Numerical study on the thermal stratification characteristics of the primary system for Lead-based cooled Fast Reactor

Thermal stratification in Lead-based cooled Fast Reactors (LFRs) may cause thermal stress and thermal fatigue of the reactor components, thereby jeopardizing the operating safety. This study presents a thermal stratification analysis of the primary system of LFRs, utilizing the computational fluid dynamics method to assess both the steady-state condition and the loss of flow accident. Under the steady-state condition, thermal stratification is observed within the upper plenum and upper region of the cold pool of the LFRs, but it is not pronounced enough to pose a a significant threat to the structural safety of the reactor. Under the loss of flow accident, the thermal stratification phenomenon in the upper plenum and the cold pool exhibits a pattern of rapid intensification followed by gradual relaxation over time. Specifically, stratification interface in upper plenum persists and stratification number increases, while in the cold pool stratification interface decreases and stratification number remains constant. Furthermore, stratification number in the upper plenum is more than that in the cold pool, indicating that thermal stratification is more pronounced in the upper plenum. This study serves as a valuable reference the analyzing thermal stratification in the primary system of LFRs.