1:1 prototypical model of the fast reactor roof slab was established and subjected to numerical calculations. These calculations determined the thermal-hydraulic characteristics of the roof slab during operating conditions, as well as the natural circulation characteristics within the annular gaps. In order to assess the reliability of the calculation methods utilized for evaluating the thermal-hydraulic properties of the fast reactor roof slab, this study developed a scaled-down model based on the scaled-down Heat-transfer Experimental Facility for Argon space at the top of the main vessel (HEFA). A comprehensive comparison was conducted between the calculated results and the corresponding experimental data. The resulting discrepancy was found to be less than 3%, indicating the effectiveness of the employed calculation methods and the credibility of the obtained results. Finally, an empirical temperature-Ra equation for the fast reactor roof slab under operating conditions was obtained by fitting the calculation results. This research provides a valuable reference for the design of the fast reactor roof slab and its associated penetration. © 2024