A Mechanism for Out-of-Phase Power Instabilities in Boiling Water Reactors

A study of the stability of subcritical neutronic modes in boiling water reactors that can result in out-of-phase power oscillations is presented. A mechanism has been identified for this type of instability, and the LAPUR code has been modified to account for it. Numerical results show that there is a region in the power flow operating map where an out-of-phase instability mode is likely even if the corewide mode is stable.