applied fracture mechanics

272Applied Fracture Mechanicsapplication is the emergency injection in the cold-leg by the emergency water reported inFigure 5.Figure 5. Mixing phenomena occurring during emergency injectionThese approaches, however, still suffer from considerable user effect and the need for bestpractice guidelines continues. Challenges for the single phase CFD user include theturbulence modeling approach which must be able to adequately simulate the variousmixing regimes which each have their own unique geometry and driving forces. In addition,the wall modeling approach is important. Mixed convection in the down-comer region isexpected and typical CFD wall treatments do not account for this phenomenon.All of the issues associated with CFD for the single phase PTS issue are compounded in themulti-phase problem by the relative immaturity of the multi-phase CFD techniques. For thenear future, system analysis codes will still provide the overall system behavior andexperimental results will provide the best source of information on the details of the multiphasebehavior related to PTS [14].For reliable simulation of PTS related mixing processes the CFD methods must be validatedto determine how well the CFD model, dened by the detail level of model geometry, themesh and the used numerical and physical models can simulate the relevant physicalprocesses and produce the needed data. The nal target data of thermal hydraulic analysisare the pressure and temperature elds on structures needed as an input for structuralanalysis. The CFD model should be able to model the complex mixing and straticationprocesses in the cold legs and the down-comer of the pressure vessel as well as the heattransfer between uid and structures accurately enough to reproducethis data. In the Figure6 an example result of the CFD calculation of the temperature profile inside the down-comeris provided.