Stability and Bifurcation Analyses of Two-Phase Flow Using a Drift Flux Model and Bifurcation Code BIFDD

Nonlinear boiling water reactor (BWR) studies are generally pursued by employing large system codes, like RAMONA and RETRAN. However, detailed investigations using this approach in which parametric studies are to be carried out over large regions of parameter space are very expensive and time consuming. Therefore, it is necessary to use the so-called reduced order models containing a 'manageable' number of system equations incorporating the essential features of the physical phenomena. Since the thermal-hydraulic model determines the main feedback gain and the associated time delay (void feedback reactivity), the modelling of the fluid dynamics is of paramount importance for the reduced order model analyses for BWRs. For a certain set of hydraulic parameter values, the system of nonlinear differential equations describing the fluid dynamics generates the so-called self-sustained density wave oscillations (DWO), which is a typical two-phase flow instability. (authors)