Nuclear power plant instabilities analysis

Abstract

We studied neutron power instability in BWRs of four different nuclear power plants (NPP). The methodology applied in this study is a properly structured, coherent and expanded use of conventional techniques in spectral analysis, Power Spectrum Density (PSD) analysis and Fast Fourier Transform (FFT). Analyses, based on time–frequency representation, allowed for characterization of time-varying spectral signal components, favoring BWR understanding and monitoring. Results show that in large amplitude events, (i.e. Laguna Verde Unit 1 and Fosmark) two coupled mechanisms are needed. The Forsmark NPP case, similarly to Laguna Verde NPP and Cofrentes NPP, confirms a frequency of 0.5316Hz for in-phase instabilities and of 1.006Hz for out-of-phase instabilities. The results of Ringhals NPP support the stated hypothesis that 1Hz frequencies indicate out-of-phase power oscillations, which could point to the existence of an additional out-of-phase instability mode in Laguna Verde NPP.