Abstract: The temperature oscillation phenomenon in the upper plenum of the reactor core is one of the key factors affecting the safe and stable operation of lead-based nuclear power plants, and its accurate description is of great significance for the analysis of thermal striping mechanisms. By employing the SST k-ω turbulence model for numerical simulation on this phenomenon, a quantitative analysis of the impact of the three parameters β₁, β₂, and β^* in the model on the temperature results and their uncertainty intervals was conducted, along with a sensitivity analysis of the parameters. The research results indicate that the distribution characteristics of temperature uncertainty are closely related to fluid flow and mixing processes. The temperature uncertainty is relatively low in areas near the nozzles due to the direct impact of the jet, while it is relatively high in the intermediate areas between the cold and hot nozzles due to intense fluid mixing. In particular, the parameters β₂ and β^* have a significant contribution to the uncertainty of the temperature results within the studied range. These findings provide scientific guidance for subsequent model improvements and engineering applications.