Servo-Analysis and Stablization of Xenon Oscillations in Large Thermal Nuclear Reactor Power Plants

A two-point coupled core reactor kinetics model (Baldwin´s model) is used to derive formulae which predict the period and damping factor of the xenon oscillations for a thermal reactor core in terms of the xenon and iodine kinetics parameters and the core parameters and coupling coefficient. The damping factor is a measure of the core stability with respect to the xenon oscillations. The dependence of the core coupling coefficient as a function of the square of the ratio of the core migration length to the core dimension is derived. Calculations are made using PWR core parameters which show that the stability with respect to the xenon oscillations is reduced by increased power density, increased core size, and decreased power reactivity feedback. The periods and damping factors predicted are within the range observed in PWR xenon oscillation experiments. A servo-analysis of the xenon oscillations is made using frequency response techniques. The stability margins are computed, and servo-analysis techniques are utilized in synthesizing a feedback control system to increase the xenon stability margins and effectively damp the xenon oscillations. A practical system for accomplishing this is proposed.