Turbulent steam jets in enclosed structures: An application to nuclear reactor accident analysis

The primary objective of this thesis is to characterize the behavior of steam jets within an enclosed structures. To satisfy the above objective, the following areas were studied and addressed: (1) study the analytical models of round turbulent jets, (2) to model the turbulent jets using commercially available CFD codes, (3) measure steam convection and stratification pattern within the PUMA Drywell and compare against numerical models. The analytical approach is limited because the solutions for complex geometry and boundary conditions are not readily available. However, the analytical studies provided the necessary understanding of the physical processes involved in turbulent steam jet discharge and convection. From this analytical study, a new mechanistic model of turbulence eddy viscosity model is introduced to replace the ad hoc model recently proposed. Numerical modeling of the current problem allows greater flexibility. Even though the present state of numerical modeling of turbulent flows is still far from complete, the slightly modified k-⪚r; models of turbulent round jets match that of experimental data extremely well. Based on the basic models of axisymmetric turbulent round jets, PUMA DW geometry and boundary conditions specific were developed. The results of these numerical models compared favorably against the PUMA MSLB tests. The 3-D simulations show that the PUMA DW environment was highly stratified and that the temperature and velocity distributions were extremely complicated. Experimentally, it was found that even though the discharged steam was stably stratified in the upper drywell, the PCCS operation was largely unaffected. Additionally, it was determined that DW wall condensation is not a significant factor in containment cooling. Additionally, it was found that homogeneous condensation within the upper drywell was not possible because steam entering the upper drywell was superheated.