Effect of superheat on non-equilibrium condensation in nuclear steam turbines

Abstract

In nuclear power turbines, the inlet steam typically operates near saturation conditions, making non-equilibrium condensation of wet steam more severe. The presence of wet steam not only affects turbine performance but also poses safety concerns. This study investigates a large nine-stage nuclear power turbine to explore the impact of non-equilibrium condensation under varying inlet steam superheat levels on flow characteristics and performance losses. First, a suitable condensation model for nuclear turbines was selected and validated by comparing simulation results with experimental data from high- and low-pressure nozzles. Based on the Euler–Euler multiphase flow approach, the pressure, temperature, and wetness distributions were analyzed for superheat levels of 0 K, 1 K, 5 K, and 10 K. The associated stage losses and efficiency variations were also evaluated. Results indicate that appropriately increasing the steam superheat can effectively delay the onset of condensation, significantly reduce exit wetness and wet steam losses, and improve both the efficiency of the final stage and the overall thermodynamic performance. Specifically, increasing the superheat by 10 K reduces the exit wetness by 12.5 %, lowers wet steam losses by 14.3 %, and raises the final-stage efficiency to 83 %. The findings of this study offer theoretical insights and engineering references for understanding thermodynamic processes and ensuring the safe and efficient operation of large nuclear steam turbines.