MODAL DECOMPOSITION METHOD FOR BWR STABILITY ANALYSIS

In-phase and out-of-phase instabilities have bem observed in BWR react ors. To improve the safety systems of these reactors, it is necessary to be able to detect in a reliable way these oscillations from the neu tronic signals. In this paper a methodology to decompose the neutronic signals in its modal amplitudes is proposed. This decomposition is ba sed on the normal and the adjoint dominant Lambda modes of a static co nfiguration id the reactor core. The calculation uf these eigenmodes f or a realistic problem is reviewed and the oscillation parameters for the modal decompositions of the neutronic signals from Ringhals reacto r have been calculated using the proposed methodology.