Contribution to BWR stability analysis. Part II: Numerical approach using a reduced order model

• We study the onset of power oscillations using a reduced order model.
• We afford formulae for decay ratios and frequencies near the stability boundary.
• We found a non-normal operator associated with the dynamics of the regional mode.
• We study some consequences of the meeting of non-normality with nonlinearity.
• A comparison between experimental data and model predictions is done.

Using the reduced order model and its related analysis done in Suárez-Ántola and Flores-Godoy (submitted for publication), we study some aspects of the onset of power oscillations using numerical methods and digital simulations. From the analytical results we illustrate the usefulness of asymptotic methods to describe the change in behavior of the decay ratio and frequency of oscillations near the stability boundary in the reactor’s parameter space. We study through a dynamical simulation a supercritical Hopf bifurcation in the global mode when the effect of the regional mode on the global mode is neglected. We found that the uncoupled and linearized dynamics of the regional mode is closed related with a non-normal operator. Some of the possible consequences of the non-normality are studied using digital techniques reintroducing the effect of the regional mode on the global mode. A comparison between experimental data and predictions obtained from the present reduced order model is presented.