Xenon induced spatial oscillations – a pattern formation approach

Pressurized water reactors (PWR) have become the mainstay of nuclear energy in the past decades. These reactors are considered both reliable and safety, therefore they constitute the large majority of all Western nuclear power plants. It is known that large cores, in terms of neutron migration length, are subject to spatial instabilities . In addition, high reactor power is also required for these instabilities to occur. Such instabilities usually rise due to delayed negative feedbacks of fission products, mainly by the formation of iodine and xenon, which yield spatial and temporal oscillations . Spatial instabilities in PWRs have been studied previously . These studies have focused on the control mechanisms which are required to prevent such instabilities in present day reactors. However, qualitative understanding of the oscillation mechanisms and thresholds, in terms of reactor size and power, are still not very clear. In present-day PWRs, the control procedures are well established to prevent unstable oscillations . new generation core designs include larger core sizes and higher power levels. Such design may be vulnerable to instabilities driven by higher harmonics, for which current reactors are susceptible. It is hence important to study the behavior and characteristics of unstable oscillatory modes in PWRs, and to analyze their dependence on the physical parameters that govern the dynamics in power reactors