Optimal Control Timing Search of Xenon Oscillations in Large PWRs Using a Characteristic Ellipse Trajectory Based on Three Axial Offsets

Abstract

We have proposed a simplified control procedure for axial xenon oscillations in large PWRs based on a characteristic ellipse trajectory method. However, this procedure cannot guarantee that the desired control rod position can be achieved when the xenon oscillation is terminated. In a previous paper, we proposed an innovative and very simple procedure to generate the trajectory for the predicted oscillation behavior, which can be expressed by trigonometric functions multiplied by an exponential function. By using this prediction capability, it is shown that the optimal control timing can be easily determined to terminate the xenon oscillation at the desired control rod position. The optimal timing is obtained at the intersection or, cross point, of two predicted trajectories, the forward trajectory beginning from the current position and the backward trajectory that is generated based on the desired control rod position. Since the trajectories are calculated by simple trigonometric functions and an exponential function, the prediction takes only a few seconds using a PC.