ABSTRACT

The phenomenon of density-wave instabilities is encountered for certain operating conditions of boiling systems, where they become unstable due to lags in the phasing of the pressure-drop feedback mechanisms. Given the appropriate set of operating conditions, these delays may lead to self-excitation. In this article, the state of the art of the assessment of density-wave instabilities is presented. The application of linear frequency domain analysis is shown for single and parallel channels, under forced and natural circulation. Non-linear effects are studied by means of Hopf bifurcation characterization, leading to the identification of metastable operating conditions, associated with subcritical bifurcations. Finally, the lumped model with finite elements of variable length is analyzed and applied to the simulation of nuclear steam generators.