Multiphase Experiments and CFD for Nuclear Reactor Safety Research

While according to the state of the art safety analyses related to nuclear reactor thermal hydraulics are done using system codes, CFD becomes more and more important as a tool to support such analyses. Often multiphase flows are involved in the flow situations that have to be considered. Since the Euler-Euler CFD modelling is not yet mature, experiments are necessary to improve and validate the CFD models.
This lecture will discuss typical topics of Nuclear Reactor Safety (NRS) research related to multiphase CFD. Several experiments done at the TOPFLOW facility of Helmholtz-Zentrum Dresden – Rossendorf (HZDR) to support the qualification of multiphase CFD for safety related issues will be presented. This includes information on the applied two-phase flow measuring techniques. The experiments range from rather generic experiments investigating vertical pipe flows at parameters relevant for safety analyses to experiments that represent specific safety related scenarios. Examples of the latter are counter-current flow limitation in a hot leg model and experiments on a model of a PWR cold leg and downcomer simulator. Finally, the applicability of Open Source codes for nuclear reactor safety research will be discussed and a German project to establish a validated CFD-tool based on OpenFOAM will be presented.