Experimental investigation on the heat transfer characteristics of argon space containing sodium vapor

Abstract

A large quantity of argon is typically provided at the top of the main vessel of a sodium-cooled fast reactor (SFR) to serve as covering gas. The sodium coolant in an SFR evaporates and mixes with the argon covering gas during reactor operation. This mixed gas has a critical influence on the heat transfer at the top of the main vessel, particularly the temperature of the roof slab. The temperature distribution in the roof slab significantly affects reactor safety as it serves as the pressure boundary of the main vessel. Research on the behavior of sodium vapor has typically employed numerical simulations, and any experimental verifications have generally used simplified experimental models. To study the heat transfer characteristics of sodium vapor and eliminate the influence of simplifications on the results, the Heat transfer Experimental Facility for Argon space at the top of the main vessel (HEFA) was established based on a scaled-down top of the main vessel. The HEFA was employed to analyze influence of sodium vapor on the heat transfer characteristics of the reactor space by evaluating the effects of various heating temperatures with and without liquid sodium on the temperature distributions in the argon and roof slab. Furthermore, the emissivity of the liquid sodium surface was measured. The results show that the radiative absorption effect of sodium vapor primarily occurs near the liquid sodium surface. When the heating temperature was less than 400 °C, the presence of sodium vapor increased the temperature of the main vessel. When the heating temperature was 540 °C, the radiative absorption effect of the sodium vapor was enhanced, reducing the roof slab temperature. The observed phenomena can be considered to ensure reactor safety during the design of SFRs.