SINGULAR PERTURBATION ANALYSIS OF LIMIT-CYCLE BEHAVIOR IN NUCLEAR-COUPLED DENSITY-WAVE OSCILLATIONS

An investigation of the potential behavior of large amplitude nuclear-coupled density-wave oscillations in a boiling water reactor (BWR) was performed. A simplified, nonlinear BWR core model was developed and used to predict the growth of oscillations as a limit cycle is approached. For high-power/low-flow initial conditions, large density-wave oscillations could cause periodic pulses in core power. The fuel temperature, which rapidly increases at high-power conditions and slowly recovers, is considered as the fast variable in a relaxation oscillation. With an appropriate transformation of the system equations, the approximate limit cycle trajectory can therefore be determined using singular perturbation analysis.