Implicit Coupling of Fluid-Dynamic Systems: Application to Multidimensional Countercurrent Two-Phase Flow of Water and Steam

The German ATHLET thermal-hydraulic system code has been coupled with a two-dimensional module simulating the downcomer of a pressurized water reactor. To be efficient, this coupling had to be implicit in time. The countercurrent two-phase flow of water and steam in the downcomer of a reactor pressure vessel was simulated using this combined code system. The implicit coupling procedure, as well as the results of a postcalculation of an experiment of the Upper Plenum Test Facility, are described.