Three-Dimensional Calculations of Fluid-Thermal Mixing in a Babcock & Wilcox Plant at Stagnated Loop Flow

Three-dimensional fluid and thermal mixing analysis of a full-scale cold leg and downcomer of a Babcock & Wilcox-designed pressurized water reactor is performed. The impetus of the present study is to provide an accurate estimation of the local fluid temperatures in the cold leg and downcomer when the cold high-pressure safety fluid is injected into the cold leg carrying a hot fluid. Such temperature predictions are needed in resolving the so-called pressurized thermal shock issue in the nuclear industry. The unique feature of this study is the use of the accurate mass-flow-weighted skew-upwind scheme to approximate the convective transport terms in the COMMIX-1A code approximation of the fluid energy equation. This new scheme is shown to considerably reduce the false diffusion that plagued multidimensional thermal-hydraulic applications. The computed fluid velocity patterns and temperature predictions have shown similar behavior to the flow visualization and temperature field measurements in scaled experiments.