Space independent xenon oscillations control in VVER reactor: A bifurcation analysis approach

•Gross nonlinear xenon induced instabilities are studied in a VVER reactor.•The phenomena are studied through a Hopf bifurcation analysis.•A Washout filter control methodology is proposed as a way to suppress the instabilities.•The control approach is quite feasible with regards to safety aspects of the reactor operation.

A comprehensive parametric bifurcation analysis has been carried out in order to control space independent xenon instabilities in a reduced order model of VVER 1000 reactor. A lumped parameter kinetic model which takes into account the fundamental mode of reactor power is developed to describe nonlinear dynamic behavior of the reactor. The usual state space controller design techniques for such a model often require canonical representations which impose certain challenges in practical implementation of a rather easy and feasible control task. Bifurcation control methods are therefore resorted which rely basically on a physical intuition into the reactor nonlinear behavior. Reactor local stability behavior is essentially related to thermal feedback effects represented by the power coefficient of reactivity, a variant parameter during system operation causing Hopf bifurcation induced oscillations. The plant is shown to experience instability as the bifurcation parameter takes value in the working region of the reactor. Control procedure is thereby carried out accordingly via manipulation of power coefficient of the reactivity as the Hopf parameter. Taking into account the power (temperature) dependent origin of the selected Hopf parameter, a Washout filter is designed and implemented to relocate this parameter outside the instability region through application of reactor power as the state feedback variable. Numerical simulations exhibit quite reasonable performance of the proposed controller to maintain reactor stability.