Effects of turbulent heat diffusion and viscosity on the simulation of turbulent mixing in autonomous PWR subchannel analysis software

In this paper the turbulent mixing models of several domestic autonomous PWR subchannel software under review by the national nuclear safety administration were evaluated and studied. Firstly, it is found that most of these subchannel software adopt the equal-mass turbulent mixing model. Then, an experimental validation study was performed on the equal-mass turbulent mixing model. Significant variations in the model’s computational coefficients were observed under different operating conditions. Finally, parameter sensitivity analysis and engineering validation were conducted. It is obtained: In single-phase conditions, energy transfer between hot and cold channels is insignificant, while momentum transfer dominates. Effective simulation of turbulent mixing is achieved by adjusting the turbulent dynamic viscosity coefficient M t . In two-phase conditions, energy transfer between hot and cold channels dominates, while the influence of momentum transfer is negligible. Effective simulation of turbulent mixing is achieved by adjusting the turbulent thermal diffusion coefficient K t . In actual PWR nuclear power plant operations, the core condition is primarily a two-phase state with subcooled boiling. Therefore, for the current subchannel software, turbulent mixing is effectively simulated mainly by adjusting the turbulent thermal diffusion coefficient K t , while the influence of turbulent dynamic viscosity is generally neglected.